RU2430910C2 - Method of producing desired organic compound via heterogeneously catalysed vapour-phase partial oxidation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves: a) heterogeneously catalysed vapour-phase partial oxidation of a starting organic compound selected from propylene, propane, isobutylene, isobutane, acrolein or methacrolein with molecular oxygen in a parallel-functioning system of oxidation reactors containing catalysts, which results in formation of two gas streams respectively containing the desired compound and respectively formed in one of two systems of oxidation reactors, and b) subsequent extraction of the desired product from two streams of the obtained gas to form at least one stream of crude desired product according to which c) before extraction of two from two streams, the obtained gas is mixed with each other into a mixed stream. In case of change in selectivity of formation of the desired product and/or by-products during operation the entire amount or partial amount of catalyst is replaced in parallel with fresh catalyst not in all parallel-functioning systems of oxidation reactors in which end products contained in the mixed stream are formed.

EFFECT: improved method of obtaining acrolein, acrylic acid, methacrolein or methacrylic acid as the desired product.

2 cl, 4 tbl, 2 ex

Description

The present invention relates to a method for producing at least one target organic compound

a) heterogeneously catalyzed vapor-phase partial oxidation of at least one starting organic compound with molecular oxygen in at least two parallel operating systems of oxidation reactors loaded with catalysts, leading to the formation of at least two streams of the resulting gas, respectively containing the target compound and correspondingly formed in one of at least two oxidation reactor systems, and

b) subsequent separation of at least one target compound from at least two streams of the resulting gas with the formation of at least one stream of crude target product,

according to which

c) before separation, at least two of the at least two streams of the produced gas, or during the separation process, at least two subsequent streams containing the target product, if necessary formed during the conversion of at least two streams of the obtained gas to at least one stream of the crude target product, and / or after isolation, the flows of the crude target product, if necessary formed in the process of separation of at least one of the two streams of the resulting gas, are mixed with each other in a mixed stream.

In the context of the present description, by the complete oxidation of an organic compound by molecular oxygen is meant the conversion of an organic compound that occurs during the reaction of molecular oxygen, due to which all of the carbon contained in the organic compound is converted to carbon oxides and all of the hydrogen contained in the organic compound is converted to hydrogen oxides.

Any organic compound conversions other than those indicated above that occur during the reaction of molecular oxygen are referred to in the context of the present description as partial oxidation of the organic compound.

Thus, the term “partial oxidation” is used in the present description also primarily to mean partial ammoxidation reactions, characterized in that the partial oxidation of the organic compound is carried out in the presence of ammonia.

In the context of the present description, partial oxidation should be understood, in particular, such transformations of organic compounds that occur during the reaction of molecular oxygen, as a result of which the organic compound to be partially oxidized (initial organic compound) after conversion contains at least one chemically bound oxygen atom more than before partial oxidation.

In the general case, it is known that partial heterogeneously catalyzed oxidation of various initial organic compounds in the vapor phase by molecular oxygen allows the synthesis of numerous chemicals. Examples of such syntheses include the conversion of tert-butanol, isobutylene, isobutane, isobutyraldehyde or methyl tert-butanol to methacrolein and / or methacrylic acid (see, for example, German patent application DE-A 2526238, European patent application EP-A 092097, EP-A 058927, German patent applications DE-A 4132263, DE-A 4132684 and DE-A 4022212), conversion of acrolein to acrylic acid, conversion of methacrolein to methacrylic acid (see, for example, German patent application DE-A 2526238), the conversion of o-xylene and / or naphthalene to phthalic anhydride (see, for example, European patent application EP-A 522871), m-xylene to isophthalic acid, p-xylene to terephthalic acid or dimethyl terephthalate, as well as the conversion of butadiene to maleic anhydride (see, for example, German patent application DE- A 2106796 and DE-A 1624921), the conversion of n-butane to maleic anhydride (see, for example, UK patent application GB-A 1464198 and GB 1291354), the conversion with the formation of acids corresponding to the above anhydrides, the conversion of propylene to acrolein and / or acrylic acid (see, for example, German patent application DE-A 2351151), conversion of indanenes, for example to anthraquinone (see, for example, German patent application DE-A 2025430), conversion of ethylene to ethylene oxide or propylene to propylene oxide (see, for example, German patent application DE- AS 1254137, DE-A 2159346, European patent application EP-A 372972, international application WO 89/0710, German patent application DE-A 4311608, as well as Beyer, Lehrbuch der organischen Chemie, 17th edition (1973), Hirzel, Stuttgart, page 261), conversion of propylene and / or acrolein to acrylonitrile (see, for example, German patent application DE-A 2351151), the conversion of isobutylene and / or methacrolein to methacrylonitrile, oxidative dehydrogenation of hydrocarbons (see, for example, German patent application DE-A 2351151), the conversion of propane to acrylonitrile or to acrolein and / or acrylic acid (see, for example, German patent application DE- A 10131297, European patent applications EP-A 1090684, EP-A 608838, German patent application DE-A 10046672, European patent application EP-A 529853, international application WO 01/96270, German patent application DE-A 10028582 ), as well as the conversion of ethane to acetic acid, benzene to phenol, 1-butene or 2-but ena in the corresponding butanediols, and so on.

The disadvantage of existing methods for heterogeneously catalyzed vapor-phase partial oxidation of the starting organic compounds is that the resulting gaseous products do not contain the target organic compound, but in the form of a mixture component, which, as a rule, additionally contains by-products, unconverted reagents and inert dilution gases (in accordance with the present description under a dilution gas, which under the conditions of a heterogeneously catalyzed vapor-phase partial oxidation is mainly caused by inert behavior, they mean such gases, more than 95 mol%, preferably more than 99 mol% of each of the components remain chemically unchanged under conditions of heterogeneously catalyzed vapor-phase partial oxidation).

The target compound is to be isolated from a similar produced gas (mixture of produced gases). To this end, the organic target compound, as a rule, is first transferred (if necessary after preliminary direct and / or indirect cooling) from the obtained gas (mixture of obtained gases) to the condensed (liquid and / or solid) phase in suitable devices. Such a transfer can be carried out, for example, due to the complete or partial condensation of the resulting gas. In a preferred embodiment, such a translation is carried out by fractional condensation method (implemented, for example, in a column equipped with a separation-assisting integrated device; see, for example, German patent application DE-A 10332758 and the prior art cited therein).

According to another embodiment, the target compound can also be converted to the condensed phase by absorption from an optionally pre-cooled produced gas (mixture of produced gases) carried out by a suitable liquid absorbent in an absorption device (for example, an absorption column equipped with a separation-assisted integrated device) (see, for example , German patent application DE-A 10336386, US patent application US-A 2004/0242826 and the prior art cited in these publications). In addition, it is possible to transfer the organic target compound from the obtained gas (mixture of obtained gases) to the condensed phase by adsorption by solid adsorbents or by freezing.

The condensed phase either already contains the target compound (target product), which has the degree of purity necessary for its further use (in this case, the condensed phase already forms the desired stream of the crude target product; the adjective “crude” means that the target product stream along with the necessary the target compound usually additionally contains analytically detectable amounts of at least one component different from the target product), or higher kai purity degree of flow of the crude desired product. In the latter case, the condensed phase forms only the subsequent stream, from which the necessary stream of the crude target product can be obtained through the use of additional, sequentially (one after another) realizable known methods of isolation. Such additional extraction methods, as a rule, are sequentially implemented extraction and / or rectification processes. Before using additional methods of isolation or in between, if necessary, it is possible to carry out the steaming of low-boiling products (low-boiling products mean by-products whose boiling point under normal conditions (at a temperature of 25 ° C and atmospheric pressure) is lower than the boiling point of the corresponding target compound). In addition, the implementation of these methods of additional isolation can be promoted by performing crystallization in the intervals between them. Similar crystallization recovery methods may also be the only additional methods used to purify the condensed phase. The material stream containing the target product, transferred from one purification stage (from one purification device) to the next purification stage (to the next purification device), forms the corresponding subsequent stream implied by the present description. In general, the next subsequent stream, obtained in another purification step (in another purification device) from the previous subsequent stream, contains the target compound, which has a higher degree of purity.

Another feature of the synthesis of target organic compounds by heterogeneously catalyzed vapor-phase partial oxidation of the starting organic compounds by molecular oxygen is that, under the catalysts used to carry out such synthesis, they usually mean solids.

The catalysts used are especially often used as oxide masses or noble metals (e.g. silver). The catalytically active oxide mass along with oxygen atoms may contain only one other element or more than one other element (polyelement oxide masses). Particularly often used as catalytically active oxide masses are products containing more than one elemental metal, especially a transition metal. In this case, we are talking about polymetallic oxide masses. Polyelement oxide masses are usually not simple physical mixtures of oxides of elementary components, but heterogeneous mixtures of complex poly compounds of similar elements.

In addition, (primarily the above), processes of heterogeneously catalyzed vapor-phase partial oxidation are carried out at elevated temperatures, which are usually several hundred degrees Celsius, usually from 100 to 600 ° C.

Since most of the processes of heterogeneously catalyzed vapor-phase partial oxidation are accompanied by a high exothermic effect, in order to ensure optimal heat removal, such processes are often carried out in a fluidized catalyst bed or in reactors (usually isothermal) with a stationary catalyst layer, and the synthesis takes place in the reaction space around which circulates providing indirect heat transfer coolant (for example, the catalyst may be in the form of a stationary about the layer inside the contact tubes of the tubular reactor, washed by a salt melt providing heat removal).

However, the processes of heterogeneously catalyzed vapor-phase partial oxidation can, in principle, also be carried out in catalyst beds located in adiabatic reactors.

It is known that in the process of heterogeneously catalyzed vapor-phase partial oxidation, the working pressure (its absolute value) can be less than 1 bar, 1 bar or more than 1 bar. Operating pressure is typically in the range of 1 to 10 bar, most often in the range of 1 to 3 bar.

The conversion of the at least one starting organic compound to the target compound (target conversion) occurs while the reaction gas mixture is in the catalyst loaded into the reactor through which the mixture is passed.

Since most processes of heterogeneously catalyzed vapor-phase partial oxidation of the starting organic compounds by molecular oxygen, as a rule, have a pronounced exothermic character, the starting reagents are usually diluted predominantly inert under the conditions of the indicated processes, which, due to its inherent heat capacity, is capable of absorbing the released heat.

One of the most commonly used inert dilution gases is molecular nitrogen, which is always automatically present in the reaction system if air is used as the oxygen source for the heterogeneously catalyzed vapor-phase partial oxidation.

Another commonly used inert dilution gas is water vapor, due to its well-known availability. Recirculated gas is also often used as an inert diluent gas (see, for example, European patent application EP-A 1180508). Thus, in accordance with the foregoing, an inert dilution gas used to carry out most heterogeneously catalyzed processes of vapor-phase partial oxidation of organic compounds, more than 90% vol., Often more than 95% vol. consists of nitrogen, water and / or carbon dioxide. Inert dilution gases, on the one hand, contribute to the absorption of the heat of reaction, and on the other hand, ensure the safety of heterogeneously catalyzed vapor-phase partial oxidation of the organic compound due to the fact that the composition of the reaction gas mixture containing them is outside the explosive range. In heterogeneously catalyzed vapor-phase partial oxidation of an unsaturated organic compound, saturated hydrocarbons, i.e., combustible gases, are often also used as inert diluent gases.

Heterogeneously catalyzed vapor-phase partial oxidation is often carried out not in one reactor, but in two or more series-connected reactors (which can also be in a common casing and can be transferred to one another without joints). Like such series-connected oxidation reactors, as well as individual oxidation reactors in the present description are referred to by the general term “oxidation reactor system”. Similarly, as an individual device or an individual device designed to isolate at least one target compound from the resulting partial oxidation of a gas (gas mixture), a sequence of such devices (devices for separation) in the present description is referred to by the term "extraction system". Neither the term “oxidation reactor system” nor the term “extraction system” imply the parallel functioning of the devices forming these systems.

So, a sequence consisting of a system of oxidation reactors (line of reactors) and a separation system (line of processing) usually forms a production system (production line) designed to produce target organic compounds by heterogeneously catalyzed vapor-phase partial oxidation of at least one of the starting organic compounds with molecular oxygen . In a system of oxidation reactors, an initial reaction gas mixture consisting of at least one initial organic compound, molecular oxygen, and at least one inert dilution gas is passed through at least one stationary catalyst bed at elevated temperature, and in the evolution system, the target the compound is isolated from gas (gas mixture) resulting from partial oxidation in the form of a crude product target stream. In the event that the extraction system consists of several devices (devices) connected in series with each other for extraction, the gas (gas mixture) obtained as a result of partial oxidation forms a material flow directed to the first device of the extraction system. The material stream leaving the last device of the separation system is a stream of the crude target product, and the material flows moving inside the separation system from one apparatus to another form flows, which, as indicated above, are called subsequent flows.

The system of oxidation reactors, consisting of more than one reactor, is used primarily if partial oxidation is carried out in the form of sequentially implemented stages. In such cases, it is often advisable to optimize both the catalyst and other reaction conditions in relation to the corresponding reaction stage and the implementation of the corresponding reaction stage in an independent zone of the reactor, respectively, in an independent reactor. A similar system of multi-stage oxidation reactors is used, for example, in the partial oxidation of propylene to acrylic acid. In the first reaction zone (in the first reactor, in the first reaction stage), propylene is oxidized to acrolein, while in the second reaction zone (in the second reactor, in the second reaction stage), acrolein is oxidized to acrylic acid. Similarly, in two series-connected reaction zones (in two series-connected reactors), as a rule, the synthesis of methacrylic acid is also carried out, for which isobutylene most often serves as the starting compound.

The reaction gas mixture between two series-connected reactors of the oxidation reactor system can obviously be cooled and / or molecular oxygen (for example, in the form of air) and / or an inert gas can be added to it. However, both of the above partial oxidation processes can also be carried out in the so-called one-reactor systems, the two reaction zones of which are connected in series with different catalysts loaded into them, are located inside a separate reactor, which in this case most often has two temperature zones. However, both of the above partial oxidation processes using appropriate catalysts can also be implemented in a single reactor having only one temperature zone.

In addition, in order to improve heat dissipation or for other reasons, the general conversion of the starting compound is often carried out in several series-connected reactors (see German patent application DE-A 19902562). In a corresponding typical embodiment, proposed, for example, in German patent application DE-A 10 2004025445, the processes of heterogeneously catalyzed vapor-phase partial oxidation are carried out in tubular reactors.

The system for separating acrylic acid obtained by heterogeneously catalyzing the partial oxidation of propane and / or propylene typically consists of series-connected devices for direct cooling, absorption and stripping, a distillation column (distillation columns) and, if necessary, crystallization devices (devices) (see, for example , German patent application DE-A 10336386 and US patent application US-A 2004/0242826).

It is relatively easy to get disposal apparatus, which are structurally suitable for the production of large volumes of products, while the availability of high-performance oxidation reactors is limited. The reason for the limited availability of such reactors is that the processes of heterogeneously catalyzed vapor-phase partial oxidation, as a rule, are highly exothermic. The consequence of increased heat dissipation is the lack of the possibility of a sufficiently complete heat removal as the productivity of the reactor used for oxidation increases.

Subject to this circumstance, Process Economics Program Report No. 6C, Acrylic Acids and Acrylic Esters, SRI International, Menlo Park California 94025 (1987), pages 1-40, for the production of acrylic acid, it is proposed to use two parallel reactors lines, each of which consists of two reactors connected in series: reactors designed for the implementation of the first stage of synthesis (propylene → acrolein), and reactors designed for the implementation of the second stage of synthesis (acrolein → acrylic acid). In this case, we are talking about the parallel operation of two systems of series-connected reactors. The gas obtained in one system of series-connected reactors is mixed with the gas obtained in another parallel-functioning system of series-connected reactors, after which the mixed stream is sent to a separation line (processing line) common to both systems of reactors in order to separate acrylic acid from it. A similar technological variant is also proposed in the international application WO 01/96271 (FIG. 6), and in the German patent application DE-A 19902562 it is called a classic parallel connection and examples of its implementation are also given. The Stanford Research Institute (SRI) publication cited above was also part of the official record of the protest against European patents EP-B 700714 and EP-B 700893, and the protesting person in US patent application US-A 2004/0242826 again tries to patent the classic parallel connection.

The disadvantage of the classic parallel connection, according to which the catalysts loaded in the reactors of both lines begin to operate simultaneously and also simultaneously carry out their subsequent operation, is that the selectivity of the formation of the target product and by-products in both reactor lines simultaneously develops throughout period of operation.

Such periods of operation of catalysts for heterogeneously catalyzed vapor-phase partial oxidation, depending on the catalytic system and the partial oxidation process, in typical cases range from several months to several years. The synchronous development of the selectivity of the formation of the target and by-products on the respective catalysts during the indicated periods of operation, which is characteristic of parallel-functioning lines of reactors with a classical compound, is a drawback because during these periods the selectivity of the formation of both the target and by-products is usually does not remain unchanged. On the contrary, during this period, in many cases, the selectivity of the formation of the target products decreases and the selectivity of the formation of by-products increases. However, situations are also known where, during the period of operation, the selectivity of the formation of the target products increases, while the selectivity of the formation of by-products decreases. The above also applies to cases where, in accordance with the recommendations given in European patent applications EP-A 990636 and EP-A 1106598, they try to counteract the aging of the catalyst layer by gradually increasing the operating temperature during the period of operation while maintaining other operating conditions that are basically unchanged (which, as a rule, simultaneously leads to an acceleration of the aging process of the catalyst) and / or from time to time, carrying out the regeneration of the catalysts loaded into the reactors in accordance with the recommendations described in European patent application EP-A 614872 and German patent application DE-A 10350822. The problem of changing selectivity cannot be solved either by replacing a portion of the catalyst recommended in German patent application DE-A 10232748, or by varying the working pressure, recommended in German patent application DE-A 10 2004025445.

However, a change in the selectivity of the catalyst during the period of its operation requires appropriate adaptation in time of the productivity of the extraction line. In the case of low selectivity for the formation of by-products, they can be satisfactorily isolated by a less costly method. In the case of high selectivity for the formation of by-products, a satisfactory solution to the more complex problem of their separation requires the use of an expensive separation line.

Thus, if during the operation of the catalyst in reactors with a classic parallel connection, the selectivity of the formation of by-products changes, to obtain the desired target product with the necessary purity during the entire period of operation of the catalyst (up to its replacement), the maximum selectivity should be oriented when designing the extraction lines the formation of by-products throughout this period. That is, the selection line should be as costly as possible. This circumstance leads to a decrease in the profitability of the production of the target product. Based on the foregoing, the present invention was based on the task of proposing a method for producing at least one target organic compound by heterogeneously catalyzed vapor-phase partial oxidation of at least one parent organic compound with molecular oxygen, which has a higher economy, indicated at the beginning of the description.

This problem is solved thanks to the method for producing at least one target organic compound

a) heterogeneously catalyzed vapor-phase partial oxidation of at least one starting organic compound with molecular oxygen in at least two parallel operating systems of oxidation reactors loaded with catalysts, leading to the formation of at least two streams of produced gas (mixture of produced gases), respectively, containing the target compound and correspondingly formed in one of the at least two oxidation reactor systems, and

b) subsequent separation of at least one target compound from at least two streams of the obtained gas (mixture of obtained gases) with the formation of at least one stream of the crude target product,

according to which

c) before separation, at least two of the at least two streams of the produced gas (mixture of produced gases), or during the separation, at least two subsequent streams containing the target product, if necessary formed during the conversion of at least two streams of the obtained gas (mixture of produced gases) into at least one stream of the crude target product, and / or after isolation, the flows of the crude target product, if necessary formed during the separation of at least one of the two streams of the obtained gas (mixture of produced gases), mixed with each other in a mixed stream,

characterized in that

at least one of the catalysts loaded in at least two parallel operating oxidation reactor systems contains a partial amount of catalyst (preferably at least 20% by weight, respectively at least 40% by weight, better at least 60% by weight, even better at least 80% of the mass, in terms of the loaded catalyst, at least the entire loaded catalyst is best), the duration of the already realized heterogeneously catalyzed vapor-phase partial oxidation on which is longer than all parts of at least one other loaded catalyst.

The number of reactor systems operating in parallel according to the invention in accordance with the method of the invention (we are talking about oxidation reactor systems in which the formation of the target compounds contained in the mixed stream occurs) is usually two. However, the number of such reactor systems may also be three, four, five or more. In addition, oxidation reactors in systems operating in parallel according to the invention in accordance with the method of the invention preferably have an identical construction. It follows that the reactors are preferably designed to produce the same volumes of the target product and have the same design parameters. In the case of tubular reactors, this means that they usually contain predominantly the same number of contact tubes having the same parameters. The same applies to the principle of heat dissipation.

However, oxidation reactor systems operating in parallel according to the invention in accordance with the method of the invention may, in principle, also be different from each other. In the case of tubular reactors, we are talking, for example, about the difference in both parameters (for example, length, wall thickness, inner diameter, material) and the number of contact tubes. In addition, completely different types of systems can be operating in parallel with the systems of the oxidation reactors according to the invention. The source gas mixtures entering the oxidation reactor systems operating in parallel according to the invention are, as a rule, identical. That is, in a normal situation, both the composition and the flow rate of gas mixtures passed through the catalysts loaded into the oxidation reactor systems operating in parallel with the invention are the same.

Therefore, for example, you can first form a common stream of the initial reaction gas mixture containing at least one initial organic compound, which can then be directed through at least two parallel operating systems of reactors (intended, for example, for the synthesis of partial acrylic acid) oxidation).

According to this embodiment, when operating at least two parallel-operating systems of oxidation reactors, usually only one air compressor is used (from which, in some cases, the necessary secondary air is also taken) and only one recirculated gas compressor (according to the invention, only recirculated gas is preferably left after the target product is isolated ) (centrifugal compressors according to German Patent Application DE-A 10353014 are preferred; wherein compression of the recycled g air and air can be carried out by means of two separate compressors driven by two separate electric motors, by means of two compressors driven by one electric motor, or by means of a single compressor driven by one electric motor), however, according to the invention, the use of only one air compressor (from which in some cases, the necessary secondary air is also taken), and only one recirculated gas compressor is advisable This is also the case if the initial reaction gas mixture for each of at least two parallel functioning systems of oxidation reactors is formed spatially independently of each other. In this case, the compressed gases, for example, located in the corresponding pipelines, are sent to the corresponding static mixer, in which they are mixed with the starting organic compound under the appropriate pressure to obtain the starting reaction gas mixture intended for introduction into the corresponding system of oxidation reactors.

In this case, it is often advisable to carry out the injection of individual gases into the pipeline supplying the static mixer in such a way as to prevent the formation of explosive mixtures (in the case of partial oxidation of propylene, for example, to acrolein and / or acrylic acid, it would be advisable, for example, to first make an inlet recirculated gas and / or water vapor, then (crude) propylene and finally air). Then, the individually prepared initial reaction gas mixture is sent to that of at least two parallel-functioning systems of oxidation reactors, which is designed to convert this particular initial reaction gas mixture.

Moreover, by the flow rate of the (initial) reaction gas mixture through the catalyst bed intended for the implementation of a particular reaction stage, in the context of the present description is meant the amount of this gas mixture expressed in normal liters (nl) (volume of the (initial) reaction gas mixture in liters, which she would occupy under normal conditions, that is, at a temperature of 25 ° C and a pressure of 1 bar), passed through one liter of catalyst layer for an hour. The flow rate can also relate to only one component of the (initial) reaction gas mixture. In this case, we are talking about the amount of such a component passed through one liter of the catalyst layer for an hour (nl / l · h). In this case, bulk layers consisting only of an inert material do not belong to the catalyst layer.

The foregoing also applies to operating pressure and operating temperature in oxidation reactor systems operating in parallel with the invention. However, these individual parameters or groups of parameters (the composition of the starting gas mixture (with the same starting compound and the same target product), the flow rate of the starting organic compound or the reaction gas mixture passing through the catalyst, operating temperature, working pressure), obviously, can also differ from friend. The catalysts loaded into the oxidation reactor systems operating in parallel according to the invention are often identical in type (i.e., in chemical and physical parameters) (except for differences due to different periods of their operation). However, different types of catalysts can also be loaded into the oxidation reactor systems operating in parallel with the invention.

An important feature of the invention is that at least one of the corresponding catalysts (we are talking about the catalysts used for the synthesis of the target compounds contained in the mixed stream), loaded into at least two oxidation reactor systems operating in parallel with the invention, contains at least part of the catalyst, the duration of the already realized heterogeneously catalyzed vapor-phase partial oxidation on which is longer than on all parts of at least one other charge loaded catalyst.

The specified feature of the invention in accordance with a simple variant can be realized, for example, due to the fact that at least two oxidation reactor systems, for example, with identical catalysts, are simultaneously commissioned at the same time, for example, introducing an identical initial gas mixture and using other identical reaction conditions, after which the catalysts are operated for a long period. If the selectivity of the formation of the target product decreases as the catalyst is used due to its aging (for example, when the selectivity decreases to a level at which it would be impossible to isolate the crude target product with the necessary degree of purity), the above-mentioned simple variant according to the invention can be implemented, for example, replacing a portion of the catalyst with a fresh catalyst in only one of at least two parallel operating oxidation reactor systems, for example, in accordance with it German patent application DE-A 10232748. After this, the parallel process carried out according to the invention can be continued. The selection of the target product is complicated only by the selectivity of the formation of a mixture of by-products, and you can synthesize the crude target product with the required degree of purity.

In the same way, it is possible to prolong the service life of one of the loaded catalysts that have not been partially replaced at no additional cost. Obviously, with a fresh catalyst, it is also possible to replace not only part of one of the loaded catalysts, but all of this catalyst, after which the process according to the invention can be continued.

According to the invention, it is preferable to combine the streams of the produced gas (mixture of the produced gases) emerging from at least two oxidation reactor systems operating in parallel according to the invention into a mixed stream, which is then sent to the first device for isolating the target product. However, in accordance with the method proposed in the invention, it is obvious that at first it is also possible to carry out parallel separation of the target product, for example, similar to its synthesis in at least two parallel-functioning reactor systems. This option is preferable in cases where the target product isolation system consists of several series-connected devices, only one of which is especially capital-intensive or otherwise critical. According to the invention, it may be appropriate to parallelly isolate the target product to a particularly capital-intensive (critical) apparatus and only then combine the subsequent streams containing the corresponding target product into a mixed stream directed further to the aforementioned critical device. After this device, if necessary, continued parallel allocation of the target product is preferably stopped.

On the other hand, in accordance with the method of the invention, the isolation of the target product can be carried out in parallel up to the production of crude product streams. In such a case, according to the invention, crude product streams with different impurity contents are usually obtained. While the content of impurities in one of these streams in some cases is lower than the level regulated in the market specification, another stream of the crude target product in terms of the content of impurities may not satisfy these requirements. By mixing these streams, it is possible to form a common stream of crude target product that satisfies the requirements specified in the market specification.

In the case of the parallel operation of three systems of oxidation reactors carried out in accordance with the invention, instead of combining the gas streams (gas mixture) obtained in all three systems and subsequent processing of the mixture, it is also possible, for example, to combine only two of the three indicated streams and process the resulting mixture. Processing the third stream can be carried out separately, and then mix the mixture of two streams of the target product with the third stream of the target product, and so on.

Different duration of operation of catalysts loaded in at least two parallel-functioning systems of oxidation reactors can be established, for example, due to a shift in the initial moment of operation of fresh loaded catalysts, as well as due to the fact that loaded catalysts are continuously or for a given period of time operated at different temperatures and / or different costs of the starting compound. Thus, a measure of the operating time of the loaded catalysts, used only under the same conditions for its implementation and with the same type of catalysts, according to the invention is the time measured. Otherwise, the measure of the duration of operation of the catalysts is the amount of the target product already synthesized on it. The larger the target product is already synthesized on the catalyst, the greater its age. In the case of a multi-stage heterogeneously catalyzed vapor-phase partial oxidation proceeding with the formation of at least one intermediate product, the cumulative amount of the intermediate product already synthesized on it is a measure of the duration of operation of the corresponding catalyst.

In the case of a two-stage synthesis of acrylic acid from propylene, for example, the total amount of acrolein already synthesized on it would serve as a measure of the duration of operation of the catalyst used to carry out the first reaction stage.

In the case of two-stage synthesis of methacrylic acid from isobutylene, a measure of the duration of operation of the catalyst used to carry out the first reaction step would, for example, be the total amount of methacrolein already synthesized on it. A measure of the operating life of the catalysts used in the second reaction stage of these processes would be the amounts of acrylic acid, respectively methacrylic acid, already synthesized on the corresponding catalysts.

Thus, in the case of a multi-stage heterogeneously catalyzed vapor-phase partial oxidation in at least two parallel operating systems of reactors, after a certain duration of operation, at least a part (preferably at least 20% by weight, preferably at least 40% by weight) is replaced with a fresh catalyst ., even better at least 60 wt. -%, or at least 80 wt. -%, preferably 100 wt. -% in terms of the loaded catalyst) only the catalyst that is used on only discharge the respective oxidation stage oxidation reactor system, after which the process is continued according to the invention. In the case of a two-stage synthesis of acrylic acid from propylene, a partial or complete replacement can be carried out for a catalyst loaded into one of at least two corresponding parallel operating oxidation reactor systems and used to carry out, for example, only the propylene → acrolein reaction step. However, it is obvious that catalysts loaded into one of at least two corresponding parallel operating oxidation reactor systems used to carry out both reaction stages can also undergo such a replacement. In addition, according to the invention, a situation is possible in which a partial or complete replacement of the catalyst in one of the at least two parallel operating systems of oxidation reactors is carried out only for the first reaction stage, and in another reactor system, such a replacement is carried out only for the second reaction stage .

In the case of increasing the selectivity of the formation of the target product and reducing the activity of the loaded catalyst, occurring during its operation, appropriate measures can be taken.

So, for example, at least two corresponding parallel-functioning systems of oxidation reactors with fresh catalysts loaded into each of them can be operated for some time under the same conditions and the mixed stream consisting of at least two streams of the obtained gas can be sent to a single system discharge. The allocation system can be calculated so that, given the high initial selectivity of the formation of by-products, first obtain a stream of crude target product with a relatively low degree of purity. A similar stream can be, for example, crude acrylic acid, which can then be used only for the synthesis of alkyl esters (for example, butyl, methyl, ethyl or 2-ethylhexyl ester). In the case of the subsequent partial or complete replacement of the catalyst provided for by the invention during the further operation of the catalyst, the average selectivity of the formation of the target product contained in the mixture of at least two corresponding streams of the obtained gas is achieved, which leads to a relatively high purity of the crude target product stream obtained in the same extraction system . The stream of such a crude target product in this case may be, for example, a "crude" acrylic acid suitable for the preparation of superabsorbent polyacrylic acids, respectively, from sodium salts.

The initially less synthesized crude acrylic acid, obviously, can also be stored in a large tank and mixed with the synthesized later crude acrylic acid, which, in terms of impurities, overrides the specification requirements to obtain a mixture that meets the relevant specification requirements.

However, the method proposed in the invention is also used if at least two parallel operating systems of oxidation reactors are loaded with catalysts, the selectivity of the formation of the target compound in the first of which increases during operation, and decreases in the second. Thus, after a short timed operation time of at least two loaded catalysts, different amounts of the target product are formed on them, and therefore, the “different” duration of operation of both loaded catalysts implied by the present invention is achieved.

In the case of the multi-stage heterogeneously catalyzed vapor-phase partial oxidation of the at least one starting organic compound according to the invention, it is preferable to combine at least two parallel gas streams resulting from the first reaction step into a mixed stream (similar to the classical German parallel compound used in practice patent application DE-A 19902562) and the subsequent implementation of the second reaction stage at least it least two parallel reactors operating systems (if necessary after adding to the mixed ongoing stream of an inert gas and / or molecular oxygen).

The inventive method is in principle suitable for carrying out all the specific processes of heterogeneously catalyzed vapor-phase partial oxidation indicated at the beginning of the present description. First of all, similar processes are also described, for example, in international patent application WO 01/96270 and German patent applications DE-A 10316465, DE-A 10245585, DE-A 10246119 heterogeneously catalyzed vapor-phase partial oxidation of propane to acrylic acid. These publications, as well as US patent application US-A 2004/0242826 and German patent application DE-A 10336386 should be considered an integral part of the present description. The process according to the invention is in principle also suitable for carrying out a heterogeneously catalyzed partial oxidation in a fluidized bed of a catalyst.

The heterogeneously catalyzed vapor-phase partial oxidation of at least one of the starting organic compounds with molecular oxygen according to the invention can preferably also be carried out in at least two parallel-acting tube reactors with a direct-flow reaction gas mixture in one of them and countercurrent in the other (if you look at the reactors from above). The counterflow, as a rule, causes accelerated aging of the catalyst if it is operated under identical conditions, except for the direction of flow of the reaction gas mixture.

According to the method of the invention, at least one of the catalysts loaded in at least two parallel-functioning oxidation reactor systems according to the invention should preferably include at least a partial amount of catalyst (in the case of multi-stage partial oxidation, for example, all or part catalyst intended for the first and / or second reaction stage), heterogeneously catalyzed vapor-phase partial oxidation at which at least 30 calendar days, preferably at least 60 or at least 90 calendar days, particularly preferably at least 120, or at least 150 calendar days, longer than on all parts of another loaded catalyst , even more preferably at least 180 calendar days, or at least 210, respectively 240 calendar days.

However, proposed in the invention are also such methods in accordance with which the above-mentioned difference in the duration of operation of the two catalysts is at least 270 days, at least 300 days, at least 330 days, at least 360 days, at least 400 days at least 450 days, at least 500 days, at least 550 days, at least 600 days, at least 700 days, at least 800 days, at least 900 days, at least 1000 days, at at least 2,000 days or at least 3,000 days, or she I It wishes to set up even more. As a rule, any difference is not more than three years, or 1,000 days, usually no more than two years, or 750 days.

The specified difference in the duration of operation, expressed as a larger total amount of the target product, respectively, of the intermediate product synthesized in at least part of the catalyst, can be at least 10 ⁶ kg, at least 2 · 10 ⁶ kg, at least 3 · 10 ⁶ kg, at least 4 · 10 ⁶ kg, at least 5 · 10 ⁶ kg, at least 6 · 10 ⁶ kg, at least 7 · 10 ⁶ kg, at least 8 · 10 ⁶ kg, at least least 9 x 10 ⁶ kg, at least 10 ⁷ kg, at least 1.5 x 10 ⁷ kg, at least 2 x 10 ⁷ kg, at least 3 × 10 ^7, respectively Twain 4 x 10 ⁷ kg, at least 5 x 10 ⁷ kg, at least 6 x 10 ⁷ kg, at least 7 x 10 ⁷ kg, at least 8 x 10 ⁷ kg, at least 10 ⁸ kg at least 2 · 10 ⁸ kg, at least 3 · 10 ⁸ kg, or at least 4 · 10 ⁸ kg. The above-mentioned difference in operating duration usually corresponds to not more than 10 ⁹ kg, most often not more than 0.5 · 10 ⁹ kg and most often not more than 10 ⁸ kg of the synthesized product.

According to the invention, the fact that already insignificant changes in the selectivity of formation of by-products can significantly complicate the preparation of a crude target product that meets the requirements of the relevant specification is of great importance. A typical example in this regard is propionic acid present as a by-product in acrylic acid. For acrylic acid sales opportunities it should contain, for example, not more than 800 million mass ^-1, propionic acid (the content of the latter depends on the use of acrylic acid). Similar limit values are characteristic, for example, of formaldehyde and acetic acid formed as by-products. In many cases, the selectivity of the formation of the target product in the processes of heterogeneously catalyzed vapor-phase partial oxidation during the first three months after the start of operation of the loaded catalyst changes by at least 0.1 or 0.2 mol%, or at least 0.3 or 0 , 5 mol%, respectively, at least 1 or 1.5 mol%, respectively, at least 2 mol%, sometimes even at least 3 mol%, at least 4 mol%. or at least 7 mol%. The total selectivity of the formation of side components during the same period, as a rule, accordingly often also changes by at least a value of 0.1 to 7 mol%. and more.

Therefore, in accordance with the proposed invention, the difference in the selectivity of the formation of the target product (for example, acrylic acid) on at least two corresponding parallel-running loaded catalysts can be, for example, 7 mol%. or more (for example, it can be 0.1 or 0.2 mol%, or from 0.3 to 7 mol%), and the difference in the total selectivity of the formation of side components can also be 7 mol%. or more (for example, it may be 0.1 or 0.2 mol%, or from 0.3 to 7 mol%).

In a particular embodiment, the method according to the invention is suitable for one-stage heterogeneously catalyzed in a stationary layer vapor-phase partial oxidation of propylene to acrolein and / or acrylic acid, which is preferably carried out in a tubular reactor, as well as for the first and second stages of a two-stage heterogeneously catalyzed vapor-phase partial oxidation of propylene into acrylic acid (via acrolein as an intermediate) in the stationary layers of tubular reactors, for example, in accordance with and with European patent applications EP-A 700893, EP-A 700714, German patent applications DE-A 19910508, DE-A 19910506, DE-A 10351269, DE-A 10350812, DE-A 10350822, European patent application EP -A 1159247, German patent applications DE-A 10313208, DE-A 10 2004021764, DE-A 19948248, European patent applications EP-A 990636, EP-A 1106598 and German patent applications DE-A 3002829, DE-A 10232482.

The method according to the invention is suitable for the vapor-phase partial oxidation of propylene to acrolein heterogeneously catalyzed in a stationary layer, especially if the active mass of the catalysts is a polyelement oxide containing molybdenum and / or tungsten, as well as at least one element from the group of bismuth, tellurium , antimony, tin and copper, or a polymetallic oxide containing molybdenum, bismuth and iron. According to the invention, particularly suitable polymetallic oxide masses of the indicated type containing molybdenum, bismuth and iron are, first of all, the active masses described in German patent applications DE-A 10344149 and DE-A 10344264. Active polymetallic oxide masses of the general formula are also particularly suitable. (I) (DE-A 19955176), general formula (I) (DE-A 19948523), general formulas (I), (II) and (III) (DE-A 10101695), general formulas (I), (II ) and (III) (DE-A 19948248) and the general formulas (I), (II) and (III) (DE-A 199551680), as well as the active polymetallic oxide masses given in European th patent application EP-A 700,714.

In addition, the method according to the invention is suitable if at least two stationary layers used according to the invention for heterogeneously catalyzed vapor-phase partial oxidation of propylene to acrolein contain polymetallic oxide catalysts with molybdenum, bismuth and iron, as described in German patent applications DE-A 10046957, DE-A 10063162, DE-C 3338380, DE-A 19902562, European patent application EP-A 15565, German patent application DE-C 2380765, European patent applications EP-A 807465, EP-A 279374, German patent application DE-A 330 0044, European patent application EP-A 575897, US patent application US-A 4438217, German patent application DE-A 19855913, international patent application WO 98/24746, German patent application DE-A 19746210 (products of general formula (II )), Japanese patent application JP-A 91/294 239 and European patent applications EP-A 293224, EP-A 700714. These are primarily the catalysts given in the respective examples, the catalysts from European applications being particularly preferred patent EP-A 15565, EP-A 575897 and German patent applications DE-A 19746210, DE-A 19855913. In this regard, special mention should be made it catalyst from Example 1c European patent application EP-A 15565 and obtained similarly catalyst whose active composition has the composition of Mo ₁₂ Ni _6,5 Zn ₂ Bi ₁ Fe ₂ P _0,0065 K _0,06 Ox · 10SiO ₂ . In addition, it should be noted the integral catalyst with a stoichiometric composition of Mo ₁₂ Co ₇ Fe ₃ Bi _0.6 K _0.08 Si _1.6 Oh) in the form of hollow cylinders with dimensions of 5 mm × 3 mm × 2 mm or 5 mm × 2 mm × 2 mm (outer diameter × height × inner diameter) from example 3 of German patent application DE-A 19855913, as well as a one-piece polymetallic oxide catalyst of formula (II) from example 1 of German patent application DE-A 19746210. In addition, it should be noted polymetallic oxide catalysts described in US patent application US-A 4438217. Indicated in this publication catalysis Orors are primarily suitable if they are hollow cylinders with dimensions 5.5 mm × 3 mm × 3.5 mm, 5 mm × 2 mm × 2 mm, 5 mm × 3 mm × 2 mm, 6 mm × 3 mm × 3 mm or 7 mm × 3 mm × 4 mm (outer diameter × height × inner diameter). Polymetallic oxide catalysts and their geometrical parameters as defined in German patent application DE-A 10101695 and international application WO 02/062737 are also suitable in accordance with the present invention.

In addition, in accordance with the invention, solid catalysts with a stoichiometric composition of [Bi ₂ W ₂ O ₉ × 2WO ₃ ] _0.5 · [Mo ₁₂ Co _5.6 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ from example 1 of German patent application DE-A 10046957, representing hollow cylinders (rings) with dimensions of 5 mm × 3 mm × 2 mm or 5 mm × 2 mm × 2 mm (outer diameter × length × inner diameter) and annular coated catalysts 1, 2 and 3 of German application DE-a 10063162 patent shell thickness corresponding to the stoichiometric composition of Mo ₁₂ Bi _1,0 Fe ₃ Co ₇ Si _1,6 K _0,08), applied to oltseobrazny carrier with the dimensions of 5 mm × 3 mm × 1.5 mm or 7 mm × 3 mm × 1.5 mm (outer diameter × length × internal diameter).

Many active polymetallic oxide masses, especially suitable as catalysts for the partial oxidation of propylene to acrolein, carried out by the proposed invention, in the General case, have the formula (I):

,

,

wherein

X ¹ means nickel and / or cobalt,

X ² means thallium, an alkali metal and / or alkaline earth metal,

X ³ means zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,

X ⁴ means silicon, aluminum, titanium and / or zirconium,

and means a number from 0.5 to 5,

b means a number from 0.01 to 5, preferably from 2 to 4,

c means a number from 0 to 10, preferably from 3 to 10,

d means a number from 0 to 2, preferably from 0.02 to 2,

e means a number from 0 to 8, preferably from 0 to 5,

f means a number from 0 to 10 and

n means a number determined by the valency and repeatability of elements other than oxygen in the catalysts of formula (I),

Such active polymetallic oxide masses can be obtained by known methods (see, for example, German patent application DE-A 4023239), and they are usually used in the form of mass-formed balls, rings or cylinders, as well as in the form of shell catalysts, i.e. coated active mass of molded inert bodies. Such masses, obviously, can also be used as catalysts in powder form.

The active masses of the general formula (I) can, in principle, be prepared by a simple method, which consists in obtaining a thoroughly mixed, preferably finely divided, dry mixture of the corresponding sources of active mass elements used in the corresponding stoichiometric ratio, and the resulting mixture is calcined at a temperature of 350 to 650 ° C. Calcination can be carried out both in an inert gas atmosphere and in an oxidizing atmosphere, for example, such as air (a mixture of inert gas and oxygen), as well as in a reducing atmosphere (for example, a mixture of inert gas, ammonia, carbon monoxide and / or hydrogen) . The duration of calcination can be from several minutes to several hours, and usually it is shorter, the higher the temperature of calcination. As sources of active polymetallic oxide mass elements of the general formula (I), compounds that are already oxides and / or compounds that can be converted to oxides by heating at least in the presence of oxygen can be used.

Along with oxides, such starting compounds can primarily be halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complexes, ammonium salts and / or hydroxides (compounds such as NH ₄ OH can be added to a thoroughly mixed dry mixture, (NH ₄ ) ₂ CO ₃ , NH ₄ NO ₃ , NH ₄ CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ and / or ammonium oxalate, capable of dissociation and / or destruction with the release of gaseous products that evaporate at the latest when subsequent calcination).

The starting compounds can be thoroughly mixed to obtain active polymetallic oxide masses of the general formula (I), both in dry and in wet state. In the case of mixing the dry starting compounds, it is advisable to use them in the form of fine powders, and after stirring and, if necessary, the compaction carried out, to calcine. However, wet starting compounds are preferably mixed thoroughly. In this case, the starting compounds are usually mixed in the form of an aqueous solution and / or suspension. Especially carefully mixed dry mixtures are obtained in a similar way if the sources of the active mass elements are exclusively in dissolved form. The solvent used is preferably water. The resulting water mass is subjected to drying, preferably carried out in a spray dryer at an outlet temperature of from 100 to 150 ° C.

Active polymetallic oxide masses of the general formula (I) are usually used in the stationary catalyst bed not in powder form, but in the form of a catalyst obtained by molding having certain geometric parameters, and molding can be performed before or after calcination. Thus, for example, solid catalysts having the necessary geometric shape can be obtained by densification of the powdered active mass or the corresponding non-calcined and / or partially calcined initial mass, realized, for example, by tabletting, extrusion or extrusion methods, and compaction can be carried out if necessary the addition of glidants and / or molding aids, for example, such as graphite or stearic acid, and reinforcement aids such as microfibers of glass, asbestos, silicon carbide or potassium titanate. A suitable geometrical shape of the whole catalysts corresponds, for example, to solid or hollow cylinders with an outer diameter and a length of 2 to 10 mm. A suitable wall thickness of the hollow cylinders is 1 to 3 mm. A solid catalyst, obviously, can also have the shape of balls, the diameter of which can be from 2 to 10 mm.

Particularly optimal sizes of hollow cylinders (especially in the case of solid catalysts) are 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter).

The formation of a powdered active mass or a corresponding powdered initial mass, not subjected to calcination and / or subjected to partial calcination, obviously, can also be carried out by applying it to a molded inert carrier for catalysts. The application of the active mass on the molded body of the carrier in order to obtain shell catalysts, as a rule, is carried out in a suitable rotating reservoir, for example, described in German patent application DE-A 2909671 or European patent applications EP-A 293859 and EP-A 714700. it is advisable to wet the powdery mass on the molded body of the carrier, and after applying it to dry, for example, with hot air. A suitable thickness of the applied layer of powder mass is from 10 to 1000 microns, preferably from 50 to 500 microns, and particularly preferably from 150 to 250 microns. In another embodiment, the pulverized mass can also be applied to the shaped bodies of the carrier directly from an appropriate suspension or solution (for example, in water).

The carrier materials may be conventional porous or non-porous aluminas, silica, thorium dioxide, zirconia, silicon carbide or silicates such as magnesium silicate or aluminum silicate. Under the conditions of the target reaction carried out in accordance with the method of the invention in the first reaction stage, such materials behave, as a rule, mainly inert. The bodies of the carrier can be given a regular or irregular shape, with the carrier bodies having a regular shape, for example, balls or hollow cylinders with a distinct surface roughness, being preferred. Rough-surface, predominantly non-porous spherical bodies of a steatite carrier (e.g., Steatit C220 from CeramTec) with a diameter of from 1 to 8 mm, preferably from 4 to 5 mm, are suitable. Also suitable are carrier bodies in the form of cylinders from 2 to 10 mm long (for example, 8 mm) and an outer diameter from 4 to 10 mm (for example, 6 mm). In the case where, according to the invention, suitable carrier bodies are rings, in addition to the indicated parameters, they are characterized by a wall thickness of usually 1 to 4 mm. Preferably used according to the invention, the annular body of the carrier have a length of from 2 to 6 mm, an outer diameter of from 4 to 8 mm and a wall thickness of from 1 to 2 mm. According to the invention, rings with geometrical parameters of 7 mm × 3 mm × 4 mm, respectively 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) are also particularly suitable as a carrier. The thickness of the layer of catalytically active oxide masses deposited on the surface of the bodies of the carrier, obviously, should be brought into line with the required thickness of the shell (see European patent application EP-A 714700).

In addition, for the stationary layer of catalysts for partial oxidation of propylene to acrolein, carried out by the proposed invention, the active polymetallic oxide masses of the general formula (II) are particularly suitable:

,

,

wherein

Y ¹ means only bismuth or bismuth and at least one of the elements of the group tellurium, antimony, tin and copper,

Y ² means molybdenum or molybdenum and tungsten,

Y ³ means alkali metal, thallium and / or samarium,

Y ⁴ means alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury,

Y ⁵ means iron or iron and at least one of the elements of the group chromium and cerium,

Y ⁶ means phosphorus, arsenic, boron and / or antimony,

Y ⁷ means rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,

a 'means a number from 0.01 to 8,

b 'means a number from 0.1 to 30,

c 'means a number from 0 to 4,

d 'means a number from 0 to 20,

e 'means a number from> 0 to 20,

f 'means a number from 0 to 6,

g 'means a number from 0 to 15,

h 'means a number from 8 to 16,

x ', y' mean numbers determined by the valency and repeatability of the elements different from oxygen in the general formula (II), and

p, q mean numbers whose ratio (p / q) is from 0.1 to 10,

containing three-dimensional regions with a chemical composition Y ¹ _{a '} Y ² _b' O _{x '} , delimited from a locally surrounding material with a different composition, the maximum diameter of which (the longest segment passing through the center of gravity and connecting two points on their surface (boundary surface)) is from 1 nm to 100 μm, often from 10 to 500 nm or from 1 to 50, respectively 25 μm.

Particularly preferred are the polymetallic oxide masses of the general formula (II) in which Y ¹ means exclusively bismuth.

The latter are preferably polymetallic oxide masses of the general formula (III):

,

,

wherein

Z ² means molybdenum or molybdenum and tungsten,

Z ³ means nickel and / or cobalt,

Z ⁴ means thallium, an alkali metal and / or alkaline earth metal,

Z ⁵ means phosphorus, arsenic, boron, antimony, tin, cerium and / or lead,

Z ⁶ means silicon, aluminum, titanium and / or zirconium,

Z ⁷ means copper, silver and / or gold,

a '' means a number from 0.1 to 1,

b "means a number from 0.2 to 2,

c '' means a number from 3 to 10,

d "means a number from 0.02 to 2,

e "means a number from 0.01 to 5, preferably from 0.1 to 3,

f '' means a number from 0 to 5,

g '' means a number from 0 to 10,

h '' means a number from 0 to 1,

x '', y '' mean numbers determined by the valency and repeatability of the elements different from oxygen in the general formula (III),

p``, q '' mean numbers whose ratio (p`` / q '') is from 0.1 to 5, preferably from 0.5 to 2,

even more preferred are the polymetallic oxide masses of the general formula (III) in which Z ² _{b ″} means (W) _{b ″} and Z ² ₁₂ means (Mo) ₁₂ .

In addition, it is preferable if at least 25 mol%. (preferably at least 50 mol%, particularly preferably 100 mol%) of the total amount of [Y ¹ _{a '} Y ² _b' O _{x '} ] _p ([Bi _a'' Z ² _b'' O _x'' ] _{p ''} ) in the polymetallic oxide masses of the general formula (II) suitable according to the invention (polymetallic oxide masses of the general formula (III)) is present in these polymetallic oxide masses in the form of three-dimensional regions with the chemical composition Y ¹ _{a '} Y ² _b' O _{x '} [ Bi _{a ''} Z ² _{b '' O x '']} , delineated by having different composition locally surrounding material, wherein the maximum diameter of such domains is about three-dimensional 1 nm to 100 microns.

The formation of catalysts with polymetallic oxide masses of the general formula (II) is carried out similarly to the formation of catalysts with polymetallic oxide masses of the general formula (I).

The preparation of active polymetallic oxide masses of the general formula (II) is described, for example, in European patent application EP-A 575897, as well as in German patent applications DE-A 19855913, DE-A 10344149 and DE-A 10344264.

As the active mass of the catalysts used in at least one stationary bed of catalysts for partial oxidation of acrolein to acrylic acid, the known polymetallic oxides containing molybdenum and vanadium are used according to the invention, which are used for carrying out reactions of this type.

Such active polymetallic oxide masses containing molybdenum and vanadium are shown, for example, in US patent applications US-A 3,775,474, US-A 3,954,855, US-A 3,893,951 and US-A 4,339,355, European patent application EP-A 614872, respectively EP- A 1041062, or international application WO 03/055835, respectively WO 03/057653.

First of all, active polymetallic oxide masses are also suitable, which are proposed in German patent applications DE-A 10325487 and DE-A 10325488.

In addition, as the active masses of the stationary layers of the catalysts for partial oxidation of acrolein to acrylic acid, carried out in accordance with a special variant of the method proposed in the invention, polymetallic oxide masses described in European patent application EP-A 427508, German patent applications DE- A 2909671, DE-C 3151805, DE-AS 2626887, DE-A 4302991, European patent applications EP-A 700893, EP-A 714700 and German patent application DE-A 19736105. In this regard, active masses are particularly preferred, offered, for example, in ev European Patent Application EP-A 714700, as well as German Patent Application DE-A 19736105.

Many such active polymetallic oxide masses containing molybdenum and bismuth possess the general formula (IV):

wherein

X ¹ means tungsten, niobium, tantalum, chromium and / or cerium,

X ² means copper, nickel, cobalt, iron, manganese and / or zinc,

X ³ means antimony and / or bismuth,

X ⁴ means one or more alkali metals,

X ⁵ means one or more alkaline earth metals,

X ⁶ means silicon, aluminum, titanium and / or zirconium,

and means a number from 1 to 6,

b means a number from 0.2 to 4,

C means a number from 0.5 to 18,

d means a number from 0 to 40,

e means a number from 0 to 2,

f means a number from 0 to 4,

g means a number from 0 to 40 and

n means a number determined by the valency and repeatability of elements that are different from oxygen in the general formula (IV).

According to the invention, active polymetallic oxides of the general formula (IV) in which

X ¹ means tungsten, niobium and / or chromium,

X ² means copper, nickel, cobalt and / or iron,

X ³ means antimony

X ⁴ means sodium and / or potassium,

X ⁵ means calcium, strontium and / or barium,

X ⁶ means silicon, aluminum and / or titanium,

and means a number from 1.5 to 5,

b means a number from 0.5 to 2,

C means a number from 0.5 to 3,

d means a number from 0 to 2,

e means a number from 0 to 0.2,

f means a number from 0 to 1 and

n means a number determined by the valency and repeatability of elements that are different from oxygen in the general formula (IV).

According to the invention, even more preferred polymetallic oxides of the general formula (IV) are those which possess the general formula (V):

,

,

wherein

Y ¹ means tungsten and / or niobium,

Y ² means copper and / or nickel,

Y ⁵ means calcium and / or strontium,

Y ⁶ means silicon and / or aluminum,

a 'means a number from 2 to 4,

b 'means a number from 1 to 1.5,

c 'means a number from 1 to 3,

f 'means a number from 0 to 0.5,

g 'means a number from 0 to 8 and

n 'means a number determined by the valency and repeatability of elements different from oxygen in the general formula (V).

Active polymetallic oxide masses of the general formula (IV) can be obtained by known methods described, for example, in German patent application DE-A 4335973 or European patent application EP-A 714700. However, according to the invention, active polymetallic oxide containing molybdenum and vanadium masses intended for the partial oxidation of acrolein to acrylic acid, the active masses proposed in the German patent application DE-A 10261186 are also particularly suitable.

In principle, such active polymetallic oxide masses containing molybdenum and vanadium, first of all of general formula (IV), can be prepared by a simple method, which consists in obtaining as thoroughly mixed as possible, preferably finely divided dry mixture of suitable sources of elements, which has the corresponding stoichiometric composition, and subjected to calcination at a temperature of from 350 to 600 ° C. Calcination can be carried out both in an inert gas atmosphere and in an oxidizing atmosphere, for example, such as air (a mixture of inert gas and oxygen), as well as in a reducing atmosphere (for example, in mixtures consisting of an inert gas and reducing gases, such as hydrogen , ammonia, carbon monoxide, methane and / or acrolein, or in said individually used reducing gases). The duration of the calcination can be from a few minutes to several hours, and usually it is shorter, the higher the calcination temperature. As sources of the elements that make up the active polymetallic oxide masses of the general formula (IV), compounds that are already oxides and / or compounds that can be converted to oxides by heating, at least in the presence of oxygen, can be used.

The starting compounds can be thoroughly mixed to obtain active polymetallic oxide masses of the general formula (IV), both in dry and in wet condition. In the case of dry starting compounds, it is advisable to use them in the form of fine powders, and after stirring and, if necessary, carried out compaction, subjected to calcination. However, wet starting compounds are preferably mixed thoroughly.

In this case, the starting compounds are usually mixed with each other in the form of an aqueous solution and / or suspension. Especially thoroughly mixed in this way dry mixtures are obtained if they come from sources of elements that are exclusively in a dissolved state. The solvent used is preferably water. The resulting water mass is preferably dried in a spray dryer at an outlet temperature of 100 to 150 ° C.

The active polymetallic oxide masses containing molybdenum and vanadium, primarily of the general formula (IV), can be used for partial oxidation of acrolein to acrylic acid, carried out by the method according to the invention, both in powder form and in the form of a catalyst obtained by molding with certain geometric parameters, and molding may be carried out before or after calcination. So, for example, by compaction of a powdered active mass or a corresponding, not calcined initial mass, carried out, for example, by tabletting, extrusion or extrusion, it is possible to obtain solid catalysts with the required geometric shape, and compaction can be carried out by adding auxiliary agents, for example, such as graphite or stearic acid, used to improve glide and / or ease molding, and reinforcing means such as microfibers of glass, asbestos, silicon carbide or potassium titanate. A suitable geometrical shape of the whole catalysts corresponds, for example, to solid or hollow cylinders with an outer diameter and a length of 2 to 10 mm. The wall thickness of the hollow cylinders is suitably from 1 to 3 mm. A solid catalyst, obviously, can also have the shape of balls, the diameter of which can be from 2 to 10 mm.

The formation of a powdered active mass or a corresponding, not calcined, powdered initial mass, obviously, can also be carried out by applying it to a molded inert support for catalysts. The application of the active mass on the molded body of the carrier in order to obtain shell catalysts, as a rule, is carried out in a suitable rotating reservoir, for example, described in German patent application DE-A 2909671 or European patent applications EP-A 293859 and EP-A 714700.

It is advisable to wet the powder mass applied to the molded body of the carrier, and, after application, to dry, for example, with hot air. A suitable thickness of the powder mass layer deposited on the carrier body is from 10 to 1000 microns, preferably from 50 to 500 microns, and particularly preferably from 150 to 250 microns.

The carrier materials may be conventional porous or non-porous aluminas, silicon dioxide, thorium dioxide, zirconia, silicon carbide or silicates such as magnesium silicate or aluminum silicate. The bodies of the carrier can be given a regular or irregular shape, with the carrier bodies of a regular shape, for example, balls or hollow cylinders with a distinct surface roughness, being preferred. Suitable are those having a rough surface, mainly non-porous spherical body of the carrier of steatite with a diameter of from 1 to 10 mm (for example, 8 mm), preferably from 4 to 5 mm. Suitable are also the body of the carrier in the form of cylinders with a length of 2 to 10 mm and an outer diameter of 4 to 10 mm. In the case where, according to the invention, suitable carrier bodies are rings, in addition to the indicated parameters, they are characterized by a wall thickness of usually 1 to 4 mm. Preferably used according to the invention, the annular body of the carrier have a length of from 3 to 6 mm, an outer diameter of from 4 to 8 mm and a wall thickness of from 1 to 2 mm. Suitable carrier bodies according to the invention are also primarily rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter). The thickness of the layer of catalytically active oxide masses deposited on the surface of the carrier body, obviously, should be brought into line with the required shell thickness (see European patent application EP-A 714700).

In addition, containing molybdenum and vanadium, the optimal active polymetallic oxide masses intended for the partial oxidation of acrolein to acrylic acid by the method proposed in the invention are active masses of the general formula (VI):

,

,

wherein

D means Mo ₁₂ V _{a ''} Z ¹ _{b ''} Z ² _{c ''} Z ³ _{d ''} Z ⁴ _{e ''} Z ⁵ _{f ''} Z ⁶ _{g ''} O _{x ''} ,

E means Z ⁷ ₁₂ Cu _{h ''} H _{i ''} C _{y ''} ,

Z ¹ means tungsten, niobium, tantalum, chromium and / or cerium,

Z ² means copper, nickel, cobalt, iron, manganese and / or zinc,

Z ³ means antimony and / or bismuth,

Z ⁴ means lithium, sodium, potassium, rubidium, cesium and / or hydrogen,

Z ⁵ means magnesium, calcium, strontium and / or barium,

Z ⁶ means silicon, aluminum, titanium and / or zirconium,

Z ⁷ means molybdenum, tungsten, vanadium, niobium and / or tantalum,

a '' means a number from 1 to 8,

b '' means a number from 0.2 to 5,

c '' means a number from 0 to 23,

d '' means a number from 0 to 50,

e '' means a number from 0 to 2,

f '' means a number from 0 to 5,

g '' means a number from 0 to 50,

h '' means a number from 4 to 30,

i '' means a number from 0 to 20,

x '', y '' mean numbers determined by the valency and repeatability of the elements different from oxygen in the general formula (VI), and

p, q mean non-zero numbers, the ratio of which (p / q) is from 160: 1 to 1: 1, which can be obtained by separate formation of a solid finely divided polymetallic oxide mass (E):

(initial mass 1) and the subsequent introduction of the formed solid initial mass 1 (subject to the required quantitative ratio p to q) in an aqueous solution, aqueous suspension or finely divided dry stoichiometric mixture (D):

sources of molybdenum, vanadium, Z ¹ , Z ² , Z ³ , Z ⁴ , Z ⁵ , Z ⁶ (initial mass 2), if necessary, carried out by drying the resulting aqueous mixture and calcining the dry initial mass before or after drying at a temperature of from 250 to 600 ° C, resulting in a catalyst with the necessary geometric parameters.

In this case, polymetallic oxide masses of the general formula (VI) obtained by introducing the formed solid starting mass 1 into the aqueous starting mass 2, carried out at a temperature below 70 ° C, are preferred. The preparation of catalysts based on polymetallic oxide masses of the general formula (VI) is described in detail, for example, in European patent application EP-A 668104 and German patent applications DE-A 19736105 and DE-A 19528646.

The formation of catalysts based on polymetallic oxide masses of the general formula (VI) is carried out similarly to the formation of catalysts based on polymetallic oxide masses of the general formula (IV).

Other molybdenum and vanadium containing optimal active polymetallic oxide masses to be used for partial oxidation of acrolein to acrylic acid by the method of the invention are the active masses of the general formula (VII):

,

,

wherein

And means Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _x ,

B means X ₁ ⁷ Cu _h H _i O _y ,

C means X ₁ ⁸ Sb _j H _k O _z ,

X ¹ means tungsten, niobium, tantalum, chromium and / or cesium, preferably tungsten, niobium and / or chromium,

X ² means copper, nickel, cobalt, iron, manganese and / or zinc, preferably copper, nickel, cobalt and / or iron,

X ³ means antimony and / or bismuth, preferably antimony,

X ⁴ means lithium, sodium, potassium, rubidium, cesium and / or hydrogen, preferably sodium and / or potassium,

X ⁵ means magnesium, calcium, strontium and / or barium, preferably calcium, strontium and / or barium,

X ⁶ means silicon, aluminum, titanium and / or zirconium, preferably silicon, aluminum and / or titanium,

X ⁷ means molybdenum, tungsten, vanadium, niobium and / or tantalum, preferably molybdenum and / or tungsten,

X ⁸ is copper, nickel, zinc, cobalt, iron, cadmium, manganese, magnesium, calcium, strontium and / or barium, preferably copper and / or zinc, particularly preferably copper,

a means a number from 1 to 8, preferably from 2 to 6,

b means a number from 0.2 to 5, preferably from 0.5 to 2.5,

c means a number from 0 to 23, preferably from 0 to 4,

d means a number from 0 to 50, preferably from 0 to 3,

e means a number from 0 to 2, preferably from 0 to 0.3,

f means a number from 0 to 5, preferably from 0 to 2,

g means a number from 0 to 50, preferably 0 to 20,

h means a number from 0.3 to 2.5, preferably from 0.5 to 2, particularly preferably from 0.75 to 1.5,

i means a number from 0 to 2, preferably from 0 to 1,

j means a number from 0.1 to 50, preferably from 0.2 to 20, particularly preferably from 0.2 to 5,

k means a number from 0 to 50, preferably from 0 to 20, particularly preferably from 0 to 12,

x, y, z mean numbers determined by the valency and repeatability of elements that differ from oxygen in regions A, B, C,

p, q mean positive numbers,

r is 0 or a positive number, preferably a positive number, and the ratio of p to (q + r) is from 20: 1 to 1:20, preferably from 5: 1 to 1:14, particularly preferably from 2: 1 to 1: 8 and when r is a positive number, the ratio of q to r is from 20: 1 to 1:20, preferably from 4: 1 to 1: 4, particularly preferably from 2: 1 to 1: 2, and even more preferably 1: 1 ,

moreover, component [A] _{p is} contained in the active mass of the general formula (VII) in the form of three-dimensional regions (phases) A having a chemical composition:

Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _x ,

component [B] _{q is} contained in the product of the general formula (VII) in the form of three-dimensional regions (phases) B having a chemical composition:

X ₁ ⁷ Cu _h H _i O _y ,

and the component [C] _{r is} contained in the product of the general formula (VII) in the form of three-dimensional regions (phases) C having a chemical composition:

X ₁ ⁸ Sb _j H _k O _z ,

moreover, the distribution of regions A, B and, if necessary, C in each other is similar to the distribution characteristic of a mixture of the finely dispersed component A, the finely dispersed component B and, if necessary, the finely dispersed component C, and wherein all the variable parameters of these regions must be selected so that the molar content of molybdenum in the total number of all elements of the active polyelement oxide mass of the general formula (VII) that are different from oxygen, was from 20 to 80 mol%, the molar ratio of molybdenum containing in the catalytically active polyelement oxide mass of the general formula (VII), the vanadium content (Mo: V) contained in it was from 15: 1 to 1: 1, the corresponding molar ratio of molybdenum to copper (Mo: Cu) was from 30: 1 to 1: 3 and the corresponding molar ratio of molybdenum to the total amount of tungsten and niobium was from 80: 1 to 1: 4.

In accordance with the invention, the preferred active polyelement oxide masses of the general formula (VII) are those active masses, regions A of which are characterized by the stoichiometric composition of the general formula (VIII):

,

,

wherein

X ¹ means tungsten and / or niobium,

X ² means copper and / or nickel,

X ⁵ means calcium and / or strontium,

X ⁶ means silicon and / or aluminum,

and means a number from 2 to 6,

b means a number from 1 to 2,

c means a number from 1 to 3,

f means a number from 0 to 0.75,

g means a number from 0 to 10 and

x means a number determined by the valency and repeatability of elements that are different from oxygen in general formula (VIII).

The term “phase” is used when considering active multi-element oxide masses of the general formula (VII) to denote three-dimensional regions whose chemical composition differs from the chemical composition of the material surrounding them. Such phases do not have the inevitable radiographically detectable uniformity. Phase A is typically a continuous phase in which particles of phase B and, if necessary, phase C are dispersed.

The finely dispersed phases B and, if necessary, phase C preferably consist of particles whose largest diameter, that is, the longest segment passing through the center of gravity connecting the two points on their surface, is up to 300 microns, preferably from 0.1 to 200 microns, particularly preferably from 0.5 to 50 microns and even more preferably from 1 to 30 microns. However, particles are also suitable, the largest diameter of which is from 10 to 80 microns or from 75 to 125 microns.

In principle, phases A, B and, if necessary, phase C contained in the active multi-element oxide masses of the general formula (VII) can be amorphous or crystalline.

Thoroughly mixed dry mixtures, which are the basis of active multi-element oxide masses of the general formula (VII) and which are subject to subsequent heat treatment in order to be converted into active masses, can be obtained, for example, by the methods described in international application WO 02/24327, German patent applications DE -A 4405514, DE-A 4440891, DE-A 19528646, DE-A 19740493, European patent application EP-A 756894, German patent applications DE-A 19815280, DE-A 19815278, European patent application EP-A 774297 , German patent application DE-A 19815281, European patent application EP-A 668104 and German Patent Application DE-A 19736105 patent.

The basic principle of obtaining carefully mixed dry mixtures that form active multielement oxide masses of the general formula (VII) after heat treatment is to form at least one finely divided multielement oxide mass B (X ₁ ⁷ Cu _h H _i O _y ) as the initial mass 1 and optionally one or more fine oxide compositions polyelement C (X _{August ¹} Sb _j H _k O _z) in an initial mass of 2, carried out independently or together, followed by the implementation of tight junction (thoroughly mixed media Vania) the initial mass 1 and optionally the initial mass 2 with a mixture comprising being in a stoichiometric ratio corresponding to sources of the elemental constituents of multi element oxide mass A

(the contacted components are used in the required proportion according to the general formula (VII)) and, if necessary, the drying of the resulting mixture of carefully mixed components.

Close contact (thorough mixing) of the initial mass 1, and also, if necessary, the initial mass 2 with a mixture containing sources of elementary components of polymetallic oxide mass A (initial mass 3), can be realized both by dry and wet methods. When using the wet method, special attention should be paid only to the fact that the formed phases (crystallites) B and, if necessary, C do not pass into the solution. A similar requirement in the case of an aqueous medium is usually fulfilled due to the fact that the pH is not too different from 7, and the stirring temperature is not too high. In the case of close contact (thorough mixing) of the components by the wet method, in conclusion, drying is usually carried out (for example, in a spray dryer), resulting in the formation of a thoroughly mixed dry mixture, which according to the invention is subject to subsequent heat treatment. In the case of dry mixing, such a dry mass is formed automatically. The formed fine phase B and, if necessary, phase C, obviously, can also be introduced into a plastic deformable mixture containing sources of polymetallic oxide mass elements A, in accordance with the recommendations contained in German patent application DE-A 10046928. Make tight contact components of the initial mass 1, as well as, if necessary, the initial mass 2 with sources of elements of the multi-element oxide mass A (initial mass 3), obviously, it is also possible by the method described in the German patent application DE-A 19815281.

Heat treatment in order to obtain an active mass and shaping can be performed similarly to the active polymetallic oxide masses of the general formulas (IV) - (VI).

In the General case, the catalysts based on active polymetallic oxide masses of General formulas (IV) to (VII) can preferably be obtained in accordance with German patent application DE-A 10325487, respectively DE-A 10325488.

In the simplest and most technically feasible embodiment, the reaction stage of the conversion of propylene to acrolein (in the system of oxidation reactors used according to the method proposed in the invention) on the above catalysts suitable for use in a stationary layer can be implemented in a tubular reactor loaded with him stationary catalyst bed, described, for example, in European patent application EP-A 700714, respectively, German patent application DE-A 4431949, or international WO 03/057653, WO 03/055835, WO 03/059857 and WO 03/076373.

Therefore, in the simplest (single-zone) version, the stationary catalyst layer is loaded in a standard manner into the metal tubes of a tubular reactor, around which a thermostatic medium moves, which is usually used as a molten salt. In this case, the molten salt (thermostatic medium) and the reaction gas mixture can be moved relative to each other by a simple forward flow or countercurrent. However, the thermostatic medium (molten salt) can also move around the tube bundle along a winding path (if you look at the reactor from above), so that the thermostatic medium moves in direct or counterflow relative to the direction of the reaction gas mixture over the entire cross section of the reactor (if you look at it from above). In this case, the volumetric flow rate of a thermostatic medium (coolant) is usually calculated in such a way that the temperature increase due to the exothermicity of the reaction when moving from the point of entry into the reactor to the point of exit from the reactor is from 0 to 10 ° C, often from 2 to 8 ° C from 3 to 6 ° C. The temperature of the coolant at the inlet to the tubular reactor, as a rule, is from 250 to 450 ° C, often from 300 to 400 ° C, respectively, from 300 to 380 ° C. In the indicated temperature ranges, a change occurs in the corresponding reaction temperature. Suitable heat transfer media are primarily liquid thermostatic media. Especially favorable is the use of molten salts, such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, or low-melting metals such as sodium, mercury, and alloys of various metals. However, ionic liquids can also be used as a heat carrier.

In a suitable embodiment, the initial reaction gas mixture is heated to the desired reaction temperature before being introduced into the stationary catalyst bed.

In accordance with the method of the invention, it is preferable to pre-prepare the initial reaction gas mixture, which is then simultaneously introduced into at least two simultaneously operating oxidation reactor systems using an appropriate distribution system.

Partial oxidation of propylene to acrolein is expediently carried out in a two-zone or multi-zone tubular reactor, especially in the case of a high specified flow rate of propylene through a stationary catalyst bed of, for example, ≥130 nl / l · h, ≥140 nl / l · h, ≥150nl / l · H or ≥160 nl / l · h, however, as a rule, ≥600 nl / l · h, often ≥350 nl / l · h, although this reaction can also be carried out in a single-zone tubular reactor. A preferred embodiment of a dual-zone tubular reactor, which according to the invention can be used for the above purpose, is given in German patent application DE-C 2830765. However, dual-zone tubular reactors proposed in German patent application DE-C 2513405, US patent application are also suitable. US-A 3147084, German patent application DE-A 2201528, European patent application EP-A 383224 and German patent application DE-A 2903582. A corresponding technology is also described in European patent application EP-A 1106598.

Thus, in accordance with a simple embodiment, at least one stationary bed of the catalyst to be used according to the invention is loaded in a standard manner into the metal tubes of a tubular reactor, around which two mainly thermostatic media move, which are usually salt melts. The reaction zone is considered to be a reactor section with tubes surrounded by a corresponding salt melt.

So, for example, molten salt A preferably flows around the tubes of that section of the reactor (reaction zone A), which corresponds to the degree of oxidative conversion of propylene (when it is passed once) from 40 to 80 mol%, while salt melt B preferably flows around the pipes of section of the reactor (reaction zone B), which corresponds to the further oxidative conversion of propylene (when it is passed once), the degree of which, as a rule, reaches at least 93 mol%. (if necessary, additional reaction zones with individual temperature conditions observed in them can adjoin reaction zones A and B).

The molten salt can, in principle, circulate inside the corresponding temperature zone, similarly to the single-zone variant. The temperature of the salt melt B at the inlet of the reactor usually exceeds the corresponding temperature of the salt melt A by a value of at least 5 to 10 ° C. The temperature of salt melts at the inlet can be, in particular, in the temperature range recommended for a single-zone variant.

Otherwise, the technology of two-zone partial oxidation of propylene to acrolein at an increased consumption of initial propylene can be implemented, for example, in accordance with German patent application DE-A 10308836, European patent application EP-A 1106598, international application WO 01/36364 or German applications Patent DE-A 19927624, DE-A 19948523, DE-A 10313210, DE-A 10313213, DE-A 19948248.

The method according to the invention is generally suitable for partial oxidation of propylene to acrolein at a flow rate of propylene through a stationary catalyst bed of ≥70 nl / l · h or ≥70 nl / l · h, ≥90 nl / l · h, ≥110 nl / l · h, ≥130 nl / l · h, ≥140 nl / l · h, ≥160 nl / l · h, ≥180 nl / l · h, ≥240 nl / l · h or ≥300 nl / l · H, which, however, is usually limited to values ≥600 nl / l · h. These data generally relate to the volume of the stationary catalyst bed, minus, if necessary, the shared sections of the stationary layer, consisting only of inert material (except as otherwise provided by the present invention).

According to the invention, it is preferable to choose the same propylene flow rate through at least two corresponding in parallel functioning oxidation reactor systems.

For the preparation of at least one stationary catalyst bed of partial oxidation of propylene to acrolein by the method of the invention, molded catalyst bodies containing the corresponding active polymetallic oxide mass or substantially homogeneous mixtures of similar molded bodies and molded bodies not containing an active polymetallic oxide mass can be used and possessing a predominantly inert behavior with respect to a heterogeneously catalyzed partial vapor-phase oxidation (in complements of an inert diluent material molded body). The materials of such inert shaped bodies can, in principle, be any of the substances also suitable for use as carrier materials for shell catalysts for the synthesis of acrolein from propylene. Suitable suitable materials may be, for example, porous or non-porous aluminas, silica, thorium dioxide, zirconia, silicon carbide, silicates such as magnesium silicate or aluminum silicate, or the steatite mentioned above (for example, CeramTec Steatit C-220) .

Corresponding inert diluting molded bodies, in principle, can have any geometric parameters. That is, they can be, for example, balls, polyhedra, solid cylinders or rings. Preferred are inert diluent molded bodies, the geometric parameters of which are similar to the geometric parameters of the molded bodies of the one-step synthesis catalysts diluted by them.

As a rule, it is favorable if the active mass used for the partial oxidation of propylene to acrolein under consideration has the same chemical composition in the entire volume of the stationary catalyst layer. Therefore, although the active mass used for individual molded catalyst bodies can be a mixture of different polymetallic oxides, for example, containing elemental molybdenum and / or tungsten, as well as at least one of the elements selected from the group consisting of bismuth, iron, antimony, tin and copper, in which case the same mixture is preferably used for all molded bodies of the stationary catalyst bed.

According to the invention, the at least two parallel operating oxidation reactor systems are preferably composed of reactors with the same catalyst loaded.

In the partial oxidation of propylene to acrolein, the activity per unit volume within the stationary catalyst bed in the direction of flow of the initial reaction gas mixture usually preferably increases continuously, abruptly or stepwise.

At the same time, the activity per unit volume can be reduced by a simple method, for example, due to the homogeneous dilution of the bulk of standard molded catalyst bodies manufactured by diluting molded bodies. The higher the content of diluting molded bodies, the lower the content of active mass in a certain volume of the stationary catalyst layer, respectively, its activity.

Thus, it is possible to control what is happening in the direction of the flow of the reaction gas mixture by at least a one-time increase in activity per unit volume of the stationary catalyst layer, for example, due to the fact that backfilling is started at a high content of inert diluting molded bodies in the molded catalyst bodies of this type, and then the high content of diluting molded bodies is reduced in the direction of flow either continuously or abrupt (for example, stepwise) at least one multiple or multiple reduction. An increase in activity per unit volume of activity can also be realized, for example, due to the fact that, with the geometric parameters of the molded shell catalyst bodies being kept constant and the type of their active mass, the thickness of the active mass layer deposited on the respective support is increased, or because the mixture of shell catalysts with the same geometric parameters, but different mass contents of the active mass, increase the proportion of molded catalyst bodies with a higher mass content a effective mass. In another embodiment, the active masses themselves can also be diluted, for which, for example, when they are prepared, inert materials with a diluting action, such as heavily calcined silicon dioxide, are introduced into the dry mixture of the starting compounds to be calcined. Varying the added amount of such a diluting material provides a corresponding automatic change in the activity of the active mass. The greater the amount of dilution material added, the lower the activity of the active mass diluted by it. A similar effect can also be achieved, for example, by varying the ratio between the whole and shell catalysts contained in the respective mixtures with identical active masses. The options discussed above can obviously also be used in combination.

Partial oxidation of propylene to acrolein according to the invention, obviously, can also be carried out in a stationary layer consisting of a mixture of catalysts that contain an active mass of different chemical composition, and, therefore, have different activity. Similar mixtures can also be diluted with inert molded diluent bodies.

In front of the active mass sections of the stationary catalyst bed used for partial oxidation of propylene to acrolein by the method of the invention and / or in addition to such sections, bulk layers consisting of only inert material (for example, only diluting molded bodies) may be present. Such bulk layers can also be heated to the temperature of the stationary catalyst bed. In this case, inert bulk layers may consist of diluting molded bodies, the geometric parameters of which are similar to the geometric parameters of the molded catalyst bodies used to create the above-mentioned sites containing the active mass. However, diluting molded bodies of inert bulk layers and molded catalyst bodies may also have different geometric parameters (for example, diluting molded bodies can be spherical rather than ring-shaped).

Molded bodies used to create such inert bulk layers often have ring shapes with dimensions of 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter) or the shape of balls with a diameter of 4 to 5 mm.

In accordance with the method of the invention, the active mass portion of the stationary bed of a catalyst for partial oxidation of propylene to acrolein is often structured in the direction of flow of the reaction gas mixture as follows (according to the invention, this preferably applies to all of the at least two parallel operating reactor systems according to the invention oxidation and performed in the same way).

In the initial (first) zone of the active mass portion of the stationary catalyst bed, the length of which is from 10 to 60%, preferably from 10 to 50%, particularly preferably from 20 to 40%, and even more preferably from 25 to 35% of the total length of this section (that is, for example, from 0.70 to 1.50 m, preferably from 0.90 to 1.20 m), there are one or two sequentially loaded homogeneous mixture (with a decreasing degree of dilution), consisting of molded catalyst bodies and diluting molded bodies (bodies of both types are preferred o possess basically the same geometric parameters), and the mass content of diluting molded bodies (molded catalyst bodies and diluting molded bodies, as a rule, only slightly differ from each other in density) is usually from 5 to 40% of the mass, preferably from 10 to 40 % of the mass, or from 20 to 40% of the mass, and particularly preferably from 25 to 35% of the mass. The first zone is followed by a second zone, often preferably extending to the end of the active mass portion of the stationary catalyst bed (i.e., the length of the second zone is, for example, from 2.00 to 3.00 m, preferably from 2.50 to 3.00 m) in which there is either a slightly diluted (like the first zone) bulk layer of molded catalyst bodies, or (in a particularly preferred embodiment) an undiluted bulk layer of molded catalyst bodies similar to those used in the first zone.

The foregoing primarily relates to the use of a stationary catalyst bed containing ring shaped solid or shell catalysts as shaped bodies (especially those which are indicated in this application as preferred). In accordance with the method of the invention, ring-shaped molded catalyst bodies, respectively carriers, and ring-shaped diluting molded bodies, which are generally 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter), are preferably used for the structuring described above.

The above also applies to the case when instead of inert diluting molded bodies, molded shell catalyst bodies are used, the content of the active mass of which is lower than its content in the molded shell of the shell catalyst at the end of the stationary layer by 2 to 15% by weight.

A bulk layer consisting only of an inert material, the length of which in an appropriate embodiment is from 5% to 20% of the total length of the stationary catalyst layer, is usually located in front of the stationary layer (in the direction of flow of the reaction gas mixture). A layer of inert material is usually used as the heating zone of the reaction gas mixture.

The contact tubes of tube reactors designed to carry out the partial oxidation of propylene to acrolein are typically made of ferrite steel, and their wall thicknesses typically range from 1 to 3 mm. The inner diameter of the tubes, as a rule, is from 20 to 30 mm, often from 21 to 26 mm. The production and technical value of the number of contact tubes placed in the tubular reactor is at least 5,000, preferably at least 10,000. The number of contact tubes in a tubular reactor is often from 15,000 to 30,000. Tubular reactors with more than 40,000 contact tubes for sale the above reaction step is used only as an exception. The contact tubes are usually evenly distributed inside the tubular reactor, and it is advisable to choose a distribution so that the so-called step of the contact tubes (the distance between the central internal axes of adjacent contact tubes) is from 35 to 45 mm (see, for example, European patent application EP-B 468290).

The step of converting acrolein to acrylic acid on known catalysts suitable for carrying out this reaction in a stationary layer, according to the simplest and most technically feasible option, can also be carried out in a tubular reactor with a stationary catalyst layer, described, for example, in the European patent application EP- A 700893, respectively, the German patent application DE-A 4431949 or in international applications WO 03/057653, WO 03/055835, WO 03/059857 or WO 03/076373.

Thus, in accordance with the simplest (single-zone) option, the stationary catalyst layer is loaded in a standard manner into the metal tubes of a tubular reactor, around which a thermostatic medium, which, as a rule, is a salt melt, moves. In this case, the molten salt (thermostatic medium) and the reaction gas mixture can be moved relative to each other by a simple forward flow or countercurrent. However, the thermostatic medium (molten salt) can also move around the tube bundle along a winding path (if you look at the reactor from above), due to which the thermostatic medium moves forward or counterflow relative to the direction of the reaction gas mixture flow over the entire cross section of the reactor (if you look at it from above) . In this case, the volumetric flow rate of a thermostatic medium (coolant) is usually calculated in such a way that the temperature increase due to the exothermicity of the reaction when moving from the point of entry into the reactor to the point of exit from the reactor is from 0 to 10 ° C, often from 2 to 8 ° C from 3 to 6 ° C. The temperature of the coolant at the inlet to the tubular reactor (in the present description, it corresponds to the temperature of the stationary catalyst bed), as a rule, is from 220 to 350 ° C, often from 245 to 285 ° C, respectively from 245 to 265 ° C. Suitable heat transfer media are primarily liquid thermostatic media. Especially favorable is the use of molten salts, such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, or low-melting metals such as sodium, mercury, and alloys of various metals. However, ionic liquids can also be used as a heat carrier.

In a suitable embodiment, the initial reaction gas mixture is heated to the desired reaction temperature before being introduced into the stationary catalyst bed.

Partial oxidation of acrolein to acrylic acid by the method proposed in the invention is expediently carried out in a two-zone or multi-zone tubular reactor, especially in the case of a high specified flow rate of acrolein through a stationary catalyst bed, for example, ≥130 nl / l · h or ≥140 nl / l · h however, as a rule, ≤350 nl / l · h or ≤600 nl / l · h, although this reaction can also be carried out in a single-zone tubular reactor. A preferred embodiment of a dual-zone tubular reactor, which according to the invention can be used for the above purpose, is given in German patent application DE-C 2830765. However, dual-zone tubular reactors proposed in German patent application DE-C 2513405, US patent application are also suitable. US-A 3147084, German patent application DE-A 2201528, European patent application EP-A 383224 and German patent application DE-A 2903582.

Thus, in accordance with a simple embodiment, at least one stationary bed of the catalyst to be used according to the invention is loaded in a standard manner into the metal tubes of a tubular reactor, around which two mainly thermostatic media move, which are usually saline melts. The reaction zone is a section of the reactor with tubes surrounded by a corresponding salt melt.

So, for example, molten salt C preferably flows around the tubes of that section of the reactor (reaction zone C), which corresponds to the oxidative conversion of acrolein (when it is passed once) from 55 to 85 mol%, while salt melt D preferably flows around the tubes of section of the reactor (reaction zone D), which corresponds to the further oxidative conversion of acrolein (when it is passed once), the degree of which, as a rule, reaches at least 90 mol%. (if necessary, additional reaction zones with the individual temperature conditions observed in them can adjoin reaction zones C and D).

The molten salt can, in principle, circulate inside the corresponding temperature zone, similarly to the single-zone variant. The temperature of the molten salt D at the inlet to the reactor usually exceeds the corresponding temperature of the molten salt C by a value of at least 5 to 10 ° C. The temperature of salt melts at the inlet can be, in particular, in the temperature range recommended for a single-zone variant.

Otherwise, the technology of two-zone partial oxidation of acrolein to acrylic acid with increased consumption of the initial acrolein can be implemented, for example, in accordance with German patent application DE-A 19948523, European patent application EP-A 1106598 or German patent application DE-A 19948248 .

Therefore, the method of the invention is suitable for partial oxidation of acrolein to acrylic acid when it is consumed through a stationary catalyst bed of ≤70 nl / l · h or ≥70 nl / l · h, ≥90 nl / l · h, ≥110 nl / l · h, ≥130 nl / l · h, ≥180 nl / l · h, ≥240 nl / l · h, ≥300 nl / l · h, but usually limited to ≤600 nl / l · h. These data generally relate to the volume of the stationary catalyst bed minus, if necessary, shared areas consisting only of inert material.

To prepare at least one stationary catalyst bed intended for partial oxidation of acrolein to acrylic acid by the method of the invention, molded catalyst bodies containing the corresponding active polymetallic oxide mass or substantially homogeneous mixtures of molded catalyst bodies containing active polymetallic oxide can be used mass, and molded bodies that do not contain active polymetallic oxide mass, with predominantly inert nym behavior relative to a heterogeneously catalyzed partial gas phase oxidation (made of inert diluent material molded body). The materials of such inert shaped bodies can, in principle, be any of the substances also suitable for use as carrier materials for shell catalysts for converting acrolein to acrylic acid. Suitable suitable materials may be, for example, porous or non-porous aluminas, silica, thorium dioxide, zirconia, silicon carbide, silicates such as magnesium silicate or aluminum silicate, or the steatite mentioned above (for example, CeramTec Steatit C-220) .

Corresponding inert diluting molded bodies, in principle, can have any geometric parameters. That is, they can be, for example, balls, polyhedra, solid cylinders or rings. According to the invention, inert diluting molded bodies are preferred whose geometric parameters are similar to those of the molded catalyst bodies diluted by them.

As a rule, it is favorable if the active mass used for the partial oxidation of acrolein to acrylic acid under consideration has the same chemical composition in the entire volume of the stationary catalyst layer. Therefore, although the active mass used for individual molded catalyst bodies may be a mixture of different polymetallic oxides, for example, containing elemental molybdenum and / or tungsten, in this case, for all molded bodies of the stationary catalyst layer, the same mixture is preferably used.

In the partial oxidation of acrolein to acrylic acid, the activity per unit volume within the stationary catalyst bed in the direction of flow of the initial reaction gas mixture is usually preferably continuously, sharply or stepwise increased.

At the same time, the activity per unit volume can be reduced by a simple method, for example, due to the homogeneous dilution of the bulk of standard molded catalyst bodies manufactured by diluting molded bodies. The higher the content of diluting molded bodies, the lower the content of active mass in a certain volume of the stationary catalyst layer, respectively, its activity.

Thus, in the case of partial oxidation of acrolein to acrylic acid according to the invention, it is possible to control at least a one-time increase in activity per unit volume of the stationary catalyst bed in the direction of the reaction gas mixture flow, by a simple method, for example, due to the fact that backfilling starts with the high content of inert diluting molded bodies in the molded catalyst bodies of this type, and then the high content of diluting molded bodies is reduced by the flow is either continuous or abrupt (for example, stepwise) at least once or multiple reduction. An increase in activity per unit volume of activity can also be realized, for example, due to the fact that, with the geometric parameters of the molded shell catalyst bodies being kept constant and the type of their active mass, the thickness of the active mass layer deposited on the respective support is increased, or because the mixture of shell catalysts with the same geometric parameters, but different mass contents of the active mass, increase the proportion of molded catalyst bodies with a higher mass content a effective mass. In another embodiment, the active masses themselves can also be diluted, for which, for example, when they are prepared, inert materials with a diluting action, such as heavily calcined silicon dioxide, are introduced into the dry mixture of the starting compounds to be calcined. Varying the added amount of such a diluting material provides a corresponding automatic change in the activity of the active mass. The greater the amount of dilution material added, the lower the activity of the active mass diluted by it. A similar effect can also be achieved, for example, by varying the ratio between solid and shell catalysts with identical active masses in the respective mixtures. The options discussed above can obviously also be used in combination.

The partial oxidation of acrolein to acrylic acid according to the invention, obviously, can also be carried out in a stationary layer consisting of a mixture of catalysts that contain an active mass of different chemical composition, and, therefore, have different activity. Similar mixtures can also be diluted with inert molded diluent bodies.

In front of the active mass sections of the stationary catalyst bed and / or in addition to such sections, bulk layers can be present which consist only of an inert material (for example, only diluting molded bodies). Such bulk layers can also be heated to the temperature of the stationary catalyst bed.

In this case, inert bulk layers may consist of diluting molded bodies, the geometric parameters of which are similar to the geometric parameters of the molded catalyst bodies used to create the above-mentioned sites containing the active mass. However, diluting molded bodies of inert bulk layers and molded catalyst bodies may also have different geometric parameters (for example, diluting molded bodies can be spherical rather than ring-shaped).

Molded bodies used to create such inert bulk layers often have ring shapes with dimensions of 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter) or the shape of balls with a diameter of 4 to 5 mm.

In accordance with the method of the invention, the active mass-containing portion of the stationary bed of the catalyst for partial oxidation of acrolein to acrylic acid is often structured in the direction of flow of the reaction gas mixture as follows (according to the invention, this preferably applies to all of the at least two parallel operating systems of the invention oxidation reactors and performed in the same way).

In the initial (first) zone of the active mass portion of the stationary catalyst bed, the length of which is from 10 to 50%, preferably from 20 to 40%, particularly preferably from 25 to 35%, and even more preferably from 25 to 35% of the total length of this section (that is, for example, from 0.70 to 1.50 m, preferably from 0.90 to 1.20 m), there are one or two sequentially loaded homogeneous mixture (with a decreasing degree of dilution), consisting of molded catalyst bodies and diluting molded bodies (bodies of both types are preferred o possess basically the same geometric parameters), and the mass content of diluting molded bodies (molded catalyst bodies and diluting molded bodies, as a rule, only slightly differ from each other in density) is usually from 10 to 50% by weight, preferably from 20 to 45% of the mass. and particularly preferably from 25 to 35% of the mass. The first zone is followed by a second zone, often preferably extending to the end of the active mass portion of the stationary catalyst bed (i.e., the length of the second zone is, for example, from 2.00 to 3.00 m, preferably from 2.50 to 3.00 m) in which there is either a slightly diluted (like the first zone, respectively two first zones) bulk layer of molded catalyst bodies, or, even more preferably, an undiluted bulk layer of molded catalyst bodies similar to those used in the first zone, respectively but in the first two zones.

The foregoing primarily relates to the use of a stationary catalyst layer containing ring-shaped or spherical shell catalysts as molded bodies (especially those which, in accordance with this application, are preferred for the partial oxidation of acrolein to acrylic acid). In accordance with the method of partial oxidation of acrolein to acrylic acid according to the invention, ring-shaped molded catalyst bodies or carriers, and ring-shaped diluting molded bodies, which are generally 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter).

The above also applies to the case when instead of inert diluting molded bodies, molded shell catalyst bodies are used, the content of the active mass of which is lower than its content in the molded shell of the shell catalyst at the end of the stationary layer by 2 to 15% by weight.

A bulk layer consisting only of an inert material, the length of which in an appropriate embodiment is from 5% to 20% of the total length of the stationary catalyst layer used for partial oxidation of acrolein, is usually located in front of the stationary layer (in the direction of flow of the reaction gas mixture). A layer of inert material is usually used as the heating zone of the reaction gas mixture.

The contact tubes of the tubular reactors used in the partial oxidation of acrolein carried out according to the invention are usually made of ferrite steel, and their wall thicknesses typically range from 1 to 3 mm. The inner diameter of the tubes, as a rule, is from 20 to 30 mm, often from 21 to 26 mm. The production-technical number of contact tubes placed in the tubular reactor is at least 5,000, preferably at least 10,000. The number of contact tubes in a tubular reactor is often from 15,000 to 30,000. Tubular reactors with more than 40,000 contact tubes for the implementation of the above reaction stage is used only as an exception. The contact tubes are usually evenly distributed inside the tubular reactor, and it is advisable to choose a distribution so that the so-called step of the contact tubes (the distance between the central internal axes of adjacent contact tubes) is from 35 to 45 mm (see, for example, European patent application EP-B 468290).

As indicated above, in accordance with the proposed invention, the partial oxidation of both propylene and acrolein can be carried out in single-zone or dual-zone tubular reactors. However, in the case of the sequential implementation of both reaction stages, a variant is also possible, according to which only the first reaction stage is carried out in a single-zone tubular reactor, while the second reaction stage is carried out in a two-zone tubular reactor (or vice versa). The mixture of gases obtained in the first reaction stage (preferably as a result of mixing all the gases generated in parallel operating systems of oxidation reactors) after the inert gas, molecular oxygen or inert gas and molecular oxygen is added, if necessary, as well as after direct and / or necessary indirect intermediate cooling is sent directly to the second reaction stage.

Moreover, between the tubular reactors intended for the implementation of the first and second reaction stages, an intermediate cooler may be located, which, if necessary, may contain inert bulk layers.

The stationary catalyst bed partial oxidation of propylene and the stationary catalyst bed partial oxidation of acrolein, designed to implement the proposed in the invention method of the two-stage partial oxidation of propylene to acrylic acid, obviously, can be located in a spatial sequence inside a single tubular reactor with a large number of contact tubes, also including, for example, two or more temperature zones, for example, inside reactors described in internationally patent application WO 03/059857 and European patent applications EP-A 911 313 and EP-A 990636. In such a case it is a one-pot two step process. In this case, one or two temperature zones refer, as a rule, to one stationary catalyst bed. Between both stationary layers of the catalysts, an additional inert bulk layer can be located, which, if necessary, corresponds to a third temperature zone with a temperature regime independently established in it. In this case, the contact tubes can pass through an inert bulk layer or interrupt.

An inert gas designed to dilute the initial gas mixture of the stage of partial oxidation of propylene to acrolein (initial reaction gas mixture 1) regardless of the selected propylene flow rate through the stationary catalyst bed (and regardless of whether the reaction stage of partial oxidation of acrolein to acrylic follows the stage of synthesis of acrolein acid) may contain, for example, ≥20% vol., ≥30% vol., ≥40% vol., ≥50% vol., ≥60% vol., ≥70% vol., ≥80% vol., ≥ 90% vol. or ≥95% vol. molecular nitrogen.

In this case, the inert dilution gas may also be a mixture containing, for example, from 2 to 35 wt%, respectively 20 wt%. H ₂ O, and from 65 to 98% vol. nitrogen.

However, when propylene is consumed through a stationary catalyst bed at the stage of its partial oxidation to acrolein in excess of 250 nl / l · h, the shared inert dilution gases recommended for the implementation of the method of the invention are propane, ethane, methane, butane, pentane, dioxide carbon, carbon monoxide, water vapor and / or inert gases. These gases, obviously, can be used together with propylene also at its low flow rate through a stationary catalyst bed to prevent the occurrence of the so-called hot spot.

The operating pressure during the vapor-phase partial oxidation of propylene to acrolein carried out according to the invention (especially during the initial period of operation of the stationary catalyst bed) may be lower than normal pressure (for example, it may be up to 0.5 bar) or may be higher than normal pressure. In typical cases, the working pressure in the vapor-phase partial oxidation of propylene is from 1 to 5 bar, often from 1 to 3 bar.

The reaction pressure during the vapor-phase partial oxidation of propylene to acrolein according to the invention usually does not exceed 100 bar. The partial oxidation of propylene carried out according to the invention in the general case, obviously, can also be implemented in combination with the catalyst bed prolongation technology recommended in European patent applications EP-A 990636, EP-A 1106598, EP-A 614872, German patent applications DE-A 1035822, DE-A 10232748, DE-A 10351269 and DE-A 10 2004025445. Thanks to this combination, the service life of the catalyst layer can reach several years.

The molar ratio of molecular oxygen to propylene in the initial reaction gas mixture 1 intended for partial oxidation of propylene to acrolein, passed through the corresponding stationary catalyst bed according to the method of the invention, is usually ≥1: 1 (mainly regardless of whether or not carry out the subsequent stage of partial oxidation of acrolein to acrylic acid). The indicated ratio is usually ≤3: 1. The molar ratio of molecular oxygen to propylene in the specified source gas mixture is often preferably in the range from 1: 1 to 2: 1, respectively, from 1.4: 1 to 2: 1. The method of partial oxidation of propylene to acrolein is often carried out with a volume ratio (nl) of propylene: oxygen: inert gas (including water vapor) in the initial reaction gas mixture 1, comprising 1: (1-3) :( 3-30), preferably 1: (1.5-2.3) :( 10-15).

In this case, the propylene content in the initial reaction gas mixture 1 can be, for example, from 4 to 20% vol., Often from 5 or 7% vol. up to 15% vol., respectively from 6 or 8% vol. up to 12% vol., or from 5 to 8% vol. (respectively, in terms of total volume).

The initial reaction gas mixture 1 (regardless of the selected flow rate, and also whether the subsequent stage of partial oxidation of acrolein to acrylic acid is carried out and not carried out) may have the following typical composition:

from 6 to 6.5% vol. propylene

from 3 to 3.5% vol. water,

from 0.3 to 0.5% vol. carbon monoxide,

from 0.8 to 1.2% vol. carbon dioxide

from 0.01 to 0.04% vol. acrolein

from 10.4 to 10.7% vol. molecular oxygen and

molecular nitrogen (up to 100%),

or

5.4% vol. propylene

10.5% vol. oxygen

1.2% vol. SB _x

80.5% vol. nitrogen and

2.4% vol. water.

The initial reaction gas mixture 1 for the partial oxidation of propylene to acrolein carried out according to the invention may also have the following composition:

from 6 to 15% vol. propylene

from 4 to 30% vol. (often 6 to 15% vol.) water,

from ≥0 to 10% vol. (preferably from ≥0 to 5% vol.) components other than propylene, water, oxygen and nitrogen,

molecular oxygen in such an amount that its molar ratio to molecular propylene is from 1.5: 1 to 2.5: 1, and molecular nitrogen (up to a total volume of 100% vol.).

Another initial reaction gas mixture 1 for the partial oxidation of propylene to acrolein carried out according to the invention may have the following composition:

6.0% vol. propylene

60% vol. air and

34% vol. water.

According to other variants of the invention, the composition of the initial reaction gas mixture 1 for the reaction stage of partial oxidation of propylene to acrolein may correspond to the following examples given in European patent applications: example 1 (EP-A 990636), example 2 (EP-A 990636), example 3 (EP-A 1106598), Example 26 (EP-A 1106598) or Example 53 (EP-A 1106598).

Other initial reaction gas mixtures 1 suitable according to the invention for carrying out the reaction stage of partial oxidation of propylene to acrolein may have the following composition:

from 7 to 11% vol. propylene

from 6 to 12% vol. water,

from ≥0 to 5% vol. components other than propylene, water, oxygen and nitrogen,

molecular oxygen in such an amount that its molar ratio to molecular propylene is from 1.4: 1 to 2.2: 1, and molecular nitrogen (to a total volume of 100% vol.).

In the initial reaction gas mixture 1, polymer grade propylene and chemically pure propylene are primarily used as propylene, for example, in accordance with German Patent Application DE-A 10232748. In accordance with a preferred embodiment of the invention, propylene subjected to a heterogeneously catalyzed vapor-phase partial oxidation by molecular oxygen to acrolein and / or acrylic acid (respectively, ammoxidation to acrylonitrile), carried out in at least two parallel fun In the operating systems of oxidation reactors, propylene obtained by heterogeneously catalyzed and / or oxidative dehydrogenation of propane can also be used, for example, according to German patent application DE-A 10245585, international application WO 03/076370, German patent applications DE-A 10316039, DE- A 3313573, US patent US 3161670 and international applications WO 01/96270, WO 01/96271, WO 03/011804. Moreover, in a preferred embodiment, the propylene to be oxidized contains propane.

Moreover, one propane dehydrogenation reactor is used to supply propylene, preferably to at least two parallel operating systems of propylene oxidation reactors according to the invention.

In such a case, the initial reaction gas mixture 1 preferably has the following composition:

from 7 to 15% vol. molecular oxygen

from 5 to 10% vol. propylene

from 10, respectively 15% vol., up to 40% vol. propane

from 25 to 60% vol. nitrogen

from 1 to 5% vol. carbon monoxide, carbon dioxide and water (total) and

from 0 to 5% vol. other components

while not taking into account the presence of ammonia, if necessary.

It should be noted that regardless of whether the reaction stage of partial oxidation of acrolein to acrylic acid follows the stage of conversion of propylene to acrolein, part of the initial gas mixture intended for the conversion of propylene to acrolein can be the so-called recirculated gas. As mentioned above, by recycle gas is meant the gas that remains after the isolation of the target product (acrolein and / or acrylic acid) from the gas obtained in the corresponding system of reactors, sold according to the invention in a sequentially connected separation system, and which is in the form of a maximally inert dilution gas, usually partially returned to the reaction stage of partial oxidation of propylene and / or, if necessary, the subsequent partial oxidation of acrolein to acrylic slot.

Air is usually used as an oxygen source.

The flow rate of the initial reaction gas mixture 1, which is passed through a stationary catalyst bed (including a bulk bed consisting only of inert material), in accordance with the invention for the production of acrolein and / or acrylic acid from propylene, is typically typically from 1000 to 10,000 nl / l · H, most often from 1000 to 5000 nl / l · h, often from 1500 to 4000 nl / l · h.

If, after the partial oxidation of propylene to acrolein, the stage of partial oxidation of acrolein is realized, the mixture of gases obtained at the stage of partial oxidation of propylene is sent to the stage of oxidation of acrolein after intermediate cooling, if necessary. According to the invention, it is preferable in this case to pre-mix at least two streams of gas mixtures resulting from the partial oxidation of propylene to acrolein. The oxygen necessary for the implementation of the stage of partial oxidation of acrolein can already be introduced in excess into the initial reaction gas mixture of stage 1 of partial oxidation of propylene, and therefore, can be a component of the gas mixture formed at this stage. In such a case, if necessary, subjected to intermediate cooling, the mixture of gases obtained at the stage of partial oxidation of propylene can serve as the initial gas mixture directly used to implement the stage of partial oxidation of acrolein. However, part of the oxygen or all of the oxygen necessary for the implementation of the stage of partial oxidation of acrolein to acrylic acid can also be added to the mixture of gases obtained in the stage of oxidation of propylene, before it enters the reaction stage of oxidation of acrolein, for example, in the form of air. The added air can simultaneously perform the function of direct cooling of the initial gas mixture intended for processing at the stage of partial oxidation of acrolein.

In view of the foregoing, the inert gas contained in the initial gas mixture for the partial oxidation of acrolein (initial reaction gas mixture 2), regardless of whether the propylene oxidation stage preceded this reaction stage, may contain, for example, ≥20% vol., ≥30 % vol., ≥40% vol., ≥50% vol., ≥ 60% vol., ≥70% vol., ≥80% vol., ≥90% vol. or ≥95% vol. molecular nitrogen.

However, an inert dilution gas in the gas mixture sent to the stage of partial oxidation of acrolein often contains from 5 to 25% by weight, respectively 20% by weight. water (it can be formed, for example, at the previous stage of oxidation of propylene and / or can be added if necessary) and from 70 to 90% vol. nitrogen.

When the consumption of acrolein through a stationary catalyst bed of partial oxidation of acrolein to acrylic acid exceeds 250 nl / l · h, it is recommended to use inert dilution gases such as propane, ethane, methane, butane, pentane, carbon dioxide to implement the method proposed in the invention water vapor and / or inert gases. However, these gases, obviously, can also be used together with a small consumption of acrolein through the catalyst bed.

The working pressure during the vapor-phase partial oxidation of acrolein to acrylic acid according to the invention (especially at the beginning of operation of the stationary catalyst bed) may be lower than normal pressure (for example, it may be up to 0.5 bar) or may correspond to normal pressure. In typical cases, the working pressure in the vapor-phase partial oxidation of acrolein is from 1 to 5 bar, often from 1 to 3 bar.

The reaction pressure during partial oxidation of acrolein carried out according to the invention usually does not exceed 100 bar. The inventive method in the general case, obviously, can also be combined with the technology for prolonging the service life of the catalyst layer recommended in European patent applications EP-A 990636, EP-A 1106598, EP-A 614872 and German patent applications DE-A 10350822 , DE-A 10232748, DE-A 10351269 and DE-A 10 2004025445. Thanks to this combination, the service life of the stationary catalyst layer can reach several years.

The molar ratio of oxygen to acrolein in the initial gas mixture intended for the reaction stage of partial oxidation of acrolein to acrylic acid, carried out by the method of the invention in the corresponding stationary catalyst bed (regardless of whether the reaction stage of partial oxidation of propylene precedes or does not precede it), is usually ≥1: 1. The ratio of these components is usually ≤3. The molar ratio of oxygen to acrolein in the specified source gas mixture according to the invention is often in the range from 1: 1 to 2: 1, respectively, from 1: 1 to 1.5: 1. The method proposed in the invention is often carried out using the initial reaction gas mixture 2 (initial gas mixture for the reaction stage of partial oxidation of acrolein) with a volume ratio of acrolein: oxygen: water vapor: inert gas (nl) of 1: (1-3) :( 0-20) :( 3-30), preferably 1: (1-3) :( 0.5-10) :( 7-20).

The content of acrolein in the initial gas mixture intended for the stage of partial oxidation of acrolein (regardless of whether or not the stage of partial oxidation of propylene is carried out before) can be, for example, from 3 or 6% vol. up to 15% vol., often from 4 or 6% vol. up to 10% vol., respectively from 5 to 8% vol. (in terms of the corresponding total volume). The flow rate of the feed gas mixture (feed the reaction gas mixture 2) through a stationary catalyst bed (excluding the bulk layer, consisting only of inert material) in accordance with the invention carried out according to the invention, the conversion of acrolein to acrylic acid in a typical case, typically similar to the reaction stage of conversion of propylene to acrolein, is from 1000 to 10000 nl / l · h, most often from 1000 to 5000 nl / l · h, often from 1500 to 4000 nl / l · h.

In the case of partial oxidation of propylene to acrolein according to the invention, the stationary layers of fresh catalyst are usually operated in such a way that after establishing a constant composition of the initial reaction gas mixture 1 and its constant flow through the stationary layers of the catalyst for partial oxidation of propylene, such a temperature is established for these layers (respectively, the temperature of the thermostatic medium to the temperature zone of the tubular reactor) at which the degree of conversion of propylene (U ^Pro ) achieved as a result of a single transmission of the reaction gas mixture 1 through stationary catalyst beds, it was at least 93 mol%. When using more efficient catalysts, the conversion of propylene (U ^Pro ) can also reach ≥94 mol%, ≥95 mol%, ≥96 mol%. or ≥97 mol%, and often even higher values.

While continuing the process of heterogeneously catalyzed partial oxidation of propylene to acrolein, the composition of the initial reaction gas mixture 1 and its flow rate through the corresponding stationary catalyst beds are observed to be constant (the flow rate of the initial reaction gas mixture 1 is brought into line with market fluctuations if necessary). The decrease in the activity of the stationary catalyst layers, which over time occurs under similar production conditions, is usually counteracted, first of all, by increasing their temperature (the temperature of the thermostatic medium entering the temperature zone of tubular reactors; the flow rate of the thermostatic medium also usually remains mostly constant), which allows you to maintain the degree of conversion of propylene, achieved by a single pass of the initial reaction gas mixture, at a given level not (i.e., U ^Pro is ≥93 mol%, ≥94 mol%, ≥95 mol%, ≥96 mol%, or ≥97 mol%).

In addition, according to the invention, it is preferable that such a technology of vapor-phase partial oxidation of propylene to acrolein, in accordance with which the technological process is interrupted from time to time, and specified in the German patent application, is passed through it at a temperature of the stationary catalyst layer of 250 to 550 ° C. DE-A 10351269 a gas mixture G consisting of molecular oxygen, an inert gas and, if necessary, water vapor. Then, the partial oxidation of propylene is continued while maintaining its conditions mostly constant (restoration of the previous flow rate of propylene through stationary catalyst beds is preferably slow) and the temperature of the stationary catalyst beds is set at which the degree of conversion of propylene reaches a predetermined value. With the same degree of conversion of propylene, the corresponding temperature, as a rule, is slightly lower than the temperature that the stationary catalyst layer had until the partial oxidation process was terminated in order to pass the gas mixture G. Partial oxidation of propylene was continued at this temperature of the stationary catalyst layers and the constancy of other reaction conditions moreover, the decrease in the activity of stationary catalyst layers occurring over time in accordance with the Option again oppose occasionally raising the temperature of the stationary catalyst beds. According to the invention, during, for example, the following calendar year, it is advisable to interrupt the partial oxidation process at least once so that gas mixture G is passed through the stationary catalyst beds. After this, the partial oxidation is continued again, as indicated above, and so on. In case the achieved selectivity of the formation of the target product ceases to satisfy the relevant requirements, for example, in one of the at least two corresponding systems of oxidation reactors, the above-mentioned replacement of part or the total amount of catalyst is carried out, after which the process according to the invention is continued.

Accordingly, when implementing the method of the invention, the stationary layers of a fresh catalyst for partial oxidation of acrolein to acrylic acid are usually operated in such a way that after establishing a constant mode of this reaction stage and a constant composition of the initial reaction gas mixture 2 and its flow rate through the stationary catalyst layers, such a temperature of these layers (respectively, the temperature at which the thermostatic medium enters the temperature zone of the tubular reactor), at which the degree the conversion of acrolein (U ^Acr ), achieved by a single pass of the reaction gas mixture 2 through stationary catalyst beds, was at least 90 mol%. When using more effective catalysts, the degree of conversion of acrolein (U ^Acr ) can reach ≥92 mol%, ≥94 mol%, ≥96 mol%. or ≥98 mol%, and often even ≥99 mol%. and higher values.

While continuing the process of heterogeneously catalyzed partial oxidation of acrolein to acrylic acid, the composition of the initial reaction gas mixture 2 and its flow rate through the corresponding stationary catalyst beds are observed to be constant (the flow rate of the initial reaction gas mixture 2 is brought into line with market fluctuations if necessary). The decrease in the activity of the stationary catalyst layers, which over time occurs under similar production conditions, is usually counteracted, first of all, by increasing their temperature (the temperature of the thermostatic medium entering the temperature zone of tubular reactors; the flow rate of the thermostatic medium also usually remains mostly constant), which allows you to maintain the degree of conversion of acrolein with a single pass of the initial reaction gas mixture 2 at a given level (i.e., U ^{A cr} is ≥90 mol%, ≥92 mol%, ≥94 mol%, ≥96 mol%, ≥98 mol% or ≥99 mol%).

In addition, it is preferable to perform the partial-phase partial oxidation of acrolein to acrylic acid, according to which, for example, before undertaking an increase in the temperature of the stationary catalyst layers by a value long-term component of ≥10 ° С or ≥8 ° С (relative to the temperature established before in this stationary layer), vapor-phase partial oxidation is interrupted at least once at a temperature of stationary catalyst layers of 200 to 450 ° C through a stationary layer atalizatora partial oxidation of acrolein to acrylic acid is passed gas mixture G (skipped when the two-step partial oxidation of propylene to acrylic acid via fixed layers partial oxidation of propylene to acrolein catalyst). Then, the process of partial oxidation of acrolein is continued while maintaining its conditions predominantly constant (restoration of the previous consumption of acrolein through an appropriate stationary catalyst bed is preferably carried out slowly, for example, in accordance with German patent application DE-A 10337788) and the temperature of the stationary catalyst beds is set at which the degree of conversion of acrolein reaches a predetermined value. With the same degree of conversion of acrolein, the corresponding temperature, as a rule, is slightly lower than the temperature that the stationary catalyst layer had until the partial oxidation process was completed in order to pass the gas mixture G. Partial oxidation of propylene is continued at this temperature of the stationary catalyst layer and the constancy of other reaction conditions, moreover, the decrease in the activity of the stationary catalyst layers occurring over time in accordance with also demanded embodiment again oppose occasionally raising the temperature of the stationary catalyst beds. For example, before undertaking an increase in the temperature of the stationary catalyst layers by a value of long-term component of ≥10 ° С or ≥8 ° С, the process of partial oxidation of acrolein is again interrupted with the aim of passing through a stationary catalyst layer the partial oxidation of acrolein to acrylic acid gas mixture G (if necessary, through a stationary catalyst bed of the reaction stage of propylene oxidation). After this, the partial oxidation of acrolein is again carried out, as described above, and so on. In case the achieved selectivity of the formation of the target product ceases to satisfy the relevant requirements, for example, in one of the at least two corresponding systems of oxidation reactors, the above-mentioned replacement of part or the total amount of catalyst is carried out, after which the process according to the invention is continued.

In general, the heterogeneously catalyzed partial oxidation of acrolein to acrylic acid should be carried out in such a way that 1.5 to 3.5% vol. oxygen. According to the invention, acrylic acid is preferably isolated from a mixture of gas streams. Such a separation of acrylic acid and, as a rule, accompanying formation of recirculated gas, can be carried out, for example, on the extraction line of the target product, as proposed in international application WO 97/48669, US patent application US-A 2004/0242826, international application WO 01 / 96271 and U.S. Patent No. 6,410,785.

Since the separation efficiency of distillation columns with increasing the number of theoretical stages, as a rule, increases, the necessary degree of purity of the crude target product according to the invention can be achieved, for example, using small, and therefore more economical distillation columns (i.e., having a small number of theoretical separation stages) with longer periods of their operation.

In the case where n oxidation reactor systems (n is ≥2) operate in accordance with the method of the invention in such a way that the mixed stream contains the target compounds obtained in all n oxidation reactor systems, according to the invention, such a difference in the durations of the operating periods n catalysts loaded into n oxidation reactor systems so that the differences between successive durations are predominantly the same and there is no coincidence of either of the following successive durations.

The present invention provides a method for producing at least one target organic compound, as set forth below in a slightly modified formulation, which comprises:

a) a heterogeneously catalyzed vapor-phase partial oxidation of at least one of the starting organic compounds with molecular oxygen in two parallel operating systems of oxidation reactors loaded with catalysts, leading to the formation of two streams of the resulting gas, respectively containing the target compound and correspondingly formed in one of the two reactor systems oxidation, and

b) the subsequent selection of at least one target compound from two streams of the resulting gas with the formation of one stream of crude target product,

according to which

c) before separation, two streams of the obtained gas, or during the separation process, two subsequent streams containing the target product, if necessary formed during the conversion of two streams of the obtained gas into one stream of the crude target product, and / or after separation, the flows of the crude target product, formed in the process of separation from two streams of the resulting gas are mixed with each other in a mixed stream,

characterized in that

one of the two catalysts loaded into two parallel operating systems of oxidation reactors contains a partial amount of catalyst, the duration of which is already realized heterogeneously catalyzed vapor-phase partial oxidation which is longer than on all parts of the other loaded catalyst.

In accordance with the method of the invention, more than one target organic compound can obviously be synthesized simultaneously. A suitable example is the partial oxidation of propane, during which, as a rule, the simultaneous formation of acrolein and acrylic acid occurs. Similarly, with partial ammoxidation of propylene and / or propane, the simultaneous formation of acrylic acid and acrylonitrile can occur, which is typical if the selected ammonia content in the reaction gas mixture is lower than the corresponding stoichiometric amount. In accordance with another embodiment, to simultaneously obtain more than one target product, you can also use the original reaction gas mixture containing more than one source compound. In conclusion, it should be noted that the principle of the method proposed in the invention can also be used for catalyzed synthesis of esters or other catalytic reactions. According to the invention, it is also important that the target compound is always formed with an appropriate specification of the content of side components.

In this case, the target organic compound can primarily be acrylic acid and / or methacrylic acid. Suitable alcohols (e.g. monohydric or polyhydric) are primarily alkanols, in particular alkanols with 1-8 carbon atoms (especially monohydric), i.e., for example, methanol, ethanol, 2-ethylhexanol, n-butanol and / or tert- butanol.

Examples and comparative examples of a two-stage heterogeneously catalyzed vapor-phase partial oxidation of propylene to acrylic acid

A) The general structure of the experiments

I. Reactors of the first reaction stage (oxidation of propylene to acrolein)

The reactor was a double-walled cylinder made of special steel (a cylindrical guide tube surrounded by a cylindrical tank). The thickness of all walls ranged from 2 to 5 mm.

The inner diameter of the cylindrical tank was 91 mm. The inner diameter of the guide tube was about 60 mm.

The double-walled cylinder was sealed on top with a lid, bottom to bottom.

The contact tube made of special steel (total length 400 cm, inner diameter 26 mm, outer diameter 30 mm, wall thickness 2 mm) was placed in the cylindrical guide tube inside the cylindrical tank so that the contact tube protruded from the upper and lower sides of the cylindrical tank sealed with appropriate cover and bottom. The coolant (salt melt, consisting of 53% by mass of potassium nitrate, 40% by mass of sodium nitrite and 7% by mass of sodium nitrate) was located in a cylindrical tank connected to the guide tube. To create the most uniform thermal boundary conditions on the outer surface of the contact tube along its entire length (400 cm), the coolant was passed through a cylindrical tank with the aid of a propeller pump to thermostat the latter, and then through the intermediate space between the guide tube and the contact tube (for the purpose of temperature control of the contact tube). Then, the molten salt was removed from the cylindrical tank.

The temperature of the coolant was controlled as necessary by means of an electric heater worn on the outer jacket of the cylindrical tank. In other cases, air cooling was carried out.

Reactor power

The salt melt and the initial reaction gas mixture 1 were passed through a single-stage reactor in a direct flow (if you look at the reactor from above). The initial reaction gas mixture 1 entered the contact tube from below. The temperature of the reaction gas mixture introduced into the contact tube was 165 ° C.

Salt melt with a temperature T ^{ein was} also fed into the cylindrical guide tube from below and removed from it from above with a temperature T ^aus exceeding its inlet temperature (T ^ein ) by up to 2 ° С. The temperature of the salt melt at the inlet ( ^Tein ), which is about 320 ° С, was always calculated in such a way that, when the reaction gas mixture was passed through the contact tube once, the propylene conversion in all cases was 97.5 ± 0.1 mol%.

Filling contact tubes (bottom to top)

Section A 90 cm long was filled with steatite balls with a diameter of 4 to 5 mm, forming a preliminary bulk layer.

Section B, 100 cm long, was filled with a catalyst, which is a homogeneous mixture of 30% of the mass, steatite rings with dimensions of 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) and 70% of the mass. a one-piece catalyst similar to the site forming catalyst C.

A 200 cm long section was filled with a one-piece ring-shaped catalyst with dimensions of 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) obtained according to example 1 from German patent application DE-A 10046957 (stoichiometric composition [Bi ₂ W ₂ O ₉ × 2 WO ₃ ] _0.5 [Mo ₁₂ Co _5.5 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ ).

Section D with a length of 10 cm was filled with steatite rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter), forming the final bulk layer.

Two reactors of the above type were operated in parallel.

II. Intermediate cooling and possible intermediate oxygen supply (in the form of air)

The flows of gases generated in both reactors of the first reaction stage, for the purpose of intermediate cooling (due to indirect heat exchange with air) were jointly passed through a connecting pipe made of special steel (length 40 cm, inner diameter 26 mm, outer diameter 30 mm, wall thickness 2 mm ; the tube is wrapped with insulating material 1 cm thick) in the middle part of which an inert bulk layer of steatite rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) was placed, which was Y-obr an off flanged directly to the contact tubes of the first reaction stage.

The temperature of the mixture of gaseous product flows at the inlet to the connecting tube was more than 320 ° C, while its temperature at the outlet of the connecting tube corresponded to an interval from 200 to 270 ° C.

At the end of the connecting tube, if necessary, air compressed to the pressure of the mixed stream could be added to the cooled mixture of gaseous product streams. Two equal parts of the resulting reaction gas mixture 2 entered directly into two parallel contact tubes intended for the second reaction stage, to which the other end of the above connecting pipe was also Y-shaped.

III. Reactors of the second reaction stage (oxidation of acrolein to acrylic acid)

We used reactors with contact tubes filled with a stationary layer, structurally similar to the reactors of the first reaction stage discussed above. Salt melt and the initial reaction gas mixture were also supplied to each of the reactors in direct flow (if you look at the reactor from above). Salt melt into the guide tube, and the initial reaction gas mixture 2 into the contact tube was also supplied from below. The temperature of the salt melt at the inlet (T ^ein ), which is about 263 ° C, was constantly controlled so that in all cases with a single pass of the reaction gas mixture, the degree of conversion of acrolein of 99.3 ± 0.1 mol% was achieved. The temperature of the salt melt at the outlet of the reactor (T ^aus ) exceeded its inlet temperature (T ^ein ) by up to 2 ° C.

Filling contact tubes (bottom to top)

Section A with a length of 70 cm was filled with steatite rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter), forming a preliminary bulk layer.

Plot In a length of 100 cm was filled with a catalyst, which is a homogeneous mixture of 30% of the mass. steatite rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) and 70% of the mass. a shell catalyst similar to the catalyst forming section C.

A 200 cm long section was filled with a shell catalyst in the form of rings with dimensions of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) obtained according to example 5 from German patent application DE-A 10046928 (stoichiometric composition of Mo ₁₂ V ₃ W _1.2 Cu _2.4 O _x ).

Section D with a length of 30 cm was filled with steatite balls with a diameter of 4 to 5 mm, forming the final bulk layer.

IV. Isolation of acrylic acid from a mixture of gas streams obtained in the second reaction stage

Both are produced in the second reaction stage, combined gas stream, said flow of gaseous products subjected in the venturi separator direct cooling water at 4 ° C containing as a polymerization inhibitor hydroquinone in a concentration of 350 million ^-1 wt. (Venturi tubes of the same design, acceleration of the gas mixture at the narrowest point of the Venturi, simultaneous injection of cooling water and intensive mixing in the turbulent flow field with high pressure losses; separation of the liquid phase in a series-connected separator), and the resulting mixture was sent to a separator with the purpose of the separation of the liquid phase. The separated aqueous phase was passed through a heat exchanger and recycled to a Venturi separator (360 L / h). The excess aqueous phase was continuously withdrawn from the system.

The mixed gas stream, cooled to a temperature of 30 ° C, entered the lower part of the absorption column with eleven cap plates 12 mm in diameter and the same distance between them, comprising 54 mm, into the upper part of which countercurrent stabilized hydroquinone was used, which was used as an absorbent and cooled to temperature 2 ° С water with a flow rate of 1.10 kg / h. 1.7 kg / h of aqueous acrylic acid with a concentration of about 40% of the mass were taken from the cube of the absorption column. The residual gas leaving the upper part of the absorption column was sent to combustion, if necessary, and / or used as a recycle gas to form the initial reaction gas mixture 1 (compressed by a compressor and returned to the reactors designed for the first reaction stage).

C) The results obtained depending on the loaded catalysts and the composition of the initial reaction gas mixture

Comparative Example 1

Fresh reactor was charged into both reactors of the first reaction stage and both reactors of the second reaction stage.

The initial reaction gas mixture, sent to both reactors of the first reaction stage, had the following composition:

5.3% vol. propylene

2.4% vol. water,

0.7% vol. components other than propylene, water, oxygen and nitrogen,

molecular oxygen in an amount corresponding to its molar ratio to propylene of 1.52: 1, and

molecular nitrogen (up to 100% vol.).

The propylene flow rate through the catalyst loaded into the contact tubes of both first stage reactors was 110 nl / l · h. Air was used as a source of fresh oxygen. One volume percent of fresh propylene in the initial reaction gas mixture corresponded to 8.0% vol. recirculated gas. Secondary air was introduced into the mixture of gaseous product streams formed in the first reaction stage. The amount of secondary air was calculated so that its ratio to fresh propylene was 1.45: 1 (respectively, in nl). In accordance with this, the residual oxygen content in the gaseous product formed in the second reaction stage was 3.0% vol. The pilot plant was continuously operated in the indicated mode for a period of more than 28 weeks. Table 1 shows the selectivity for the formation of the target product (acrylic acid) S ^AA depending on the duration of operation of the pilot plant (in weeks), as well as the selectivity for the formation of by-products: acetic acid (S ^HAc ) and formaldehyde (S ^F ), respectively, in% mol . in terms of converted propylene, depending on the duration of operation of the pilot plant (all data relate to the products of the second reaction stage). In addition, table 1 shows the molar ratio of acrylic acid to acetic acid (V) in the aqueous absorbate.

Table Operating time S ^AA S ^HAc S ^f V Starting period 86.8 2 1,2 43,4 four 88 1.9 1,1 46.3 8 88.7 1.8 1.05 49.3 12 89.4 1.75 0.95 51,4 16 89.9 1.7 0.9 52,4 twenty 90.3 1.65 0.85 54.7 24 90.8 1,62 0.82 56.0 28 91.2 1,6 0.8 57

Subsequent separation was subject to the aqueous absorbent containing the target product with a V ratio of 43.4.

Example 1

At the beginning of the synthesis, comparative example 1 was repeated. After 2,200 kg of acrylic acid were synthesized without interrupting the process carried out in accordance with comparative example 1, the process was stopped and the catalyst loaded in only one of the two systems of two-stage oxidation reactors was replaced a similar but fresh catalyst. Then the synthesis was continued similarly to comparative example 1. The results obtained after interruption of the technological process, depending on the duration of operation of the experimental setup (in weeks), are shown in table 2.

Table Operating time S ^AA S ^HAc S ^f V Starting period 89 1.7 1,0 52,4 four 89.6 1,6 0.9 56 8 89.9 1,6 0.9 56.2 12 90.2 1,6 0.9 56.4 16 90.5 1,5 0.8 60.3 twenty 90.7 1,5 0.8 60.5 24 91.0 1,5 0.8 60.7 28 91.2 1,5 0.8 60.8

Subsequent separation was only subject to the aqueous product containing the target product with a V ratio of 52.4.

Reference Example 2

Comparative example 1 was repeated (upon dilution of the catalyst of section B of the second reaction stage, comprising 40% by mass), however, the gas mixture entering the first reaction stage had the following composition:

7.3% vol. propylene

10% vol. water,

0.7% vol. components other than propylene, water, oxygen and nitrogen,

molecular oxygen in an amount corresponding to its molar ratio to propylene of 1.73: 1, and

molecular nitrogen (up to 100% vol.).

Secondary air was not added. One volume percent of fresh propylene in the initial reaction gas mixture corresponded to 3.5% vol. recirculated gas.

The experimental results depending on the duration of operation of the experimental installation (in weeks) are shown in table 3.

Table 3 Operating time S ^AA S ^HAc S ^f V Starting period 86.7 2.25 1.35 38.5 four 87.9 2.15 1.25 40.9 8 88.7 2.05 1,2 43.3 12 89.3 2 1,1 44.7 16 89.5 1.95 1.05 45.9 twenty 90.1 1.9 one 47.4 24 90.3 1.87 0.97 48.3 28 90.6 1.85 0.95 49.0

Subsequent separation was subject to the aqueous absorbent containing the target product with a V ratio of 38.5.

Example 2

At the beginning of the synthesis, comparative example 2 was repeated. After, without interrupting the process carried out in accordance with comparative example 1, 2,200 kg of acrylic acid were synthesized, the process was stopped and the catalyst loaded in only one of the two systems of two-stage oxidation reactors was replaced a similar but fresh catalyst. Then the synthesis was continued similarly to comparative example 2. The results obtained after the interruption of the technological process, depending on the duration of operation of the experimental setup (in weeks), are shown in table 4.

Table 4 Operating time S ^AA S ^HAc S ^f V Starting period 88.8 2.1 1,2 42.3 four 89.4 2.0 1,1 44.7 8 89.8 1.9 1,1 47.3 12 90.1 1.9 1,0 47.4 16 90.2 1.9 1,0 47.5 twenty 90.5 1.8 1,0 50.3 24 90.6 1.8 0.9 50.3 28 90.8 1.8 0.9 50,4

Subsequent separation was subject only to the aqueous product containing the target product with a V ratio of 42.3.

The method according to paragraphs 13-18 of the claims is the basis, for example, for the application proposed in the invention method.

Preliminary descriptions of applications for US patent number 60 / 656,881 (filed March 1, 2005) and number 60 / 670,289 (filed April 12, 2005) are incorporated into this application by reference. These descriptions may contain numerous changes and discrepancies compared to this description. In this regard, it should be assumed that the implementation of the invention in accordance with the following formula may differ from these preliminary descriptions.

Claims (18)

1. The method of obtaining acrolein, acrylic acid, methacrolein or methacrylic acid as the target product
a) heterogeneously catalyzed vapor-phase partial oxidation of at least one starting organic compound selected from propylene, propane, isobutylene, isobutane, acrolein or methacrolein, with molecular oxygen in at least two parallel functioning oxidation reactor systems with catalysts loaded into them, leading to the formation of at least two streams of produced gas, respectively containing the target compound and correspondingly forming in one of at least two ctor oxidation, and
b) subsequent separation of the target product from at least two streams of the obtained gas with the formation of at least one stream of crude target product, in accordance with which
c) before isolation, at least two of the at least two streams of the resulting gas are mixed with each other in a mixed stream, and
in the case of a change in the selectivity of the formation of the target product and / or by-products that occurs during operation, not in all at least two parallel-functioning oxidation reactor systems in which the target products contained in the mixed stream are formed, in parallel, the entire amount or partial amount is replaced with a fresh catalyst catalyst. 2. The method according to claim 1, characterized in that at least one of the catalysts loaded in at least two parallel-functioning systems of oxidation reactors, on which the desired products contained in the mixed stream were formed, contains at least a partial amount of catalyst, duration already realized heterogeneously catalyzed vapor-phase partial oxidation on which at least 30 calendar days more than on all parts of at least one other loaded catalyst. 3. The method according to claim 1 or 2, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is carried out in two parallel operating systems of oxidation reactors and the selection of the target product from the mixed stream of two product streams. 4. The method according to claim 1 or 2, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is a two-stage heterogeneously catalyzed partial oxidation of propylene to acrylic acid. 5. The method according to claim 1 or 2, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is a one-stage heterogeneously catalyzed partial oxidation of propane to acrylic acid. 6. The method according to claim 1 or 2, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is a two-stage heterogeneously catalyzed partial oxidation of isobutylene to methacrylic acid. 7. The method according to claim 1 or 2, characterized in that at least two parallel-functioning systems of oxidation reactors consist of two parallel-functioning twin tubular reactors. 8. The method according to claim 4, characterized in that the catalysts of the first reaction stage include polymetallic oxide masses containing molybdenum (Mo), bismuth (Bi) and iron (Fe). 9. The method according to claim 4, characterized in that the catalysts of the second reaction stage include polymetallic oxide masses containing molybdenum (Mo) and vanadium (V). 10. The method according to claim 8, characterized in that the catalysts of the second reaction stage include polymetallic oxide masses containing molybdenum (Mo) and vanadium (V). 11. The method according to claim 1 or 2, characterized in that the selection of at least one target product from at least two streams of the resulting gas includes fractionating condensation. 12. The method according to claim 1 or 2, characterized in that the allocation of at least one target product from at least two streams of the resulting gas includes absorption. 13. A method of producing acrolein, acrylic acid, methacrolein or methacrylic acid as the target product by heterogeneously catalyzed vapor-phase partial oxidation of at least one starting organic compound selected from propylene, propane, isobutylene, isobutane, acrolein or methacrolein, with molecular oxygen in at least two parallel-functioning systems of oxidation reactors with catalysts loaded in them, leading to the formation of at least two streams of produced gas, with respectively containing the target product and correspondingly formed in one of the at least two oxidation reactor systems, first forming a common stream of the initial reaction gas mixture containing at least one initial organic compound, which is then sent through the distribution system to at least two parallel functioning oxidation reactor systems, and in the case of changes in the selectivity of the formation of the target product and / or by-products during operation, not in of at least two parallel operating systems oxidation reactor, in which formed in the mixed stream contained the target compound, parallel replaced with fresh catalyst entire amount or a partial amount of catalyst. 14. The method according to p. 13, characterized in that at least one of the catalysts loaded into at least two parallel-functioning systems of oxidation reactors, contains at least a partial amount of catalyst, the duration of the already implemented heterogeneously catalyzed vapor-phase partial oxidation, on which at least 30 calendar days more than all parts of at least another loaded catalyst. 15. The method according to item 13 or 14, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is a two-stage heterogeneously catalyzed partial oxidation of propylene to acrylic acid. 16. The method according to item 13 or 14, characterized in that the heterogeneously catalyzed vapor-phase partial oxidation is a one-stage heterogeneously catalyzed partial oxidation of propane to acrylic acid. 17. The method according to item 13 or 14, characterized in that at least two parallel-functioning systems of oxidation reactors consist of two parallel-functioning twin tubular reactors. 18. The method according to clause 15, wherein the catalysts of the first reaction stage include polymetallic oxide masses containing molybdenum (Mo), bismuth (Bi) and iron (Fe), and the catalysts of the second reaction stage include polymetallic oxide masses containing molybdenum ( Mo) and vanadium (V).