EP1174485B1 - Process comprising two gasoline hydrodesulphurisation steps with intermediary elimination of H2S - Google Patents

Description

The present invention relates to a process for producing gasolines with a low sulfur content, which makes it possible to recover the whole of a sulfur-containing gasoline fraction, to reduce the total sulfur contents of said gasoline fraction to very low levels, without significant reduction in gasoline yield, and minimizing the decrease in octane number due to the hydrogenation of olefins. This method is particularly applicable when the gasoline to be treated is a catalytic cracking gasoline containing a sulfur content greater than 1000 ppm by weight and / or an olefin content greater than 30% by weight, when the desired sulfur content in the Desulfurized gasoline is less than 50 ppm by weight.

Prior art:

The specifications on fuels, aimed at reducing pollutant emissions have been severely tightened for several years. This trend is likely to continue in the coming years. For gasoline, the most stringent specifications include olefins, benzene and sulfur.

Cracking gasolines, which can represent 30 to 50% of the gasoline pool, have the disadvantage of containing significant concentrations of sulfur, which means that the sulfur present in the reformulated gasolines is attributable, at nearly 90%, to the gasoline species. cracking (catalytic cracking gas in fluidized bed or FCC, steam cracking gasoline, coking gasolines ...). Desulphurisation (hydrodesulphurisation) of gasolines and mainly cracking gasolines is therefore of obvious importance for achieving specifications.

These gasolines, however, contain olefins which contribute significantly to the octane of the reformulated gasoline and thus it is desirable to minimize or control their saturation during the desulfurization treatments to minimize the resulting octane losses.

Much research has been conducted in recent years to provide processes or catalysts for desulfurizing gasolines by attempting to minimize losses of olefins due to hydrogenation. This work led the emergence of a number of processes, some of which are now commercialized, and which are capable of minimizing the hydrogenation rate of olefins while achieving desulfurization rates required to reach specifications in force.

However, future specifications will be tightened, that is to say that they will impose sulfur specifications even more severe. Therefore, there is a continuing need for catalysts, or processes, to achieve even lower sulfur contents while preserving olefins, even for cracking gasolines that may contain high sulfur contents. , ie contents greater than 1000 ppm by weight and / or for gasolines containing high olefin contents (greater than 30% by weight relative to the starting gasoline).

The patent application EP-A-0 725 126 discloses a method for hydrodesulfurizing a cracking gasoline in which the gasoline is separated into a plurality of fractions comprising at least a first fraction rich in easily desulfurized compounds and a second fraction rich in difficult to desulphurize compounds. Before carrying out this separation, it is necessary to first determine the distribution of sulfur-containing products by means of analyzes.

The patent French FR-A-2 790 000 describes a two-stage hydrodesulphurization process, a step of hydrogenation of unsaturated sulfur compounds and a step of decomposition of saturated sulfur compounds. There is no elimination of H2S present or formed between these two stages. WO-A-9,807,805 describes the removal of heteroatoms using countercurrent absorption. EP-A-0 870 817 describes a method of HDS of hydrocarbon feeds.

SUMMARY OF THE INVENTION :

The present invention relates to a three-stage desulfurization process for gasolines as defined in the wording of claim 1, and with a hydrogenation pretreatment of diolefins in the feed. This process is particularly particularly suitable for cracking gasolines having a sulfur content greater than 1000 ppm by weight, which it is desired to lower to a level of less than 50 ppm by weight and preferably less than 15 ppm by weight.

• A) une première étape dans laquelle les composés soufrés présents dans l'essence sont au moins partiellement transformés en H2S et en composés soufrés saturés.
• B) une deuxième étape visant à éliminer l'H2S de l'essence produite dans l'étape A) ;
• C) une troisième étape dans laquelle les composés soufrés saturés restant dans l'essence sont transformés en H2S, et est caractérisé en ce qu'une étape de prétraitement visant à hydrogéner les dioléfines de la charge est effectuée avant l'étape A.

The method according to the invention as described in the wording of claim 1, comprises at least three steps:

• A) a first step in which the sulfur compounds present in the gasoline are at least partially converted to H2S and saturated sulfur compounds.
• B) a second step to remove H2S from the gasoline produced in step A);
• C) a third step in which the saturated sulfur compounds remaining in the gasoline are converted to H2S, and is characterized in that a pretreatment step for hydrogenating the diolefins of the feed is carried out before step A.

The selective hydrogenation prior to step A of the diene compounds may optionally hydrogenate acetylenic compounds.

Other optional technical features of the invention are described in the claims of dependent claims 2 to 10.

The present invention therefore relates to a process for the production of gasolines with a low sulfur content, which makes it possible to recover the whole of a petrol fraction containing sulfur and olefins, to reduce the sulfur contents in said petrol fraction to very low levels. levels and generally at a value of less than 50 ppm or even less than 15 ppm by weight, without a substantial decrease in the yield of gasoline, and by minimizing the reduction in the octane number due to the hydrogenation of the olefins. The process is particularly suitable for the treatment of gasolines with a high sulfur content, ie a sulfur content greater than 1000 ppm by weight and / or when the gasoline has a high olefin content, that is to say greater than 30% weight.

The process according to the invention comprises a treatment of the feedstock on a first catalyst making it possible to at least partially hydrogenate aromatic sulfur compounds such as, for example, thiophene compounds by placing under conditions in which the hydrogenation of the olefins is limited on this catalyst (step A), a step for removing at least part of the H2S gasoline thus treated (step B), then a third treatment on at least one catalyst for decomposing at least partially saturated sulfur compounds with limited hydrogenation of olefins (step C).

In certain cases it is possible to envisage that step C is carried out on a chain of catalysts, for example the sequence described in the patent. FR-A-279000 while meeting the criteria for the H2S concentration at the entry of the third step according to the present invention.

The feedstock of the process according to the invention is a gasoline cutter containing sulfur and olefins, preferably a petrol cut from a cracking unit, and preferably a gasoline predominantly from a catalytic cracking unit. The treated gasoline can also be a mixture of gasolines from different conversion processes such steam cracking processes, coking or visbreaking (visbreaking according to the English terminology) or even gasoline directly from the distillation of petroleum products. The gasolines having high olefin concentrations are particularly suitable for being subjected to the process according to the invention.

Detailed Description the invention:

It has been described in the patent FR-A-2790000 the combination of two catalysts suitable for the hydrotreatment of catalytic cracking gasolines, one of which makes it possible to convert unsaturated sulfur compounds present in gasoline, such as, for example, thiopheneic compounds, and the other to transform selectively sulfur-saturated compounds already present in gasoline or produced during the first stage of the gasoline treatment, makes it possible to obtain a desulfurized gasoline that does not have a significant decrease in the olefin content or the 'octane. It has now been discovered, and this is the subject of the present invention, that it was possible to obtain improved performance of the process, especially when the sulfur content of the gasoline is high, ie greater than 1000 ppm by weight and / or when the olefin content is greater than 30% by weight and the sulfur content of the target gasoline is less than 50 ppm by weight or even less than 15 ppm by weight.

The sulfur species contained in the fillers treated by the process of the invention may be mercaptans or heterocyclic compounds, such as, for example, thiophenes or alkylthiophenes, or heavier compounds, such as for example benzothiophene or dibenzothiophene. These heterocyclic compounds, unlike mercaptans, can not be removed by conventional extractive processes. These sulfur compounds are consequently removed by the process according to the invention which leads to their at least partial decomposition into hydrocarbons and H 2 S.

The sulfur content of catalytic cracked gasoline (FCC) gasoline cuts depends on the sulfur content of the FCC treated feed as well as the end point of the cut. Generally, the sulfur contents of the entirety of a petrol cut, in particular those coming from the FCC, are greater than 100 ppm by weight and most of the time greater than 500 ppm by weight. For gasolines with end points higher than 200 ° C., the sulfur contents are often greater than 1000 ppm by weight, and in some cases they may even reach values of the order of 4000 to 5000 ppm by weight.

The gasolines which are particularly suitable for the process according to the invention therefore contain olefin concentrations which are generally between 5 and 60% by weight. When the gasoline contains a sulfur content of less than 1000 ppm, the gasoline treated in the process according to the invention preferably contains more than 30% by weight of olefins.

The gasolines may also contain significant concentrations of diolefins, that is to say diolefin concentrations of up to 15% by weight. Generally the diolefin content is between 0.1 and 10% by weight. The diolefin content is typically greater than 1% by weight or even greater than 0.5% by weight. The gasoline is, before undergoing stages A, B and C subjected to a selective hydrogenation treatment aimed at hydrogenating at least partly the diolefins present in said gasoline, as described in the wording of claim 1.

Gasoline can also naturally contain nitrogen compounds. The nitrogen concentration of the gasoline is generally less than 1000 ppm by weight and is generally between 20 and 500 ppm by weight.

This gasoline preferably contains a sulfur content greater than 1000 ppm by weight. The range of boiling points typically extends from about the boiling points of the 5-carbon hydrocarbons (C5) to about 250 ° C. The end point of the gasoline cut depends on the refinery from which it comes and the constraints of the market, but generally remains within the limits indicated above. In some cases, and in order to optimize the configuration of the process, it may be advantageous to subject the gasoline to various treatments before subjecting it to the process according to the invention. The gasoline may, for example, undergo splitting or other treatment before being subjected to the process according to the invention without these treatments limiting the scope of the invention.

For this type of gasoline, analysis of the nature of the sulfur compounds shows that the sulfur is essentially present in the form of thiophene compounds (thiophene, methylthiophenes, alkylthiophenes, etc.) and, depending on the end point of the gasoline to treated, benzothiophene compounds, alkylbenzothiophene, or even compounds derived from dibenzothiophene.

The method according to the invention firstly comprises a treatment (step A) of the gasoline on a catalyst for hydrogenating at least partly unsaturated sulfur compounds such as for example thiophene compounds, in saturated compounds such as by for example thiophanes (or thiacyclopentane) or mercaptans according to a succession of reactions described below:

This hydrogenation reaction can be carried out on a conventional hydrotreating (hydrodesulphurization) catalyst comprising a Group VIII metal and a Group VIb metal partially in the form of sulfides. When such a catalyst is used, the operating conditions are adjusted so as to be able to hydrogenate at least part of the thiophene compounds while limiting the hydrogenation of the olefins.

During this step, the thiophene, benzothiophenic and dibenzothiophenic compounds, if they are present in the gasoline to be treated, are generally transformed significantly, that is to say that at the end of the first stage, the content of Thiophenic, benzothiophene or dibenzothiophene compounds represent at most 20% of that of the starting gasoline. In addition, this hydrogenation step is accompanied by the significant production of H2S by total decomposition of the sulfur compounds initially present in the feedstock. The decomposition rate of the sulfur compounds present in the H2S feed, which accompanies the hydrogenation of the unsaturated sulfur compounds, is generally greater than 50%.

The method according to the invention comprises a second step where the H2S is at least partly removed from the effluent obtained at the end of step A. This step can be carried out using any techniques known to man of career. It can be carried out directly under the conditions in which the effluent is at the end of step A or after these conditions have been changed in order to facilitate the removal of at least a portion of the H2S. As a possible technique, one can cite, for example, a gas / liquid separation (where the gas is concentrated in H2S and the liquid is depleted in H2S and is sent directly to step C), a step of stripping the gasoline practiced on a liquid fraction of the gasoline obtained after step A, an amine washing step, again performed on a liquid fraction of the gasoline obtained after step A, an uptake of the H2S by an absorbing mass operating on the gaseous or liquid effluent obtained after the step, a separation of the H2S from the gaseous or liquid effluent by a membrane. At the end of this treatment, the sulfur content in the form of H 2 S is generally less than 500 ppm by weight relative to the starting gasoline. In a preferred manner, this content is reduced, at the end of step B, to a value of between 0.2 and 300 ppm by weight and even more preferably to a value of between 0.5 and 150 ppm by weight.

The process according to the invention comprises a third step (step C) in which the saturated sulfur compounds are converted into H 2 S according to the reactions:

This treatment can be carried out using any catalyst allowing the conversion of saturated sulfur compounds (mainly thiophane or mercaptan type compounds). It may for example be carried out using a catalyst based on nickel, molybdenum, cobalt, iron tungsten or tin. Preferably, the treatment is carried out in the presence of a catalyst based on nickel, nickel and tin, cobalt and iron, cobalt and tungsten.

The thus desulphurized gasoline is then optionally stripped in order to remove the H2S produced during step C.

• de pouvoir atteindre des taux de désulfuration de l'essence plus élevées, c'est à dire des teneurs en soufre résiduelles beaucoup plus basse et ce notamment lorsque l'essence à traiter présente une teneur élevée en soufre c'est à dire une teneur en soufre supérieure à 1000 ppm et/ou une teneur en oléfine supérieure à 30 % poids;
• d'opérer l'étape C dans des conditions de températures beaucoup plus douces, ce qui présente des avantages au niveau du procédé notamment en permettant une intégration thermique mieux optimisée entre la section réactionnelle de l'étape A et de l'étape C.

Compared to the invention described in the patent FR-A-2790000 . the invention proposed here has the advantage:

• to be able to achieve higher rates of desulphurization of gasoline, ie much lower residual sulfur contents, especially when the gasoline to be treated has a high sulfur content, that is to say a content in sulfur greater than 1000 ppm and / or an olefin content greater than 30% by weight;
• to perform step C under much milder temperature conditions, which has advantages in the process including allowing a better optimized thermal integration between the reaction section of step A and step C.

In the case of gasoline with a high sulfur content and / or when the rate of conversion of unsaturated sulfur compounds to saturated sulfur compounds is not in step A, it may be advantageous to carry out step C with a series of catalysts comprising at least one catalyst described for step A and at least one catalyst described for step C.

The steps of the process according to the invention are described in more detail below.

Hydrogenation of dienes (step before step A):

Hydrogenation of dienes is a step which eliminates, before hydrodesulphurization, almost all the dienes present in the gasoline cutter containing sulfur to be treated. It generally takes place in the presence of a catalyst comprising at least one Group VIII metal, preferably selected from the group consisting of platinum, palladium and nickel, and a support. For example, use will be made of a nickel-based catalyst deposited on an inert support, such as, for example, alumina, silica or a support containing at least 50% alumina. This catalyst operates at a pressure of 0.4 to 5 MPa, at a temperature of 50 to 250 ° C, with a liquid hourly space velocity of 1 to 10 h ^-1 . Another metal may be combined to form a bimetallic catalyst, such as, for example, molybdenum or tungsten.

It may be particularly advantageous, especially when treating cuts having a boiling point below 160 ° C, to operate under conditions such that at least partial softening of the gasoline is obtained; that is, some reduction in the mercaptan content. To do this, one can use the procedure described in the patent application FR-A-2,753,717 which uses a palladium catalyst.

The choice of operating conditions is particularly important. The operation will generally be carried out under pressure in the presence of a quantity of hydrogen in small excess relative to the stoichiometric value necessary for hydrogenating the diolefins. The hydrogen and the feedstock to be treated are injected in ascending or descending streams into a reactor preferably with a fixed bed of catalyst. The temperature is most generally between about 50 and about 250 ° C, and preferably between 80 and 230 ° C, and more preferably between 120 and 200 ° C.

The pressure is sufficient to maintain more than 80%, and preferably more than 95% by weight of the gasoline to be treated in the liquid phase in the reactor; it is most generally between 0.4 and 5 MPa and preferably greater than 1 MPa. The pressure is advantageously between 1 and 4 MPa. The space velocity is from about 1 to about 10 h ^-1 , preferably from 4 to 10 h ^-1 .

The catalytic cracked gasoline may contain up to a few weight percent of diolefins. After hydrogenation, the diolefin content is generally reduced to less than 3000 ppm, or even less than 2500 ppm and more preferably less than 1500 ppm. In some cases, it can be obtained less than 500 ppm. The diene content after selective hydrogenation can even if necessary be reduced to less than 250 ppm.

According to one embodiment of the invention, the step of hydrogenation of the dienes takes place in a catalytic hydrogenation reactor which comprises a catalytic reaction zone traversed by the entire charge and the amount of hydrogen necessary to effect the desired reactions. .

Hydrogenation of Unsaturated Compounds of Sulfur (Step A)

This step consists of converting at least a portion of the unsaturated sulfur compounds, such as the thiophene compounds, into saturated compounds, for example thiophanes (or thiacyclopentanes) or mercaptans.

This step may, for example, be carried out by passing the feedstock to be treated, in the presence of hydrogen, over a catalyst containing at least one element of group VIII and / or at least one element of group VIb at least partly in sulphide form, at a temperature of between 220 ° C. and 320 ° C. and more preferably between 220 ° C. and 290 ° C., under a pressure generally of between 1 and 5 MPa, preferably between 1 and 4 MPa and more preferably between 1 and 4 MPa. , 5 and 3MPa. The liquid space velocity is between 1 and 10 h ^-1 (expressed as volume of liquid per volume of catalyst and per hour), preferably between 3 h ^-1 and 8 h ^-1. The ratio H ₂ / HC is between 100 to 600 liters per liter and preferably 300 to 600 liters per liter.

To achieve, at least in part, the hydrogenation of unsaturated sulfur compounds of gasoline according to the process of the invention, use is generally made of at least one hydrodesulfurization catalyst, comprising at least one element of group VIII (metals of groups 8, 9 and 10 of the new classification, ie iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium or platinum) and / or at least one element of group VIb (metals of group 6 of the new classification, ie chromium, molybdenum or tungsten), on a suitable support. Preferably, the group VIII element, when present, is generally nickel or cobalt, and the element of group VIb, when present, is generally molybdenum or tungsten. Combinations such as nickel-molybdenum or cobalt-molybdenum are preferred. The catalyst support is usually a porous solid, such as for example an alumina, a silica-alumina or other porous solids, such as, for example, magnesia, silica or titanium oxide, alone or in mixture with alumina or silica-alumina.

After introduction of the element or elements and possibly shaping of the catalyst (when this step is performed on a mixture already containing the base elements), the catalyst is in a first activated step. This activation may correspond to either an oxidation, then a reduction, or a direct reduction, or a calcination only. The calcination step is generally carried out at temperatures of from about 100 to about 600 ° C and preferably from 200 to 450 ° C under an air flow rate.

The catalyst preferably used in this step is a catalyst comprising an alumina-based support whose specific surface area is less than 200 m 2 / g, and comprising at least one element selected from the group consisting of cobalt, molybdenum, nickel or tungsten and preferably selected from the group consisting of cobalt, molybdenum and tungsten. Even more preferably, the catalyst according to the invention contains at least cobalt and molybdenum. In addition, the molybdenum content, when this element is present is preferably greater than 10% by weight expressed as molybdenum oxide, the cobalt content, when this element is present, is preferably greater than 1% by weight (expressed as oxide cobalt II). For molybdenum catalysts, the molybdenum density in the catalyst, expressed in grams of MoO3 per square meter of support is greater than 0.05 g / m ² of support.

The reduction step is performed under conditions to convert at least a portion of the oxidized forms of the base metal to metal. Generally, it consists of treating the catalyst under a flow of hydrogen at a temperature of at least 300 ° C. The reduction can also be achieved in part by means of chemical reducers.

The catalyst is preferably used at least in part in its sulfurized form. The introduction of sulfur can occur between different activation steps. Preferably, no oxidation step is performed when the sulfur or a sulfur compound is introduced on the catalyst. The sulfur or a sulfur compound can be introduced ex situ, that is to say outside the reactor where the process according to the invention is carried out, or in situ, that is to say in the reactor used for process according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulfided by passing a feed containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge may be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur compound.

In a preferred manner, the sulfur compound is added to the ex situ catalyst . For example, after the calcination step, a sulfur compound may be introduced onto the catalyst in the presence of possibly another compound. The catalyst is then dried and then transferred to the reactor for carrying out the process of the invention. In this reactor, the catalyst is then treated in hydrogen to convert at least a portion of the main metal sulfide. A procedure which is particularly suitable for the invention is that described in the patents FR-B-2,708,596 and FR-B-2,708,597 .

In the process according to the invention, the conversion of the unsaturated sulfur compounds is greater than 15% and preferably greater than 50%. At the same time, the degree of hydrogenation of the olefins is preferably less than 50% and preferably less than 40% during this step.

The effluent which has undergone this first treatment is then sent to stage B which makes it possible to eliminate at least part of the H2S present at the end of stage A.

Removal of the H2S from the effluent of step A (Step B):

In this step the concentration of H2S is decreased. The removal of the H 2 S can be carried out in various ways, most of which are known to those skilled in the art. For example, the adsorption of a part of the H 2 S contained in the effluent of stage A by an absorbent mass based on a metal oxide, preferably chosen from the group consisting of zinc, copper oxide or molybdenum oxide. This adsorbent mass is preferably regenerable. Its regeneration can be carried out continuously or discontinuously, for example by means of a heat treatment in an oxidizing or reducing atmosphere. The absorbent mass can be used in a fixed bed or in a moving bed. It can operate directly on the effluent of stage A, or on this effluent having undergone treatments (for example a cooling or a separation ...). Another method is to perform membrane separation of H2S using a selective membrane operating on a liquid or gaseous effluent from step A. One of the zones of the separation may contain an absorbent mass to promote the transfer H2S through the wall of the membrane. Another method may be to cool the effluent of step A and produce a gas rich in H2S and a liquid phase depleted in H2S. The gas phase can then be treated in an amine washing unit. The liquid phase and the gas phase can then be remixed and sent to step C. The liquid fraction can also undergo other treatments such as stripping with hydrogen, nitrogen or steam. water, extraction of H2S, washing with amines, washing with sodium hydroxide solution in order to reduce its H2S content.

- Decomposition of compounds saturated with sulfur (Step C):

In this step, the saturated sulfur compounds are converted, in the presence of hydrogen on a suitable catalyst. This transformation is carried out without hydrogenation of the olefins, that is to say that during this step the hydrogenation of the olefins is limited to 20% with respect to the content of the starting gasoline, and preferably limited to 10% in relation to the olefin concentration of gasoline.

Catalysts which may be suitable for the invention, without this list being limiting, are catalysts comprising at least one metal selected from the group consisting of nickel, cobalt, iron, molybdenum and tungsten and. More preferably, the catalysts of this step are based on nickel. These metals are preferably supported and used in their sulfurized form.

The metal content of the catalyst used according to the invention is generally between about 1 and about 60% by weight and preferably between 5 and 20% by weight. Preferably, the catalyst is generally shaped, preferably in the form of beads, extrudates, pellets, or trilobes. The metal may be incorporated in the catalyst on the preformed support, it may also be mixed with the support before the shaping step. The metal is generally introduced in the form of a precursor salt, generally soluble in water, such as for example nitrates, heptamolybdates. This mode of introduction is not specific to the invention. Any other mode of introduction known to those skilled in the art is suitable for the implementation of the invention.

The supports of the catalysts used in the process of the invention are generally porous solids chosen from refractory oxides, such as, for example, aluminas, silicas and silica-aluminas, magnesia, as well as titanium oxide and zinc oxide, the latter oxides may be used alone or in admixture with alumina or silica-alumina. Preferably, the supports are transition aluminas or silicas whose specific surface is between 25 and 350 m ² / g. The natural compounds (for example kieselguhr or kaolin) may also be suitable as supports for the catalysts of the process according to the invention.

After introducing the metal and possibly forming the catalyst (when this step is carried out with a mixture already containing the base metal), the catalyst is in a first activated step. This activation may correspond to either an oxidation, then a reduction, or a direct reduction, or a calcination only. The calcination step is generally carried out at temperatures of from about 100 to about 600 ° C and preferably from 200 to 450 ° C under an air flow rate. The reduction step is carried out under conditions making it possible to convert at least a portion of the oxidized forms of the metal basic metal. Generally, it consists of treating the catalyst under a flow of hydrogen at a temperature of at least 300 ° C. The reduction can also be achieved in part by means of chemical reducers.

The catalyst is preferably used at least in part in its sulfurized form. This has the advantage of minimizing the risks of hydrogenation of unsaturated compounds such as olefins or aromatic compounds during the start-up phase. The introduction of sulfur can occur between different activation steps. Preferably, no oxidation step is performed when the sulfur or a sulfur compound is introduced on the catalyst. The sulfur or a sulfur compound can be introduced ex situ , that is to say outside the reactor where the process according to the invention is carried out, or in situ , that is to say in the reactor used for process according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulfided by passing a feed containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge may be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur compound.

In a preferred manner, the sulfur compound is added to the ex situ catalyst . For example, after the calcination step, a sulfur compound may be introduced onto the catalyst in the presence of possibly another compound. The catalyst is then dried and then transferred to the reactor for carrying out the process according to the invention. In this reactor, the catalyst is then treated in hydrogen to convert at least a portion of the main metal sulfide. A procedure which is particularly suitable for the invention is that described in the patents FR-B-2 708 596 and FR-B-2,708,597 .

After sulfurization, the sulfur content of the catalyst is generally between 0.5 and 25% by weight, preferably between 4 and 20% by weight.

The hydrotreatment carried out during this step is intended to convert the saturated sulfur compounds of gasoline that has already undergone prior treatment to H ₂ S, so as to obtain an effluent that will meet the desired specifications in terms of content. in sulfur compounds. The gasoline thus obtained has a slightly higher octane number low, because of the partial but inevitable saturation of olefins, than that of the gasoline to be treated. However this saturation is limited.

The operating conditions of the catalyst for decomposing the saturated sulfur compounds into H 2 S must be adjusted to achieve the desired hydrodesulphurization level, and to minimize the octane loss resulting from olefin saturation. The second catalyst (catalyst of step C) used in the process according to the invention generally makes it possible to convert at most 20% of the olefins, preferably at most 10% of the olefins.

The treatment for decomposing the saturated sulfur compounds in the first process step (step A) is carried out in the presence of hydrogen, with the metal catalyst, such as more preferably nickel, at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C, more preferably between 260 ° C and 320 ° C, under a low to moderate pressure generally between 0.5 and 5 MPa, preferably between 0.5 MPa and 3 MPa, more preferably between 1 and 3 MPa. The space velocity of the liquid is generally between 0.5 and 10 h ^-1 (expressed in volume of liquid per volume of catalyst per hour), preferably between 1 and 8 h ^-1 . The H ₂ / HC ratio is adjusted according to the desired hydrodesulphurization rates in the range generally between about 100 and about 600 liters per liter, preferably between 100 and 300 liters per liter. All or part of this hydrogen can come from stage A or from a recycling of the unconsumed hydrogen resulting from stage C.

- Implementation of the process:

One of the possibilities of implementing the process according to the invention may, for example, consist in passing the gasoline to be hydrotreated through a reactor containing a catalyst allowing, at least in part, the hydrogenation of the unsaturated sulfur compounds, such as for example the thiophenic compounds, sulfur saturated compounds (step A) and the removal of H 2 S (step B), then through a reactor containing a catalyst for decomposing sulfur saturated compounds into H 2 S (step C) . The step of removing the H2S can also be carried out in the reactor of step C or partly in each of the two reactors. The removal step may also be partly or wholly outside the reactors of steps A and C.

In another configuration which is also suitable, the two catalysts of steps A and C are placed in series in the same reactor and an adsorbing mass of H2S is placed between the two catalysts in order to eliminate at least partly the H2S product in the first catalytic zone (step B). In such a configuration the absorbent mass, once saturated with H2S can be either replaced or regenerated. In the latter case the regeneration can be performed discontinuously or continuously depending on the adsorbent mass used.

In all cases, the two catalytic zones can operate under different conditions of pressure, VVH, temperature, H2 / load ratio. Systems can be implanted to dissociate the operating conditions from the two reaction zones.

It can also be envisaged to carry out a sequence which consists in passing the gasoline to be hydrotreated through a reactor containing a catalyst allowing, at least in part, the hydrogenation of the unsaturated sulfur compounds, into saturated sulfur compounds (stage A). , then separately or simultaneously carry out a step of removing the H 2 S, and then carry out step C in a reactor containing a series of catalysts comprising at least one catalyst of the same type as that used in the first step of the method (step A) and at least one catalyst for decomposing sulfur saturated compounds into H2S (step C).

With the sequences proposed for the process according to the invention, it is possible to achieve high levels of hydrodesulphurization while limiting the loss of olefins and consequently the decrease of the octane number.

The examples below illustrate the invention without limiting its scope.

Example 1 Pretreatment of the Charge by Selective Hydrogenation

• chromatographie en phase gaz (CPG) pour les constituants hydrocarbonés ;
• méthode NF M 07052 pour le soufre total ;
• méthode NF EN 25164/M 07026-2/ISO 5164/ASTM D 2699 pour l'indice d'octane recherche ;
• méthode NF EN 25163/M 07026-1/ISO 5163/ASTM D 2700 pour l'indice d'octane moteur.

Tableau 1 : Caractéristiques de la charge utilisée Charge Densité 0,78 Point initial (°C) 63°C Point final (°C) 250°C Teneur en oléfines (% pds) 31.3 Teneur en diènes 1,4 S total (ppm) 2062 RON 91 MON 80 (RON + MON)/2 85.5 Table 1 shows the characteristics of the feedstock (catalytic cracking gasolines) treated by the process according to the invention. The analytical methods used to characterize the loads and effluents are as follows:

• gas phase chromatography (GC) for hydrocarbon constituents;
• method NF M 07052 for total sulfur;
• method NF EN 25164 / M 07026-2 / ISO 5164 / ASTM D 2699 for the research octane number;
• method NF EN 25163 / M 07026-1 / ISO 5163 / ASTM D 2700 for the motor octane number.

<b> Table 1: Characteristics of the load used </ b> Charge Density 0.78 Initial point (° C) 63 ° C End point (° C) 250 ° C. Olefin content (% wt) 31.3 Dienes content 1.4 S total (ppm) 2062 RON 91 MY 80 (RON + MON) / 2 85.5

This charge is pretreated by means of a selective hydrogenation step. The hydrogenation of the diolefins is carried out on a HR945® catalyst based on nickel and molybdenum, sold by the company Procatalyse. The test is carried out in a continuous bed-type continuous reactor, the feedstock and the hydrogen being introduced through the bottom of the reactor. 60 ml of catalyst are introduced into the reactor after having been previously sulphurized ex situ for 4 hours, under a pressure of 3.4 MPa, at 350 ° C., in contact with a constituting charge of 2% by weight of sulfur in the form of of dimethylsulfide in n-heptane. The catalyst is then transferred to the reactor where the hydrogenation of the diolefins is carried out. The hydrogenation is then carried out under the following conditions: T = 190 ° C., P = 2.7 MPa, VVH = 6 h -1 and H 2 / HC = 151/1. After hydrogenation of the diolefins, the diolefin content is 1.0% by weight.

After hydrogenation, the charge contains ..... (ppm or% weight) of dienes

EXAMPLE 2 Hydrodesulfurization of Hydrogenated Gasoline According to Step A (Comparative)

The hydrogenated gasoline under the conditions of Example 1 is hydrodesulfurized.
A catalyst A is obtained by impregnation "without excess solution" of a transition alumina, in the form of beads, with a specific surface area 130 m 2 / g and a pore volume of 0.9 ml / g, with an aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate. The catalyst is then dried and calcined under air at 500 ° C. The cobalt and molybdenum content of this sample is 3% CoO and 10% MoO3.
25 ml of catalyst A are placed in a fixed-bed tubular hydrodesulfurization reactor. The catalyst is first sulphurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a feedstock consisting of 2% of sulfur in the form of dimethyl disulphide in n-heptane.
The operating conditions of the hydrodesulphurization are as follows: VVH = 4 h ^-1 (VVH = volume of feed treated per hour and per volume of catalyst), H ₂ / HC = 360 I / I, P = 2.0 MPa. The temperature of the catalytic zone is between 280 ° C and 320 ° C. The results obtained are shown in Table 2 <b> Table 2 </ b> Temperature of the catalytic zone (° C) Sulfur Content of Desulfurized Gasoline (ppm) Olefin content of desulphurised gasoline (% by weight) Octane of desulfurized gasoline (RON + MON) / 2 280 ° C 184 23.9 83.5 300 ° C 90 20.2 82.4 305 ° C 50 17.1 80.4 320 ° C 12 13.6 76.5

Example 3 Hydrodesulfurization According to Steps A and C (Comparative)

The hydrogenated gasoline under the conditions of Example 1 is hydrodesulfurized. A second catalyst (catalyst C) is prepared from a transition alumina of 140 m ² / g in the form of beads 2 mm in diameter. The pore volume is 1 ml / g of support. 1 kilogram of support is impregnated with 1 liter of nickel nitrate solution. The catalyst is then dried at 120 ° C and calcined under a stream of air at 400 ° C for one hour. The nickel content of the catalyst is 20% by weight. 25 ml of catalyst A of Example 1 and 50 ml of catalyst C are placed in the same hydrodesulfurization reactor, so that the feedstock to be treated (heavy fraction) first meets catalyst A and then the Catalyst C. The catalysts are first sulphurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a feedstock consisting of 2% of sulfur in the form of dimethyl disulphide in n-heptane. .

The operating conditions of the hydrodesulfurization are as follows: VVH = 1.33 h ^-1 relative to the entire catalytic bed H ₂ / HC = 360 I / I, P = 2.0 MPa. The temperature of the catalytic zone comprising catalyst A is 250 ° C to 290 ° C, the temperature of the catalytic zone containing catalyst C is 330 ° C.

The results obtained under these conditions are reported in Table 3. <b> Table 3. </ b> Temperature of the catalytic zone A (° C) Sulfur Content of Desulfurized Gasoline (ppm) Olefin content of desulphurised gasoline (% by weight) Octane of desulfurized gasoline (RON + MON) / 2 270 ° C. 50 20.4 82.3 290 ° C. 13 15.6 78.7

Example 4 Hydrodesulfurization According to Steps A, B and C of the Process According to the Invention

The hydrogenated gasoline under the conditions of Example 1 is hydrodesulfurized. An experiment is carried out under the same conditions as those of Example 3, except that the two catalysts are placed in two different reactors and that the H2S is separated between these two reactors. The effluent from the first reactor is cooled to room temperature, the liquid phase and the gas phase are separated, the H2S from the liquid phase is stripped by a stream of nitrogen to remove the H2S up to a content of 50 ppm by weight relative to the liquid. The liquid thus obtained is then heated to the temperature of the second catalyst and reinjected in the presence of hydrogen introduced with a hydrogen flow rate of 330 I / I of charge corresponding approximately to the flow rate of hydrogen entering the second reactor of the example 3.

The sulfurization and test conditions correspond to those of Example 3.

The results obtained under these conditions are reported in Table 4. <b> Table 4. </ b> Temperature of the catalytic zone A (° C) Sulfur Content of Desulfurized Gasoline (ppm) Olefin content of desulphurised gasoline (% by weight) Octane of desulfurized gasoline (RON + MON) / 2 260 ° C 48 21.3 82.5 280 ° C 12 16.2 79.4

Example 5: Another mode of hydrodesulfurization according to steps A, B and C of the process according to the invention.

The hydrogenated gasoline under the conditions of Example 1 is hydrodesulfurized. 25 ml of catalyst A are placed in a tubular reactor. This reactor is coupled with a second hydrodesulfurization reactor containing 13 ml of catalyst A of Example 1 and 25 ml of catalyst C of Example 3, so that the feedstock first meets catalyst A and then catalyst C. The effluent of the first reactor is cooled to ambient temperature, the liquid phase and the gas phase are separated, the H2S of the liquid phase is stripped by a stream of nitrogen allowing the H2S to be removed up to at a content of 50 ppm by weight with respect to the liquid. The liquid thus obtained is then heated to the temperature of the second reactor and reinjected in the presence of hydrogen introduced with a flow rate and under a pressure corresponding to that of the second reactor of Example 2. The temperature of the first reactor is indicated in the table. 5. The temperature of the catalyst present in the second zone is raised to 270 ° C and the temperature of the catalyst C present in the second reactor is raised to 330 ° C.

The results obtained are shown in Table 5. <b> Table 5. </ b> Temperature of the catalytic zone A (° C) Sulfur Content of Desulfurized Gasoline (ppm) Olefin content of desulphurised gasoline (% by weight) Octane of desulfurized gasoline (RON + MON) / 2 260 ° C 49 23.6 83.3 280 ° C 10 20.2 82.3

Claims (10)

1. Process for the production of gasoline with a low sulfur content comprising at least three stages :

   A) a first stage in which the sulfur-containing compounds present in the gasoline are at least partially transformed into H2S and into saturated sulfur-containing compounds by sending the feedstock, in the presence of hydrogen, over a catalyst comprising at least one element of group VIII and/or at least one element of group Vlb, at least in part in sulfide form, said stage being carried out at a temperature of between 220°C and 320°C, under a pressure that is generally between 1 and 5 MPa, with a volumetric flow rate of the liquid of between 1 and 10 h^-1, and an H₂/HC ratio of between 100 and 600 liters per liter,

   B) a second stage whose purpose is to eliminate the H2S from the gasoline produced in stage A,

   C) a third stage in the presence of a catalyst at least in part in its sulfurized form comprising at least one metal selected in the group consisting of nickel, cobalt, iron, molybdenum and tungstenin wherein the saturated sulfur-containing compounds remaining in the gasoline are transformed into H2S, said stage being carried out at a temperature of between 200°C and 350°C, a pressure of between 0.5 and 5 MPa, a liquid volumetric flow rate that is between 0.5 and 10 h^-1 and an H₂/HC ratio of between 100 and 600 liters per liter,

   characterized in that a pretreatment stage whose purpose is to hydrogenate the diolefins of the feedstock is carried out before stage A.
2. Process according to claim 1, wherein the feedstock is a catalytic cracking gasoline.
3. Process according to claim 1 or 2, wherein in the step A the element of group VIII, when it is present, is nickel or cobalt, and the element of group Vlb, when it is present, is molybdenum or tungsten.
4. Process according to claim 1 to 3, wherein the base metal content in step C is between 1 and 60% by weight.
5. Process according to claim 1 to 4, wherein the base metal in step C is nickel.
6. Process according to claim 1 to 5, wherein the sulphur content of the catalyst in step C is between 0,5 and 25% by weight.
7. Process according to any of claims 1 to 6 implemented with at least two separate reactors, not including a feedstock pretreatment reactor, whereby the first reactor contains the catalyst that is necessary for stage A and the second at least the one that is necessary for stage B.
8. Process according to any of claims 1 to 7 implemented with at least two separate reactors, not including a feedstock pretreatment reactor, whereby the first reactor contains at least a portion of the catalyst necessary for stage A and the second at least the other portion of the one necessary for stage A and the one necessary for stage B.
9. Process according to any of claims 1 to 8, wherein stage B for the elimination of H2S is carried out by adsorption in the presence of an adsorbent mass selected in the group consisting of zinc oxide, copper oxide and molybdenum oxide.
10. Process according to claims 1 to 9, wherein H2S is separated using a membrane.