EP1174485A1 - Process comprising two gasoline hydrodesulphurisation steps with intermediary elimination of H2S - Google Patents

Abstract

The invention relates to a process for producing gasoline with a low sulfur content comprising at least three stages: a first stage in which the sulfur compounds present in the petrol are at least partially transformed into H2S and into saturated sulfur compounds, a second step to remove H2S from the gasoline produced in the first step and a third step in which the saturated sulfur compounds remaining in the gasoline are converted to H2S. The method according to the invention optionally further comprises a pretreatment step aimed at hydrogenating the diolefins of the feed before the first step.

Description

The present invention relates to a method for producing gasolines with low sulfur content, which makes it possible to recover the entire petrol cut containing sulfur, to reduce the total sulfur contents of said petrol cut to very low levels, without appreciable reduction in fuel efficiency, and minimizing the decrease in octane number due to hydrogenation of olefins. This process particularly applicable when the essence to be treated is a cracked essence catalytic containing a sulfur content higher than 1000 ppm by weight and / or a olefin content greater than 30% by weight, when the sulfur content sought in the desulphurized petrol is less than 50 ppm by weight.

Prior art:

The fuel specifications, aimed at reducing emissions of pollutants have been severely curtailed for several years. This trend risks to continue in the years to come. With regard to the species, the the most stringent specifications relate in particular to the olefin content, in benzene and sulfur.

Cracked essences, which can represent 30 to 50% of the petrol pool, have the disadvantage of containing significant concentrations of sulfur which fact that the sulfur present in reformulated gasolines is attributable to almost 90%, with cracked gasolines (catalytic cracked gasolines in a fluidized bed or FCC, steam cracking essence, coking essence ...). Desulfurization (hydrodesulfurization) of essences and mainly cracking essences is therefore of obvious importance for achieving the specifications.

These essences, however, contain olefins which contribute significantly significant octane reformulated gasoline and so it is desirable to minimize or to control their saturation during desulfurization treatments in order to minimize the resulting octane losses.

Much research has been carried out in recent years to propose processes or catalysts for desulfurizing gasolines trying to minimize losses in olefins due to hydrogenation. This work led to the emergence of a number of processes, some of which are today that are capable of minimizing the rate of hydrogenation of olefins while making it possible to reach the desulphurization rates required to reach the specifications in force.

However the specifications to come will be tightened, that is to say that they will impose even more stringent sulfur specifications. Therefore, there is a continual need to have catalysts, or processes, to achieve even lower sulfur contents while preserving the olefins and even for cracked essences which may contain high sulfur contents, i.e. contents higher than 1000 ppm by weight and / or for species containing high olefin contents (greater than 30% by weight relative to the starting essence).

Patent application EP-A-0 725 126 describes a hydrodesulfurization process of a cracked gasoline in which the gasoline is separated into a plurality of fractions comprising at least a first fraction rich in compounds easy to desulfurization and a second fraction rich in compounds difficult to desulfurize. Before to carry out this separation, it is first necessary to determine the distribution of products sulfur by means of analyzes.

French patent application 99 / 02.336 describes a hydrodesulfurization process in 2 steps, 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.

SUMMARY OF THE INVENTION:

The present invention relates to a three-stage desulfurization process for species. This process is particularly particularly well suited to essences of cracking with a sulfur content greater than 1000 ppm by weight, which wish to lower to a level below 50 ppm weight and preferably below 15 ppm 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.

The method according to the invention comprises at least three steps:

- A) a first step in which the sulfur compounds present in the gasoline are at least partially transformed into H2S and into saturated sulfur compounds.

- B) a second step aimed at eliminating the H2S from the gasoline produced in step A);

- C) a third step in which the saturated sulfur compounds remaining in the gasoline are transformed into H2S.

It moreover optionally and preferably includes a hydrogenation step selective of diene and possibly acetylenic compounds, located before step A.

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

The method according to the invention comprises a treatment of the load on a first catalyst making it possible to at least partially hydrogenate the sulfur-containing compounds aromatics such as for example thiophenic compounds by being placed in conditions where the hydrogenation of olefins is limited on this catalyst (step A), a step making it possible to at least partially remove the H2S from the gasoline thus treated (step B), then a third treatment on at least one catalyst making it possible to decompose at least partially the saturated sulfur compounds with limited hydrogenation of olefins (step C).

In some cases it is possible to envisage that step C is carried out on a sequence of catalysts, for example the sequence described in the application for patent 99 / 02.336 while respecting the criteria concerning the H2S concentration at the entry of the third step according to the present invention.

The charge of the process according to the invention is a petrol cut containing sulfur and olefins, preferably a gasoline cut from a unit of cracked, and preferably a gasoline coming mainly from a unit of catalytic cracking. The treated essence can also be a mixture of essences from different conversion processes such as steam cracking processes, coking or visbreaking (visbreaking according to Anglo-Saxon terminology) or even gasolines directly from the distillation of petroleum products. The essences with high olefin concentrations are particularly suitable to be subjected to the process according to the invention.

Detailed description of the invention:

It has been described in patent application 99 / 02.336 that the combination of two suitable catalysts for the hydrotreatment of catalytic cracked gasolines of which one for transforming the unsaturated sulfur compounds present in the essence, such as for example thiophenic compounds, and the other allowing to selectively transform the saturated sulfur compounds already present in gasoline or products in the first stage of gasoline processing, allows to obtain a desulphurized petrol having no significant reduction in the olefin content or octane number. We have now discovered and this is the subject of the present invention, that it was possible to obtain increased performance of the process, especially when the sulfur content of gasoline is high, i.e. greater than 1000 ppm by weight and / or when the olefin content is greater than 30% by weight and the sulfur content of the gasoline concerned is less than 50 ppm by weight or even less than 15 ppm weight.

The sulfur species contained in the charges treated by the process of the invention may be mercaptans or heterocyclic compounds, such as by for example thiophenes or alkyl thiophenes, or heavier compounds, such as for example benzothiophene or dibenzothiophene. These heterocyclic compounds, unlike mercaptans, cannot be eliminated by conventional extraction processes. These sulfur compounds are therefore eliminated by the process according to the invention which leads to their decomposition at least partial in hydrocarbons and H2S.

The sulfur content of gasoline cuts produced by catalytic cracking (FCC) depends on the sulfur content of the feed treated with FCC, as well as the point end of the cut. Generally, the sulfur contents of an entire cut gasoline, especially those from the FCC, are greater than 100 ppm by weight and most of the time greater than 500 ppm by weight. For species with endpoints above 200 ° C, sulfur contents are often greater than 1000 ppm by weight, they can even in some cases reach values of on the order of 4000 to 5000 ppm by weight.

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

Species can also contain significant concentrations of diolefins, ie diolefin concentrations of up to 15% by weight. Generally the content of diolefins is between 0.1 and 10% by weight. When the diolefin content is greater than 1% by weight or even greater than 0.5% by weight, the gasoline can, before undergoing steps A, B and C of the process according to the invention, be subjected to a selective hydrogenation treatment aimed at hydrogenating at least in part of the diolefins present in said essence.

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

This essence preferably contains a sulfur content greater than 1000 ppm weight. The range of boiling points typically extends from about the boiling points of hydrocarbons with 5 carbon atoms (C5) up to approximately 250 ° C. The end point of the petrol cut depends on the refinery from which it comes and market constraints, but generally remains within the limits indicated above. In some cases, and in order to optimize the configuration of the process, it can be advantageous to subject the essence to different treatments before submitting it to the method according to the invention. Gasoline can, for example, undergo splitting or any other treatment before being subjected to the process according to the invention without these processing does not limit the scope of the invention.

For this type of gasoline, the analysis of the nature of the sulfur compounds show that sulfur is mainly present in the form of thiophenic compounds (thiophene, methylthiophenes, alkylthiophenes ...) and, depending on the end point of gasoline to be treated, benzothiophenic, alkylbenzothiophenic compounds, even of compounds derived from dibenzothiophene.

The method according to the invention firstly comprises a treatment (step A) of the gasoline on a catalyst making it possible to at least partially hydrogenate unsaturated sulfur compounds such as for example thiophenic compounds, into saturated compounds such as by example thiophanes (or thiacyclopentane) or mercaptans according to a succession of reactions described below:

This hydrogenation reaction can be carried out on a hydrotreating catalyst (hydrodesulfurization) conventional comprising a group VIII metal and a metal of the Vlb group partly in the form of sulphides. When such a catalyst is used, the operating conditions are adjusted in order to be able to at least partially hydrogenate the thiophenic compounds while limiting the hydrogenation of olefins.

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

The method according to the invention comprises a second step where the H2S is at less partially removed from the effluent obtained at the end of step A. This step can be carried out using any technique known to those skilled in the art. She may be performed directly under the conditions in which the effluent is found after step A or after these conditions have been changed to facilitate disposal at least part of the H2S. As a possible technique, one can for example quote, a gas / liquid separation (where the gas concentrates in H2S and the liquid is depleted in H2S and is sent directly to step C), a stripping step of the gasoline practiced on a liquid fraction of the gasoline obtained after step A, a amine washing step, again performed on a liquid fraction of the gasoline obtained after step A, an H2S uptake by an absorbent mass operating on the gaseous or liquid effluent obtained after the step, a separation of the H2S from the effluent gaseous or liquid by a membrane. At the end of this treatment, the sulfur content as H2S is generally less than 500 ppm weight compared to petrol of departure. Preferably, this content is reduced, at the end of step B to a value between 0.2 and 300 ppm weight and more preferably at a value between 0.5 and 150 ppm weight.

The process according to the invention comprises a third step (step C) in which the saturated sulfur compounds are converted into H2S according to the reactions:

This treatment can be carried out using any catalyst allowing the conversion of saturated sulfur compounds (mainly type compounds thiophanes or mercaptans type). It can for example be done using a catalyst based on nickel, molybdenum, cobalt, tungsten, iron 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 gasoline thus desulphurized is then optionally stripped, in order to remove the H2S produced in 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 patent application 99 / 02.336, the invention proposed here has the advantage:

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

In the case of petrol with a high sulfur content and / or when the level of transformation of unsaturated sulfur compounds into saturated sulfur compounds is not sufficient in step A, it may be advantageous to perform step C with a sequence of catalysts comprising at least one catalyst described for step A and at least one catalyst described for step C.

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

- Hydrogenation of dienes (optional step before step A):

The hydrogenation of dienes is an optional but advantageous step, which makes it possible to eliminate, before hydrodesulfurization, almost all of the dienes present in the gasoline fraction containing sulfur to be treated. It generally takes place in the presence of a catalyst comprising at least one metal from group VIII, preferably chosen from the group formed by platinum, palladium and nickel, and a support. Use will be made, for example, 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 under a pressure of 0.4 to 5 MPa, at a temperature of 50 to 250 ° C, with an hourly space velocity of the liquid from 1 to 10 h ^-1 . Another metal can be combined to form a bimetallic catalyst, such as for example molybdenum or tungsten.

It can be particularly advantageous, especially when dealing with cuts whose the boiling point is below 160 ° C, to operate under conditions such as at least partial softening of the essence is obtained, i.e. a certain reduction in mercaptans content. To do this, we can use the procedure described in patent application FR-A-2 753 717, which uses a catalyst based on palladium.

The choice of operating conditions is particularly important. We will operate on more generally under pressure in the presence of a small quantity of hydrogen excess over the stoichiometric value required to hydrogenate the diolefins. The hydrogen and the charge to be treated are injected in updrafts or descendants in a reactor preferably with a fixed catalyst bed. 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 between approximately 1 and approximately 10 h ^-1 , preferably between 4 and 10 h ^-1 .

The catalytic cracking gasoline can contain up to a few% by weight 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. Content dienes after selective hydrogenation can even be reduced to less than 250 ppm.

According to one embodiment of the invention, the hydrogenation step of the dienes is takes place in a catalytic hydrogenation reactor which includes a zone catalytic reaction crossed by the entire charge and the quantity of hydrogen necessary to carry out the desired reactions.

- Hydrogenation of unsaturated sulfur compounds (step A):

This step consists in transforming at least part of the unsaturated compounds sulfur such as thiophenic compounds, in saturated compounds for example in thiophanes (or thiacyclopentanes) or mercaptans.

This step can, for example, be carried out by passing the feed to be treated, in the presence of hydrogen, over a catalyst containing at least one element from group VIII and / or at least one element from group Vlb at least partially in sulphide form, at a temperature between about 210 ° C and about 350 ° C, preferably between 220 ° C and 320 ° C and more preferably between 220 ° C and 290 ° C, under a pressure generally between about 1 and about 5 MPa, preferably between 1 and 4MPa and more preferably between 1.5 and 3MPa. The liquid space velocity is between about 1 and about 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 H ₂ / HC ratio 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 sulfur compounds gasoline unsaturated according to the process of the invention, in general at least one hydrodesulfurization catalyst, comprising at least one element from group VIII (metals of groups 8, 9 and 10 of the new classification, i.e. iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium or platinum) and / or at least one element of group Vlb (metals of group 6 of the new classification, i.e. chromium, molybdenum or tungsten), on a support appropriate. Preferably, the element of group VIII, when present, is usually nickel or cobalt, and the Vlb group element, when present, is usually 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 as a mixture with alumina or silica-alumina.

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

The catalyst preferably used in this step is a catalyst comprising an alumina-based support whose specific surface is less than 200 m2 / g, and comprising at least one element chosen from the group consisting of cobalt, molybdenum, nickel or tungsten and preferably chosen 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-based catalysts, the density of molybdenum 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 stage is carried out under conditions allowing conversion to minus some of the oxidized forms of the base metal metal. Generally it consists in treating the catalyst under a stream of hydrogen at a temperature at least equal to 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 stages. Preferably, no oxidation step is carried out when the sulfur or a sulfur-containing compound is introduced onto the catalyst. The sulfur or a sulfur-containing 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 the method according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulphurized by passing a charge containing at least one sulfur compound, which once decomposed leads to the fixing of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur-containing compound.

Preferably, the sulfur-containing compound is added to the catalyst ex situ. For example, after the calcination step, a sulfur-containing compound can be introduced onto the catalyst in the optional presence of another compound. The catalyst is then dried, then transferred to the reactor used to carry out the process of the invention. In this reactor, the catalyst is then treated under hydrogen in order to transform at least part of the main metal into sulphide. A procedure which is particularly suitable for the invention is that described in patents FR-B- 2,708,596 and FR-B- 2,708,597.

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

The effluent which has undergone this first treatment is then sent to stage B which at least partially eliminates the H2S present at the end of step A.

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

In this stage the H2S concentration is reduced. Elimination of H2S can be carried out in various ways, most of which are known to those skilled in the art job. We can for example cite the adsorption of part of the H2S contained in the effluent from step A by an absorbent mass based on a metal oxide, preference chosen from the group consisting of zinc oxide, copper oxide or molybdenum oxide. This adsorbent mass is preferably regenerable. Her regeneration can be carried out continuously or discontinuously for example at by means of a heat treatment under an oxidizing or reducing atmosphere. The mass absorbent can be used in a fixed bed or a mobile bed. It can operate directly on the effluent from step A, or on this effluent having undergone treatments (for example a cooling or separation ...). Another method is to perform a 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 can contain an absorbent mass to promote the transfer of H2S through the wall of the membrane. Another method may be to cool the effluent from step A and to 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 fraction liquid can also undergo other treatments such as stripping with hydrogen, nitrogen or water vapor, extraction of H2S, washing with amines, washing with a sodium hydroxide solution to reduce its H2S content.

- Decomposition of saturated sulfur compounds (Step C):

In this step, the saturated sulfur compounds are transformed into presence of hydrogen on a suitable catalyst. This transformation is carried out, without hydrogenation of olefins, i.e. during this stage the hydrogenation of olefins is limited to 20% based on the content of the starting gasoline, and preferably, limited to 10% relative to the olefin concentration of the gasoline.

Catalysts which may be suitable for the invention, without this list being limiting, are catalysts comprising at least one metal chosen from the group consisting of nickel, cobalt, iron, molybdenum and tungsten and. So more preferred the catalysts of this stage 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 approximately 1 and approximately 60% by weight and preferably between 5 and 20% by weight. Preferably, the catalyst is generally shaped, preferably under in the form of beads, extrudates, pellets, or trilobes. Metal can be incorporated into catalyst on the preformed support, it can 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. Other mode of introduction known to the skilled person suitable for the implementation of the invention.

The catalyst supports 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 can be used alone or as a mixture with alumina or silica-alumina. Preferably, the supports are transition aluminas or silicas whose specific surface is between 25 and 350 m ² / g. Natural compounds (for example kieselguhr or kaolin) can also be suitable as supports for the catalysts of the process according to the invention.

After introduction of the metal and possibly shaping of the catalyst (when this step is carried out with a mixture already containing the base metal), the catalyst is in a first activated stage. This activation can correspond either to an oxidation, then to a reduction, either to a direct reduction, or to a calcination only. The calcination step is generally carried out at temperatures ranging from approximately 100 to approximately 600 ° C. and preferably between 200 and 450 ° C, under an air flow. The reduction step is carried out in conditions for converting at least some of the oxidized forms of the metal metal base. Generally, it consists in treating the catalyst under a flow of hydrogen at a temperature at least equal to 300 ° C. The reduction can also be carried out in part by chemical reducers.

The catalyst is preferably used at least in part in its sulfurized form. This has the advantage of minimizing the risk 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 stages. Preferably, no oxidation step is carried out when the sulfur or a sulfur-containing compound is introduced onto the catalyst. The sulfur or a sulfur-containing 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 the method according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulphurized by passing a charge containing at least one sulfur compound, which once decomposed leads to the fixing of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur-containing compound.

Preferably, the sulfur-containing compound is added to the catalyst ex situ. For example, after the calcination step, a sulfur-containing compound can be introduced onto the catalyst in the optional presence of another compound. The catalyst is then dried, then transferred to the reactor used to carry out the process according to the invention. In this reactor, the catalyst is then treated under hydrogen in order to transform at least part of the main metal into sulphide. A procedure which is particularly suitable for the invention is that described in patents FR-B-2 708 596 and FR-B-2 708 597.

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

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

The operating conditions of the catalyst making it possible to decompose the saturated sulfur compounds in H2S should be adjusted so as to reach the desired level of hydrodesulfurization, and in order to minimize the loss of octane resulting from saturation of olefins. The second catalyst (catalyst of step C) used in the process according to the invention generally makes it possible to convert only at most 20% of the olefins, preferably at most 10% of the olefins.

The treatment aimed at decomposing the saturated sulfur compounds during the first step of the process (step A) is carried out in the presence of hydrogen, with the catalyst based on a metal, such as more preferably nickel, at a temperature between about 200 ° C and about 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 about 0.5 and about 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 approximately 0.5 and approximately 10 h ^-1 (expressed in volume of liquid per volume of catalyst and per hour), preferably between 1 and 8 h ^-1 . The H ₂ / HC ratio is adjusted as a function of the desired hydrodesulfurization rates in the range generally between approximately 100 and approximately 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 coming from stage C.

- Implementation of the process:

One of the possibilities of implementing the method according to the invention, can by example consist of passing the gasoline to be hydrotreated through a reactor containing a catalyst allowing, at least in part, the hydrogenation of the compounds unsaturated sulfur, such as for example thiophenic compounds, in compounds saturated with sulfur (step A) and removal of H2S (step B), then through a reactor containing a catalyst for decomposing the saturated compounds of the sulfur in H2S (step C). The H2S removal step can also be performed in the reactor of step C or partly in each of the 2 reactors. The elimination stage can also be partially or entirely located outside reactors of stages A and C.

In another configuration which is also suitable, the two catalysts of the stages A and C are placed in series in the same reactor and an adsorbent mass of the H2S is placed between the two catalysts in order to at least partially eliminate 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 regeneration can be carried out discontinuously or continuously depending on the adsorbent mass used.

In all cases, the two catalytic zones can operate in different conditions of pressure, VVH, temperature, H2 / charge ratio. of the systems can be implemented to dissociate the operating conditions of 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 unsaturated sulfur compounds, saturated sulfur compounds (step A), then to be carried out separately or in a simultaneous H2S removal step, then perform step C in a reactor containing a chain of catalysts comprising at least one catalyst of the same type as that used in the first step of the process (step A) and at least a catalyst for decomposing saturated sulfur compounds into H2S (step C).

With the sequences proposed for the method according to the invention, it is possible to achieve high hydrodesulfurization rates while limiting the loss of olefins and therefore the decrease in 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.

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 presents the characteristics of the charge (catalytic cracking gasolines) treated by the process according to the invention. The analysis methods used to characterize the loads and effluents are as follows:

• gas chromatography (GC) for the hydrocarbon constituents;
• NF M 07052 method 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 engine octane number.

Characteristics of the load used Charge Density 0.78 Initial point (° C) 63 ° C End point (° C) 250 ° C Olefin content (% wt) 31.3 Content of dienes 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 diolefins is carried out on an HR945® catalyst based on nickel and molybdenum, sold by the company Procatalyse. The test is performed in a continuous reactor of the crossed bed type, the charge and the hydrogen being introduced by the bottom of the reactor. 60 ml of catalyst are introduced into the reactor after having been previously sulfurized ex situ for 4 hours, under a pressure of 3.4 Mpa, at 350 ° C, in contact with a charged load of 2% by weight of sulfur in the form of dimethylsisulfide in n-heptane. The catalyst is then transferred to the reactor where the hydrogenation of diolefins is carried out. The hydrogenation is then performed under the following conditions: T = 190 ° C, P = 2.7 Mpa, VVH = 6h-1 and H2 / HC = 151/1. After hydrogenation of the diolefins, the diolefin content is., 1% weight.

After hydrogenation, the charge contains ..... (ppm or% by 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 130 m2 / g and a pore volume 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 in 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 tubular hydrodesulfurization reactor with a fixed bed. The catalyst is first sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C, in contact with a charge consisting of 2% sulfur in the form of dimethyldisulfide in n-heptane.
The operating conditions for hydrodesulfurization 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 presented in Table 2 Temperature of the catalytic zone (° C) Sulfur content of desulphurized petrol (ppm) Olefin content of desulfurized gasoline (% by weight) Desulfurized gasoline octane (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 (comparison)

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 of 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 in an air stream 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 feed to be treated (heavy fraction) first meets catalyst A and then the catalyst C. The catalysts are first of all sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a charge consisting of 2% of sulfur in the form of dimethyldisulphide in n-heptane .

The operating conditions for 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 from 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. Temperature of catalytic zone A (° C) Sulfur content of desulphurized petrol (ppm) Olefin content of desulfurized gasoline (% by weight) Desulfurized gasoline octane (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. A test 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 making it possible to remove the H2S to a content of 50 ppm weight relative to the liquid. The liquid thus obtained is then warmed 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 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. Temperature of catalytic zone A (° C) Sulfur content of desulphurized petrol (ppm) Olefin content of desulfurized gasoline (% by weight) Desulfurized gasoline octane (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 method 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 example 1 and 25 ml of catalyst C of example 3, so that the charge first meets catalyst A then catalyst C. The effluent from the first reactor is cooled to room temperature, the liquid phase and the gas phase are separated, the H2S of the liquid phase is stripped by a stream of nitrogen allowing eliminate 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 reactor and reinjected into 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 table 5. The temperature of the catalyst A present in the second zone is brought to 270 ° C. and the temperature of the catalyst C present in the second reactor is brought to 330 ° C.

The results obtained are reported in Table 5. Temperature of catalytic zone A (° C) Sulfur content of desulphurized petrol (ppm) Olefin content of desulfurized gasoline (% by weight) Desulfurized gasoline octane (RON + MON) / 2 260 ° C 49 23.6 83.3 280 ° C 10 20.2 82.3

Claims (13)

Process for producing gasoline with a low sulfur content, characterized in that it comprises at least three stages: A) a first step in which the sulfur compounds present in the gasoline are at least partially transformed into H2S and into saturated sulfur compounds, B) a second step aimed at eliminating the H2S from the gasoline produced in step A, C) a third step in which the saturated sulfur compounds remaining in the gasoline are transformed into H2S. The method of claim 1, wherein a preprocessing step to hydrogenating the feed diolefins is carried out before step A. A method according to any of claims 1 or 2 in which the charge is a catalytic cracking gasoline. Method according to any one of Claims 1 to 3, in which step A is carried out by passing the charge, in the presence of hydrogen, over a catalyst comprising at least one element from group VIII and / or at least one element from group Vlb, at least partly in sulphide form. The method of claim 4 wherein the group VIII element, when it is present, is nickel or cobalt, and the element of group Vlb, when present, is molybdenum or tungsten. The method of claim 5 wherein step A is performed at a temperature between about 210 ° C and about 350 ° C, under a pressure generally between about 1 and about 5 MPa, with a space velocity of the liquid between about 1 and approximately 10 h ^-1 , and an H ₂ / HC ratio of between approximately 100 and approximately 600 liters. Method according to one of Claims 1 to 6, in which step C is carried out in presence of a catalyst comprising at least one base metal chosen from the group formed by nickel, cobalt, iron, molybdenum, tungsten. The method of claim 7 wherein the base metal content is between 1 and 60% by weight and said metal is sulfurized. Method according to one of claims 1 to 8 wherein step C is carried out at a temperature between about 200 ° C and about 350 ° C, a pressure between about 0.5 and about 5 MPa, a space velocity of the liquid between approximately 0.5 and approximately 10 h ^-1 and an H ₂ / HC ratio between approximately 100 and approximately 600 liters per liter. Method according to any one of Claims 1 to 9, implemented by means at least two separate reactors, charge pretreatment reactor not understood, the first reactor containing the catalyst required in step A and the second at least that required in step B. Method according to any one of Claims 1 to 9, implemented by means at least two separate reactors, charge pretreatment reactor not understood, the first reactor containing at least part of the necessary catalyst in step A and the second at least the other part of that needed in step A and the one needed in step B. The method of any of claims 1 to 11, wherein step B is elimination of H2S is carried out by adsorption in the presence of a mass adsorbent selected from the group consisting of zinc oxide, copper oxide and molybdenum oxide. Process according to Claims 1 to 11, in which the H2S is separated by means of a membrane.