RU2314284C2 - Aromatic dicarboxylic acid continuous production process - Google Patents

Abstract

FIELD: process for continuous production of terephthalic or isophthalic acid by liquid phase oxidation of respective aromatic dialkyl hydrocarbon.

SUBSTANCE: in order to prepare reaction solvent at least part of mother liquor separated from produced acid is used. Oxidation catalyst concentration in mother liquor is measured beforehand and then oxidation catalyst concentration is continuously corrected due to direct control (regardless of water content). Predetermined quantities of solvent and aromatic hydrocarbon as raw material are continuously supplied to oxidizing reactor for oxidizing aromatic hydrocarbon by means of molecular oxygen. Water concentration in condensate returned from reactor is measured and controlled by means of discharged quantity of returned condensate for stabilizing water concentration in reaction system in order to obtain in the result dicarboxylic acid. Oxidation temperature is sustained stable due to controlling pressure; oxygen concentration in exhaust gas is sustained stable due to controlling feed of oxygen containing gas.

EFFECT: production of stable quality acid, rational consumption of resources, power and water for performing process.

Description

State of the art

The invention relates to a method for the continuous production of aromatic dicarboxylic acid by liquid-phase oxidation of a dialkylaromatic hydrocarbon to produce an acid of stable quality, in particular to a method for the continuous production of terephthalic acid and isophthalic acid.

A method for the continuous production of carboxylic acids by liquid-phase oxidation by molecular oxygen (or an oxygen-containing gas) in the presence of a catalyst containing a heavy metal compound and a bromine donor compound (hereinafter, the combination of metal and bromine compounds will be referred to as oxidation catalyst) in acetic acid as a solvent is described in the patent JP-B-39-8818. This method is widely used / implemented in the industrial production of carboxylic acids, based on the method described in the patent. In particular, terephthalic and isophthalic acids are produced on a large scale in a continuous process, since they are widely used in industry.

The liquid phase oxidation of an alkyl aromatic hydrocarbon, which is the basis of the process, is an instant free radical reaction of an alkyl aromatic hydrocarbon with activated oxygen. Since many parameters directly affect the reaction proceeding in the reactor, the effect on the reaction of each of them is successively investigated while maintaining the values of the other parameters constant. A production method is proposed that takes into account all these effects in general.

In addition, in patent applications JP-A-50-32140 and JP-A-10-259160 as a production system, a method is proposed in which the resulting aromatic carboxylic acid is separated from the mixture of oxidation products and at least part of the resulting mother liquor without its further processing is recycled for reuse as a solvent.

Thus, in the industrial method for producing aromatic carboxylic acid, many parameters influence both the reaction and the reuse of the resulting mother liquor as a result of its recirculation. The amount of recycled mother liquor and the content of catalyst and water in it may vary depending on the method of processing the solvent after the oxidation step, and the preparation of the reaction solvent further increases the number of parameters affecting the oxidation. Therefore, upon receipt of continuous action in plants, a greater number of parameters affect oxidation, which, in turn, leads to a less stable oxidation process.

Therefore, the method is complex and ineffective for continuous and stable production for a long period of time on an industrial scale, although the oxidation step can be effectively carried out for a short period of time as a result of independent from each other regulation of individual parameters that determine the reaction conditions, as described in the above patent applications.

The recycled mother liquor contains a high concentration of water and, as a result of some losses in the reaction system (the loss varies from 15 to 50 wt.%) Associated with the course of the reaction, a lower concentration of the oxidation catalyst and less bromine. To prepare the reaction solvent from the mother liquor, regenerated acetic acid and the addition of a catalyst component are necessary to simultaneously maintain its amount and composition (with indication of the corresponding concentrations of cobalt, manganese, bromine, and water) within controlled ranges. However, in practice it is difficult to prepare a reaction solvent of a stable composition for feeding it into the reactor. A change in the composition of the reaction solvent so adversely affects the catalytic activity, which leads to less stability of the oxidation process and the quality of the resulting carboxylic acid. Along with this, the oxidation process, as well as the pressure and temperature of the reaction are affected by a change in the concentration of water, the reaction inhibitor, which as a result makes the reaction itself less stable.

In addition, a compromise has been found between the quality of carboxylic acid (depending on the content of impurities represented by 4-carboxybenzaldehyde (4-KBA)) obtained by oxidation in acetic acid medium and the amount of acetic acid loss due to oxidative degradation due to possible oxidation, as described in patent applications JP-A-51-127037 and JP-A-51-136642. Therefore, in order to efficiently and stably carry out the oxidation reaction and ensure higher economic indicators of obtaining and product quality stability when producing carboxylic acid on an industrial scale, it is necessary to carefully analyze the situation with the compromise between higher purity of carboxylic acid and lower losses of acetic acid.

SUMMARY OF THE INVENTION

The traditional block diagram of the production of aromatic dicarboxylic acid is shown in Fig. 8, where the oxidation step is depicted in the central part of the scheme, and hereinafter, a method with those problems to be solved will be generally described.

First of all, a container 101 is used as a mixer for supplying p-xylene to it, in which hydrocarbons are mixed with a solvent, or a solvent is prepared in it, as described in patent applications JP-A-10-218837 and JP-A-10 -259160.

Capacity 101 is used to prepare the reaction solvent from a recyclable / reusable mother liquor from reservoir 110 and acetic acid (fresh / regenerated acetic acid) and to replenish the amount of oxidation catalyst, regardless of whether raw materials are introduced, p-xylene or not, and, in addition to in addition, to adjust the composition of the pre-prepared solvent by using a fresh catalyst in the form of a metal compound (in the form of a solution or liquid) and a fresh bromine compound (in the form of a solution or liquid) to fill the deficiency in the solvent of a metal catalyst and bromine. The deficiency of the metal catalyst and bromine is determined by measuring their concentrations (analyzed at A10) and the required quantities of fresh metal and bromine compounds are calculated respectively (analyzer / flow regulator, AFC10). When introducing raw materials, p-xylene, the raw material mixer 101 is used to provide p-xylene, replenish the amount of solvent so that it satisfies its predetermined ratio to p-xylene (p-xylene concentration), and also to replenish the amount of oxidation catalyst (catalyst concentration ) upon receipt of them mixtures. On the other hand, when the feed, p-xylene, is not added, this capacity is used to make up the amount of solvent, as well as the oxidation catalyst (catalyst concentration), to prepare the reaction solvent. The composition of the mixture (or solvent) thus obtained is analyzed, which is then adjusted by feedback control.

With this technique, the amount of solvent can be replenished to its predetermined ratio to raw materials, p-xylene (relative solvent consumption or p-xylene concentration), but the concentration or composition of the oxidation catalyst cannot be quickly, without delay, restored, since the amount of circulating stock solution and the concentration of catalyst in it, which leads to instability of the cooking process. In addition, during the circulation of the mother liquor, it is practically impossible to control the water content, which reaches a high level in it.

To overcome this problem, part of the condensate return from the oxidation reactor 2 is withdrawn from the bottom of the gas-liquid separator 104 and fed to the oxidation reactor 102 such an appropriate amount of fresh acetic acid so that the water content in the reaction solution, which may increase due to the high water content in the solvent and the formation of water as a result of the reaction, was maintained at a constant value (15 wt.%) or less, as described in patent application JP-A-50-32140. In an industrial-scale continuous process, the acetic acid supply corresponding to the condensate removed is carried out in advance to a tank for mixing the feed 101 in order to maintain the water content in the mother liquor at 15 wt.% Or lower.

With this approach, a change in the amount of condensate removed (increasing or decreasing) is an effective measure to change the water content (higher or lower) in the reaction solution, but this can lead to a violation of the material balance in the reaction system and, thus, make the oxidation process unstable . A change in the supply of acetic acid leads to a change in the content of materials (the content of catalyst and water) in the tank for mixing raw materials 101 and the composition of the mixture containing raw materials prepared in it, which also leads to unstable oxidation.

More specifically, by additionally introduced acetic acid is meant regenerated acetic acid, discharged from the bottom of the distillation column dehydration 112 with a water content of about 5 wt.% (From 2 to 10 wt.%). The water content in acetic acid can constantly change. It should be noted that under fresh / regenerated acetic acid is meant acetic acid, optionally replenished by fresh industrial acetic acid (acetic acid 99.5 wt.% Purity), and it corresponds in quality to regenerated acetic acid. Washed acetic acid is added to fresh / regenerated acetic acid, which is obtained by washing / absorbing acetic acid vapors from the reaction exhaust gas on the lower plate of the high pressure gas absorber 105. Such addition of washed acetic acid can lead to a significant change in the water content in fresh / regenerated acetic acid supplied for the preparation of the reaction solvent in a tank for mixing raw materials 101.

When applying the method in which the obtained solid terephthalic acid after its separation in the separator of the "solid phase-liquid" type 107 is washed with acetic acid and the washing (waste) liquid is mixed with the mother liquor for recycling / reuse, the content of the catalyst can also change in the mother liquor and water, depending on the amount of washing (spent) liquid in the mixture.

Thus, in the traditional method for the industrial production of aromatic dicarboxylic acid, the raw material mixture prepared in the tank for mixing the raw material 101 can at any time change a number of technological parameters (relative solvent consumption, concentration and composition of the catalyst, water content). This method is ineffective, since it, in particular, does not apply control measures to accurately control the changing water content.

For oxidation reactor 102, a predetermined amount of a mixture containing a feed (containing p-xylene) or a reaction solvent from a feed mixer 101 is supplied to the reactor along with a predetermined amount of p-xylene, if necessary, supplied via another line (not shown) ; and at the same time, a predetermined amount of an oxygen-containing gas (usually air) is introduced into the reactor 102 through the bottom to conduct oxidation.

In the reactor 102, oxidation occurs in the liquid phase in a certain temperature range while maintaining high pressure in the system. A significant amount of exothermic reaction heat is removed from the reactor 102 through the top with the reaction exhaust gas (exhaust gas) containing solvent vapors generated in the reaction system. The off-gas containing the generated steam is then fed to a condenser / cooler 103 located above the reactor 102 to condense almost all of the generated steam, and the resulting condensate is captured by a gas-liquid separator 104 (at 100 ° C. or lower) and returned to the reactor 102. Therefore, this the design of the system allows the acetic acid (water-containing acetic acid) used as a reaction solvent to be almost completely retained in the system. Since it is necessary that the water content in the reaction solution be maintained at a predetermined level or lower in order to recycle or otherwise use the mother liquor, a portion of the condensate returned to the reactor 102 is withdrawn.

Prior to such a partial withdrawal of condensate, an appropriate amount of acetic acid is supplied to the mixing tank of the raw material 101, as described above. Condensate withdrawal, supply of acetic acid and the water contained in it leads to a change in water content, concentration and composition of the catalyst. In this regard, the traditional method adversely affects the reactivity of the system. The reaction temperature also changes, since the reactor 102 is under pressure, which leads to less stable oxidation.

As for the product, the product mixture containing the obtained terephthalic acid is kept in the reactor 102 for a predetermined period of time, and then sent to a second oxidation reactor (not shown) at a lower pressure than in the reactor 102, following the indications of the LIC liquid level controller which is equipped with the reactor 102, and is subjected to final additional oxidation. The product is then sent to crystallizer 106 and cooled under reduced pressure to crystallize terephthalic acid.

The second oxidation reactor is used to oxidize small amounts of unreacted p-xylene and reaction intermediates such as 4-KBA present in the mixture of products fed from the first oxidation reactor 102, as described in patent applications JP-A-51-39642 and JP-A-56-10138. This oxidation is carried out at the same temperature as in the first oxidation reactor 102, or lower.

The crystalline terephthalic acid formed in the mother liquor in the crystallizer 106 is then sent to a solid phase-liquid separator 107 when it is repeatedly recycled to the product mixture and separated, and washed to obtain a recoverable terephthalic acid precipitate that is impregnated with washing liquid (acetic acid) ) The precipitate is then sent to dryer 108 and dried to obtain the final product, terephthalic acid.

The separated mother liquor is stored for some time in the mother liquor vessel 110 and recycled to prepare the reaction solvent. Acetic acid is usually used to wash the separated terephthalic acid, and the wash acetic acid (spent) can be stored for some time in the tank 111 for reuse with the mother liquor for preparing the reaction solvent.

To stabilize the oxidation reaction of the continuous oxidation method for the industrial production of aromatic carboxylic acid, it is important to prepare a stable reaction solvent and it is important to stabilize the flow of the reaction solvent and its relation to the feedstock, dialkyl aromatic hydrocarbon (relative solvent consumption), as well as the concentration and ratio of components in the catalyst and the concentration of water in the reaction system, as described in detail above. It is also necessary to stabilize the temperature and pressure of the reaction system, and the residence time of the raw materials in it.

However, the reaction solvent is prepared from a mother liquor in which the water content, the concentration of the catalyst and bromine and their ratio in the catalyst composition (the water content from 8 to 15 wt.%, The concentration of the catalyst and bromine and the ratio of bromine to metal are variable) and acetic acid are changed with variable water content (fresh / regenerated acetic acid with a water content of 2 to 10 wt.%). The reaction solvent should be prepared in such a way as to stabilize the relative consumption of the solvent (its relation to the feedstock, dialkyl aromatic hydrocarbon) and the water content, as well as the concentration and ratio of the components of the oxidation catalyst in the reaction system, when the reaction solvent is introduced with partially withdrawn return condensate and the object of the invention is the preparation of the reaction solvent in such a way as to have its exact composition and precisely regulate its flow y.

Another object of the invention is the stabilization of the reaction conditions after the introduction of the reaction solvent, such as the temperature in the reaction system and the oxygen content in the gas used.

The aim of the present invention is to develop a continuous method for the production of aromatic dicarboxylic acid, which primarily allows for a stable oxidation process to obtain a product of dicarboxylic acid, stable quality and oxidation while saving resources and energy, as a result of which the above goals can be achieved.

To achieve the above objectives, the present invention provides a method for producing aromatic dicarboxylic acid containing liquid-phase oxidation of a dialkylaromatic hydrocarbon containing molecular oxygen gas in the presence of a catalyst containing cobalt, manganese and bromine in acetic acid as a solvent, and which contains:

a preliminary step of preparing the reaction solvent in a vessel for preparing the reaction solvent by introducing a cobalt compound, a manganese compound and a bromine compound into a mixture of at least a part of the mother liquor and acetic acid, the mother liquor being obtained by isolating the product, dicarboxylic acid from it; and

an oxidation step comprising an oxidation process, a condensation / cooling process, an output control process, and a feed process, wherein the oxidation process comprises continuously feeding 1 part by weight of dialkyl aromatic hydrocarbon to the oxidation reactor as a feed and from 2.5 to 4 parts by weight of a reaction solvent, which prepare at a preliminary stage, the simultaneous supply of a gas containing molecular oxygen to the oxidation reactor, and the oxidation of the feed in a liquid state in the oxidation reactor; wherein the condensation / cooling process comprises cooling the reaction exhaust gas containing steam that is generated in the oxidation reactor in order to maintain a constant reaction temperature as the oxidation proceeds during the oxidation process, returning condensate obtained by cooling the reaction exhaust gas to the oxidation reactor and withdrawing at least a portion of the return condensate; in which the process of regulating the output includes measuring the concentration of water present, at least in part of the condensate discharged during the condensation / cooling process, and adjusting the amount of output to achieve a predetermined amount of water concentration; and in which the feed process further comprises a feed corresponding to the supply of acetic acid, which is associated with the withdrawn amount, to the oxidation reactor while controlling the withdrawal amount in the process of adjusting the output,

in which, in the oxidation step, the reaction mixture obtained by oxidation in the oxidation reactor is continuously or periodically withdrawn by adjusting the liquid level in the oxidation reactor to obtain a terephthalic acid product.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the condensation / cooling process of the oxidation step comprises cooling the exhaust reaction gas containing steam that forms in the oxidation reactor using two or more condensers / coolers connected in series to each other, condensate recovery from the respective condensers / coolers to the oxidation reactor, and removing at least part of the return condensate from the last condenser / olodilnika.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the preliminary step comprises preparing a reaction solvent containing predetermined amounts of cobalt, manganese and bromine by measuring in advance the concentrations of cobalt, manganese and bromine in the mother liquor introduced by recirculation, and combining the mother liquor with a solution of cobalt and manganese compounds and a solution of bromine compounds in the appropriate amounts required, depending on the measured concentrations of Obalt, manganese and bromine in the mother liquor.

The present invention also provides a process for preparing aromatic dicarboxylic acid, wherein the preliminary step comprises the use of a plurality of containers for preparing a reaction solvent.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the oxidation process of the oxidation step comprises mixing 1 part by weight of dialkyl aromatic hydrocarbon as a feed and from 2.5 to 4 parts by weight of the reaction solvent, which is prepared in the preliminary step, and introducing the resulting mixture into the reactor oxidation.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the oxidation step further comprises a process for controlling the reaction temperature, which controls the reaction temperature in the oxidation reactor by controlling the pressure in the oxidation reactor.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the process of controlling the reaction temperature comprises controlling the pressure in the oxidation reactor by obtaining an uncondensed off-gas reaction gas separated from condensate in a gas-liquid separator, which is obtained in the condensation / cooling process, washing the non-condensed off-gas in the absorber high-pressure gas, and regulating the pressure of the obtained washed off-gas.

The present invention also provides a method for producing aromatic dicarboxylic acid, in which the oxidation step further comprises an oxygen concentration control process that controls the oxygen concentration in the exhaust gas discharged from the oxidation reactor at a predetermined concentration of 8 vol.% Or less, by controlling the supply of oxygen-containing gas supplied to oxidation reactor.

The present invention also provides a method for producing aromatic dicarboxylic acid, wherein the oxygen concentration control process comprises controlling the oxygen concentration in the exhaust gas discharged from the oxidation reactor by supplying a non-condensed reaction gas separated from the condensate to the gas-liquid separator, which is supplied to the condensation / cooling process washing the non-condensed off-gas in the high pressure gas absorber and adjusting the concentration oxygen in the resulting washed off-gas.

Such a system structure and regulation for this method according to the present invention, first of all, allowed to stabilize the oxidation process and thereby obtain a dicarboxylic acid product of stable quality, as well as the implementation of oxidation while saving resources and energy. In particular, stabilization of product quality affects the stability of cleaning operations and polymerization systems at subsequent stages of processing and, most importantly, ensures the receipt of appropriate products of uniform quality. In order for the overall effective production method to be realized, it is also important that the corresponding systems provide a higher yield of the product, as well as a higher saving of resources.

The oxidation unit according to the present invention by suppressing adverse reactions that can occur as a result of changes in the amounts of oxidation catalyst, acetic acid and oxygen-containing gas, gives a direct effect of stabilizing the product yield, optimizing the amount of secondary materials and reducing fluctuations in the consumption of electricity and process steam, leading to efficient production of dicarboxylic acid.

It should be noted that during the oxidation of alkyl aromatic hydrocarbon, a compromise is usually established between the quality of the carboxylic acid produced and the losses due to the oxidative degradation of acetic acid. Therefore, when it is produced commercially, it is desirable to stably produce carboxylic acid of the required quality, but under reaction conditions under which the losses due to oxidative degradation of acetic acid are low.

For example, the relationship between the purity (content of 4-KBA, that is, an intermediate reaction product) of the obtained terephthalic acid and losses due to oxidative degradation of acetic acid is shown in FIG. 4 as one example of industrial scale oxidation of p-xylene. Higher purity of terephthalic acid (lower 4-KBA) leads to higher losses of acetic acid. Thus, when producing terephthalic acid with a given 4-CBA content, the stability (or deviation) of the 4-CBA content in the produced terephthalic acid is the dominant factor for the production economy.

Namely, in the case when the content of 4-CBA according to the technical characteristics of the product is 3000 ppm, an unstable production process with a deviation of ± 500 ppm of 4-CBA should be carried out at a given content of 4-CBA of 2500 ppm (oxidative loss acetic acid destruction: about 43 kg / ton TK). However, if the stability of the process is increased so that it has a deviation of 4-KBA ± 100 ppm, then it can be carried out at a given 4-CBA content of 2900 ppm (losses during oxidative degradation of acetic acid: about 41 kg / ton TC ), which provides a more stable product quality and lower losses during oxidative degradation of acetic acid.

According to the present invention, such an improvement in operational stability can be achieved, respectively, by increasing the number of analysis positions and the frequency of analysis and modification of the control system, which includes, for example, the installation of regulator / setpoint devices and the modification of the pipeline system.

As described in detail above, stable industrial production using appropriate amounts of materials and appropriate energy costs improves product quality, such as product uniformity, and reduces production costs, along with the economies of scale up.

Brief Description of the Drawings

Figure 1 shows the technological scheme of the improved production of terephthalic acid and the implementation of a control system for stabilizing the oxidation reaction according to the present invention.

Figure 2 shows an example of a control system for more stable preparation of the reaction solvent according to the present invention.

Figure 3 shows the relationship between the concentration of water in the mother liquor and the concentration of water in the return condensate in the present invention, which is the dependence of the concentration of water on the return liquid of the first stage and the return liquid of the second stage in the case when the condenser and the refrigerator are connected to the upper part of the reactor in two stages.

Figure 4 presents a graph of the relationship between the content of 4-KBA in the product, (obtained) terephthalic acid, and losses due to oxidative degradation of acetic acid in the example (black circles) and comparative example (white circles) of the present invention.

Figure 5 presents a graph of the concentration of cobalt, bromine and water (H ₂ O) in the reaction solvent (feed solution) and the mother liquor versus reaction time in an example of the present invention.

Figure 6 presents a graph of the content of 4-CBA in the obtained terephthalic acid versus reaction time in the example (black circles) and comparative example (white circles) of the present invention.

Figure 7 presents a graph of the dependence of the concentrations of cobalt, bromine and water (H ₂ O) in the mixture of raw materials (feed solution) and the mother liquor from the reaction time in a comparative example of the present invention.

On Fig presents a flow chart of the traditional general production of terephthalic acid.

Description of symbols

1 - tank for the preparation of the reaction solvent, 1A - tank A for the preparation of the reaction solvent, 1B - tank B for the preparation of the reaction solvent, 2 - oxidation reactor, 3 - condenser / refrigerator, 3A - condenser / refrigerator (steam generator: first stage), 3B - condenser / refrigerator (part with water cooling: the second stage), 4 - gas-liquid separator, 5 - high-pressure gas absorber, 6 - crystallizer, 7 - separator type "solid phase-liquid", 8 - dryer, 9 - product collection, 10 - reservoir for uterine solution a, 11 - a reservoir for washing (spent) liquid, 12 - a distillation column of dehydration, 13 - a vaporizer of the mother liquor, 21 - fresh / regenerated acetic acid, 22 - p-xylene, 23 - a metal catalyst, 24 - a bromine compound, 25 - fresh / regenerated acetic acid, 26 - regenerated acetic acid, 31 - exhaust gas, 32 - water, 33 - fresh / regenerated acetic acid, 34 - waste water, 35 - sediment, 36 - regenerated acetic acid, 37 - fresh / regenerated acetic acid, 40 - product, terephthalic acid, A0 to A4, A1A, A1B - analyzer or analysis position, from FC1 to FC10, FC1B, FC2A, FC3A, FC3B, FC4A, FC4B - flow regulator, PIC1 - pressure regulator, TI - temperature indicator, LIC1 and LIC2 - indicator / liquid level regulator, FFC1 and FFC2 - flow ratio adjuster, TPC1 - temperature-pressure regulator, AFC0, AFC1, AFC3, AFC1A, AFC1B - flow analyzer / adjuster.

Preferred Embodiments

Embodiments of a process for continuously producing an aromatic dicarboxylic acid of the present invention are described with reference to the figures. The authors of the present invention studied the effects of various parameters on the oxidation reaction and conducted studies on the stable preparation and supply of the reaction solvent to achieve a stable continuous oxidation reaction. The inventors of the present invention also developed a method that allows uniformly controlling the progress of the reaction in order to stabilize the oxidation reaction system. As a result, to conduct a continuous oxidation reaction in equipment for the industrial production of aromatic dicarboxylic acid in the preparation of the reaction solvent, only the amount of the reaction solvent, the concentration of the oxidation catalyst contained in it and their ratio in the composition should be taken into account, and the problems were solved by the method of controlling water concentrations in the reaction system without taking into account the concentration of water in the input reaction solvent, based on the following system. Other reaction parameters, such as reaction temperature and oxygen concentration in the exhaust gas, are controlled by the creation of the following process system and its control system, which are developed in the present invention.

The implementation of the process system and its control system according to the present invention is described with reference to figure 1.

(1) The mother liquor from the mother liquor tank 10 and acetic acid (fresh / regenerated acetic acid) are supplied to a tank 1 for preparing a reaction solvent based on predetermined quantities distributed by the flow adjuster FFC1 to prepare a predetermined amount of the reaction solvent. The predetermined quantities in the flow adjuster FFC1 are determined based on information on the supply of solvent supplied to the oxidation reactor 2 from the preparation tank of the reaction solvent 1 through the flow regulator FC5.

At the same time, using an analyzer (analysis position) A1, each concentration of the oxidation catalyst in the circulating mother liquor is measured, and a reaction solvent is prepared in combination with the recycle amount from the flow adjuster FFC1 by adding the metal compound of catalyst 23 and the bromine compound 24 when adjusting the FC4 flow regulators and FC3 analyzer / flow adjuster AFC1 so that the oxidation catalyst in the reaction solvent has a given concentration and a given ratio of components with leaving.

However, in this method, the concentrations of the oxidation catalyst and water in the separated mother liquor, separated in a “solid phase-liquid” separator 7, vary depending on the amount of washing (spent) liquid, as described above. The proportion of bromine in the composition of the catalyst also varies depending on the degree of reactivity. In addition, the concentration of the oxidation catalyst and water varies depending on the ratio of the separated mother liquor and acetic acid. The concentration of water in the prepared solvent also changes due to changes in the concentration of water in the prepared acetic acid (also due to the content of washed acetic acid 26 from the high pressure gas absorber 5). Thus, in the present invention, only a predetermined amount of solvent (or relative solvent consumption, solvent / dialkyl aromatic hydrocarbon weight ratio: 2.5 to 4), concentration and ratio of components in the oxidation catalyst (heavy metal and bromine) in oxidation reactor 2 are controlled in the capacity of the preparation of the reaction solvent 1, and the regulation and preparation are carried out on the basis of a direct-acting regulation system without taking into account water concentrations.

The stability of the concentrations of the oxidation catalyst in the reaction solvent can be confirmed by measurement using an analyzer (analysis position) A2. However, when the concentration of the catalyst in the circulating mother liquor and other similar indicators deviates, they cannot be sufficiently stabilized due to the delay in the measurements of the deviation of the catalyst concentration or because of the relatively small volume of the preparation of the reaction solvent 1 (short residence time), but if of preparation of the reaction solvent, two containers 1A and 1B are used and a double control system of catalyst concentrations is used, containing crude control If the concentration of the catalyst in the tank for preparing the reaction solvent 1A and the precise control of the concentrations of the catalyst in the tank for preparing the reaction solvent 1B, as shown in FIG. 2, the amount of the reaction solvent and the concentration of the catalyst can be stable. In other words, when the solvent prepared in the reaction solvent preparation vessel 1A is introduced into the reaction solvent preparation vessel 1B, the catalyst concentrations at the A1B analysis position are measured and, based on the predetermined amount, the metal catalyst compound and the bromine compound are introduced into the preparation tank 1B in the flow analyzer / AFC1B by adjusting the flow regulators FC4B, FC3B, and, if necessary, acetic acid 25 is introduced therein using the FC2B flow regulator. Thanks to this double concentration control, based on a direct-acting control system, the accuracy of the preparation is improved.

Moreover, in order to supply a stable amount of solvent (relative solvent consumption), it is preferable to use a method in which the amount of solvent in the solvent preparation tanks 1A and 1B is adjusted primarily based on the flow rates determined by the flow adjuster FFC1. For example, a solvent may be supplied to a reaction solvent preparation tank 1B from a reaction solvent preparation vessel 1A in accordance with a liquid level controller LIC2.

(2) The reaction solvent prepared in the vessel for preparing the reaction solvent 1 with a given catalyst concentration is introduced into the oxidation reactor 2 together with a predetermined amount of solvent calculated on the basis of the feed of the raw material, dialkyl aromatic hydrocarbon (determined by the amount of dicarboxylic acid produced), separately or together with the feed dialkylaromatic hydrocarbon 22, when corrected by flow controllers FC5, FC6, based on flow adjuster FFC2. Preferably, the feed, the dialkyl aromatic hydrocarbon 22, and the reaction solvent are mixed in predetermined quantities and then introduced into the oxidation reactor to stabilize the reaction. Even if they are administered separately, it is preferable that they be mixed homogeneously in the mixing vessel or mixer in line before introducing oxidation reactor 2.

In the above system, a reaction solvent containing a stable, predetermined concentration of the oxidation catalyst is supplied at a stable feed (relative solvent flow) relative to the feed of the dialkyl aromatic hydrocarbon.

In this case, the amount of solvent (relative solvent consumption) and the concentration of the catalyst (metal and bromine) relative to the raw materials expected in the oxidation reaction system are determined before feeding oxidation reactor 2, which allows each of them to be supplied as a result of a simple adjustment. Such regulation stabilizes the amount of reaction solvent and the concentration of the catalyst, being the primary method of stabilizing the oxidation reaction.

(3) The concentration of water in the oxidation reaction system includes water introduced with the reaction solvent and water generated by the oxidation reaction. The absolute value of the concentration varies depending on the concentration of water in the solvent supplied and the solvent supply (relative solvent consumption), and under the usual condition it is assumed that the water concentration in the oxidation reaction system is from 15 to 25% by weight. For this reason, the next important parameter is the stabilization of the concentration of water in the system, which reduces the rate of the oxidation reaction to a low level.

Having established this, the authors of the present invention found that the concentration of water in the discharge condensate and the concentration of water in the reaction system (mother liquor) are closely related, as shown in FIG. 4, and that the concentration of water in the reaction system can be adjusted by adjusting the concentration of water in the discharge condensate.

Namely, after the analyzer A3 measures the concentration of water in the return condensate, partially removed from the bottom of the gas-liquid separator 4, the concentration of water in the oxidation reaction system, for example, in the analyzer / flow controller AFC3, is measured, and the discharge amount is adjusted by adjusting the flow controller FC9.

The return condensate consists of steam formed in the oxidation reaction system. It was found that the composition of the formed vapor, i.e., the concentration of water, directly depends on the concentration of water in the reaction system (the concentration of water in the mother liquor), and the concentration of water in the system can be determined most quickly from the composition of the vapor.

Regardless of the water contained in the feed reaction solvent, the concentration of water in the oxidation reaction system, including water in the feed solvent and water formed, is instantly estimated based on the measurement of the concentration of water in the return condensate, and then the FC9 flow regulator is adjusted to control the amount of return water containing condensate, which makes it possible to directly control the concentration of water in the oxidation reaction system.

On the other hand, acetic acid (fresh / regenerated acetic acid) 21 is introduced into the oxidation reaction system in an equivalent amount corresponding to the discharge determined by the analyzer / flow adjuster AFC3 by adjusting the FC8 flow regulator, and the solvent is continuously replaced by introducing into the reaction system and draining from an acetic acid reaction system having a different water content. Accordingly, the amount of solvent (relative solvent flow rate) in the reaction system can be maintained whose feed from the above solvent preparation tank 1 is determined, and the concentration of the oxidation catalyst can be maintained and stabilized.

The preferred method is direct and quick measurement of the concentration of water in the discharge condensate using an A3 analyzer (conductometry or spectrophotometry) or a method using the analyzer in real time. The discharge quantity based on the measurement results is determined automatically or manually using the AFC3 analyzer / flow transmitter. In a simple and easy control method, the equivalent amount of acetic acid supplied, corresponding to the amount discharged, is equal to the amount discharged, but taking into account the amount of solvent (relative solvent consumption) in the reaction system. Acetic acid may be supplied in an amount deviating by ± 0.5 parts by weight, preferably ± 0.2 parts by weight, from the feed, hydrocarbon, relative to the amount discharged. However, in any case, it is necessary that the supply of acetic acid is stable and appropriate to the amount discharged.

Thus, in the present invention, the reaction solvent is prepared by stabilizing the concentration of the oxidation catalyst and supplying the solvent (relative solvent consumption) without taking into account the concentration of water in the feed solvent or water formed during the reaction, and then introduced into the oxidation reaction system. Then, the condensate returned to the system is removed and the water concentration is measured in it at the analysis position A3, and on the basis of the relationship found between the concentration of water in the condensate and the concentration of water in the reaction system, the discharge amount is determined using an AFC3 analyzer / flow regulator, and appropriate amount of condensate. Next, acetic acid (fresh / regenerated acetic acid) 21 is introduced into oxidation reactor 2 in an equivalent amount corresponding to the amount determined by the flow adjuster AFC3, or equal to it, through another line.

This method consists in the constant regulation of only the concentration of water in the return condensate, and it makes it possible to carry out the oxidation reaction while stabilizing the concentration of water in the reaction system, regardless of the supply of the reaction solvent and the concentration of water in it.

As for the correlation between the concentration of water in the reaction system (the concentration of water in the mother liquor) and the concentration of water in the return condensate, the correlation between the mother liquor and the return condensate shown in Fig. 3 was found when using the inventors of the production equipment. This graphical dependence is the dependence of the concentration of water in the output fluid on the measured concentrations of water in the separated mother liquor (the expected mother liquor) when using the oxidation reaction system shown in the diagram in figure 1, in which two condenser / refrigerator apparatus 3A, 3B (3A is by a steam generator and 3B - part of water cooling) are installed in series, condensate is returned from each condenser / refrigerator 3A, 3B, and part of the condensate is returned to the first stage and returned to the second stage condensate is removed.

This figure shows the correlation between the concentration of water in the mother liquor and the concentration of water in the return condensate, in which the return condensate of the second stage has a higher concentration of water, and it is assumed that the condensate is removed with a more stable concentration of water.

This correlation means that depending on the design of the condenser / refrigerator 3A, 3B connected to the oxidation reactor 2, and the condensate withdrawal method, the relationship may be different. It has been found that by removing the condensate to be recovered at the final stage using a condenser / refrigerator comprising two or more stages, water can be removed at a high and stable concentration. Given the difference in the concentration of water in the condensate and the acetic acid supplied, corresponding to the output, the system can be controlled with a smaller output, and it can be said that using two or more condenser / refrigerator stages is an effective control method.

As described above, a predetermined amount of a feedstock, a dialkyl aromatic hydrocarbon 22, and a predetermined amount of a reaction solvent in which the concentration of the oxidation catalyst is adjusted are continuously introduced into the oxidation reactor 2 at a constant ratio. Regardless of the water content in the feed solvent, the concentration of water in the reaction system is directly controlled by adjusting the concentration of water in the condensate in the oxidation reactor 2. Accordingly, stationary parameters such as compositions (hydrocarbon, acetic acid, water) and concentration can be constantly adjusted to stabilize catalyst in the oxidation reaction system.

(4) Then, the reaction continuously occurs, since oxygen containing gas 30 is sent to oxidation reactor 2, and excess oxygen unnecessary for the reaction is withdrawn as an oxygen component in the exhaust reaction gas. The flue gas concentration is measured and confirmed using an A0 analyzer for safety reasons. Since the oxygen concentration in the exhaust gas positively affects the purity of the resulting terephthalic acid, setting the oxygen concentration in the exhaust gas in a specific area (from 1.5 to 6% by volume) is an important factor for controlling the reactivity of the reaction system. To this end, since measuring the oxygen concentration in the exhaust gas using an A0 analyzer and stabilizing the concentration is one of the factors for stabilizing the oxidation reaction, it is preferable to use a method in which the oxygen concentration in the exhaust gas is controlled by supplying an oxygen-containing gas to the reaction system.

Usually in the technique it is difficult to control the oxygen concentration in the exhaust gas (reactivity) only by supplying gas, since the oxygen concentration is affected by changes in composition, such as catalyst and water in the reaction system. Since the stationary system is established in the reaction system, as described above, the oxygen concentration in the exhaust gas is mainly associated only with the amount of oxygen-containing gas supplied to the reaction system, which makes it possible to control the oxygen concentration.

Thus, it was found that it is preferable to adjust the oxygen-containing gas supply by means of the flow adjuster AFC2 so that the deviation in the oxygen concentrations measured by the analyzer A0 is ± 0.5% by volume, preferably + 0.2% by volume.

(5) The temperature in oxidation reactor 2 most affects the regulation of reactivity. In the present oxidation reaction without the use of direct heating or cooling of the reaction system, the heat balance is achieved due to the pressure balance in the pressure of the vapor-gas mixture, consisting of the generated steam and exhaust gas discharged outside the reaction system to remove the reaction heat. Accordingly, in conventional industrial production equipment in which an oxidation reaction is carried out while maintaining a given pressure, stabilization of the reaction temperature was the main problem, since the temperature-pressure dependence changes as a result of changes in the amount of generated steam in the reaction system, the water content in it, and the amount of exhaust gas.

By decreasing the deviation in the temperature-pressure dependence in industrial production equipment based on pressure control by achieving a steady state in the reaction system, as described above, the method of constant temperature control by changing the pressure is more preferable, and the temperature can be further stabilized.

Therefore, in the present invention, the temperature in the oxidation reactor 2, measured by the temperature indicator TI, is constantly controlled by adjusting the pressure at the outlet of the high pressure gas absorber 5 (corresponding to the pressure in the oxidation reactor 2) by a device that sets the pressure TPC1 through the pressure regulator PIC1 without affecting other parameters, and thus stabilizing the reaction temperature.

(6) Another parameter that affects the product of the oxidation reaction is the reaction time. The reaction time in oxidation reactor 2 corresponds to the average residence time during which the feed mixture is fed and the reaction product mixture is withdrawn from the bottom of oxidation reactor 2. Since the residence time is related to the feed ratio of the feed mixture (feed, dialkyl aromatic hydrocarbon, and reaction solvent), specific to the production equipment, to the reaction volume of the reactor, it is important to stabilize the reaction volume.

Therefore, in the present invention, after supplying the aforementioned mixture of raw materials of stable composition (2), the reaction volume in oxidation reactor 2 is stabilized by measuring with a liquid level indicator / regulator LIC1 and adjusting the liquid level to a predetermined position using the outlet valve of FC10 flow regulator at the bottom of oxidation reactor 2 , thereby further stabilizing the reaction time.

The level of the reaction liquid is adjusted to a predetermined position by continuous withdrawal of the reaction product or by periodic withdrawal of a suspension of the reaction product due to its high fluidity.

As described above, the present invention provides a system that can continuously adjust many of the complexly dependent oxidation reaction parameters. Upon reaching the stationary conditions described above (1), (2) and (3), active parameters based on the dynamic mode of the oxidation reaction, such as the oxygen-containing gas introduced and the reaction temperature, described above (4), (5) and 6), subjected to regulation without affecting other parameters. Only when all these parameters are stabilized can a real oxidation reaction occur stably and can an effective continuous production of dicarboxylic acid be achieved.

In particular, the possibility of combined regulation of water concentrations in the reaction system by measuring and controlling water concentrations in the return condensate makes a great contribution to the stabilization and increase in the efficiency of the oxidation reaction.

As described above, with respect to the mixture of reaction products obtained by stabilizing various conditions of the continuous oxidation reaction, the dicarboxylic acid produced, uniform in quality, is removed from the oxidation reactor 2. Then, the dicarboxylic acid is sent to the second stage of the oxidation reaction (not shown) and is subjected to continuous processing therein and at the stage of continuous subsequent processing, including crystallization in a crystallizer 6, separation into a solid phase and a liquid in a separator of the type "solid phase-liquid" 7 and drying in shilka 8. Then a product is obtained, dicarboxylic acid (product, terephthalic acid) 40, the separated mother liquor can be reused, and acetic acid can be regenerated without making big changes to the traditional technological system shown in Fig. 8, which allows efficiently producing homogeneous quality products.

The following describes the specific conditions for the implementation of the method of continuous production of aromatic dicarboxylic acids of the present invention.

As described above, the oxidation reaction in oxidation reactor 2 according to the present invention is the oxidation of a dialkylaromatic hydrocarbon in liquid state with gaseous molecular oxygen using acetic acid as a solvent in the presence of an oxidation catalyst containing cobalt, manganese and bromine to produce aromatic dicarboxylic acid. The reaction can be carried out under various reaction conditions. The aim of the present invention is to provide a system in which the conditions of the oxidation reaction are constantly regulated to predetermined values, and the implementation of a continuous stable oxidation reaction as a result of the organization and regulation of the system for producing dicarboxylic acid.

More specifically, it is an object of the present invention to provide a system for controlling water concentrations in a reaction system by withdrawing return condensate from an oxidation reactor 2 and measuring water concentrations in return condensate using analyzer A3, without taking into account the concentration of water in the feed solvent, thereby constantly controlling water which is an inhibitor of the reaction.

First of all, the oxidation can be carried out using a solvent, acetic acid, with a ratio of about two times more or more than the raw material, dialkyl aromatic hydrocarbon 22. The required amount of acetic acid must be such that the resulting suspension of the mixture does not cause problems with operations such as transportation by piping during cooling after the reaction. From the point of view of losses during oxidative degradation of acetic acid in the reaction system (losses during oxidative degradation of acetic acid from 40 to 42 kg / ton TK, as shown in Fig. 4) (losses of acetic acid per dicarboxylic acid), it is preferable to carry out the oxidation at using less solvent. For this reason, for the application of the present invention, the solvent is used at a ratio of from 2.5 to 4 parts by weight, preferably from 2.5 to 3.5 parts by weight of the feed, dialkyl aromatic hydrocarbon 22, and it is necessary to maintain a constant flow without deviating from this ratio. However, from a practical point of view, it is preferable that the solvent is supplied by adjusting the deviation region of several percent.

In the vessel for preparing the reaction solvent 1 (1A, 1B), the circulating separated mother liquor is used to prepare the solvent. The entire circulating mother liquor can be used for the reaction solvent, or the oxidation reaction can also be carried out without the use of a circulating mother liquor. However, typically 40 to 95% by weight of the mother liquor is used and the solvent is prepared by adding fresh / regenerated acetic acid 25 to make up for its deficiency. In the present invention, the deviation in the ratio during cooking does not cause any problems, but since it is necessary to constantly adjust the amount of the prepared reaction solvent, the ratio of solvent to feed, dialkyl aromatic hydrocarbon 22 (relative solvent flow: amount of solvent / feed, dialkyl aromatic hydrocarbon) is constantly controlled using the flow adjuster FFC2.

As for the oxidation catalyst used in the reaction, compounds of such heavy metals as cobalt, manganese, nickel and chromium can be used as catalyst 23. When regenerating these compounds in a mother liquor on an industrial scale, catalysts based on cobalt and manganese compounds are preferred. In the present invention, compounds of metals such as cobalt and manganese are used. The solvent is prepared without regard to the ratio in the preparation of the circulating mother liquor, using additional amounts of the metal compound and the bromine compound, i.e., from 0.02 to 0.2% by weight of cobalt, based on the prepared solvent, from 1 to 150% by weight of manganese in based on cobalt and from 0.5 to 5 parts by weight of bromine 24 based on the number of metal catalysts (cobalt + manganese).

As for these concentrations, the concentrations of cobalt, manganese and bromine are determined in each apparatus along with other parameters, such as the temperature and time of the reaction taking into account the yield and quality of the products, and the solvent is prepared when the established corresponding concentrations are stabilized. With regard to stability, the concentration and ratio of components in the composition is preferably adjusted in the range of changes of several percent.

Further, when the washing (spent) liquid for the resulting dicarboxylic acid is mixed with a reusable separated mother liquor from the washing (spent) liquid tank 11, the solvent, which is a reaction solvent, is constantly prepared under the condition that the concentration of oxidation catalyst is constant, so that the catalyst concentration does not change due to a change in ratio when mixed.

The following metal compounds of the catalyst are used in the form of acetate or naphthenate, and the bromine compound is used in the form of a metal salt of the catalyst or compound not containing other inorganic elements. In the present invention, metal compounds are used in the form of acetate or bromide, and hydrobromic acid is used as the bromine compound. To facilitate further administration and preparation, they are dissolved in water or acetic acid and used in the form of a solution, which is preferred from the point of view of ease of use.

Due to dilution with water, the concentration of cobalt and manganese in the mother liquor is sometimes lower than the concentration of cobalt and manganese in the feed solvent, but the ratio in the composition usually does not change during regeneration. On the other hand, since 15 to 60% by weight of bromine, based on the amount introduced, disappears as a result of the oxidation reaction, the mother liquor, in which the bromine concentration is lower than the bromine concentration in the feed solvent by 20-70%, is regenerated . Accordingly, for each solution of additionally introduced catalyst compounds, when cobalt and manganese are dissolved in a solution identical to the metal catalyst solution so that the cobalt content is from 3 to 8% by weight and the adjusted ratio of manganese to cobalt in the composition is equal to their ratio in the composition in the prepared reaction solvent, the subsequent introduction and preparation will not cause difficulties. As for the bromine solution, it is possible to directly add commercially available hydrobromic acid (47% by weight of HBr (aqueous) solution) directly to its preparation.

When controlling the concentrations of these oxidation catalysts, the concentrations of the oxidation catalysts in the circulating mother liquor are measured by analyzer A1, as shown in FIG. 1 and FIG. 2, and while dealing with an additional quantity as a result of adjusting the flow regulators FC4, FC3 through the flow analyzer / regulator AFC1 , it is necessary that a stable adjustment of the concentration of oxidation catalysts is achieved. And finally, a quick response method to correction can be used, such as increasing the number of regular measurements in the laboratory or shortening the measurement time. However, since adjusting the concentration of oxidation catalysts is an important parameter for stabilizing the oxidation reaction, it is more preferable to use automatic analysis and automatic control in real time. For automatic analyzers A1, A2, a real-time analyzer based on fluorescence X-ray analysis is used, which allows simultaneous measurement of cobalt, manganese and bromine (for example, On-Line Catalyst Analyzer manufactured by SPECTRO, USA), and it is preferable to use the method of controlling additional quantities catalyst compounds by adjusting the flow rate.

Further, the reaction solvent prepared in the vessel for preparing the reaction solvent 1 (1A, 1B) is constantly supplied to the oxidation reactor 2 in a ratio of 2.5 to 4 parts by weight of the raw material, dialkyl aromatic hydrocarbon 22. At the same time, oxygen containing 2 is continuously fed from the bottom of the oxidation reactor 2 gas 30 for carrying out the oxidation reaction. When using air as an oxygen-containing gas 30, air is introduced at a ratio of about or more than 3.5 nm ³ per 1 kg of raw material, dialkyl aromatic hydrocarbon. The air supply is limited by adjusting the FC7 flow regulator through the AFC0 analyzer / flow adjuster so that the oxygen concentration in the exhaust gas measured by the A0 analyzer is 8% by volume or lower. In the present invention, it is also preferable that the supply of oxygen-containing gas is controlled so that the oxygen concentration in the exhaust gas is maintained in a constant range from 2 to 5% by volume. With regard to the stability of the oxygen concentration in the exhaust gas, the oxygen concentration is controlled by supplying an oxygen-containing gas so that the deviation of the oxygen concentration is within the range of ± 0.5% by volume.

It is known that water, including the resulting water, is an inhibitor of the present oxidation reaction. In the present invention, however, the concentration of water in the reaction system is controlled by measuring: the concentrations of water in the condensate to be returned and in its withdrawn amounts, without taking into account the water content in the feed solvent. The concentration of water in the return condensate is measured by analyzer A3 and the output amount of return condensate is adjusted by adjusting the FC9 flow regulator through the analyzer / flow controller AFC3. The concentration of water in the reaction system (or the concentration of water in the mother liquor) used in industrial production is usually adjusted in the range from 8 to 14% by weight. However, the aim of the present invention is to constantly control the concentration constancy, and it is necessary that the concentration control region is in the range of ± 1% by weight, preferably ± 0.5% by weight.

Accordingly, in the present invention, to adjust the concentration of water in the mother liquor to a predetermined concentration, the concentration of water in the return condensate is measured by analyzer A3 and the output amount is adjusted by the FC9 flow regulator to obtain a given concentration of water. A predetermined water concentration is determined, for example, by an AFC3 analyzer / flow controller from a predetermined concentration of water in the mother liquor based on the relationship between the concentration of water in the return condensate and the concentration of water in the mother liquor.

As for this dependence, the concentration of water in the returned liquid and the concentration of water in the mother liquor are interconnected, as shown in Fig. 3, which is a consequence of the correlation characteristic of the oxidation reaction apparatus system, including the design of the condenser / cooler 3A, SV and the place of the return condensate. In particular, as shown in FIG. 3, the relationship between the concentration of water in the returned liquid from the second stage 3B and the concentration of water in the mother liquor, plotted in white circles, and the correlation line (solid line) shows a stable relationship, and the concentration of water in the returned liquid is greater from 2.5 to 3.5 times the concentration of water in the mother liquor. Thus, by controlling the concentration of water in the return fluid, the regulation of the reaction systems becomes more stable.

For example, to control the concentration of water in a system with a deviation of ± 0.5% by weight, as described above, the FC9 flow regulator is adjusted so that the deviation of the concentration of water in the return condensate is within ± 1% by weight. Such a system for the return of condensate through two or more stages and its removal from the last stage is preferred, as this increases the stability of the regulation of the measured values.

Accordingly, for the application of the present invention, it is preferable that the return for the return condensate to the oxidation reactor 2 is divided into at least two stages (3A, 3B) and that the concentration of water in the return liquid in the last stage (the condensate of the last stage) is controlled by analyzer A3 and analyzer / flow adjuster AFC3, and so that the condensate output is regulated by the flow regulator FC9.

Regarding the goal of controlling water concentrations, a stable reaction is carried out by adjusting the set value of the deviation region of the water concentration in the mother liquor ± 1% by weight, preferably ± 0.5% by weight, although it is believed that the correlation with the concentration of water in the mother liquor varies in depending on the design and system of the oxidation reactor 2 and the condenser / refrigerator 3A, 3B.

Further, in the present invention, in order to improve the regulation of the output amounts by the FC9 flow regulator and the regulation of acetic acid supply by the FC8 flow regulator, it is necessary that the concentration of water in the return condensate be quickly measured by analyzer A3. Thus, it is preferable that each concentration is adjusted and adjusted based on real-time measurements by an automatic water concentration analyzer. Since the condensate returned is mainly composed of acetic acid and water, an optical analyzer (e.g. Photometric Analyzer manufactured by Shimadzu Corporation) can be used as the A3 analyzer, which measures the absorption of light at a specific wavelength, or the concentration of water can be measured based on electrical conductivity.

On the other hand, in order to maintain a stable amount of solvent in the reaction system, an equivalent amount of solvent, acetic acid, is separately introduced into the reaction system when the condensate is returned to the system, as described above. It is preferable that the amount of acetic acid be equal to the amount of recovered condensate, since in this case the regulation is simplified. However, the deviation of the amount of acetic acid from this equality within the interval, which does not significantly change the relative solvent consumption in the reaction system, for example, within 0.5 times the weight of p-xylene 22, does not cause problems.

However, in order to continuously maintain a stable amount of solvent in the system, it is necessary to maintain a stable output quantity and a stable supply without deviation.

As for the temperature, which is an important factor for the stable progress of the oxidation reaction, the reaction is carried out in the temperature range from 185 to 210 ° C. The control range is set for a stable temperature range of ± 1 ° C, preferably ± 0.5 ° C. In the present invention, the desired reaction temperature is constantly maintained in the above temperature region and the regulation region by regulating the pressure by the pressure regulator PIC1, based on the pressure determined by the temperature-pressure regulator TPC1 according to the temperature measured by the temperature indicator TI, instead of the commonly used constant regulation pressure.

Regarding the reaction time, which is another important parameter for a stable reaction, the present oxidation reaction is carried out during an average residence time of from 30 minutes to 3 hours. In the oxidation reactor, in which the working volume is determined as described above, the residence time is kept stable by adjusting the position of the liquid level, as measured by a liquid level indicator-controller LIC1 with a flow regulator FC10. Thus, it is necessary to provide a good output stream of the mixture of the reaction product.

For this reason, it is necessary that the mixture of reaction products discharged from oxidation reactor 2 is continuously processed in a second-stage reactor (not shown) and after-treatment systems and plants such as crystallizer 6 and a solid-liquid separator 7, and violations in the operation of installations that may have an effect on stable production, should be excluded.

To create the control system of the present invention described above, it is preferable that the analyzers (assay positions) from A1 to A3 and the regulators for determining the flow rate FFC1, FFC2, AFC0, AFC1, AFC3 quickly adjust the oxidation reaction parameters, and an automatic analyzer and automatic installation are preferred regulation parameters. However, as long as the oxidation reaction can be stabilized by regulation, including human decision making and manpower to increase the frequency of analysis, these devices may not be fully automatic and the only ones possible.

Further, in the control system of the present invention, the oxygen concentration in the uncondensed off-gas from the reaction gas, from which condensate is evolved in the gas-liquid separator 14, is measured by the gas analyzer A0, and after confirming compliance with the safety conditions, the gas is sent to the high pressure gas absorber 5. In the high gas absorber At a pressure of 5, the gas is washed with acetic acid 33 and then with water 32 to absorb and remove components contained in the reaction gas, such as acetic acid, p-xylene and methyl acetate in the vapor state, and the resulting the resulting product released into the atmosphere as exhaust gas 31.

The washing acetic acid (spent) used for absorption and washing in the lower part of the high pressure gas absorber 5 is used repeatedly as acetic acid 26 to prepare the reaction solvent, and the washing water (spent) used for absorption and washing in the upper part is directed in a distillation column dehydration 12 for the recovery of acetic acid 36.

The pressure of the exhaust reaction gas is maintained at a pressure value at the outlet of the high pressure gas absorber 5 and is adjusted by the pressure indicating regulator PIC1 on the discharge line to create pressure in the oxidation reactor 2.

Since the condensate removed has a high concentration of water, it is usually directly sent to a distillation column dehydration 12 to regenerate acetic acid 36.

An industrial process for the preparation of terephthalic acid also includes a post-treatment step for regenerating acetic acid from an acetic acid-containing liquid, such as an additional mother liquor that is not reused. At that stage, the separated mother liquor (not used) remaining in the mother liquor tank 10 and the additional washing acetic acid (spent) are promptly fed to the mother liquor evaporator 13, and the evaporated fractions, such as acetic acid (acetic acid, water, p-xylene, methyl acetate) is recovered from the top of the unit.

On the other hand, non-volatile components (components of the oxidation catalyst, terephthalic acid, 4-CBA (4-carboxybenzaldehyde), p-toluic acid, benzoic acid) dissolved in the mother liquor are removed from the bottom of the evaporator 13 as a precipitate 35 in the form of a suspension or pasta. Evaporated fractions recovered from the upper part of the evaporation plant 13 mainly contain acetic acid and water. The fractions are then sent to a dehydration distillation column 12 to recover acetic acid and acetic acid 36 is removed from the bottom of the column, and the extracted acetic acid (water content: 2 to 10% by weight) is reused to prepare the reaction solvent or to wash terephthalic acid crystals and t .d.

Next, the resulting water 34, containing water as the main component, is drained from the top of the distillation column 12. Since the resulting water contains traces of p-xylene and methyl acetate, the resulting water is subjected to further post-processing, such as separation and recovery, and then discarded.

Water with a low content of acetic acid, which is extracted from each zone of the present production stages, such as washing water (waste) from the upper part of the high pressure gas absorber 5, is directly sent to the distillation column dehydration 12 or the evaporation unit of the reaction solvent 13, and acetic acid is recovered and reused. On the other hand, effluent with high concentrations of acetic acid (acetic acid with a water content of 20% by weight or less), such as washing acetic acid (spent) from the bottom of the high pressure gas absorber of gas 5, is used as acetic acid for preparing reaction solvent.

The embodiments and advantages of the present invention are further described in detail in a specific example. Regarding the stabilization of the oxidation reaction, which is an advantage of the present invention, the homogeneity of the products and the stability of the oxidation reaction were evaluated based on the content of 4-KBA in the resulting terephthalic acid. Whether the reaction proceeds stably or not, was estimated by calculating the losses due to oxidative degradation of the solvent, acetic acid with respect to the obtained terephthalic acid based on the concentrations of CO ₂ (carbon dioxide) and CO (carbon monoxide) and the amount of p-xylene introduced.

Example

The continuous production of terephthalic acid was carried out using a system of equipment based on the technological scheme shown in figure 1.

As equipment for the oxidation reaction, a high pressure oxidation reactor 2 (diameter: 3.1 m, height: 6 m, volume: about 48 m ³ ) equipped with a rotary mixer was used. A condenser / refrigerator 3A, 3B is connected to the top of oxidation reactor 2 to condense and cool the condensed component of the resulting reaction gas and cool the non-condensed gas component. The equipment has a structure in which the condensate is divided into two parts and returned to oxidation reactor 2, and then the waste reaction gas 31, separated in a gas-liquid separator 4, is washed in a high pressure gas absorber 5 and the resulting gas is removed from the system. The first stage 3A of the condenser / cooler 3 is a steam generator for generating steam by heat exchange with a high temperature waste reaction gas containing steam and water, and the second stage 3B is designed to further condense and cool the steam containing exhaust gas by heat exchange with water. To divert the resulting water from the reaction system, a structure was used that was able to divert part of the return condensate to the second stage 3B through a gas-liquid separator 4.

First, the mother liquor, from which the obtained terephthalic acid was removed, supplied from the tank for preparing the mother liquor 10 and the wash liquid reservoir 11, or the circulating mother liquor containing the wash acetic acid (spent) used to wash the separated terephthalic acid, was continuously fed into the capacity for preparing the reaction solvent 1 at a flow rate of 230 weight parts / hour and fresh / regenerated acetic acid 25 were continuously fed into the capacity for preparing the reaction solvent 1 from an acetic acid tank (not shown) at a flow rate of 70 parts by weight / hour for preparing the reaction solvent. In this case, cobalt, manganese and bromine in the circulating mother liquor were measured at the site of analysis A1 and then the amount of additional metal catalyst solution (cobalt: 3.44 wt.%, Manganese: 1.67 wt.%) And 47% by weight of hydrobromic acid were determined using an AFC1 analyzer / flow adjuster so that the cobalt, manganese and bromine content in the reaction solvent in the reaction solvent preparation tank 1 is 565 ppm, 275 ppm and 1470 ppm, each of the catalysts is added so that the concentration is adjusted catalysis ora. At this stage, the composition and concentration of the catalyst in the reaction solvent prepared in the vessel for preparing the reaction solvent 1 was measured and confirmed at analysis position A2. To measure at the analysis position A1, an automatic analysis was performed using the SPECTRO Online-Catalyst Analyzer, and the measured signals were transmitted to a digital process control system for automatic control using a controller.

Then the feed, p-xylene, from the p-xylene tank (not shown) at a flow rate of 100 parts by weight / hour and the reaction solvent from the vessel of the reaction solvent 1 at a flow rate of 300 parts by weight / hour (relative solvent consumption: 3.0 weight parts) continuously introduced into the mixer on a line (not shown) installed on the feed line of oxidation reactor 2, and after mixing they were introduced into oxidation reactor 2. At the same time, air was fed from the bottom of oxidation reactor 2 at a ratio of 4.0 nm ³ / p-xylene kg Then, the amount of air supplied was manually controlled by the FC7 flow regulator so that the concentration of gaseous oxygen in the exhaust gas from the gas-liquid separator 4 (analysis position A0, real-time oxygen analyzer) was 3.5 + 0.5% by volume, and the oxidation reaction was carried out continuously . At the same time, CO ₂ , CO components in the exhaust gas were measured (analysis position A0, real-time gas analyzer) and the losses of acetic acid during oxidative degradation were calculated.

During this period, the pressure at the outlet of the high pressure gas absorber 5 was adjusted using the pressure regulator PIC1 so that the temperature in oxidation reactor 2 was 195 ± 1 ° C. As a result, the pressure could be controlled in the range from 14.1 to 15.0 kg / cm ² G. Next, part of the return condensate was removed in the second stage of the condenser / refrigerator 3 connected to the oxidation reactor 2, and the concentration of water in the condensate was measured in the analysis position A3. The withdrawn amount of condensate was adjusted based on the setting of the AFC3 flow regulator so that the concentration was 33 wt.%, And at the same time fresh / regenerated acetic acid 21 was added to the reactor in an amount equal to the removed amount. The concentration of water in the condensate at that point was measured at analysis position A3 every hour, and the output amount and supply of acetic acid were adjusted using the flow adjuster AFC3.

On the other hand, the mixture of reaction products obtained in oxidation reactor 2 was discharged into the second stage of the reactor (not shown, temperature: about 188 ° C) by adjusting the outlet flow rate so that the LIC indicator / regulator of the liquid level based on the liquid level meter with the source of gamma radiation attached to oxidation reactor 2 maintained a value of 35% (residence time about 60 minutes). Further, according to the flow chart in FIG. 1, the product mixture was sent to a crystallizer 6, a solid-liquid separator 7 and a dryer 8 to obtain the product, terephthalic acid 40, and the product was stored in the product storage 9. On the other hand, acetic acid 37 was introduced into a solid-liquid separator 7. At this stage, in the A4 analysis position, a sample of the reaction suspension formed in crystallizer 6, cooled to 95 ° C, was analyzed and subjected to separation of the solid phase from the liquid. The concentration of water and the catalyst content in the separated mother liquor, which was used as the mother liquor, were measured. The content of 4-KBA in the product, terephthalic acid, was measured from dryer 8 and this content was considered as an indicator of the quality of the reaction product.

Data was collected and measured every 4 hours for 120 hours after the above continuous reaction became stable.

"The composition of the reaction solution (H ₂ O, cobalt (Co) and bromine (Br) in the feed solution in the example shown in figure 5; manganese (Mn): from 154 to 187 ppm; Br / (Co + Mn): 1.71 to 1.78) "refers to measured values confirmed at assay position A2. "Condensate" means the condensate discharged from the bottom of the gas-liquid separator 4, and its discharged amount was adjusted in the range from 90 to 130 parts by weight per hour, and the water concentration in it (H ₂ O, wt.%) Was measured in analysis position A3 (from 32 5 to 33.2 wt.%). "The composition of the mother liquor" (H ₂ O, cobalt and bromine in the mother liquor in the example shown in figure 5; manganese: from 248 to 255 ppm) refers to the measured value, confirmed by analysis at position A4. The content of 4-KBA in the product, terephthalic acid, and the loss of acetic acid as a result of oxidative degradation (every 12 hours) at that point in the example are shown in FIG. 4 and FIG. 6.

These results show that, despite the deviation of the concentration of water in the reaction solvent, the concentration of water can be controlled in the range from 32.5 to 33.2 wt.% By adjusting the output amount of condensate in a wide range from 90 to 130 parts by weight / hour. As shown in the example of FIG. 5, the concentration of catalyst in the mother liquor can also be constantly maintained. As a result, as shown in the example of FIG. 4, losses due to oxidative degradation of acetic acid can be kept low, and as shown in the example of FIGS. 4 and 7, the 4-KBA content in the resulting product was stable.

Comparative example

Terephthalic acid was produced using the equipment system shown in the flow chart of Fig. 8. While the oxidation reactor 102 and other apparatuses were the same as the apparatuses in the equipment for producing terephthalic acid in the above example, the positions of the analyzes and the regulation system of the oxidation reaction were based on the flow chart shown in Fig. 8. A condenser / cooler 103 connected to the top of the oxidation reactor 102 uses the two-stage return system shown in FIG. 1, and the condensate is removed from the second liquid return stage.

Initially, the feed, p-xylene, was introduced into the reagent mixer 101 at a flow rate of 100 parts by weight / hour. At the same time, a mother liquor was introduced therein, from which the obtained terephthalic acid was isolated, from the mother liquor reservoir 110 at a flow rate of 230 weight parts / hour, and fresh / regenerated acetic acid was introduced therefrom from an acetic acid reservoir (not shown) at a flow rate of 220 weight parts / hour, and they were mixed to prepare a mixture of raw materials at a flow rate of 550 parts by weight / hour. Next, to adjust the concentration of the oxidation catalyst, an additional solution of catalyst metal compounds with a cobalt concentration of 3.44% by weight and a manganese concentration of 1.67% by weight was added to the reagent mixer 101 at a flow rate of 2.1 weight parts / hour and 47% by weight of hydrobromic acid added to the mixer 101 at a flow rate of 0.6 weight parts / hour.

In the comparative example used here, acetic acid containing wash acetic acid (spent) from the lower part of the high pressure gas absorber 105 was used as fresh / regenerated acetic acid at a ratio of about 50 weight parts / hour. To prevent deviations of the concentration of the catalyst in the circulating mother liquor, a raw material mixture (or reaction solution) was prepared without using a circulating mother liquor containing the washing (waste) liquid used to wash the terephthalic acid separated in the solid-liquid separator 107. Thus washing (spent) liquid was discharged into the evaporator installation of the mother liquor 113.

The raw material mixture prepared as described above was fed to oxidation reactor 102 at a flow rate of 550 parts by weight / hour (p-xylene: 100 parts by weight / hour, reaction solvent: 450 parts by weight / hour). At the same time, the condensate returned from the second stage was continuously withdrawn at a flow rate of 110 weight parts / hour with an air supply of 4.0 nm ³ / hour / p-xylene kg and, while maintaining a pressure in the reactor of 14.5 kg / cm ² G, an oxidation reaction was carried out to obtain terephthalic acids.

At these stages, the composition and concentration of the catalyst in the feed mixture introduced into oxidation reactor 102 was measured at position A10, and it was confirmed that there was no significant deviation from the desired composition (p-xylene: 18.2 wt.%, Cobalt: 340 h ppm, manganese: 165 ppm, bromine: 900 ppm). During this period, the condensate output varied in the range from 105 to 120 weight parts / hour based on the results of measuring the water concentration in the feed mixture introduced, the reaction temperature TI varied from 193 to 199 ° C, and the oxygen concentration in the exhaust gas (Al1) varied from 2.3 to 4.4% by volume. From the measurements of CO ₂ , CO components in the exhaust gas (Al1), losses due to oxidative degradation of acetic acid were also calculated, as described above.

The reaction product mixture was discharged into a second stage oxidation reactor (not shown, temperature: about 185 ° C) based on a LIC10 liquid level indicator / regulator so that a liquid level meter with a γ-radiation source connected to reactor 102 maintained a value of 45% ( stay time: about 60 minutes). Then, after obtaining a suspension of the reaction product in the crystallizer 106, as in the above example, was measured (analysis position A12) and the concentration of water and the catalyst content in the mother liquor were confirmed. The 4-KBA content of the obtained product, terephthalic acid, was measured, and this content was considered as an indicator of the quality of the reaction product.

As in the above example, data was collected and measured every 4 hours for 120 hours after the above continuous reaction became stable. "The composition of the mixture of raw materials" (H ₂ O, cobalt (Co) and bromine (Br) in the feed solution, shown in Fig.7) ", which is the composition of the mixed raw materials, p-xylene and the reaction solvent, refers to the measurement results at the position A10 analysis, and other measurements are the results of measurements at the same position as in the example. Further, "the composition of the mother liquor (H ₂ O, cobalt and bromine in the mother liquor in the comparative example is shown in Fig. 7)" refers to the measured values confirmed at analysis position A12 4-KBA in terephthalic acid e and the loss of acetic acid due to oxidative degradation (every 12 hours) at that point in a comparative example are shown in figure 4 and figure 6.

These results show that the oxidation reaction caused a larger deviation of the parameters compared with the data in the above example, and an increase in the amount of terephthalic acid produced caused a loss of acetic acid as a result of oxidative degradation in the production process.

Claims (11)

1. A continuous method for the preparation of terephthalic or isophthalic acid, including liquid-phase oxidation of the corresponding dialkylaromatic hydrocarbon with a gas containing molecular oxygen, in the presence of a catalyst containing cobalt, manganese and bromine, in acetic acid as a solvent, which includes a preliminary stage of the preparation of the reaction solvent in a preparation tank the reaction solvent by introducing a cobalt compound, a manganese compound and a bromine compound into the mixture, at least e, parts of the mother liquor and acetic acid, wherein the mother liquor is obtained by separating the terephthalic or isophthalic acid product from it; an oxidation step including an oxidation process, a condensation / cooling process, a discharge control process, and a feed process, wherein the oxidation process includes a continuous feed of 1 part by weight the corresponding dialkylaromatic hydrocarbon as a raw material and from 2.5 to 4 parts by weight the reaction solvent, which is obtained at the preliminary stage, in the oxidation reactor while simultaneously introducing a gas containing molecular oxygen into the oxidation reactor, and oxidizing the feed in a liquid state in the oxidation reactor, in which the condensation / cooling process involves cooling the exhaust reaction gas containing steam, which is formed in the oxidation reactor, so as to maintain a constant reaction temperature during the oxidation process, the return of condensate obtained by cooling the exhaust reaction gas to an oxidation reactor, and discharging at least a portion of the condensate to be returned, in which the process for regulating the discharge includes measuring the concentration of water present in at least a portion of the condensate removed in the condensation / cooling process, and adjusting the amount of discharge to achieve in advance a predetermined value of the concentration of water, in which the supply process includes an additional supply corresponding to the supply of acetic acid, which is associated with the discharged amount, into the oxidation reactor, simultaneously with the regulation the withdrawn amount in the regulation of retraction, wherein the oxidation step, the reaction mixture obtained by oxidation in an oxidation reactor, continuously or periodically withdrawn when adjusting the liquid level in the oxidation reactor subsequent to recovery of the product of isophthalic or terephthalic acid. 2. The method according to claim 1, in which the condensation / cooling process in the oxidation step comprises cooling the exhaust reaction gas containing steam that is generated in the oxidation reactor using two or more condensers / coolers connected in series to each other, returning condensates from respective condensers / coolers to the oxidation reactor, and removing at least a portion of the return condensate from the last condenser / cooler. 3. The method according to claim 1 or 2, in which the preliminary stage includes the preparation of a reaction solvent containing predetermined amounts of cobalt, manganese and bromine by measuring predetermined concentrations of cobalt, manganese and bromine in the mother liquor introduced by recirculation, and adding the mother liquor to the solution compounds of cobalt and manganese and a solution of a bromine compound in the appropriate amounts required, depending on the measured concentrations of cobalt, manganese and bromine in the mother liquor. 4. The method according to claim 1 or 2, in which the preliminary stage includes the use of a number of containers for the preparation of the reaction solvent. 5. The method according to claim 1 or 2, in which the oxidation process of the oxidation step involves mixing 1 part by weight the corresponding dialkylaromatic hydrocarbon as a raw material and from 2.5 to 4 parts by weight the reaction solvent, which is prepared in the preliminary stage, and the introduction of the resulting mixture into the oxidation reactor. 6. The method according to claim 1 or 2, in which the oxidation step includes the process of controlling the reaction temperature in the oxidation reactor by adjusting the pressure in the oxidation reactor. 7. The method according to claim 3, in which the oxidation step includes the process of controlling the reaction temperature in the oxidation reactor by adjusting the pressure in the oxidation reactor. 8. The method according to claim 6, in which the process of controlling the temperature of the reaction includes regulating the pressure in the oxidation reactor by obtaining in the gas-liquid separator non-condensable exhaust reaction gas separated from the condensate obtained in the condensation / cooling process, washing the non-condensable exhaust reaction gas in the gas absorber high pressure, and regulating the pressure of the obtained washed off-gas. 9. The method according to claim 1 or 2, in which the oxidation step further comprises a process for controlling the oxygen concentration, which regulates the oxygen concentration in the exhaust gas discharged from the oxidation reactor by controlling the supply of oxygen-containing gas supplied to the oxidation reactor. 10. The method according to claim 3, in which the oxidation step further comprises a process for controlling the oxygen concentration, regulating the oxygen concentration in the exhaust gas discharged from the oxidation reactor, by controlling the supply of oxygen-containing gas supplied to the oxidation reactor. 11. The method according to claim 9, in which the process of controlling the oxygen concentration includes controlling the oxygen concentration in the exhaust gas discharged from the oxidation reactor as a result of obtaining in the gas-liquid separator a non-condensable exhaust reaction gas separated from the condensate that is formed during the condensation / cooling process, washing the non-condensable off-gas from the high pressure gas absorber and adjusting the oxygen concentration in the resulting washed off-gas.

Images