FR2821850A1 - PROCESS FOR PRODUCTION OF LOW SULFUR CONTENT COMPRISING HYDROGENATION, FRACTIONATION, STAGE OF PROCESSING OF SULFUR COMPOUNDS AND DESULFURATION - Google Patents

Abstract

The invention relates to a method for producing petrol having a low sulphur content comprising at least one selective hydrogenation of diolefins, optionally at least one transformation stage, preferably an increase stage, of light sulphur compounds present in petrol, at least one fractioning of the petrol obtained into at least two fractions, light petrol and heavy petrol, then an optional transformation stage, preferably alkylation or adsorption of sulphur compounds and a one-stage desulphurization treatment of at least one part of the heavy fraction.

Description

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The invention relates to a method for producing low sulfur gasoline comprising hydrogenation, fractionation, a step of converting sulfur compounds and desulfurization. This method makes it possible to upgrade a gasoline cutoff optionally further comprising hydrocarbons having two three or four carbon atoms, reducing the total sulfur content of said cut to very low levels compatible with current or future specifications. This desulphurization is also carried out without a substantial reduction in fuel efficiency and minimizing the reduction of the octane number.

PRIOR ART: The production of reformulated species meeting the new environmental standards requires, in particular, that their concentration in olefins be reduced slightly but their concentration of aromatics (especially benzene) and sulfur be significantly increased. Catalytic cracking gasolines, which can represent 30 to 50% of the gasoline pool, have high olefin and sulfur contents. The sulfur present in the reformulated gasolines is attributable, to nearly 90%, to the catalytic cracking gasoline (FCC, Fluid Catalytic Cracking or catalytic cracking in fluidized bed). The desulphurisation (hydrodesulphurization) of gasolines and mainly FCC species is therefore of obvious importance for the achievement of specifications.

Hydrotreating (hydrodesulphurisation) of the feedstock sent to catalytic cracking leads to gasolines typically containing 100 ppm of sulfur. The catalytic cracking feed hydrotreating units, however, operate under severe temperature and pressure conditions, which implies a high hydrogen consumption and a high investment. In addition, the entire charge must be desulfurized, resulting in the processing of very large load volumes.

The hydrotreating (or hydrodesulphurization) of catalytic cracking gasolines, when carried out under standard conditions known to those skilled in the art, makes it possible to reduce the sulfur content of the cut. However, this process has the major drawback of causing a very significant drop in the octane number of the

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 cut, due to the saturation of all olefins during the hydrotreatment.

catalyseur comprenant au moins un métal du groupe VIB et/ou du groupe VIII. Il est indiqué dans ce brevet que le plus grand bénéfice est obtenu lorsqu'on fractionne l'essence en trois coupes, et lorsque la coupe présentant des points d'ébullition intermédiaires est traitée dans des conditions douces. On the other hand, US Pat. No. 4,131,537 teaches the advantage of splitting the gasoline into several cuts, preferably three, depending on their boiling point, and of desulfurizing them under conditions which can be different and in the presence of a

catalyst comprising at least one Group VIB and / or Group VIII metal. It is stated in this patent that the greatest benefit is obtained when the gasoline is split into three cuts, and when the cut having intermediate boiling points is treated under mild conditions.

The patent application EP-A-0 755 995 describes a process for desulphurizing FCC species comprising at least two stages. The first is a catalytic hydrodesulfurization at a temperature between 200 and 350 C, with a desulfurization rate of between 60 and 90% and is carried out in the presence of a filler containing less than 0.1% by volume of hydrogen sulfide (H2S). The second, and optionally the following, are also catalytic hydrodesulfurization steps operated between 200 and 300 C and in the presence of a feed comprising less than 0.05% by volume of H2S. The desulfurization rate is between 60 and 90% in this step. In this process, the concentration of H 2 S must be kept at a very low level. In the case of recycling the excess hydrogen, it is therefore generally necessary to remove the H2S, for example by means of an amine absorption step, after the second step and the following, so that the recycle gas contains less than 0.1% H2S volume. It is also preferred to remove the H2S between the first and second stages in order to respect the maximum content of H2S entering the second stage (0.05% volume). For sulfur-laden gasolines, such an elimination is therefore necessary taking into account the desulphurization rate greater than 60% in the first stage. The patent application EP-A-0 725 126 describes a process for the hydrodesulfurization of a cracking gasoline in wherein the essence is separated into a plurality of fractions comprising at least a first fraction rich in easily de-friable compounds and a second fraction rich in difficult to desulphurize compounds. Before carrying out this separation, the distribution of the sulfur-containing compounds must be determined beforehand.

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 means of analysis. These analyzes are necessary to select the equipment and the separation conditions.

In this application it is thus indicated that a light fraction of cracking gasoline sees its olefin content and octane drop significantly when it is desulfurized without being fractionated. On the other hand, the fractionation of said light fraction into 7 to 20 fractions, followed by analyzes of the sulfur and olefin contents of these fractions, makes it possible to determine the fraction or fractions richest in sulfur compounds which are then desulphurized simultaneously 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 gasoline to be treated.

In French Patent 2,785,908, it is taught the interest of splitting gasoline into a light fraction and a heavy fraction and then to perform a specific hydrotreatment of light gasoline on a nickel-based catalyst, and a hydrotreatment heavy gasoline on a catalyst comprising at least one Group VIII metal and / or at least one Group VIb metal.

It has also been proposed, for example in US Pat. No. 5,290,427, methods for hydrotreating gasolines consisting of splitting gasoline and then introducing the fractions at different levels of a hydrodesulfurization reactor and converting the desulfurized fractions to a ZSM-5 zeolite to compensate for the recorded octane loss by means of isomerization. This isomerization is accompanied by a cracking of gasoline towards lighter compounds.

In these processes, the gasolines to be treated generally have an initial point greater than 70 ° C., and again it is necessary to treat the light gasoline separately (fraction corresponding to compounds with a boiling point of between C5 hydrocarbons having 5 atoms. of carbon and 70 C) for example by means of a softening.

US-A-5,318,690 proposes a process comprising fractionation of gasoline and softening of light gasoline, while heavy gasoline is desulphurized, then converted to zeolite ZSM-5 and desulphurized again in of the

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 mild conditions. This technique is based on a separation of the crude gasoline so as to obtain a light cut, preferably substantially free of sulfur compounds other than mercaptans. This makes it possible to treat said cut only by means of a softening which removes the mercaptans.

As a result, the olefins present in a relatively large amount in the heavy fraction are partly saturated during the hydrotreatment. To compensate for the drop in the octane number related to the hydrogenation of olefins, the patent advocates cracking zeolite ZSM-5 which produces olefins, but at the expense of yield. In addition, these olefins can recombine with the H2S present in the medium to reform mercaptans. It is then necessary to perform additional softening or hydrodesulfurization.

Patent application WO 00/15319 describes a process for simultaneously fractionating and treating a light naphtha. In this process, the light cut contains mercaptans generally ranging from methyl mercaptan to hexyl mercaptan. These sulfur compounds are removed from the light fraction only in the case where the fractionation column contains a hydrodesulfurization section at the top of the column. In the absence of this section, it is therefore not possible to eliminate the mercaptans which either end up in the desulfurized gasoline when the light fraction is recombined with the heavy desulphurized fraction, or can be eliminated with the whole of the light fraction, which causes a loss of the yield of gasoline after desulfurization.

US Pat. No. 6,083,379 describes a process for the desulfurization and improvement of the octane number of gasolines comprising a fractionation of gasoline into at least two sections, the treatment of the light fraction in the presence of a zeolite, fractionation of the light fraction thus treated, the mixture of the heavy fractions obtained during the two fractionation steps and the hydrodesulfurization of the mixture of these fractions.

The patent application WO 94/22980 describes a gasoline desulfurization process comprising a fractionation in two sections, the heavier section is desulfurized in a hydrodesulfurization reactor and then treated in the presence of an acid catalyst.

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 which makes it possible to compensate for the loss of octane. The lighter cut is also desulfurized by non-hydrogenating mercaptan extraction.

US Patent 5,968,346 discloses a method of hydroconversion of a hydrocarbon feedstock for removing impurities such as compounds comprising heteroatoms. This method comprises a first step of hydroconversion of the entire charge, followed by a separation of the liquid and the vapor present in the effluent of this first step and a contact of the gas with a liquid. The mixture of the two liquid fractions resulting from the contacting and the fractionation is then treated in a second hydroconversion stage in the presence of a catalyst.

SUMMARY OF THE INVENTION The present invention relates to a process for the production of gasolines with a low sulfur content, which makes it possible to recover the whole of a sulfur-containing gasoline fraction, preferably a catalytic cracking or coking gasoline fraction ( coking according to the English terminology), or pyrolysis, or visbreaking (visbreaking according to English terminology), and reduce sulfur levels in said gasoline cut at very low levels, without substantially reducing the gasoline yield while minimizing the reduction of the octane number due to the hydrogenation of the olefins. The feedstock of the process according to the invention may also optionally comprise, in addition to a gasoline cut, a C4-cut comprising hydrocarbons containing two, three or four carbon atoms.

The process according to the invention is a process for producing gasoline with a low sulfur content, from a gasoline cut containing sulfur (initial gasoline). It comprises at least the following steps: a) at least one selective hydrogenation of the diolefins present in the initial gasoline. b) optionally at least one step of chemical transformation of the light sulfur compounds present in the gasoline, preferably this chemical conversion aims to increase, that is to say to increase the molecular weight of sulfur compounds, preferably substantially compounds sulfur

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 having a boiling point lower than that of thiophene. This step may optionally be carried out simultaneously in step a on all or part of the initial gasoline, in the same reactor or a different reactor. It can also be carried out separately on all or part of the hydrogenated gasoline in step a. Finally, it can be carried out simultaneously with the fractionation step c described below. In this step, thiophene and thiophene compounds are poorly processed. c) at least one fractionation of the gasoline obtained in step a or b in at least two fractions (or cuts), a light fraction preferably substantially free of sulfur and containing the lighter olefins of the initial gasoline ( light gasoline or light fraction), and a heavy fraction in which most of the sulfur compounds initially present in the initial gasoline are concentrated (gasoline or heavy fraction). It is also possible to separate the gasoline obtained in step a or b in addition to two fractions, that is to say for example a light fraction, at least an intermediate fraction and a heavy fraction. d) optionally a step of transforming the sulfur compounds different from step b. It is preferably a step of alkylation or adsorption of sulfur compounds selected from the group consisting of thiophene, thiophene compounds and mercaptans, preferably mercaptans having 1 to 6 carbon atoms present in at least one cut obtained in step c, preferably in the light cut and / or in at least one intermediate cut. The mercaptans possibly present are either formed in step a and / or b, or present in the initial gasoline and not converted to step a and / or b. e) optionally at least one step comprising a desulphurization treatment of at least a portion of at least one intermediate fraction resulting from fractionation in step c or step d of transformation of sulfur compounds, in the presence of at least one minus a hydrodesulfurization catalyst or an absorbent. f) a desulfurization treatment in one step of at least a portion of the heavy fraction, resulting from fractionation in step c or step d of transformation of the thiophene compounds and optionally

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mercaptans, en présence d'au moins un catalyseur d'hydrodésu ! furation ou d'un absorbant. g) éventuellement une étape de mélange de la fraction légère issue de l'étape c ou d, et éventuellement d'au moins une fraction intermédiaire, issue de l'étape c ou d ou e, avec la fraction lourde désulfurée issue de l'étape f.

mercaptans, in the presence of at least one hydrodesulfide catalyst! furation or absorbent. g) optionally a step of mixing the light fraction resulting from step c or d, and possibly at least one intermediate fraction, resulting from step c or d or e, with the heavy fraction desulphurized resulting from step f.

Preferably, all of the heavy gasoline desulphurized from step f is mixed with the light gasoline from step c or d, without separation of the liquid and the gas contained in the heavy gasoline after desulphurization, optionally a simple stripping with an inert gas can be carried out to remove H2S from the totally desulfurized heavy gasoline. In certain specific cases, the recovery of light gasoline, desulphurised heavy gasoline, and possibly at least one intermediate gasoline, is carried out separately. It is then unnecessary to perform step g.

The feedstock of the process according to the invention is a sulfur-containing gasoline cutter, preferably a gasoline cutter from a catalytic cracking unit, whose boiling point range typically extends from about the boiling points of hydrocarbons with 2 or 3 carbon atoms (C 2 or C 3) up to about 250 ° C., preferably from about the boiling points of hydrocarbons with 2 or 3 carbon atoms (C 2 or C 3) up to about 220 ° C, more preferably since about the boiling point of hydrocarbons with 5 carbon atoms up to about 220 C. The end point of the gasoline cut depends on the refinery from which it is derived and the constraints of the market, but generally remains in the limits indicated above.

The invention is described in the present invention a process for obtaining a gasoline preferably from a catalytic cracking, coking or visbreaking unit and having a limited sulfur content in which the gasoline first undergoes a selective hydrogenation treatment of diolefins, then possibly a stage of transformation of the lighter sulfur compounds of the gasoline which should after fractionation be in the light gasoline so that it is found essentially in the heavy fraction after the fractionation step of

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 process according to the invention. The thus treated gasoline then undergoes a fractionation in at least two cuts. Optionally, at least one fraction resulting from the fractionation step, preferably the light fraction or an intermediate fraction, may be treated in a step of conversion of the sulfur compounds chosen from the group consisting of thiophene, thiophene compounds and mercaptans. . Said step is preferably an alkylation or adsorption step.

The heavy gasoline is treated in a desulfurization section, preferably in the presence of a hydrodesulfurization catalyst or an absorbent. No desulfurization of the light fraction is necessary in the process according to the invention, since most of the sulfur compounds initially present in the gasoline are found in the heavy fraction and optionally in the intermediate fraction or fractions after the steps of hydrogenation, transformation of light sulfur compounds (step b), fractionation (step c), and optionally transformation of sulfur compounds, especially thiophene compounds and optionally mercaptans, in particular residual mercaptans that are not converted and / or formed in steps a and b ( step d).

This sequence makes it possible ultimately to obtain a desulfurized gasoline without significant reduction in the olefin content or the octane number, even for high desulfurization rates, and this without it being necessary to treat the light gasoline by means of a hydrodesulphurization or softening section, or by using methods to restore the octane number of gasoline. Thanks to this process, high desulphurization rates are achieved under reasonable operating conditions specified below.

The fractionation point of the gasoline is preferably limited in order to avoid the presence of thiophene in light gasoline. Since the latter forms azeotropes with a certain number of hydrocarbons, only C5 olefins and a small part of the C6 olefins can be separated into the light gasoline, as this would cause a too large fraction of thiophene in this section. In this case, it is advantageous to add to the process according to the invention a step d of transformation of thiophene and more generally of thiophene compounds, for example by means of an adsorption section or an alkylation reactor coupled to the fractionation section or integrated in said section according to a detailed mode in the following description.

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In order to make it possible to recover a larger fraction of the olefins present in the light gasoline while limiting the sulfur content of this fraction without additional treatment, it is preferably proposed to treat the feed in step b and / or d in conditions and on catalysts which make it possible to convert the sulfur-containing compounds, preferably the light sulfur-containing compounds, into higher-boiling sulfur-containing compounds found after separation, optionally in at least an intermediate fraction or in heavy gasoline . These intermediate and / or heavy cuts can then be desulfurized.

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

The method according to the invention is particularly applicable when high desulphurization rates of gasoline are required, ie when the desulphurized gas must contain at most 10% of the sulfur of the initial gasoline and possibly at most 5% or even more than 2% of the sulfur of the initial gasoline which corresponds to desulfurization rates greater than 90% or even greater than 95 or 98%.

a) au moins une étape effectuée par passage de la charge, constituée de préférence par l'ensemble de la coupe essence, sur un catalyseur permettant d'hydrogéner sélectivement les dioléfines de l'essence sans hydrogéner les oléfines. b) éventuellement au moins une étape optionnelle consistant à passer tout ou partie de l'essence initiale ou de l'essence hydrogénée à l'étape a, de préférence l'ensemble de l'essence initiale ou hydrogénée à l'étape a, sur un catalyseur permettant de transformer au moins en partie les composés soufrés légers (par exemple : ethylmercaptan, propyl mercaptan), par réaction avec tout ou partie des oléfines, en composés soufrés plus lourds. The method according to the invention comprises at least the following steps:

a) at least one step carried out by passing the feed, preferably consisting of the entire gasoline cut, on a catalyst for selectively hydrogenating the diolefins of the gasoline without hydrogenating the olefins. b) optionally at least one optional step consisting in passing all or part of the initial gasoline or hydrogenated gasoline in step a, preferably all of the initial gasoline or hydrogenated gasoline in step a, on a catalyst for converting at least partially light sulfur compounds (eg ethyl mercaptan, propyl mercaptan), by reaction with all or part of the olefins, into heavier sulfur compounds.

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 This step is preferably carried out simultaneously in step a, for example by passing the initial gasoline over a catalyst capable of both hydrogenating the diolefins and converting the light sulfur compounds, preferably with the olefins, into sulfur compounds more heavy, or on a separate catalyst but to achieve this transformation in the same reactor as step a. It is possible to observe on certain types of fillers the formation of certain mercaptans at the end of step a or b, this formation is probably due to a hydrogenolysis of disulphides of high molecular weight. (c) at least one step to separate the original gasoline into a light gasoline and a heavy gasoline. The cutting point of light gasoline and heavy gasoline is determined in order to limit the sulfur content of light gasoline and to allow its use in the gasoline pool preferably without additional post treatment. It is also possible to separate the gasoline obtained in step a or b in addition to two fractions, that is to say for example a light fraction, at least one or more intermediate fractions and a heavy fraction. d) optionally a step of transforming the sulfur compounds, preferably alkylation or adsorption of the compounds selected from the group consisting of thiophene, the thiophene compounds and optionally the mercaptans present in at least one cut obtained in step c preferably in the light cut and / or in at least one intermediate cut. e) optionally at least one step comprising a desulfurization treatment of at least a portion of at least one intermediate fraction resulting from fractionation in step c or step d of transformation of sulfur compounds, in particular thiophene, compounds thiophenics and optionally mercaptans, in the presence of at least one hydrodesulfurization catalyst or an absorbent. Optionally stripping may also be carried out between two zones or hydrodesulfurization reactors, optionally used to desulphurize said intermediate fraction. f) a desulfurization treatment in one step of at least a portion of the heavy fraction resulting from fractionation in step c or step d of transformation of sulfur compounds, especially thiophenic compounds, in the presence of at least one catalyst; hydrodesulfurization or absorbent. Gasoline

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g) éventuellement une étape de mélange de la fraction légère issue de l'étape c ou d avec éventuellement au moins une fraction intermédiaire issue de l'étape c, d ou e et avec la fraction lourde désulfurée issue de l'étape f. Ces fractions peuvent également être valorisées séparément sans être mélangées. heavy and / or at least one intermediate gas thus desulfurized may then optionally be stripped (that is to say that a gaseous stream, preferably containing one or more inert gases passed through this gasoline), in order to remove the H2S possibly produced during the desulfurization.

g) optionally a step of mixing the light fraction resulting from step c or d with possibly at least one intermediate fraction resulting from step c, d or e and with the heavy desulphurized fraction resulting from step f. These fractions can also be valued separately without being mixed.

According to a variant of the process according to the invention, it is possible to associate at least one reaction section with the fractionation column. Said said reaction section or sections then operate on at least one fraction taken from the inside of the fractionation column and the effluent from the reaction section is returned to the fractionation column. The reaction section or sections thus coupled to the fractionation column of step c may be chosen from the group consisting of the reaction sections of the following stages: hydrogenation of the diolefins (step a): when step b is absent, or when stage a is carried out simultaneously with stage b of transformation of the light sulfur compounds.

 - optionally transformation of light sulfur compounds (optional step b).

 transformation of sulfur compounds such as thiophene, thiophenic compounds and optionally mercaptans (optional step d).

 - optionally desulfurization of the intermediate fractions (optional step e).

 - Desuturation of the heavy fraction (step f).

Such devices comprising a fractionation column associated with an external reactor and that can be used in the process according to the invention have for example been described for applications in the field of refining and petrochemistry in US Patents 5,1777, 283, US 5,817, 227 and US 5,888, 355

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désulfuration, lorsqu'une section de désulfuration est interne à la colonne de fractionnement, ladite section réactionnelle ne sera généralement pas placée en tête de colonne. According to other variants of the process according to the invention, it is also possible to use a reactive column instead of the fractionation column, that is to say to place at least one of said reaction sections in the column of fractionation (internal column reaction section), preferably in a zone where the reagent concentration is maximum. For example, in the case of step d of transformation of the thiophene compounds, the reaction section will preferably be placed in a zone having the maximum concentration of these compounds. The light fraction of gasoline that does not require

desulfurization, when a desulfurization section is internal to the fractionation column, said reaction section will generally not be placed at the top of the column.

According to a preferred variant of the process according to the invention, the reaction section internal to the column is chosen from the group consisting of the following reaction sections: hydrogenation (step a), transformation of light sulfur compounds (optional step b), transformation of the compounds sulfur compounds such as thiophene, thiophene compounds and optionally mercaptans (optional step d), desulfurization of the intermediate fractions (optional step e), desulfurization of the heavy fraction (step f).

In a very preferred embodiment of the process according to the invention, the reaction section is placed in the middle of a fractionation column, so as to treat the compounds having intermediate boiling points, that is to say the compounds which can constitute a intermediate cut and which are recovered alone or with the heavy fraction at the bottom of the column, at the end of the fractionation step. The heavy fraction is then treated in an external reactor that may or may not be associated with the fractionation column.

Such reactive columns are known to those skilled in the art and have been described, for example, in patents or patent applications US Pat. Nos. 5,368,691, 5,523,062, 2,737,131, 2,737,132 and EP-A-0461,855. .

Another variant of the process according to the invention consists both in using a reactive column comprising at least one reaction section and an external reactor coupled or not to said column. Such variants are for example described in the patent application WO00 / 15319.

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 The variants described above are only an illustration of the possible variants of the process according to the invention. The method according to the invention can indeed be implemented by combining reaction sections (steps a, b, d, e or f) or associated with the fractionation column of step c, or internal (s). ) to said column, either external (s) and uncoupled (s) to said column in that the effluent of said reaction section (s) (s) is not recycled to the fractionation column.

l'essentiel de ces composés dans la fraction lourde, et éventuellement dans la ou les fractions intermédiaires. One of the advantages of the process according to the invention lies in the fact that it is not necessary to desulphurize the light fraction of the gasoline resulting from the fractionation. The transformation of the sulfur and / or thiophene compounds (steps b and / or d) makes it possible to considerably reduce the content of sulfur compounds in the light cut and optionally at least one intermediate cut, and generally to recover

most of these compounds in the heavy fraction, and possibly in the intermediate fraction or fractions.

Steps b and d are distinguished inter alia by the fact that the conversion of the thiophene compounds is generally less than 60% by weight, or even less than 40% by weight in step b, whereas the conversion or adsorption of said compounds is more often greater than 80% by weight, preferably greater than 90% by weight, very preferably greater than 95% by weight in step d. In fact, step b essentially increases the weight of light mercaptans.

This operation is carried out while maintaining most of the olefins in the light fraction, possibly in at least one intermediate fraction that does not require extensive desulfurization. The content of sulfur compounds of the light fraction thus obtained is generally less than 50 ppm, preferably less than 20 ppm, more preferably less than 10 ppm and very preferably less than 5 ppm.

Another advantage lies in the fact that the residual content of sulfur compounds of the desulfurized gasoline by means of the process according to the invention is particularly low, and that the octane number of the gasoline is maintained at a high level.

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

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- Hydrogenation of diolefins (step a): The hydrogenation of dienes is a step which eliminates, before hydrodesulfurization, almost all the dienes present in the petrol fraction containing sulfur to be treated. It preferably takes place in the first step (step a) of the process according to the invention, generally in the presence of a catalyst comprising at least one metal of group VIII, preferably chosen from the group consisting of platinum, palladium and nickel , and a support. For example, a catalyst based on nickel or palladium deposited on an inert support, such as, for example, alumina, silica or a support containing at least 50% alumina, will be used.

The pressure employed is sufficient to maintain more than 60%, preferably 80%, and more preferably 95% by weight of the gasoline to be treated in the liquid phase in the reactor; it is most generally between about 0.4 and about 5 MPa and preferably greater than 1 MPa, more preferably between 1 and 4 MPa. The hourly space velocity of the liquid to be treated is between about 1 and about 20 hl (volume of filler per volume of catalyst per hour), preferably between 2 and 10 h -1, very preferably between 3 and 8 h -1. 1. The temperature is most generally between about 50 and about 250 C, and preferably between 80 and 220 C, and more preferably between 100 and 200 C, to ensure a sufficient conversion of diolefins. Very preferably, it is limited to 180 ° C. The charge-based hydrogen ratio expressed in liters is generally between 1 and 50 liters per liter, preferably between 3 and 30 liters per liter, more preferably between 8 and 25 liters per liter. liter.

The choice of operating conditions is particularly important. It will operate most generally under pressure and in the presence of a quantity of hydrogen in small excess relative to the stoichiometric value necessary to hydrogenate the diolefins. The hydrogen and the feedstock to be treated are injected in ascending or descending streams into a reactor preferably comprising a fixed bed of catalyst.

Another metal may be associated with the main metal to form a bimetallic catalyst, such as, for example, molybdenum or tungsten. The use of such catalytic formulas has for example been claimed in patent FR 2 764 299.

The catalytic cracked gasoline may contain up to a few weight percent of diolefins. After hydrogenation, the diolefin content is generally reduced to

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 less than 3000 ppm, or even less than 2500 ppm and more preferably less than 1500 ppm. In some cases, it can be obtained less than 500 ppm. The diene content after selective hydrogenation can even if necessary be reduced to less than 250 ppm.

According to a particular embodiment of the process according to the invention, the hydrogenation stage of the dienes takes place in a catalytic hydrogenation reactor which comprises a catalytic reaction zone traversed by the entire charge and the quantity of hydrogen necessary to effect the desired reactions.

transformation of light sulfur compounds (step b): This optional step consists in transforming the light sulfur compounds. That is, the compounds that at the end of the separation step b would be found in the light gasoline, in heavier sulfur compounds entrained in the heavy gasoline. Preferably, the light compounds transformed have a boiling point lower than that of thiophene. This transformation is preferably carried out on a catalyst comprising at least one element of group VIII (groups 8, 9 and 10 of the new periodic classification), or comprising a resin. The choice of catalyst is made in particular to promote the reaction between light mercaptans and olefins, which leads to heavier mercaptans.

de la teneur en mercaptans est obtenue. Pour ce faire, on peut utiliser la procédure d'hydrogénation des diènes décrite dans la demande de brevet EP-A-0 832 958, qui utilise avantageusement un catalyseur à base de palladium, ou celle décrite dans le brevet FR 2 720 754. This optional step may possibly be performed at the same time as step a. For example, it may be particularly advantageous to operate, during the hydrogenation of the diolefins, under conditions such that at least a portion of the compounds in the form of mercaptan are converted. So some reduction

the mercaptan content is obtained. For this purpose, it is possible to use the diene hydrogenation procedure described in patent application EP-A-0 832 958, which advantageously uses a catalyst based on palladium, or that described in patent FR 2 720 754.

du catalyseur de l'étape a, tel que par exemple le catalyseur préconisé dans le procédé du brevet US-A-3 691 066, qui permet de transformer les mercaptans (butylmercaptan) en composés soufrés plus lourds (sulfures). Another possibility is to use an identical or different nickel-based catalyst

the catalyst of step a, such as for example the catalyst recommended in the process of US-A-3,691,066, which makes it possible to convert mercaptans (butyl mercaptan) into heavier sulfur compounds (sulphides).

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Another possibility for carrying out this step consists in hydrogenating thiophene at least in part to thiophane whose boiling point is greater than that of thiophene (boiling point 121 ° C.). This step can be carried out on a catalyst based on nickel, platinum or palladium. In this case, the temperatures are generally between 100 and 300 ° C. and preferably between 150 and 250 ° C. The ratio H2 / charge is adjusted to between 1 and 20 liters per liter, preferably between 3 and 15 liters per liter, to favor if additionally possible hydrogenation of the thiophene compounds and minimize the hydrogenation of olefins present in the feed. The space velocity is generally between 1 and 10 h -1, preferably between 2 and 4 h -1 and the pressure between 0.5 and 5 MPa, preferably between 1 and 3 MPa.

separation of the essence into at least two fractions (step c) According to a first variant of the process according to the invention, the gasoline is split into two fractions: a light fraction containing a limited residual sulfur content, preferably less than about 200 ppm, more preferably less than
100 ppm, very preferably less than about 20 ppm, and allowing the use of this cup without performing other treatment aimed at reducing its sulfur content, except possibly step d of treatment of thiophene and / or thiophene compounds .

 a heavy fraction in which preferably most of the sulfur initially present in the feedstock is concentrated.

This separation is preferably carried out by means of a conventional distillation column also known as a splitter. This fractionation column must make it possible to separate a light fraction of the gasoline containing a small sulfur fraction and a heavy fraction preferably containing most of the sulfur initially present in the initial gasoline.

This column generally operates at a pressure of between 0.1 and 2 MPa and preferably between 0.2 and 1 MPa. The number of theoretical plates of this separation column is generally between 10 and 100 and preferably between 20 and 60.

The reflux ratio, expressed as the ratio of liquid flow in the column

<Desc / Clms Page number 17>

 divided by the distillate flow rate expressed in kg / h, is generally less than unity and preferably less than 0.8.

The light gasoline obtained after the separation generally contains at least all the C5 olefins, preferably the C5 compounds and at least 20% of the C6 olefins. Generally, this light fraction has a low sulfur content, ie it is not generally necessary to treat the light cut before using it as fuel.

According to a second variant of the process according to the invention, the gasoline is fractionated into at least 3 fractions: a light fraction, a heavy fraction and at least an intermediate fraction.

In the case where the step d of transformation of sulfur compounds, especially thiophene compounds is present in the process according to the invention, the gasoline is preferably fractionated into at least two sections having the following properties: a so-called light section (L-section) whose boiling points are preferably below about 60 C. This temperature is given as an indication, it is in fact the maximum temperature for which the thiophene content is less than 5 ppm, - at least one so-called heavy cup (section H1) whose boiling points are (for information only) greater than about 60 C.

The light cut L is preferably injected into a liquid gas separation tank in order to separate the unconsumed hydrogen and the H 2 S, formed during step a and / or b, from olefins generally having from 5 to 7 carbon atoms. carbon.

The so-called heavy cut H1, that is to say the cut whose temperatures are greater than approximately 60 ° C., is sent to a distillation column or any other separation process capable of separating this cut into at least two cuts:

<Desc / Clms Page number 18>

- une coupe intermédiaire 12 dont les points d'ébullition à titre d'exemple sont au minimum de 60 C et au maximum d'environ 120 C voire environ 160 C. Cette coupe peut être traitée à l'étape d du procédé selon l'invention.

an intermediate cut 12 whose exemplary boiling points are at least 60 ° C. and at most about 120 ° C. or even about 160 ° C. This cut can be treated in step d of the process according to invention.

 a heavier H2 cut, whose boiling points are generally greater than about 160 ° C. or about 120 ° C.

The heavy cut H2 whose boiling temperatures are generally greater than about 160 ° C. or about 120 ° C. is sent to the f) desulfurization step.

In another version of the process according to the invention, it is also possible to directly split the gasoline into at least three sections, a light section (L), at least one intermediate section (12) and at least one heavy section (H2). having the properties described above.

Intermediate section 12, whose boiling points are included as examples between about 60 ° C. and about 120 ° C. or about 160 ° C., can be sent to a sulfur compounds conversion unit according to step d.

After step d, the sections 12 may again be fractionated into an intermediate section 13 and a heavy section H 3, especially when stage d is an alkylation stage of the thiophenic compounds. The H3 cut thus obtained may optionally be mixed with the H2 cut, preferably before desulfurization.

présents dans la coupe légère et/ou dans au moins une fraction intermédiaire. - Transformation of sulfur compounds, especially thiophene compounds, preferably by alkylation or adsorption (step d): Step d is a step of transformation of sulfur compounds selected from the group consisting of thiophene, thiophene compounds and mercaptans

present in the light cut and / or in at least one intermediate fraction.

This step consists in passing preferably the light fraction and / or optionally at least one intermediate fraction resulting from the fractionation (step c) on an absorbent or on a catalyst having an acid function which makes it possible to carry out the addition of the sulfur compounds in the form of of mercaptans on olefins and the alkylation reaction of thiophene and thiophene derivatives by these same

<Desc / Clms Page number 19>

 olefins. The operating conditions are adjusted to achieve the desired conversion with conversion or adsorption rates of thiophene and / or thiophenics and / or light mercaptans, preferably mercaptans having 1 to 6 carbon atoms, greater than 80% by weight, preferably greater than 90% by weight, very preferably greater than 95% by weight. Other compounds such as COS or CS2 may optionally also be adsorbed or converted.

To minimize the oligomerizing activity of the acid catalyst optionally used, the gasoline may be additive of a compound known to inhibit the oligomerizing activity of acid catalysts such as alcohols, ethers or water.

This transformation can be carried out, for example, according to the procedures and using the diagrams described in French Patent Application No. 00/08113 and No. 00/10233 for steps a to d of the process according to the invention, or by combining the steps a to c of the process according to the invention and as described above with step d detailed as follows.

When this optional step is present in the process according to the invention, the light cut or the intermediate cut obtained in step c is treated in a section for transforming, preferably by alkylation or adsorption, the compounds selected from the group consisting of by thiophene, thiophene compounds and mercaptans. In the case of alkylation, the thiopheneic compounds contained in section 60 C-160 C will react with conversion rates of greater than 80% by weight, preferably greater than 90% by weight, with the olefins to form thiophene alkyls according to the following reaction for thiophene:

Une partie ou la totalité du benzène peut également être éliminée par alkylation avec les o ! éfines. Ces composés de poids moléculaires plus élevés sont surtout caractérisés

Some or all of the benzene can also be removed by alkylation with the o! -olefins. These compounds of higher molecular weight are especially characterized

<Desc / Clms Page number 20>

par des températures d'ébullition plus élevées que celles qu'ils avaient avant alkylation. Ainsi la température théorique d'ébullition qui est de 80 C se trouve déplacée vers 250 C pour les alkyls thiophènes et cette réaction conduit donc le plus souvent à un alourdissement de l'essence, notamment dans le cas où la fraction d'essence et/ou l'essence de départ sont légères.

by higher boiling temperatures than they had before alkylation. Thus, the theoretical boiling temperature of 80 ° C. is displaced towards 250 ° C. for thiophene alkyls, and this reaction therefore most often leads to a heavier gasoline, especially in the case where the gasoline fraction and / or or the starting gasoline are light.

aquosoluble (choisi dans le groupe constitué par les alkys. et/ou les alcoxy. métaux d'au moins un élément tels que titane, zirconium silicium, germanium, étain, tantale, niobium...) sur au moins un oxyde tel que l'alumine (formes gamma, delta, éta, seules ou en mélange) la silice, les silices alumines, les silices titane, les silices zircone ou tout autre solide présentant une acidité quelconque. Un mode particulier de l'invention peut consister à mettre en oeuvre un mélange physique d'au moins deux des catalyseurs ciavant dans des proportions variant de 95/5 à 5/95, préférentiellement de 85/15 à 15/85 et très préférentiellement de 70/30 à 30/70". This alkylation step is carried out in the presence of an acid catalyst. This catalyst may be indifferently a resin, a zeolite, a clay, any functionalized silica or any silico-aluminate having acidity, or any grafted support of acidic functional groups. The ratio of the charge volume injected onto the catalyst volume is between 0.1 and 10 liter / liter / hour and preferably between 0.5 and 4 liter / liter / hour. More precisely, this alkylation step is carried out in the presence of at least one acidic catalyst selected from the group consisting of silicoaluminates, titanosilicates, mixed titanium alumina, clays, resins, mixed oxides obtained by grafting with minus an organo-metallic organosoluble compound or

water-soluble (selected from the group consisting of alkys and / or alkoxy, metals of at least one element such as titanium, zirconium silicon, germanium, tin, tantalum, niobium ...) on at least one oxide such as alumina (gamma, delta, eta, alone or in mixture) silica, silica aluminas, titanium silicas, zirconia silicas or any other solid having any acidity. A particular embodiment of the invention may consist in using a physical mixture of at least two of the catalysts hereinabove in proportions ranging from 95/5 to 5/95, preferably from 85/15 to 15/85 and most preferably from 70/30 to 30/70 ".

The temperature for this step is generally between 10 and 350 C depending on the type of catalyst or the strength of the acidity. Thus, for an acidic resin of ion exchange type, the temperature is between 50 and 150 ° C., preferably between 50 and 120 ° C.

The molar ratio olefin on thiophene compounds is between 0.1 and 1000 mol / mol, preferably between 0.5 and 500 mol / mol.

<Desc / Clms Page number 21>

 The operating pressure of this step is generally between 0.1 and 3 MPa and preferably such that the charge is in liquid form under the conditions of temperature and pressure, ie at a pressure greater than 0.5 MPa.

The effluent from step d, of transformation of the sulfur compounds, preferably alkylation or adsorption may optionally be mixed at least in part with a heavy cut from the fractionation in step c.

The effluent from step d of transformation of the sulfur compounds can also optionally be sent to a new fractionation unit to be separated into two fractions, an untreated or optionally desulfurized intermediate fraction without being mixed, and a heavy fraction which is preferably mixed with the heavy fraction resulting from stage d before being desulphurized in stage f.

- une coupe dont les températures d'ébullition sont supérieures à 180 C ou 100 C (coupe D3). For example, the effluent D1 resulting from an alkylation can be separated into: a 60 C-180 C or 60 C-100 C section (D2 section) devoid of any thiophenic compound that is collected,

a section whose boiling temperatures are greater than 180 C or 100 C (section D3).

In the case of alkylation, step d may advantageously be carried out on the light fraction from step c. In fact, the alkylation of the light mercaptans present in this fraction then facilitates the desired removal of the sulfur compounds, but also makes it possible to reduce the vapor pressure (RVP or Reid Vapor Pressure index according to the Anglosaxon terminology) of the final desulfurized gasoline. .

All of the effluent D1 from said alkylation unit (step d) or the D3 cut resulting from the fractionation after alkylation may be preferably mixed at least in part with a heavy cut (for example the H2 cut) and sent to the desulfurization section of step f.

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 - Desulfurization of the heavy fraction (step f) and optionally at least one intermediate fraction (step e): This step may for example be a hydrodesulphurization step performed by passing the heavy or intermediate gasoline, in the presence of hydrogen, on a catalyst comprising at least one element of group Vt) and / or at least one element of group Vlb at least partly in sulfur form, at a temperature of between about 210 ° C. and about 350 ° C., preferably between 220 ° C. C and 320 C, at 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 about 1 and about 20 h -1 (expressed as volume of liquid per volume of catalyst per hour), preferably between 1 and 10 h -1, very preferably between 3 and 8 h -1. The H2 / HC ratio is between 100 to 600 liters per liter and preferably between 300 and 600 liters per liter.

The content of Group VIII metal expressed as oxide is generally between 0.5 and 15% by weight, preferably between 1 and 10% by weight. The metal content of the group VIb is generally between 1.5 and 60% by weight, preferably between 3 and 50% by weight.

The element of group VIII, when present, is preferably cobalt, and the element of group VIb, when present, is usually molybdenum or tungsten.

Combinations such as cobalt-molybdenum are preferred. The catalyst support is usually a porous solid, such as for example an alumina, a silica-alumina or other porous solids, such as, for example, magnesia, silica or titanium oxide, alone or in mixture with alumina or silicalumin. To minimize the hydrogenation of the olefins present in heavy gasoline, it is advantageous to preferentially use a catalyst in which the density of molybdenum, expressed in% by weight of MoO 3 per unit area, is greater than 0.07 and preferably greater than 0.07. at 0.10. The catalyst according to the invention preferably has a specific surface area of less than 190 m 2 / g, more preferably less than 180 m 2 / g, and very preferably less than 150 m 2 / g.

<Desc / Clms Page number 23>

 After introduction of the element or elements and possibly shaping of the catalyst (when this step is performed on a mixture already containing the base elements), the catalyst is in a first activated step. This activation can correspond to either an oxidation then a reduction, a direct reduction, or a calcination only. The calcination step is generally carried out at temperatures ranging from about 100 to about 600 ° C. and preferably between 200 ° C. and 450 ° C. under an air flow rate. The reduction step is performed under conditions to convert at least a portion of the oxidized forms of the base metal to metal. Generally, it consists in treating the catalyst under a flow of hydrogen at a temperature preferably of at least 300 CC. 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.

gazeuse ou liquide, par exemple de l'hydrogène contenant de l'H2S, ou un liquide contenant au moins un composé soufré. The introduction of sulfur may occur before or after any activation step, that is, calcination or reduction. Preferably, no catalyst oxidation step is performed when the sulfur or a sulfur compound has been introduced on the catalyst. The sulfur or a sulfur compound can be introduced ex situ, that is to say outside the reactor where the process according to the invention is carried out, or in situ, that is to say in the reactor used for process according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulfided by passing a feed containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge can be

gaseous or liquid, for example hydrogen containing H2S, or a liquid containing at least one sulfur compound.

l'invention. Dans ce réacteur, le catalyseur est alors traité sous hydrogène afin de transformer au moins une partie du métal principal en sulfur. Une procédure qui convient particulièrement à l'invention est celle décrite dans les brevets FR-B-2 708 596 et FR-B-2 708 597. In a preferred manner, the sulfur compound is added to the ex situ catalyst. For example, after the calcination step, a sulfur compound may be introduced onto the catalyst in the presence of possibly another compound. The catalyst is then dried and then transferred to the reactor for carrying out the process according to

the invention. In this reactor, the catalyst is then treated in hydrogen to convert at least a portion of the main metal into sulfur. 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.

<Desc / Clms Page number 24>

 The desulfurization of the heavy gasoline and / or at least one intermediate gasoline can also be carried out by means of an absorber comprising an absorbent mass, for example based on zinc oxide. Said desulfurization can also be carried out by means of a combination of a hydrodesulfurization section and an absorber, preferably located after the hydrodesulfurization section.

For heavy gasoline, the desulfurization section preferably comprises only one absorber and / or one reactor. Said reactor contains only one type (in terms of chemical formulation) of hydrodesulfurization catalyst, possibly arranged in several separate beds. Preferably said catalyst is cobalt-based, most preferably it is a catalyst comprising cobalt and molybdenum or tungsten. Preferably, the catalyst employed in this section is sulfided.

On the other hand, the optional treatment section of at least one intermediate section can comprise several reactors possibly associated with one or more absorbers. Said section may comprise two reactors in series, possibly with a separation of the gas containing H2S and the liquid between the two reactors. It is also possible to use two different catalysts arranged in at least two beds inside said reactors, optionally with an intermediate addition of hydrogen (also called quench according to English terminology). For example, it is possible to use a catalyst comprising cobalt and molybdenum or tungsten associated with a catalyst comprising nickel.

Preferably, said catalysts are sulphurized.

toutes ces variantes, la charge est admise par la conduite 1 et mélangée avec de l'hydrogène arrivant via la conduite 2. Le mélange 3 est introduit dans le réacteur 4 contenant un catalyseur d'hydrogénation sélective des dioléfines (étape a). L'effluent issu de ce réacteur est introduit dans un réacteur 7, éventuellement après addition d'hydrogène via la conduite 6. Le réacteur 7 contient un catalyseur qui permet d'alourdir les composés soufrés legers, tels que les mercaptans légers, par réaction avec les oléfines (étape b). L'effluent 8 issu du réacteur 7 est introduit dans une colonne de fractionnement (9) permettant de réaliser une séparation de l'essence en au moins 2 Figure 1 illustrates some preferred variants of the method according to the invention. In

all these variants, the feedstock is admitted via line 1 and mixed with hydrogen arriving via line 2. Mixture 3 is introduced into reactor 4 containing a catalyst for the selective hydrogenation of diolefins (step a). The effluent from this reactor is introduced into a reactor 7, optionally after the addition of hydrogen via line 6. The reactor 7 contains a catalyst which makes it possible to weigh up light sulfur compounds, such as light mercaptans, by reaction with olefins (step b). The effluent 8 from the reactor 7 is introduced into a fractionation column (9) making it possible to separate the gasoline in at least 2

<Desc / Clms Page number 25>

coupes : une coupe légère 10 qui n'est pas traitée, et une coupe lourde 13 qui est désulfurée dans un réacteur 20 contenant un catalyseur d'hydrodésulfuration, après mélange avec de l'hydrogène ammené par la conduite 19. La fraction lourde désulfurée 21 est mélangée à la fraction légère 10 pour conduire à l'essence désulfurée 22.

sections: a light cut which is untreated, and a heavy cut 13 which is desulfurized in a reactor 20 containing a hydrodesulphurization catalyst, after mixing with hydrogen taken up by line 19. The heavy desulfurized fraction 21 is mixed with the light fraction to yield the desulfurized gasoline 22.

According to another variant described in FIG. 1, the fractionation column 9 makes it possible to separate the effluent 8 from the reactor 7 in 4 sections: an untreated light section 10, a first intermediate section 11 introduced into a reactor 11 alkylation 14 which allows the alkylation of thiophene, thiophenic compounds and optionally mercaptans and whose effluent is returned to the fractionation column 9 via line 15, a second intermediate fraction 12 treated in the presence of hydrogen brought via line 16 in a reactor containing a hydrodesulphurization catalyst, and a heavy cut 13 which is also desulphurized in the presence of hydrogen taken via line 19 in a reactor 20 containing a hydrodesulfurization catalyst. The desulphurized heavy fraction 21, and the desulfurized intermediate fraction 18 are mixed with the light fraction to yield the desulfurized gasoline 22.

In summary, according to one variant, the process according to the invention is a process for producing gasoline with a low sulfur content, comprising at least the following steps: at least one selective hydrogenation of the diolefins present in the initial gasoline (step a) at least one step of transforming the light sulfur compounds present in the gasoline (step b), at least one fractionation (step c) of the gasoline obtained in step a or b into at least two fractions a light fraction and a heavy fraction, a desulfurization treatment in one step (step f) of at least a portion of the heavy fraction resulting from the fractionation in step c.

moins deux fractions une fraction lègère et une fraction lourde, une étape (étape d) de transformation des composés soufrés choisis dans le groupe constitué par le According to another variant, the process according to the invention is a process for producing gasoline with a low sulfur content, comprising at least the following stages: at least one selective hydrogenation of the diolefins present in the initial gasoline (step a), less a fractionation (step c) of the gasoline obtained in step a in

at least two fractions a light fraction and a heavy fraction, a step (step d) of transformation of the sulfur compounds chosen from the group consisting of

<Desc / Clms Page number 26>

 thiophene, the thiophene compounds and the mercaptans present in at least one cut obtained in step c, a desulphurization treatment in one step (step f) of at least a portion of the heavy fraction resulting from the fractionation in step c . In this case, it may also further comprise at least one step of transforming the light sulfur compounds present in the gasoline (step b).

According to a preferred variant of the process according to the invention, steps a and b are carried out simultaneously in the same reactor.

Preferably, steps b and / or d make it possible to increase the molecular weight of the sulfur compounds, in order to separate them mainly in the heavy fraction of step c.

The gasoline from steps a or b can also alternatively be fractionated into a light fraction, at least an intermediate fraction and a heavy fraction. In this case, the process according to the invention may also comprise at least one step d of transformation of the sulfur compounds chosen from the group consisting of thiophene, the thiophenic compounds and the mercaptans present in the light cut and / or in at least one an intermediate fraction.

Preferably, step d of transformation of the sulfur compounds is an alkylation or an adsorption.

The process according to the invention may also further comprise a step e of desulphurizing at least a portion of at least one intermediate fraction resulting from fractionation in step c or step d of transformation of sulfur compounds.

Preferably, the heavy gasoline is desulfurized in step f in the presence of a hydrodesulphurization catalyst or an absorbent, and more preferably the heavy gasoline desulfurized in step f is stripped by means of an inert gas.

The process according to the invention may also comprise a step g of mixing the light fraction resulting from step c or d and optionally at least one fraction

<Desc / Clms Page number 27>

 intermediate from step c or d or e with the heavy fraction desulphurized from step f. According to a preferred variant, the process according to the invention comprises at least one reaction section internal to the column and selected from the group consisting of the following reaction sections: hydrogenation (step a), transformation of light sulfur compounds (optional step b), transformation of the sulfur compounds selected from the group consisting of thiophene, thiophene compounds and mercaptans (optional step d), desulfurization of the intermediate fractions (optional step e) and desulfurization of the heavy fraction (step f).

selon l'invention est couplée à la colonne et choisie dans le groupe constitué par les sections réactionnelles suivantes : hydrogénation (étape a), transformation des composés soufrés légers (étape optionnelle b), transformation des composés soufrés choisis dans le groupe constitué par le thiophène, les composés thiophèniques et les mercaptans (étape optionnelle d), désulfuration des fractions intermédiaires (étape optionnelle e) et désulfuration de la fraction lourde (étape f). According to another preferred variant, at least one reaction section of the process

according to the invention is coupled to the column and selected from the group consisting of the following reaction sections: hydrogenation (step a), transformation of light sulfur compounds (optional step b), transformation of the sulfur compounds selected from the group consisting of thiophene , thiophenic compounds and mercaptans (optional step d), desulfurization of the intermediate fractions (optional step e) and desulfurization of the heavy fraction (step f).

The effluent from step d of transformation of the sulfur compounds may optionally be mixed at least in part with a heavy cut from the fractionation in step c. Said effluent may also be sent to a new fractionation unit to be separated into two fractions, an untreated or optionally desulfurized intermediate fraction without being mixed, and a heavy fraction which is preferably mixed with the heavy fraction resulting from step c before being desulphurized in step f.

The following examples illustrate the invention:
Example 1 (comparative).

A catalytic cracking gasoline whose characteristics are shown in Table 1 is separated into two fractions (step c), a light fraction whose cutting point corresponds to a temperature of 63 C and a heavy fraction. The light fraction represents 25% by weight of the starting gasoline and contains 88% of the compounds

<Desc / Clms Page number 28>

 olefins having 5 carbon atoms which were present in the starting gasoline and 23% of the olefins having 6 carbon atoms. The characteristics of the separation column are as follows: 30 theoretical plates, reflux balloon pressure = 5 MPa, supply temperature 100 C.

The characteristics of the light fraction and the heavy fraction are presented in Table 1.

<Tb>
<tb> gasoline <SEP> of <SEP> catalytic cracking <SEP>
<tb> fraction <SEP> fraction
<tb> slight <SEP> heavy
<tb> gasoline <SEP> Pt-63-220 C
<tb> total <SEP> 63
<tb> IND. <SEP> REFRACTION <SEP> to <SEP> 200C <SEP> 1.43 <SEP> 1.38 <SEP> 1.45
<tb> MASS <SEP> VOLUMIC <SEP> 15/4 <SEP> 0.76 <SEP> 0.67 <SEP> 0.79
<tb> IBr <SEP> (g / 100g) <SEP> 78 <SE> 166 <SEP> 48
<tb> MAV <SEP> (mg / g) <SEP> 6.4 <SEP> 5.2 <SEP> 6.8
<tb> NITROGEN <SEP> TOTAL <SEP> (mqll) <SEP> 40 <SEP> 2, <SEP> 7 <SEP> 50
<tb> RON <SEP> 93, <SEP> 0 <SEP> 95.8 <SEP> 92.0
<tb> MON <SEP> 80, <SEP> 3 <SEP> 84.1 <SEP> 78.9
<tb> SULFUR <SEP> NO <SEP> 1509 <SEP> 37 <SEP> 2000
<tb> MERCAPTANS <SEP> (mg / Kg)
<tb> MERCAPTANS <SEP> (mg / kg) <SEP> 58 <SEP> 158 <SEP> 24
<tb> SULFUR <SEP> TOTAL <SEP> (mg / Kg) <SEP> 1567 <SEP> 195 <SEP> 2024
<Tb>
At the end of this separation, the light fraction has a content of sulfur, mercaptan and diolefin such that it is no longer necessary to carry out additional treatment of this fraction before using it.

The heavy fraction is subjected to hydrodesulfurization on a catalyst in isothermal tubular reactor. The catalyst is obtained by impregnation without excess solution of a transition alumina, in the form of beads, with a specific surface area of 130 m 2 / g and a pore volume of 0.9 ml / g, with an aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate. The catalyst is then dried and calcined in air at 500 ° C. The cobalt and molybdenum content of this catalyst sample A is 3% CoO and 14% MioO 3. The catalyst is previously sulphurized by treatment for 4 hours

<Desc / Clms Page number 29>

sous une pression de 3, 4 MPa à 350 C, au contact d'une charge contenant 2% pds de S sous forme de diméthylsulfure dilué dans du n-heptane.

at a pressure of 3, 4 MPa at 350 ° C., in contact with a feedstock containing 2% by weight of S in the form of dimethylsulphide diluted in n-heptane.

The operating conditions for desulfurization are as follows: VVH = 4h-1, H 2 / HC = 300) /), P = 2 MPa. The temperature of the reaction zone is 280 ° C. The characteristics of the effluents obtained are shown in Table 2.

Table 2: Characteristics of heavy gasoline after hydrodesulfurization

<Tb>
<tb> Gasoline <SEP> Heavy <SEP> Gasoline <SEP> Heavy
<tb> desulfurized
<tb> S <SEP> total <SEP> ppm <SEP> 2024 <SEP> 182
<tb> S <SEP> RSH <SEP> ppm <SEP> 24 <SEP> 80
<tb> Ibr <SEP> gBr / 1 <SEP> 00g <SEP> 48 <SEP> 33
<tb> RON <SEP> 92, <SEP> 0 <SEP> 86, <SEP> 5
<tb> MON <SEP> 78, <SEP> 9 <SEP> 75, <SEP> 8
<tb> H2S <SEP>% <SEP> flight <SEP> 0, <SEP> 2
<Tb>
The desulphurized heavy gasoline is then mixed with the light gasoline whose composition is given in Table 1. The gasoline thus constituted contains 185 ppm of sulfur including 100 ppm of mercaptans. Such gasoline will therefore require additional treatment before use.

 Example 2 (according to the invention): The gasoline whose characteristics are described in Example 1 is subjected to a hydrogenation treatment of diolefins (step a) under conditions such that the light sulfur compounds present in the feed are partly converted to heavier compounds (step b performed simultaneously at step a.

This treatment is carried out in a continuous reactor operating in updraft. The catalyst is an HR945 catalyst marketed by the company Procatalyse. The reaction is carried out at 160 ° C. under a total pressure of 13 bar, with a space velocity of 6 h -1. The H2 / feed ratio, expressed in liters of hydrogen per liter of feed and 10.

The characteristics of the effluent after hydrogenation of diolefins and conversion of light compounds present in gasoline are presented in Table 3.

<Desc / Clms Page number 30>

<Tb>
<Tb>

Essence <SEP> of <SEP> cracking
<tb> ca <SEP> alytic
<tb> essence <SEP> Gasoline <SEP> after
<tb> total <SEP> treatment
<tb> IND. <SEP> REFRACTION <SEP> to <SEP> 200C <SEP> 1.44 <SEP> 1.43
<tb> MASS <SEP> VOLUMIC <SEP> 15/4 <SEP> 0.78 <SEP> 0.77
<tb> IBr <SEP> (g / 100g) <SEP> 78 <SEP> 75.5
<tb> MAV <SEP> (mg / g) <SEP> 6.4 <SEP> 0.2
<tb> NITROGEN <SEP> 40
<tb> RON <SEP> 93.0 <SEP> 92.2
<tb> MON <SEP> 80, <SEP> 3 <SEP> 79.9
<tb> SULFUR <SEP> NO <SEP> 1509 <SEP> 1561
<tb> MERCAPTANS <SEP> (mg / Kg)
<tb> MERCAPTANS <SEP> (mg / kg) <SEP> 58 <SEP> 6
<tb> SULFUR <SEP> TOTAL <SEP> (mg / Kg) <SEP> 1567 <SEP> 1567
<Tb>

At the end of this treatment, the essence is separated into two fractions (step c) under the conditions described in Example 1. The characteristics of the two fractions obtained are specified in Table 4.

<Desc / Clms Page number 31>

Table 4: Characteristics of light and heavy cuts after fractionation (step c)

<Tb>
<tb><SEP> Gasoline <SEP> Catalytic cracking <SEP>
<tb> fraction <SEP> fraction
<tb> slight <SEP> heavy
<tb> gasoline <SEP> PI-63 <SEP> 63-220 C
<tb> total
<tb> IND. <SEP> REFRACTION <SEP> to <SEP> 200C <SEP> 1.44 <SEP> 1.38 <SEP> 1.45
<tb> MASS <SEP> VOLUMIC <SEP> 15/4 <SEP> 0.78 <SEP> 0.67 <SEP> 0.79
<tb> IBr <SEP> (g / 100g) <SEP> 75.5 <SEQ> 158 <SEP> 48
<tb> MAV <SEP> (mg / g) <SEP> 0.2 <SEP> 0, <SEP> 0 <SEP> 0, <SEP> 3
<tb> NITROGEN <SEP> TOTAL <SEP> (mag / 1) <SEP> 40 <SEP> 2.7 <SEP> 50
<tb> RON <SEP> 92, <SEP> 2 <SEP> 92.8 <SEP> 92.0
<tb> MON <SEP> 79, <SEP> 9 <SEP> 82.9 <SEP> 78.9
<tb> SULFUR <SEP> NO <SEP> 1561 <SEP> 31 <SEP> 2071
<tb> MERCAPTANS <SEP> (mg / Kg)
<tb> MERCAPTANS <SEP> (mg / kg) <SEP> 6 <SEP> 2 <SEP> 7
<tb> SULFUR <SEP> TOTAL <SEP> (mg / Kg) <SEP> 1567 <SEP> 33 <SEP> 2078
<Tb>

A l'issue de cette séparation, la fraction légère contient une teneur en soufre, en mercaptan et en dioléfine telle qu'il n'est plus nécessaire de réaliser un traitement supplémentaire de cette fraction avant de l'utiliser.

At the end of this separation, the light fraction contains a content of sulfur, mercaptan and diolefin such that it is no longer necessary to carry out additional treatment of this fraction before using it.

The heavy fraction is subjected to hydrodesulfurization on the catalyst A of Example 1 in an isothermal tubular reactor. The catalyst is previously sulphurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a feedstock containing 2% by weight of S in the form of dimethylsulphide diluted in nheptane.

The desulfurization operating conditions are as follows: VVH = 4h-1, H2 / HC = 3001/1, P = 2MPa. The temperature of the reaction zone is 280 ° C. The characteristics of the effluents obtained are shown in Table 5.

<Desc / Clms Page number 32>

Table 5: Characteristics of heavy gasoline after hydrodesulfurization

<Tb>
<tb> Gasoline <SEP> Heavy <SEP> Gasoline <SEP> Heavy
<tb> desulfurized
<tb> S <SEP> total <SEP> ppm <SEP> 2078 <SEP> 185
<tb> S <SEP> RSH <SEP> ppm <SEP> 7 <SEP> 90
<tb> Ibr <SEP> gBr / 100g <SEP> 48 <SEP> 33
<tb> RON <SEP> 92, <SEP> 0 <SEP> 86, <SEP> 5
<tb> MON <SEP> 78, <SEP> 9 <SEP> 75, <SEP> 8
<tb> H2S <SEP>% <SEP> flight <SEP> 0, <SEP> 2
<Tb>

L'essence lourde désulfurée est ensuite mélangée avec l'essence légère non traitée dont la composition est donnée dans le tableau 4. L'essence désulfurée ainsi constituée contient 147 ppm de soufre dont 68 ppm de mercaptans.

The desulphurized heavy gasoline is then mixed with the untreated light gasoline whose composition is given in Table 4. The desulphurized gasoline thus constituted contains 147 ppm of sulfur including 68 ppm of mercaptans.

Claims (16)

 A process for producing low sulfur gasoline comprising at least the following steps: at least one selective hydrogenation of the diolefins present in the initial gasoline (step a), at least one step of transformation of the light sulfur compounds present in the the gasoline (step b), at least one fractionation (step c) of the gasoline obtained in step a or b in at least two fractions a light fraction and a heavy fraction, a desulfurization treatment in one step (step f) at least a portion of the heavy fraction resulting from the fractionation in step c. 2. A process for producing low sulfur gasoline comprising at least the following steps: at least one selective hydrogenation of the diolefins present in the initial gasoline (step a), at least one fractionation (step c) of the gasoline obtained in step a in at least two fractions a light fraction and a heavy fraction, a step (step d) of transformation of the sulfur compounds selected from the group consisting of thiophene, thiophene compounds and mercaptans present in at least one cut obtained in step c, a desulfurization treatment in one step (step f) of at least a portion of the heavy fraction from the fractionation in step c. 3. The method of claim 2 further comprising at least one step of transforming the light sulfur compounds present in the gasoline (step b). 4. The method of claim 1 or 3 wherein steps a and b are performed simultaneously in the same reactor. 5. Method according to one of claims 1 to 4 wherein step b and / or d increases the molecular weight of said sulfur compounds. 6. Method according to one of claims 1 to 5 wherein the gasoline from steps a or b is fractionated into a light fraction, at least an intermediate fraction and a heavy fraction. <Desc / Clms Page number 34>  7. The method of claim 6 further comprising at least one step d of transformation of sulfur compounds selected from the group consisting of thiophene, thiophenic compounds and mercaptans present in the light cut and / or in at least one intermediate fraction. 8. Method according to one of claims 6 or 7 wherein the step d of transformation of the sulfur compounds is an alkylation or adsorption. 9. Method according to one of claims 6 to 8 further comprising a step e of desulphurizing at least a portion of at least one intermediate fraction from the fractionation in step c or step d of transformation of sulfur compounds. 10. Method according to one of claims 1 to 9 wherein the heavy gasoline is desulfurized in step f in the presence of a hydrodesulphurization catalyst or an absorbent. 11. Process according to any one of claims 1 to 10 wherein the desulfurized heavy gasoline in step f is stripped by means of an inert gas. 12. Method according to one of claims 1 to 11 further comprising a step g

 mixing the light fraction resulting from step c or d and optionally at least one intermediate fraction resulting from step c or d or e with the heavy desulphurized fraction resulting from step f. 13. Method according to one of claims 1 to 12 wherein at least one reaction section is internal to the column and selected from the group consisting of the following reaction sections: hydrogenation (step a), transformation of light sulfur compounds (optional step b), transformation of the sulfur compounds selected from the group consisting of thiophene, thiophenic compounds and mercaptans (optional step d), desulfurization of the intermediate fractions (optional step e) and desulfurization of the heavy fraction (step f). <Desc / Clms Page number 35>  14. Process according to one of claims 1 to 13 wherein at least one reaction section is coupled to the column and selected from the group consisting of the following reaction sections: hydrogenation (step a), transformation of light sulfur compounds (optional step b), transformation of the sulfur compounds selected from the group consisting of thiophene, thiophenic compounds and mercaptans (optional step d), desulfurization of the intermediate fractions (optional step e) and desulfurization of the heavy fraction (step f). 15. Method according to one of claims 1 to 14 wherein the effluent from step d of transformation of the sulfur compounds is mixed at least in part with a heavy cut from the fractionation in step c. 16. Method according to one of claims 1 to 14 wherein the effluent from step d of transformation of the sulfur compounds is sent to a new fractionation unit to be separated into two fractions, an untreated intermediate fraction or optionally desulfurized without being mixed, and a heavy fraction which is preferably mixed with the heavy fraction from step c before being desulphurized in step f.