EP1031622A1 - Process for the production of low sulphur gasolines - Google Patents

Abstract

Production of low-sulfur gasoline comprises: (A) hydrogenating unsaturated sulfur compounds; and (B) decomposing saturated sulfur compounds.

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.

Prior art:

The production of reformulated essences meeting the new standards environment requires in particular that their concentration is slightly reduced in olefins but significantly their aromatic concentration (especially the benzene) and sulfur. Essences of catalytic cracking, which can represent 30 to 50% of the petrol pool have high olefin and sulfur contents. Nearly 90% of the sulfur in reformulated gasolines is due to the essence of catalytic cracking (FCC, "Fluid Catalytic Cracking" or cracking fluidized bed catalytic). Desulfurization (hydrodesulfurization) of gasolines and mainly FCC essences is therefore of obvious importance for achievement of specifications.

Hydrotreating (hydrodesulfurization) of the charge sent to the cracking catalytic leads to gasolines typically containing 100 ppm of sulfur. The However, catalytic cracking charge hydrotreating units operate in severe temperature and pressure conditions, which requires effort significant investment. In addition, the entire feed must be desulphurized, which entails the processing of very large load volumes.

Hydrotreatment (or hydrodesulfurization) of cracked essences catalytic, when carried out under conventional conditions known to those skilled in the art loom reduces the sulfur content of the cut. However, this process has the major disadvantage of causing a very large drop in the index octane from the cut, due to the saturation of all the olefins during hydrotreating.

The separation of light and heavy petrol before hydrotreatment has already been claimed in patent US-A-4,397,739. In this patent, it is claimed a process for hydrodesulfurization of gasolines comprising a splitting gasoline into a light fraction and a heavy fraction and a specific hydrodesulfurization of the heavy fraction.

On the other hand, in US-A-4 131 537 it is taught that it is interesting to split the essence into several cuts, preferably three, according to their boiling point, and desulfurize them under conditions which may be different and in the presence of a catalyst comprising at least one metal from group VIB and / or group VIII. It is stated in this patent that the greatest benefit is obtained when the gasoline is divided into three cuts and when the cut having intermediate boiling points is treated under mild conditions.

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 the products sulfur by means of analyzes. These analyzes are necessary to select apparatus and separation conditions.

In this application it is thus indicated that a slight fraction of petrol of cracking sees its olefin content and its octane number drop so important when it is desulphurized without being fractionated. However, the fractionation of said light fraction into 7 to 20 fractions followed by content analyzes in sulfur and in olefins of these fractions makes it possible to determine the fraction (s) richer in sulfur compounds which are then simultaneously desulfurized or separately and mixed with the other desulfurized fractions or not. Such a procedure is complex and must be reproduced with each change in the composition of the essence to be treated.

In French patent application n ° 98 / 14,480, the interest of split gasoline into a light fraction and a heavy fraction and then perform a specific hydrotreating of light petrol on a nickel-based catalyst, and hydrotreating of heavy petrol on a catalyst comprising at least one group VIII metal and / or at least one group Vlb metal.

In the French patent application n ° 98/02 944, there is described a process for the treatment of catalytic cracking gasolines comprising the sequence of 2 stages: a mild hydrotreatment with possible stripping of the H ₂ S product, then elimination mercaptans. This process makes it possible to eliminate the mercaptans almost completely during the second stage, but the overall rate of hydrodesulfurization at the end of the two stages remains limited, especially when operating with recycling of the hydrogen not consumed and containing optionally hydrogen sulfide (H ₂ S).

It has also been proposed, for example in patent US-A-5 290 427, gasoline hydrotreatment processes consisting of splitting gasoline and then desulfurize the fractions and convert the desulfurized fractions on a ZSM-5 zeolite, in order to compensate for the loss of octane recorded by means of isomerization.

US-A-5 318 690 proposes a process with fractionation of the essence and a softening of the light fraction, while the heavy fraction is desulfurized, then converted to ZSM-5 and desulfurized again under conditions sweet. This technique is based on a separation of the raw petrol so as to obtain a light cut practically free from sulfur compounds other than mercaptans. This makes it possible to treat said cut only by means of a softening which removes the mercaptans.

Therefore, the heavy cut contains a relatively large amount of olefins which are partially saturated during hydrotreatment. To compensate for the fall in the octane number linked to the hydrogenation of olefins, the patent recommends cracking on zeolite ZSM-5 which produces olefins, but to the detriment of the yield. In addition, these olefins can recombine with the H ₂ S present in the medium to reform mercaptans. It is then necessary to carry out additional softening or hydrodesulfurization.

Summary of the invention:

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, preferably a gasoline catalytic cracked cut, and reduce sulfur contents in said gasoline cut at very low levels, without reduction appreciable fuel efficiency while minimizing the decrease in octane number due to the hydrogenation of olefins.

The process according to the invention is a process for producing low-grade petrol in sulfur, from a gasoline cut containing sulfur. In the process according to the invention, there is no need to split the charge, which is therefore preferably made up of the entire petrol cut. This constitutes a both technical and economic advantage over most processes described in the prior art. The method according to the invention comprises at least one treatment of the charge on a first catalyst making it possible to hydrogenate at least partially unsaturated sulfur compounds, especially sulfur compounds cyclic, even aromatic, such as, for example, thiophenic compounds placing in conditions where the hydrogenation of olefins is limited on this catalyst, then a second treatment on a second catalyst allowing decompose the saturated linear and / or cyclic sulfur compounds, with a limited hydrogenation of olefins.

The two catalytic treatments can be carried out either in a reactor common with a chain of the two catalysts, ie in two reactors different. It is also desirable in some cases to add a step of pretreatment, preferably catalytic, aimed at hydrogenating the diolefins of the charge before the first step of the process according to the invention.

The charge of the process according to the invention is a petrol cut containing sulfur, preferably a petrol cut from a catalytic cracking unit, whose range of boiling points typically extends from about the points boiling of hydrocarbons with 5 carbon atoms (C5) up to around 250 ° C. The end point of the gasoline cut depends on the refinery from which it comes and constraints of the market, but generally remains within the limits indicated above.

For this type of gasoline, a chromatographic analysis of the sulfur compounds shows that the various compounds described below are encountered, among others: methanethiol, ethanethiol, propanethiol, thiophene, thiacyclobutane, butanethiol, pentanethiol, 2-methylthiophene, 3-methylthiophene, thiacyclopentane, 2-methylthiacyclopentane, 2-ethylthiophene, 3-ethylthiophene, 2-5 dimethylthiophene, 3-methylthiacyclopentane, 2,4-dimethylthiophene, 2,3-dimethylthiophene, 2,5-dimethylthiacyclopentane, 3,3-dimethylthiacyclopentane, 3,4-dimethylthiophene, 2,3-dimethylthicyclopentane, 2-isopropyl thiophene, 3-isopropylthiophene, 3-ethyl2methylthiophene, thiophenol, 2,3,4 trimethylthiophene, 2,3,5 trimethylthiophene, benzothiophene.

Depending on the cutting point of the fuel and the operating conditions of the catalytic cracking unit, certain compounds can obviously be absent from this essence. In addition, when dealing with boiling point charges high, the presence of alkylated benzothiophene compounds is also possible, or even compounds derived from dibenzothiophene.

The method according to the invention generally comprises at least a first step (step a), carried out by passing the charge, preferably consisting of the entire gasoline cut, over a catalyst making it possible to at least partially hydrogenate the compounds unsaturated sulfur present in said feed, such as for example thiophenic compounds, in saturated compounds, such as for example thiophanes (or thiacyclopentane), or mercaptans according to a succession of reactions described below:

This hydrogenation reaction can be carried out on any catalyst which promotes these reactions such as for example a catalyst comprising at least one metal of group VIII and / or at least one metal from group Vlb, preferably at least in part in the form of sulfides. When such a catalyst is used, the conditions are adjusted in order to be able to at least partially hydrogenate the compounds saturated, such as thiophenic compounds, while limiting the hydrogenation of olefins.

The method according to the invention comprises a second step (step b) in which the saturated sulfur compounds are converted into H ₂ S according to the reactions:

This treatment can be carried out on any catalyst allowing the conversion of saturated sulfur compounds (mainly thiophanes or mercaptans type). It can for example be carried out on a nickel-based catalyst, molybdenum, or cobalt.

The gasoline thus desulphurized is then optionally stripped (that is to say that a gas stream, preferably containing one or more inert gases is passed through this gasoline), in order to eliminate the H ₂ S produced. during hydrodesulfurization.

The expressions first step (step a) and second step (step b), do not exclude the possible presence of another stage, in particular a stage of pretreatment of the charge, consisting for example of the selective hydrogenation of dienes present in the charge. Such an optional pretreatment step is to preferably located before step a of the method according to the invention.

Detailed description of the invention:

It has been unexpectedly discovered that the combination of two suitable catalysts, a first catalyst promoting the transformation of the unsaturated sulfur compounds present in gasoline, such as for example thiophenic compounds, and at least one second catalyst promoting the transformation selective of the saturated sulfur compounds, linear or cyclic already present in the gasoline or produced during the first stage, allows to obtain in the end a desulfurized gasoline presenting no significant reduction in the content of olefins or in the index d 'octane; this without the need to split the gasoline, or to have recourse to processes making it possible to restore the octane number of the gasoline. Significant hydrodesulfurization rates are reached, under reasonable operating conditions specified below, including when operating with recycling of hydrogen that is not consumed and possibly containing hydrogen sulfide (H ₂ S).

The sulfur species contained in the feeds treated by the process of the invention can be mercaptans or heterocyclic compounds, such as for example thiophenes or alkyl thiophenes, or heavier compounds, such as for example benzothiophene or dibenzothiophene . These heterocyclic compounds, unlike mercaptans, cannot be removed by the extractive processes. These sulfur-containing compounds are however eliminated 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 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.

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

- Hydrogenation of dienes:

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 preferably takes place before the first step (step a) of the process according to the invention, generally 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 hydrogenation of dienes described in patent application EP-A-0 832 958, which advantageously uses a palladium-based catalyst.

The choice of operating conditions is particularly important. We will operate most 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 comprising a fixed bed of catalyst. The temperature is more generally between approximately 50 and approximately 250 ° C., and preferably between 80 and 200 ° C, and more preferably between 160 and 190 ° C.

The pressure used 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 approximately 0.4 and approximately 5 MPa and preferably greater than 1 MPa, and more preferably 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 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, to a temperature between about 210 ° C and about 320 ° C, preferably between 220 ° C and 290 ° C, under a pressure generally between about 1 and about 4 MPa, preferably between 1.5 and 3 MPa. The space velocity of the liquid is between approximately 1 and approximately 10 h ^-1 (expressed in volume of liquid per volume of catalyst and per hour), preferably between 3 and 8 h ^-1 . The H ₂ / HC ratio is between 100 to 600 liters per liter and preferably between 300 and 600 liters per liter.

To achieve, at least in part, the hydrogenation of sulfur compounds unsaturated gasoline according to the method of the invention, in general at least one uses a catalyst, comprising at least one element from group VIII (metals from 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 the group Vlb (metals of group 6 of the new classification, i.e. chromium, molybdenum or tungsten), on a suitable support. The element of group VIII, when present, is usually nickel or cobalt, and the group element Vlb, when present, is generally molybdenum or tungsten. Of combinations such as nickel-molybdenum or cobalt-molybdenum are preferred. The catalyst support is usually a porous solid, such as for example a alumina, silica-alumina or other porous solids, such as for example magnesia, silica or titanium oxide, alone or in admixture 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 reduction stage is carried out under conditions allowing at least part of the oxidized forms to be converted metal base metal. Generally, it consists in treating the catalyst under a flow of hydrogen at a temperature preferably at least equal to 300 ° C. The reduction can also be achieved in part by chemical reducers.

The catalyst is preferably used at least in part in its sulfurized form. The introduction of sulfur can occur before or after any activation step, that is to say calcination or reduction. Preferably, no oxidation step is carried out when the sulfur or a sulfur-containing compound has been 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.

According to the process of 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 from this first hydrogenation step is then sent to the level of the catalyst which makes it possible to decompose the saturated sulfur compounds into H2S.

- Decomposition of saturated sulfur compounds (step b):

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

The catalysts which may be suitable for this stage of the process according to the invention, without this list being exhaustive, are catalysts comprising at least one metal base chosen from the group formed by nickel, cobalt, iron, molybdenum, tungsten. These metals can be used alone or in combination, they are preferably supported and used in their sulfurized form.

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

The catalyst supports used in this stage of the process according to the invention are generally porous solids chosen from refractory oxides, such as, for example, aluminas, silicas and silica-aluminas, magnesia, as well as titanium 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, such as, for example, kieselguhr or kaolin, may also be suitable as supports for the catalysts used in this stage of the process.

After introduction of the base metal and possibly shaping of the catalyst (when this step is carried out from 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, or to a direct reduction, or still only to a calcination. 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 reduction stage is carried out under conditions allowing at least part of the oxidized forms to be converted metal base metal. 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 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.

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 and very preferred between 4 and 10% by weight.

The purpose of the hydrodesulfurization carried out during this stage is to convert into H2S saturated sulfur compounds in gasoline which has already undergone at least one the prior hydrogenation of the unsaturated sulfur compounds, so as to obtain a effluent, which will meet the desired specifications in terms of content of compounds sulfur. The gasoline thus obtained has only a small loss of octane.

It has been found that the use of this second catalyst in this step, under specific operating conditions, allows the compounds to be broken down saturated, contained in the effluent from the previous step, in H2S. This setting work achieves a high overall level of hydrodesulfurization at the end of all the steps of the process according to the invention, while minimizing the loss in octane resulting from the saturation of olefins, because the conversion of olefins during of step b is generally limited to at most 20% by volume of the olefins, of preferably at most 10% by volume.

The treatment aimed at decomposing the saturated sulfur compounds resulting from the first step of the process is carried out in the presence of hydrogen, with the catalyst comprising at least one base metal chosen from the group formed by nickel, cobalt, iron, molybdenum, tungsten, at a temperature between about 250 ° C and about 350 ° C, preferably between about 260 ° C and about 350 ° C, more preferably between about 260 ° C and about 320 ° C, under a low to moderate pressure, generally between approximately 0.5 and approximately 5 MPa, preferably between 0.5 and 3MPa, more preferably between 1 and 3 MPa. The space velocity of the liquid is 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 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 step a or from recycling of the unconsumed hydrogen from step b. This hydrogen resulting from steps a or b may optionally contain unseparated H ₂ S.

- Preferred implementations of the method according to the invention:

One of the possibilities of implementing the method according to the invention consists, for example, in passing the gasoline to be hydrodesulfurized through two separate reactors containing respectively for the first reactor: all or part, preferably all, of a catalyst allowing, at least in part, the hydrogenation of unsaturated sulfur compounds (step a), such as for example thiophenic compounds, into saturated sulfur compounds (such as thiacyclopentanes or mercaptans) and for the second reactor: a catalyst allowing decomposing the saturated sulfur compounds into H ₂ S (step b), and optionally another part of the catalyst required in step a, preferably at the head of the bed. Between the two reactors, systems can be installed to optionally dissociate the operating conditions of the two reaction zones.

In another configuration of the process according to the invention, the two catalysts can be placed in series in the same reactor.

In both cases, the two catalytic zones can operate in different or identical conditions of pressure, temperature, VVH, and H2 / charge ratio

a) une étape d'hydrogénation des composés soufrés insaturés.

b) une étape de décomposition des composés soufrés saturés.

dans lequel :

• une étape de prétraitement visant à hydrogéner les dioléfines de la charge est éventuellement effectuée avant l'étape a.
• la charge est de préférence constituée par l'ensemble d'une coupe esence, de préférence une essence de craquage catalytique.
• l'étape a est effectuée par passage de la charge, en présence d'hydrogène, sur un catalyseur permettant d'hydrogéner les composés insaturés du soufre, et de préférence comprenant au moins un élément du groupe VIII et/ou au moins un élément du groupe Vlb au moins en partie sous forme sulfure, et dans lequel l'élément du groupe VIII, lorsqu'il est présent, est de préférence le nickel ou le cobalt, et l'élément du groupe Vlb, lorsqu'il est présent, est de préférence le molybdène ou le tungstène.
• l'étape a est effectuée à une température comprise entre environ 210°C et environ 320°C, sous une pression généralement comprise entre environ 1 et environ 4 MPa, avec une vitesse spatiale du liquide comprise entre environ 1 et environ 10 h^-1 , et un rapport H₂/HC compris entre environ 100 et environ 600 litres.
• l'étape b est effectuée en présence d'un catalyseur permettant de décomposer les composés saturés du soufre, comprenant de préférence au moins un métal de base choisi dans le groupe formé par le nickel, le cobalt, le fer, le molybdène, le tungstène, la teneur en métal de base étant comprise entre 1 et 60 % poids de manière préférée entre 5 et 20 % en poids, et ledit métal étant de préférence sulfuré.
• l'étape b est effectuée à une température comprise entre environ 250°C et environ 350°C, une pression comprise entre environ 0,5 et environ 5 MPa, une vitesse spatiale du liquide comprise entre environ 0,5 et environ 10 h^-1 et un rapport H2/HC entre environ 100 et environ 600 litres par litres.
• le procédé peut éventuellement être mis en oeuvre au moyen d'un seul réacteur contenant les catalyseurs nécessaires aux étapes a et b, réacteur de prétraitement de la charge ( tel que par exemple un réacteur d'hydrogénation des diènes) non compris. Il peut également être éventuellement mis en oeuvre au moyen d'au moins deux réacteurs séparés, réacteur de prétraitement de la charge non compris, le premier réacteur contenant le catalyseur nécessaire à l'étape a et le deuxième au moins celui nécessaire à l'étape b .

In summary, the process according to the invention consists of a process for producing gasoline with a low sulfur content, characterized in that it comprises at least two stages:

a) a step of hydrogenation of the unsaturated sulfur compounds.

b) a step of decomposing saturated sulfur compounds.

in which :

• a pretreatment step aimed at hydrogenating the diolefins of the feedstock is optionally carried out before step a.
• the charge is preferably constituted by the whole of a gasoline cut, preferably a catalytic cracking gasoline.
• step a is carried out by passing the charge, in the presence of hydrogen, over a catalyst making it possible to hydrogenate the unsaturated sulfur compounds, and preferably comprising at least one element of group VIII and / or at least one element of group Vlb at least partly in sulphide form, and in which the element of group VIII, when it is present, is preferably nickel or cobalt, and the element of group Vlb, when it is present, is preferably molybdenum or tungsten.
• step a is carried out at a temperature between approximately 210 ° C and approximately 320 ° C, under a pressure generally between approximately 1 and approximately 4 MPa, with a space velocity of the liquid ranging between approximately 1 and approximately 10 h ^-1 , and an H ₂ / HC ratio of between approximately 100 and approximately 600 liters.
• step b is carried out in the presence of a catalyst making it possible to decompose the saturated sulfur compounds, preferably comprising at least one base metal chosen from the group formed by nickel, cobalt, iron, molybdenum, tungsten , the base metal content being between 1 and 60% by weight, preferably between 5 and 20% by weight, and said metal being preferably sulfurized.
• step b is carried out at a temperature between approximately 250 ° C. and approximately 350 ° C., a pressure comprised between approximately 0.5 and approximately 5 MPa, a space velocity of the liquid comprised between approximately 0.5 and approximately 10 h ^{- 1} and an H2 / HC ratio between approximately 100 and approximately 600 liters per liter.
• the process can possibly be implemented by means of a single reactor containing the catalysts necessary for steps a and b, reactor for pretreatment of the feed (such as for example a dienes hydrogenation reactor) not included. It can also optionally be implemented by means of at least two separate reactors, not including the charge pretreatment reactor, the first reactor containing the catalyst necessary for step a and the second at least that necessary for step b.

With the method according to the invention as described, it is possible to achieve high hydrodesulfurization rates while limiting the loss of olefins and by consequently the decrease in the octane number.

The following examples illustrate the invention.

• 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 0,75 Point initial (°C) 40°C Point final (°C) 200°C teneur en oléfines (% vol.) 32 S total (ppm) 1200 RON 90 MON 78 (RON + MON)/2 84

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 0.75 Initial point (° C) 40 ° C End point (° C) 200 ° C olefin content (% vol.) 32 S total (ppm) 1200 RON 90 MY 78 (RON + MON) / 2 84

Analysis of the sulfur-containing compounds in the feed by gas chromatography coupled with a specific detector of the PFDP (Pulse Flame Photometry Detector) type leads to the results presented in Table 2. Nature and concentration of sulfur compounds present in the feed. Sulfur compounds identified Concentration (ppm) THIOPHENE 235 Mercaptans 0 Methylthiophenes 487 Thiacyclopentane 82 Methylthiacyclopentane 40 C2 Thiophenes 227 diethylsulfide 11 C3 Thiophenes 26 C2 Thiacyclopentanes 46 C3 Thiacyclopentanes 46

Example 1 (comparative): hydrodesulfurization of gasoline on a catalyst allowing the conversion of unsaturated sulfur products.

25 ml of HR306C® catalyst, sold by the company Procatalyse, are placed in an insulated tubular reactor, with a fixed bed of catalyst. The catalyst is first sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C, in contact with a load consisting of 2% by weight of sulfur in the form of dimethyldisulfide in n-heptane.

The hydrodesulfurization operating conditions are as follows: VVH = 4 h ^-1 , H ₂ / HC = 400 l / l, P = 2.7 MPa. Under these conditions, the effluent after desulphurization at 220 ° C, 230 ° C and 250 ° C, the characteristics described in Table 3. Comparison of the characteristics of the charge and of the desulphurized effluent. Temperature (° C) Charge Effluent 220 ° C Effluent 230 ° C Effluent 250 ° C S total (ppm) 1200 587 305 96 Olefins (% vol.) 32 27 24 16 MY 78 77.5 77 75 RON 90 89.1 87.7 83 (RON + MON) / 2 84 83.3 82.4 79 Octane loss - 0.7 1.6 5 % HDS 51 75 92 % HDO 16 25 50

These results show that on the catalyst based on cobalt and molybdenum, achieving high desulfurization rates is accompanied by a significant loss in olefins and therefore a significant loss in octane.

On the other hand, the analysis of the nature of the sulfur compounds present in the effluents leads to the results presented in Table 4. Sulfur compounds identified Charge concentration (ppm) Effluent concentration 51% HDS (ppm) Effluent concentration 75% HDS (ppm) Effluent concentration 92% HDS (ppm) Thiophene 235 45 19 0 Mercaptans 0 161 125 68 Methylthiophenes 487 53 25 0 Thiacyclopentane 82 71 16 8 Methylthiacyclopentane 40 105 55 15 C2 Thiophenes 227 68 16 0 Diethylsulfide 11 0 0 0 C3 Thiophenes 26 8 4 0 C2 Thiacyclopentanes 46 65 35 5 C3 Thiacyclopentanes 46 11 10 5

It can be noted that on this catalyst the unsaturated sulfur compounds are converted significantly, even if the desulfurization rate is less than 75%.

Example 2 (comparative): hydrodesulfurization of gasoline on a catalyst allowing the conversion of saturated sulfur compounds.

The gasoline whose characteristics are described in Table 1 is subject hydrotreatment on a nickel-based catalyst in a tubular reactor isothermal, with fixed catalyst bed. The catalyst is prepared as follows.

It 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 in an air stream at 400 ° C for one hour. The nickel content of the catalyst is 20% by weight. The catalyst (100 ml) is then sulphurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a feed containing 2% by weight of sulfur in the form of dimethyldisulphide in n-heptane.

The gasoline is then subjected to a hydrotreatment under the following conditions: VVH = 2 h -1, P = 2.7 MPa, H2 / HC = 400 expressed in liters of hydrogen per liter of charge. The test temperature is 300 ° C and 350 ° C. The characteristics of the effluents thus obtained are presented in Table 5. Characteristics of gasolines after hydrodesulfurization (HDS) on the nickel catalyst Charge Effluent obtained after HDS at 300 ° C Effluent obtained after HDS at 350 ° C S total (ppm) 1200 660 300 Olefins (% vol.) 32 31 29 MY 78 78 78 RON 90 90 89 (RON + MON) / 2 84 84 83.5 Octane loss 0 0.5 % of HDS 45 75 % of HO 3 9

The nickel-based catalyst therefore makes it possible to desulfurize petrol without consumption of olefins. However with this catalyst it is difficult to achieve high hydrodesulfurization rates, except when working at temperatures significantly above 300 ° C, which results in more octane loss important and imposes constraints at the process level.

The results of analysis of the nature and of the concentration of the sulfur compounds obtained after hydrodesulfurization (HDS) are reported in Table 6. Sulfur compounds identified Charge concentration (ppm) Effluent concentration 45% HDS (ppm) Effluent concentration 75% HDS (ppm) Thiophene 235 132 147 Mercaptans 0 30 3 Methylthiophenes 487 271 92 Thiacyclopentane 82 12 2 Methylthiacyclopentane 40 5 1 C2 Thiophenes 227 202 47 diethylsulfide 11 0 0 C3 Thiophenes 26 8 8 C2 Thiacyclopentanes 46 0 0 C3 Thiacyclopentanes 46 0 0

It can therefore be noted that on this type of catalyst, the saturated compounds of sulfur are converted significantly.

Example 3 (comparative): hydrodesulfurization with a cobalt-molybdenum catalyst and a recycle of hydrogen.

The gasoline whose characteristics are described in Table 1 is subject to a hydrodesulfurization on a conventional hydrotreatment catalyst in a reactor insulated tubular. 25 ml of HR306C® catalyst, sold by the company Procatalyse, are placed in the hydrodesulfurization reactor. The catalyst is everything first sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C, in contact with a load consisting of 2% by weight of sulfur in the form of dimethyldisulfide in n-heptane.

The operating conditions for hydrodesulfurization are as follows:
VVH = 4 h ^-1 , H ₂ / HC = 400 l / l, P = 2.7 MPa. The partial pressure of H ₂ S at the inlet of the reactor of 0.023 MPa in order to simulate the H ₂ S provided by the recycling of hydrogen at the level of the unit. The temperature was brought to 250 ° C. then 270 ° C. The characteristics of the effluents thus obtained are presented in Table 7. Characteristics of gasolines after hydrodesulfurization with the catalyst based on cobalt and molybdenum Charge Effluent obtained after HDS at 250 ° C Effluent obtained after HDS at 270 ° C S total (ppm) 1200 1100 953 Olefins (% vol.) 32 19 12 MY 78 76 75 RON 90 84 81 (RON + MON) / 2 84 80 78 Octane loss 4 6 % of HDS 8 21 % of HO 41 63

These results show that in the presence of H ₂ S, it is difficult to obtain a high HDS level with conventional sulfide catalysts with a limited loss of olefins. This type of catalyst therefore requires the use of hydrogen free of H2S to lead to good performance, which can in some cases increase the cost of the process.

Table 8 presents the results of analysis of the nature and of the concentration of the sulfur-containing compounds obtained after hydrodesulfurization. Sulfur compounds identified Charge concentration (ppm) Effluent concentration 8% HDS (ppm) Effluent concentration 20% HDS (ppm) Thiophene 235 10 0 Mercaptans 0 699 631 Methylthiophenes 487 5 0 Thiacyclopentane 82 150 173 Methylthiacyclopentane 40 85 60 C2 Thiophenes 227 18 0 diethylsulfide 11 0 0 C3 Thiophenes 26 0 0 C2 Thiacyclopentanes 46 98 53 C3 Thiacyclopentanes 46 35 36

Example 4 (according to the invention): Hydrodesulfurization with a chain of catalysts for hydrogenation of unsaturated compounds and then for decomposition of saturated sulfur compounds, and with hydrogen recycling.

The gasoline whose characteristics are described in Table 1 is subject to a hydrodesulfurization on a chain of catalysts in an insulated tubular reactor. 25 ml of HR306C® catalyst, sold by the company Procatalyse, and 50 ml of catalyst obtained according to the same protocol as that described in Example 2 are placed in the hydrodesulfurization reactor. The catalysts are 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 = 1.33 h ^-1 relative to the entire catalytic bed H ₂ / HC = 400 l / l, P = 2.7 MPa. The temperature of the catalytic zone comprising the HR306C® catalyst is 250 ° C., the temperature of the catalytic zone containing the catalyst of Example 2 is 290 ° C. In order to simulate the H ₂ S provided by the recycling of hydrogen, an amount of H ₂ S corresponding to a partial pressure of 0.023 MPa is injected at the inlet of the reactor.

The characteristics of the effluent thus obtained are presented in Table 9. Characteristics of gasolines after hydrodesulfurization with the sequence of catalysts Charge Effluent S total (ppm) 1200 96 Olefins (% vol.) 32 23 MY 78 77 RON 90 87 (RON + MON) / 2 84 82 Octane loss 2.0 % of HDS 92 % of HO 28

Thus with the chain of catalysts, it is possible to reach rates high hydrodesulfurization, with a limited consumption of olefins and a operating temperature of the catalyst for converting the compounds saturated with sulfur lower than in the case where it is used alone to treat gasoline of departure.

Example 5 (according to the invention): hydrodesulfurization with a chain of catalysts for hydrogenation of unsaturated compounds and decomposition of saturated sulfur compounds, with recycle of hydrogen.

The gasoline whose characteristics are described in Table 1 is subject to a hydrodesulfurization on a chain of catalysts in an insulated tubular reactor. 25 ml of HR306C® catalyst, sold by the company Procatalyse, and 50 ml of catalyst obtained according to the same protocol as that described in Example 2 are placed in the hydrodesulfurization reactor. The catalysts are 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 = 1.33 h ^-1 relative to the entire catalytic bed H ₂ / HC = 400 l / l, P = 2.7 MPa. The temperature of the catalytic zone comprising the HR306C® catalyst is 230 ° C., the temperature of the catalytic zone containing the catalyst of Example 2 is 270 ° C. In order to simulate the H ₂ S provided by the recycling of hydrogen, an amount of H ₂ S corresponding to a partial pressure of 0.023 MPa is injected at the inlet of the reactor.

The characteristics of the effluent thus obtained are presented in Table 10. Characteristics of gasolines after hydrodesulfurization with the sequence of catalysts Charge Effluent S total (ppm) 1200 240 Olefins (% vol.) 32 26 MY 78 77.8 RON 90 88.6 (RON + MON) / 2 84 83.2 Octane loss 0.8 % of HDS 80 % of HO 19

Thus with the chain of catalysts, it is possible to reach rates high hydrodesulfurization, with a limited consumption of olefins and a operating temperature of the catalyst for converting the compounds saturated with sulfur lower than in the case where it is used alone.

Example 6 (comparative): hydrodesulfurization with a chain of catalysts for hydrogenation of unsaturated compounds and decomposition of saturated sulfur compounds operating at low temperature, with recycle of hydrogen.

The gasoline whose characteristics are described in Table 1 is subject to a hydrodesulfurization on a chain of catalysts in an insulated tubular reactor. 25 ml of HR306C® catalyst, sold by the company Procatalyse, and 50 ml of catalyst obtained according to the same protocol as that described in Example 2 are placed in the hydrodesulfurization reactor. The catalysts are 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 = 1.33 h ^-1 relative to the entire catalytic bed H ₂ / HC = 400 l / l, P = 2.7 MPa. The temperature of the catalytic zone comprising the HR306C® catalyst is 230 ° C., the temperature of the catalytic zone containing the catalyst of Example 2 is 200 ° C. In order to simulate the H ₂ S provided by the recycling of hydrogen, an amount of H ₂ S corresponding to a partial pressure of 0.023 MPa is injected at the inlet of the reactor.

The characteristics of the effluent thus obtained are presented in Table 11. Characteristics of gasolines after hydrodesulfurization with the sequence of catalysts, the catalyst used to decompose the saturated sulfur compounds operating at low temperature Charge Effluent S total (ppm) 1200 900 Olefins (% vol.) 32 25 MY 78 77.5 RON 90 88 (RON + MON) / 2 84 82.8 Octane loss 1.2 % of HDS 25 % of HO 22

So with the sequence of catalysts, but with an operating temperature of catalyst decomposing the saturated sulfur compounds of 200 ° C, it is not possible to achieve high hydrodesulfurization rates.

Claims (12)

Process for producing gasoline with a low sulfur content, characterized in that it comprises at least two stages: a) a step of hydrogenation of the unsaturated sulfur compounds, b) a step of decomposing saturated sulfur compounds. The method of claim 1, wherein a preprocessing step to hydrogenating the feed diolefins is carried out before step a. Method according to one of claims 1 or 2 in which the load is constituted by the whole petrol cut. Method according to any one of Claims 1 to 3, in which the charge is a catalytic cracking gasoline. Method according to any one of Claims 1 to 4, 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 VIb, at least partly in sulphide form. The method of claim 5 wherein the element of group VIII, 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 320 ° C, under a pressure generally between about 1 and about 4 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 7 wherein step b 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 8 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 10 wherein step b is carried out at a temperature between about 250 ° 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 11 implemented in means of a single reactor containing the catalysts necessary for steps a and b, charge pretreatment reactor not included. Method according to any one of claims 1 to 11 implemented in using at least two separate reactors, charge pretreatment reactor not included, the first reactor containing the catalyst required in step a and the second at least that required in step b.