EP3228683A1 - Method for treating a gasoline - Google Patents

Abstract

The present invention relates to a process for treating a gasoline containing sulfur compounds, olefins and diolefins, comprising the following steps: a) the gasoline is fractionated so as to recover at least one MCN intermediate gasoline cut comprising hydrocarbons and whose temperature difference (T) between the points at 5% and at 95% of distilled mass is less than 60°C ; b) desulfurizing the MCN intermediate gasoline cut alone and in the presence of a hydrodesulfurization catalyst and hydrogen so as to produce a partially desulfurized MCN intermediate gasoline cut; and c) the at least partially desulphurized MCN intermediate gasoline cut which has not undergone catalytic treatment subsequent to step b) is fractionated in a fractionation column so as to recover at the top of the column an intermediate gasoline with low sulfur contents and in mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans.

Description

The present invention relates to a process for reducing the content of sulfur compounds of an olefinic type gasoline, so as to produce a so-called desulfurized gasoline. The process according to the invention makes it possible in particular to produce petrol cuts with a low mercaptan content and in particular recombinant mercaptans.

State of the art

The production of species that meet the new environmental standards requires that their sulfur content be substantially reduced to values generally not exceeding 50 ppm (mg / kg), and preferably below 10 ppm.

It is also known that the conversion gasolines, and more particularly those from catalytic cracking, which can represent 30 to 50% of the gasoline pool, have high levels of olefins and sulfur.

The sulfur present in gasoline is for this reason attributable, to nearly 90%, to the gasoline from catalytic cracking processes, which will be called in the following essence of FCC (Fluid Catalytic Cracking according to the English terminology, that it can be translated by catalytic cracking in a fluidized bed). FCC gasolines thus constitute the preferred filler of the process of the present invention.

Among the possible routes for producing fuels with a low sulfur content, that which has been widely adopted consists in specifically treating the sulfur-rich gasoline bases by hydrodesulfurization processes in the presence of hydrogen and a catalyst.

The traditional processes desulphurize the species in a non-selective manner by hydrogenating a large part of the mono-olefins, which generates a strong loss in octane number and a high consumption of hydrogen. The most recent processes, such as the Prime G + (trade mark) process, make it possible to desulphurize the olefin-rich cracking species, while limiting the hydrogenation of the mono-olefins and consequently the octane loss and the high consumption. of hydrogen that results. Such methods are for example described in patent applications EP 1077247 and EP 1174485 .

As described in the patent applications EP 1077247 and EP 1800748 , it is advantageous to carry out before the hydrotreatment step a step of selective hydrogenation of the feedstock to be treated. This first hydrogenation step consists essentially of selectively hydrogenating the diolefins, while simultaneously transforming the saturated light sulfur compounds (by increasing their molecular weight) by weighting. These sulfur compounds may have a boiling point below the boiling point of thiophene, such as methanethiol, ethanethiol, propanethiol and dimethylsulfide. By fractionation of the gasoline resulting from the selective hydrogenation stage, a light desulphurized gasoline (or LCN for Light Cracked Naphtha according to the English terminology) cut-off section is produced consisting mainly of mono-olefins with 5 or 6 carbon atoms without octane loss, which can be upgraded to the gasoline pool for vehicle fuel formulation. Under specific operating conditions, this hydrogenation selectively carries out the hydrogenation, at least partial or complete, of the diolefins present in the feedstock to be treated with monoolefinic compounds, which have a better octane number.

Another effect of the selective hydrogenation is to prevent the progressive deactivation of the selective hydrodesulfurization catalyst and / or to avoid a progressive plugging of the reactor due to the formation of polymerization gums on the surface of the catalysts or in the reactor. Indeed, the polyunsaturated compounds are unstable and tend to form gums by polymerization.

The patent application EP 2161076 discloses a process for selective hydrogenation of polyunsaturated compounds, and more particularly diolefins, for jointly carrying out the weighting of light sulfur compounds such as mercaptans or sulfides. This process uses a catalyst containing at least one metal of group VIb and at least one non-noble metal of group VIII deposited on a porous support.

Obtaining a gasoline with a very low sulfur content, typically at a content of less than 10 ppm by weight as required in Europe, also requires at least one hydrodesulphurization stage which consists in converting the organo-sulfur compounds into H ₂ S.

However, if this step is not properly controlled, it can lead to the hydrogenation of a large part of the mono-olefins present in the gasoline and which then results in a sharp decrease in the octane number of the gasoline. as well as overconsumption of hydrogen. Another problem encountered during the hydrodesulfurization step is the formation of mercaptan-type compounds resulting from the addition reaction of the H ₂ S formed in the hydrodesulfurization reactor on the mono-olefins present in the gasoline feedstock. . The mercaptans, of chemical formula R-SH, where R is an alkyl group, are also called recombinant thiols or mercaptans and generally represent between 20% and 80% by weight of the residual sulfur in the desulphurized species.

In order to limit these disadvantages, various solutions are described in the literature for desulfurizing the cracking species by combining hydrodesulphurization steps and eliminating the recombination mercaptans by a technique that is judiciously chosen to avoid the hydrogenation of the mono-olefins present, in order to preserve the octane number (see for example US 7799210 , US 6960291 , US 6387249 and US 2007114156 ).

It appears however that if these combinations implementing a final stage of elimination of recombinant mercaptans are particularly suitable when a very low sulfur content is sought, these can be very expensive when the quantity of mercaptans to be removed is high; indeed this requires for example high consumption of adsorbent or solvent.

Among the solutions proposed in the literature to produce gasoline with reduced sulfur content, some propose the separation by distillation of the wide cut of the gasoline resulting from a cracking process (or FRCN for Full Range Cracked Naphtha according to the English terminology -saxonne). Distillation has the objective in certain patents (for example, patents EP 1077247 , EP 1174485 , US 6596157 , US 6913688 ) to obtain 2 cuts: a light cut (LCN) and a heavy cut (HCN or Heavy Cracked Naphtha according to the English terminology). The FRCN gasoline can be treated upstream of the distillation for example by a process allowing the selective hydrogenation of the diolefins of the gasoline and / or allowing the weighting of the light sulfur compounds, so that after the operation of distillation, these sulfur compounds are recovered in the HCN heavy cut. The sulfur compounds of the heavy cut are then removed from the gasoline by various methods, for example, via catalytic hydrodesulphurization performed with one or more reactors.

Other solutions involve separation by distillation of FRCN large cut gasoline in addition to two cuts to produce a gasoline with reduced sulfur content or even very low sulfur content, of the order of 10 ppm by weight. . In this type of process, the cuts obtained are treated separately or in part together for the removal of organic sulfur from at least a portion of the cuts obtained, the aim being to obtain a desulfurized gasoline after mixing all or at least one part of the treated sections.

For example, the patent application US2004188327 discloses a method of reducing the sulfur content of an FCC gasoline by separating the FRCN gasoline by a distillation operation in three sections: a light cut, an intermediate cut and a heavy cut.

The heavy cut is desulfurized and the effluent is combined with the intermediate cut, the whole being desulphurized during a second hydrodesulfurization step. It is specified that the mercaptans contained in the light cut can be eliminated either by thioetherification upstream of the separation in three sections, or by a caustic treatment downstream.

The patent US 6103105 describes a similar process, the FRCN gas being also separated in three sections by a distillation operation. It is specified that the light cut represents between 50 and 80% of the gasoline and that the heavy cut represents from 5 to 20% of the FRCN gasoline. It is also specified that the intermediate cut and the heavy cut are hydrodesulfurized in a single reactor containing two catalytic beds. The heavy fraction is treated in the 1 ^st catalytic bed and the intermediate section is added between the two beds so as to produce a co-treatment with the heavy fraction partially desulphurized end of the bed ¹ in the ^2nd catalytic bed. The authors indicate an almost total elimination of sulfur as well as an almost complete hydrogenation of the olefins of the heavy cut.

The patent FR2807061 also discloses a gasoline desulfurization process comprising a selective hydrogenation step followed by separation into at least three fractions. The lightest fraction is practically free of sulfur. The heavier fraction is treated at least once to desulfurize the unsaturated sulfur compounds in the cut. The intermediate fraction is characterized by a relatively low olefin and aromatic content. This cut undergoes partially or completely at least one desulfurization and denitrogenation step followed by catalytic reforming.

The patent US9260672 discloses a process for producing gasoline with low octane loss. According to the inventors, after saturation of the diolefins, the FRCN gasoline is separated by distillation into a light end-point cut 70 ° C, an intermediate cut (70-90 ° C) and a heavy cut (90-210 ° C). The mercaptans of the light cut are removed with a caustic treatment in equipment known as CFC (or Continuous Film Contactor according to the English terminology). The heavy cut, containing mainly thiophene sulfur compounds, is desulphurized by a catalytic hydrodesulphurization or reactive adsorption process. The intermediate cut can be sent to an isomerization or catalytic reforming unit. Optionally the intermediate cut can be co-processed with the light cut in a CFC equipment to reduce the mercaptan content, or this cut can be co-treated with the heavy cut. This process does not provide separate desulfurization treatment for the intermediate cut.

The document US 2004/0195151 discloses a process for the selective desulphurization of FRCN gasoline. The FRCN gasoline is introduced into a reactive distillation column which makes it possible both to carry out a thioetherification treatment of the mercaptans contained in the feed and to separate into a light cut, an intermediate cut and a heavy cut. The intermediate cut is withdrawn by a side withdrawal and is treated in a desulfurization reactor.

The document US 2014/0054198 discloses a process for reducing the sulfur content of a hydrocarbon stream, the method comprising contacting a FRCN gasoline with a hydrogenation catalyst to hydrogenate at least a portion of the dienes and convert to at least a portion of mercaptans to thioethers. This FRCN gasoline is then fractionated into a light fraction, an intermediate fraction and a heavy fraction. The heavy fraction is desulfurized in a catalytic hydrodesulfurization process. The intermediate fraction is mixed with hydrogen and a gas oil fraction to form a mixture which is contacted with a catalyst in a hydrodesulfurization reactor and then separated to obtain the desulphurized intermediate fraction and recover the diesel fraction which is recycled. in the process and optionally purged. In this process, the hydrodesulphurization of the intermediate fraction is systematically carried out in mixture with a diesel fraction or a part of the heavy fraction in order to be able to use a technology of the trickle bed type (Trickle Bed Reactor) according to the English terminology. reactive distillation (which then allows hydrodesulphurization and separation in a single step).

The hydrodesulfurization of the intermediate fraction is thus carried out in three-phase gas / liquid / solid medium. The use of a gasoil fraction mixed with the intermediate fraction, however, generally requires the use of a larger amount of catalyst than in the case where the intermediate fraction was treated alone, the flow to be treated is greater.

An object of the present invention is to provide a process for the desulfurization of an olefinic gasoline which is capable of producing, by limiting the loss of octane number, a gasoline with a low total sulfur content, typically less than 30 ppm, or still preferably less than 15 ppm by weight and also with a low mercaptan content (of recombination), that is to say typically less than 15 ppm by weight (expressed as sulfur), or even more preferentially less than 5 ppm by weight (expressed as sulfur).

Summary of the invention

1. a) on fractionne l'essence de manière à récupérer au moins une coupe essence intermédiaire MCN comprenant des hydrocarbures et dont la différence de température (ΔT) entre les points à 5% et à 95% de masse distillée est inférieure ou égale à 60°C;
2. b) on désulfure la coupe essence intermédiaire MCN seule et en présence d'un catalyseur d'hydrodésulfuration et de l'hydrogène, à une température comprise entre 160 et 450°C, à une pression comprise entre 0,5 et 8 MPa, avec une vitesse spatiale liquide comprise entre 0,5 et 20 h^-1 et avec un rapport entre le débit d'hydrogène exprimé en normaux m³ par heure et le débit de charge à traiter exprimé en m³ par heure aux conditions standards compris entre 50 Nm³/m³ et 1000 Nm³/m³ de manière à produire une coupe intermédiaire MCN au moins partiellement désulfurée ; et
3. c) on fractionne dans une colonne de fractionnement la coupe essence intermédiaire MCN partiellement désulfurée n'ayant pas subi de traitement catalytique postérieur à l'étape b) de manière à récupérer en tête de la colonne une essence intermédiaire à basses teneurs en soufre et en mercaptans et en fond de la colonne une coupe hydrocarbures contenant des composés soufrés dont des mercaptans.

The present invention relates to a process for treating a gasoline containing sulfur compounds, olefins and diolefins, the process comprising the following steps:

1. a) the gasoline is fractionated so as to recover at least one intermediate gasoline fraction MCN comprising hydrocarbons and whose temperature difference (ΔT) between the points at 5% and at 95% of distilled mass is less than or equal to 60 ° VS;
2. b) the intermediate gasoline fraction MCN is desulfurized alone and in the presence of a hydrodesulfurization catalyst and hydrogen, at a temperature of between 160 and 450 ° C., at a pressure of between 0.5 and 8 MPa, with a space velocity liquid between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in normal m ³ per hour and the charge flow rate to be treated expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ to produce an at least partially desulfurized MCN intermediate cut; and
3. c) fractionating in a fractionation column the partly desulfurized intermediate gasoline fraction MCN that has not undergone catalytic treatment subsequent to step b) so as to recover at the column head an intermediate gasoline with low sulfur contents and mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans.

The process according to the invention makes it possible, by virtue of the combination of the successive stages a), b) and c), to produce an intermediate gasoline with low levels of sulfur and mercaptans and with a high octane number. Indeed, fractionation step a) is carried out under specific conditions in order to separate an intermediate gasoline fraction MCN boiling in a narrow temperature range, ie the difference in temperature (ΔT) between the points at 5% and at 95% of distilled mass (measured according to the CSD method described in Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) is less than or equal to 60 ° C.

Preferably, the intermediate cut MCN resulting from step a) has a difference in temperature (ΔT) between the temperatures corresponding to 5% and 95% of the distilled mass (measured according to the CSD method described in document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ), which is between 20 ° C and 60 ° C and more preferably between 25 and 40 ° C.

Said gasoline intermediate cut MCN alone, that is to say without being mixed with any hydrocarbon cut internal or external to the process, is then treated in a hydrodesulfurization step (step b) so as to convert the sulfur compounds in hydrogen sulfide H ₂ S and under conditions to limit the hydrogenation of olefins and thus the loss of octane number. During this step b), so-called "recombination" mercaptans are formed by reaction between the olefins of the intermediate cut MCN and the H ₂ S. These recombination mercaptans which have higher boiling points than those of the olefins from which they are derived are then separated from the partially desulphurized intermediate gasoline fraction MCN in step c). In the context of the invention, the process may comprise a step of degassing the H ₂ S present in the effluent from step b) which may be carried out before, during or after step c). The step c) of separation of the recombinant mercaptans is generally carried out by means of a column of fractionation which provides a bottom section loaded with mercaptans and a top cut (intermediate gasoline) with low levels of sulfur and mercaptans, that is to say with a total sulfur content typically less than 30 ppm by weight or even more preferentially lower than 15 ppm weight. In the case where the effluent from step b) has not undergone a degassing step to separate hydrogen and hydrogen sulphide (stabilization of gasoline) before the fractionation of step c), hydrogen and hydrogen sulfide can be separated at the top of the fractionation column c) operated so that the stabilization and separation of the mercaptans are then carried out in the same column and the intermediate gasoline with low sulfur content and in mercaptans being then obtained by a near lateral withdrawal, typically some theoretical plates below the head of this same column. Finally, in the case where the effluent of step b) is not stabilized neither upstream of step c) nor during step c), the stabilization operation can be carried out downstream, on the intermediate gasoline flow with low sulfur and mercaptan contents. The fractionation in step c) is preferably carried out so that the intermediate head gas has a temperature difference (ΔT) between the 5% and 95% distilled mass points (measured according to the CSD method described in US Pat. the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ), which is equal to the difference in temperature (ΔT) between the points at 5% and at 95% of the distilled mass of the intermediate gasoline fraction MCN resulting from stage a). Alternatively, step c) is carried out so that the top cut (intermediate gasoline with low sulfur and mercaptan contents) has a temperature corresponding to 95% of the distilled mass which is less than the maximum of 10 ° C. relative to at the temperature corresponding to 95% of the distilled mass of the intermediate cut MCN from step a).

When step c) is carried out in a separation column (or fractionation), the stream of the bottom cut that is taken continuously or discontinuously, can then be treated by hydrodesulphurization in mixture with a HHCN heavy gasoline, heavier than the intermediate gasoline cut MCN.

The process according to the invention has the advantage of producing an intermediate gasoline with low sulfur and mercaptan contents without significant loss of octane number since the recombination mercaptans which are inevitably formed in the desulfurization step b) are not converted by a subsequent hydrodesulfurization step but are separated from the partly desulphurized intermediate gasoline cut in a suitably chosen fractionation step.

1. a) on fractionne l'essence en au moins :
   • une coupe essence légère LCN;
   • une coupe essence intermédiaire MCN comprenant des hydrocarbures et dont la différence de température (ΔT) entre les points à 5% et à 95% de masse distillée est inférieure ou égale à 60°C; et
   • une coupe essence lourde HHCN contenant des hydrocarbures;
2. b) on désulfure la coupe essence intermédiaire MCN seule et en présence d'un catalyseur d'hydrodésulfuration et de l'hydrogène, à une température comprise entre 160 et 450°C, à une pression comprise entre 0,5 et 8 MPa, avec une vitesse spatiale liquide comprise entre 0,5 et 20 h^-1 et avec un rapport entre le débit d'hydrogène exprimé en normaux m³ par heure et le débit de charge à traiter exprimé en m³ par heure aux conditions standards compris entre 50 Nm³/m³ et 1000 Nm³/m³ de manière à produire une coupe essence intermédiaire MCN au moins partiellement désulfurée ;
3. c) on fractionne dans une colonne de fractionnement la coupe essence intermédiaire MCN partiellement désulfurée n'ayant pas subi de traitement catalytique postérieur à l'étape b) de manière à récupérer en tête de la colonne une essence intermédiaire à basses teneurs en soufre et en mercaptans et en fond de la colonne une coupe hydrocarbures contenant des composés soufrés dont des mercaptans;
4. d) on désulfure la coupe essence lourde HHCN seule ou en mélange avec la coupe hydrocarbures de fond issue de l'étape c) en présence d'un catalyseur d'hydrodésulfuration et d'hydrogène, à une température comprise entre 200 et 400°C, à une pression comprise entre 0,5 et 8 MPa, avec une vitesse spatiale liquide comprise entre 0,5 et 20 h^-1 et avec un rapport entre le débit d'hydrogène exprimé en normaux m3 par heure et le débit de charge à traiter exprimé en m³ par heure aux conditions standards compris entre 50 Nm³/m³ et 1000 Nm³/m³ de manière à produire une coupe lourde HHCN au moins partiellement désulfurée.

Preferably, the intermediate gasoline fraction MCN resulting from stage a) has temperatures corresponding to 5% and 95% of the distilled mass (measured according to the CSD method described in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ), which are respectively between 50 and 68 ° C and between 88 and 110 ° C. According to a preferred embodiment, the method comprises the following steps:

1. a) the gasoline is split into at least:
   • a light LCN petrol cut;
   • an intermediate gasoline fraction MCN comprising hydrocarbons and whose temperature difference (ΔT) between the points at 5% and at 95% of distilled mass is less than or equal to 60 ° C; and
   • a HHCN heavy gasoline cut containing hydrocarbons;
2. b) the intermediate gasoline fraction MCN is desulfurized alone and in the presence of a hydrodesulfurization catalyst and hydrogen, at a temperature of between 160 and 450 ° C., at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio of the flow rate of hydrogen expressed in normal m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 and Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce an at least partially desulphurized intermediate gasoline fraction MCN;
3. c) fractionating in a fractionation column the partly desulfurized intermediate gasoline fraction MCN that has not undergone catalytic treatment subsequent to step b) so as to recover at the column head an intermediate gasoline with low sulfur contents and mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans;
4. d) the heavy gasoline fraction HHCN is desulphurized alone or in admixture with the bottom hydrocarbon fraction resulting from stage c) in the presence of a hydrodesulfurization and hydrogen catalyst, at a temperature of between 200 and 400 ° C. , at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in normal cubic meters per hour and the flow rate of charge at treat expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce a heavy cut HHCN at least partially desulfurized.

• a1) on fractionne l'essence en une coupe essence légère LCN et une coupe essence lourde intermédiaire HCN;
• a2) on fractionne la coupe essence lourde intermédiaire HCN en au moins une coupe essence intermédiaire MCN et une coupe essence lourde HHCN.

In this embodiment, step a) can be carried out in two fractionation steps, that is to say:

• a1) the gasoline is split into a light LCN gasoline cut and an HCN heavy gasoline intermediate cut;
• a2) the HCN intermediate heavy gasoline fraction is fractionated into at least one intermediate gasoline fraction MCN and a heavy gasoline fraction HHCN.

In this particular embodiment, it is also possible to desulphurize the intermediate heavy gasoline cut HCN resulting from step a1) before the fractionation step a2).

Alternatively, step a) is carried out in a single fractionation step. This step is preferably carried out in a divided wall distillation column.

In one embodiment, step a2) is performed in a divided wall distillation column and the partially desulfurized intermediate gasoline fraction CMN from step b) is passed into said divided wall distillation column to be fractionated.

According to one particular embodiment, the LCN light gasoline fraction has a final boiling point of 65 ° C. ± 2 ° C., the intermediate gasoline fraction MCN has a final boiling point of less than or equal to 100 ° C. ± 2 ° C. C and the HHCN heavy gasoline cut has an initial boiling point above 100 ° C ± 2 ° C.

According to the invention, step d) uses at least one hydrodesulfurization reactor. Preferably step d) involves a first and a second hydrodesulfurization reactor arranged in series. Preferably, the effluent from the first hydrodesulfurization reactor undergoes a degassing step of the H ₂ S formed before being treated in the second hydrodesulfurization reactor.

The hydrodesulfurization catalysts of steps b) and / or d) comprise at least one element of group VIII (groups 8, 9 and 10 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ), at least one element of group Vlb (group 6 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and a support.

In a particular embodiment, part of the desulfurized HHCN heavy gasoline cut from step d) is recycled to step c) so as to promote the entrainment of the recombination mercaptans at the bottom of the fractionation column. For example, a portion of the desulphurized HHCN heavy gasoline cut from step d) is mixed with the partly desulfurized intermediate gasoline fraction CMN from step b) and said mixture is fractionated in step c). Alternatively, part of the desulphurized HHCN heavy gasoline cut from step d) is sent directly to the fractionation column of step c).

Before step a), the gasoline can be treated in the presence of hydrogen and a selective hydrogenation catalyst so as to at least partially hydrogenate the diolefins and perform a weighting reaction of a portion of the sulfur compounds , step a) being carried out at a temperature of between 50 and 250 ° C., at a pressure of between 1 and 5 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between hydrogen flow rate expressed as normal m ³ per hour and the flow rate of the charge to be treated expressed in m ³ per hour at standard conditions of between 2 Nm ³ / m ³ and 100 Nm ³ / m ³ . According to the invention, the catalyst of the hydrogenation step is a sulphurized catalyst comprising at least one element of group VIII (groups 8, 9 and 10 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and possibly at least one element of group Vlb (group 6 of the new periodic Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and a support.

Detailed description of the invention

• Figure 1 est un schéma de principe du procédé selon l'invention;
• Figure 2 est un schéma de principe d'une variante du procédé selon l'invention;
• Figure 3 est un schéma de principe d'une autre variante du procédé selon l'invention ;
• Figure 4 est un schéma de principe d'une autre variante du procédé selon l'invention ;
• Figure 5 est un schéma de principe d'une autre variante du procédé selon l'invention ;

The other features and advantages of the invention will appear on reading the description which follows, given by way of illustration only and not by way of limitation, and with reference to the following figures:

• Figure 1 is a block diagram of the method according to the invention;
• Figure 2 is a schematic diagram of a variant of the method according to the invention;
• Figure 3 is a block diagram of another variant of the method according to the invention;
• Figure 4 is a block diagram of another variant of the method according to the invention;
• Figure 5 is a block diagram of another variant of the method according to the invention;

Generally, similar elements are denoted by identical references in the figures.

- Description of the load:

The process according to the invention makes it possible to treat any type of sulfur-containing olefinic gasoline cut, preferably a gasoline cut from a catalytic or non-catalytic cracking unit, whose range of boiling points typically extends from about the boiling points of the hydrocarbons with 2 or 3 carbon atoms (C2 or C3) up to about 250 ° C., preferably from about the boiling points of the hydrocarbons with 2 or 3 carbon atoms (C2 or C3) up to about 220 ° C, more preferably from about the boiling points of the 4-carbon hydrocarbons to about 220 ° C. The process according to the invention can also treat feeds having end points lower than those mentioned previously, such as, for example, a C5-200 ° C or C5-160 ° C cut.

The sulfur content of catalytic cracking (FCC) or non-catalytic gasoline sections depends on the sulfur content of the treated feedstock, the presence or absence of 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, they can even, in certain cases, reach values of the order of 4000 to 5000 ppm by weight.

For example, gasoline from catalytic cracking units (FCC) contain, on average, between 0.5% and 5% by weight of diolefins, between 20% and 50% by weight of olefins, between 10 ppm and 0.5% sulfur weight of which generally less than 300 ppm of mercaptans. Mercaptans are generally concentrated in the light ends of gasoline and more precisely in the fraction whose boiling point is below 120 ° C.

The sulfur species contained in the feedstocks treated by the process of the invention may be mercaptans or heterocyclic compounds, such as, for example, thiophenes or alkylthiophenes, or heavier compounds, for example benzothiophene. These heterocyclic compounds, unlike mercaptans, can not be removed by the extractive processes. These sulfur compounds are consequently eliminated by hydrotreatment, which leads to their conversion into hydrocarbons and H ₂ S.

- Detailed description of the scheme of the invention:

1. a) on fractionne l'essence de manière à récupérer au moins une coupe essence intermédiaire MCN comprenant des hydrocarbures et dont la différence de température (ΔT) entre les points à 5% et à 95% de masse distillée est inférieure ou égale à 60°C; et
2. b) on désulfure la coupe intermédiaire MCN seule et en présence d'un catalyseur d'hydrodésulfuration et de l'hydrogène, à une température comprise entre 160 et 450°C, à une pression comprise entre 0,5 et 8 MPa, avec une vitesse spatiale liquide comprise entre 0,5 et 20 h^-1 et avec un rapport entre le débit d'hydrogène exprimé en normaux m³ par heure et le débit de charge à traiter exprimé en m³ par heure aux conditions standards compris entre 50 Nm³/m³ et 1000 Nm³/m³ de manière à produire une coupe intermédiaire MCN au moins partiellement désulfurée ;
3. c) on fractionne dans une colonne de fractionnement la coupe intermédiaire au moins partiellement désulfurée n'ayant pas subi de traitement catalytique postérieur à l'étape b) de manière à récupérer en tête de la colonne une essence intermédiaire à basses teneurs en soufre et en mercaptans et en fond de la colonne une coupe hydrocarbure contenant des composés soufrés dont des mercaptans.

The present invention relates to a process for treating a gasoline containing sulfur compounds, olefins and diolefins, the process comprising the following steps:

1. a) the gasoline is fractionated so as to recover at least one intermediate gasoline fraction MCN comprising hydrocarbons and whose temperature difference (ΔT) between the points at 5% and at 95% of distilled mass is less than or equal to 60 ° VS; and
2. b) the intermediate cut MCN is desulfurized alone and in the presence of a hydrodesulfurization catalyst and hydrogen, at a temperature of between 160 and 450 ° C., at a pressure of between 0.5 and 8 MPa, with a liquid space velocity between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in normal m ³ per hour and the charge flow rate to be treated expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce an intermediate cut MCN at least partially desulfurized;
3. c) fractionating in a fractionation column the intermediate cut at least partially desulphurized that has not undergone catalytic treatment subsequent to step b) so as to recover at the head of the column a gasoline intermediate to low levels of sulfur and mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans.

In order to obtain the intermediate gasoline fraction MCN, the conditions of the column or fractionation columns are adjusted so as to obtain a hydrocarbon fraction whose temperature difference (ΔT) between the temperatures corresponding to 5% and 95% of the distilled mass that is less than or equal to 60 ° C, preferably between 20 ° C and 60 ° C and even more preferably between 25 and 40 ° C.

The temperature corresponding to 5% of the distilled mass of the middle gasoline fraction MCN is preferably between 50 ° C. and 68 ° C. and the temperature corresponding to 95% of the distilled mass of the middle gasoline fraction MCN is preferably between 88 ° C and 110 ° C. For example, the intermediate gasoline fraction MCN has a temperature corresponding to 5% of the distilled mass which is equal to 65 ° C. ± 2 ° C., preferably equal to 60 ° C. ± 2 ° C. and more preferably equal to 55 ° C. C ± 2 ° C. Preferably, the intermediate gasoline fraction MCN has a temperature corresponding to 95% of the distilled mass which is equal to 100 ° C. ± 2 ° C., or even equal to 90 ° C. ± 2 ° C. The method used to determine the temperatures corresponding to 5% and 95% of the distilled mass is described in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 under the name "CSD method" (abbréviation of "Conventional Simulated Distillation" according to the English terminology) and which can be translated by "Simulated Simulated Distillation".

In a preferred embodiment, the intermediate essence cut MCN essentially contains hydrocarbons having from 6 to 7 carbon atoms and predominantly hydrocarbons with 6 carbon atoms.

1. a) est réalisée de manière à séparer trois coupes :
   • une coupe essence légère LCN;
   • une coupe essence intermédiaire MCN; et
   • une coupe essence lourde HHCN.

According to a preferred embodiment of the treatment method, the fractionation step

1. a) is made so as to separate three sections:
   • a light LCN petrol cut;
   • an intermediate essence cut MCN; and
   • a heavy gasoline cut HHCN.

The splitting of the gasoline into three sections can be carried out in a single fractionation step or in several fractionation steps. If the fractionation is carried out in a single step with a single column, said distillation column is preferably a divided wall distillation column or Divided Wall Column according to the English terminology. In the case where the fractionation is carried out with two fractionation columns, the separation will preferably be carried out so that two sections are withdrawn from the first column: at the top the LCN light fuel cut and at the bottom an HCN intermediate heavy cut, the HCN intermediate heavy cut being then fractionated in the second fractionation column in order to obtain at the head the intermediate fuel cut MCN and in the background the HHCN heavy gasoline cut.

The cutting point between the LCN and MCN or HCN species is preferably adjusted so as to produce an LCN light gasoline cut with a sulfur content typically of at most 15 ppm or 10 ppm by weight. Thus the cutting point between LCN and MCN gasoline cuts may be between 50 ° C and 68 ° C and preferably between 50 and 65 ° C. In a preferred embodiment, the LCN light cut is a C 5 ^- hydrocarbon cut, i.e. containing at most 5 carbon atoms.

According to a preferred embodiment, the HHCN heavy gasoline fraction drawn off at the bottom of the fractionation column or at the bottom of the second fractionation column if two columns are used to carry out the fractionation in three sections, generally contains hydrocarbons having 7 and more of 7 carbon atoms.

According to step b) of the process according to the invention, the intermediate gasoline fraction MCN is desulfurized alone (ie without being mixed with any other hydrocarbon fraction) in the presence of a hydrodesulfurization catalyst and with hydrogen, at a temperature between 160 and 450 ° C, at a pressure between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to convert the sulfur-containing products into H ₂ S.

This hydrodesulphurization step is aimed in particular at converting the mercaptans, sulphides and thiophenics compounds present in the MCN intermediate gasoline fraction into H ₂ S.

During this step b) the reaction of recombinant mercaptans formation is also carried out by addition of the H ₂ S formed on the olefins. In general, recombinant mercaptans have higher boiling temperatures than the olefins from which they are derived. For example, 2-methyl-2-pentene (normal boiling point under normal conditions: 67 ° C) can form a recombinant mercaptan with 5 carbon atoms such as 2-methyl-2-penthanethiol (d-point). boiling in pure body under normal conditions: 125 ° C).

• soit une coupe plus lourde que la coupe essence intermédiaire MCN, telle que par exemple une partie de l'essence HHCN désulfurée récupérée à l'issue de l'étape d) décrite ci-dessous, est mélangée avec l'essence issue de l'étape b) et le mélange est fractionné selon l'étape c). Alternativement, la coupe lourde est envoyée dans la colonne de fractionnement de l'étape c) à un niveau situé en-dessous du point d'injection de la coupe essence intermédiaire MCN partiellement désulfurée.
• soit la colonne est opérée à reflux total en fond et avec un soutirage discontinu de la coupe de fond contenant les mercaptans (la colonne est alors dite de redistillation (Rerun Column selon la terminologie anglo-saxonne)).

This property is used to separate the recombination mercaptans from the partially desulfurized MCN intermediate cut according to step c) of the method. According to step c) of the process, the intermediate cut MCN after the hydrodesulphurization step b) is sent to a separation unit comprising at least one fractionation column which is designed and operated so as to provide at the top of the fractionation unit an intermediate gasoline MCN with low sulfur contents, that is to say typically less than 30 ppm by weight of sulfur and preferably less than 15 ppm by weight of sulfur and low content of mercaptans (preferably less than 15 ppm by weight expressed as sulfur). In order to recover the mercaptans at the bottom of the fractionation column, the latter is preferably operated according to two modes:

• a heavier cut than the intermediate gasoline fraction MCN, such as for example a part of the desulfurized HHCN gasoline recovered at the end of step d) described below, is mixed with the gasoline resulting from the step b) and the mixture is fractionated according to step c). Alternatively, the heavy cut is sent to the fractionation column of step c) at a level below the injection point of the partially desulphurized intermediate gasoline cutter MCN.
• either the column is operated at total reflux in the bottom and with a discontinuous withdrawal of the bottom section containing the mercaptans (the column is then called redistillation (Rerun Column according to the English terminology)).

In both cases, the stream containing the (recombinant) mercaptans withdrawn from the bottom of the column, continuously or discontinuously, can advantageously be treated by hydrodesulfurization in a mixture with the HHCN heavy gasoline.

According to the invention, step c) is carried out so that the intermediate head gasoline at low sulfur and mercaptan contents has substantially the same narrow distillation range as that of the intermediate gasoline fraction MCN before desulfurization step b), so that the recombination mercaptans, whose boiling temperatures are higher than those of the olefins from which they are derived, are drawn into the bottom of the distillation column. Thus, the intermediate gasoline at low sulfur and mercaptan content preferably has a temperature difference (ΔT) (temperature difference corresponding to 5% and 95% of the distilled mass (determined according to the described CSD method). in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) which is equal to the temperature difference (ΔT) of the intermediate gasoline fraction MCN of step a). Alternatively, the head cut has a temperature corresponding to 95% of the distilled mass (determined according to the CSD method described in document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) which is less than the maximum of 10 ° C relative to the temperature corresponding to 95% of the distilled mass of the intermediate gasoline section MCN of step a).

The process according to the invention may comprise a step of degassing H ₂ S and hydrogen (also referred to as "stabilization step") present in the effluent from step b) which may be performed before, during or after step c). In the case where the effluent of step b) has not undergone a degassing step to separate hydrogen and hydrogen sulfide before the fractionation of step c), these can be separated into head of the fractionation column c) which is operated so that stabilization and separation of mercaptans are then carried out simultaneously in the same column and in such a way that the intermediate gasoline with low sulfur and mercaptan contents is obtained by a lateral racking located near the head of this same column, typically some theoretical plates below.

In a preferred embodiment, when step a) produces three hydrocarbon cuts with a HHCN heavy cut, the HHCN heavy gasoline cut is desulfurized (step d) alone or in admixture with the bottom withdrawal of the fractionation column described in FIG. step c). Desulfurization of the HHCN section (alone or in mixture) can be carried out with one or two reactors in series. If the desulfurization is carried out with a single reactor, it is operated so as to obtain a desulphurized HHCN heavy gasoline with a sulfur content typically less than or equal to 30 ppm by weight and preferably less than or equal to 15 ppm by weight.

The desulfurization can also be carried out with two reactors in series, with or without an intermediate degassing step of the H ₂ S formed during the course in the first reactor. The reactors are operated so as to obtain after the second reactor a desulfurized HHCN gasoline with a sulfur content typically less than 30 ppm by weight and preferably less than or equal to 15 ppm by weight. The desulfurization of the heavy gasoline (alone or mixed with the bottom cut recovered in step c)) in one or two reactors in series, with or without an intermediate step of degassing the H ₂ S, is carried out in the presence of one or more hydrodesulfurization catalysts and hydrogen, at a temperature between 200 and 400 ° C, at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ .

With reference to the figure 1 which represents a particular embodiment of the invention, an olefinic gasoline feed for example a catalytic cracking gasoline described above is treated in an optional step which carries out the selective hydrogenation of the diolefins and the conversion (weighting) of part of the mercaptan compounds (SHRs) present in the charge in thioethers, by reaction with olefins. Typically mercaptans that can react during the optional selective hydrogenation step are the following (non-exhaustive list): methyl mercaptan, ethyl mercaptan, n-propyl mercaptan, iso-propyl mercaptan, iso-butyl mercaptan , tert-butyl mercaptan, n-butyl mercaptan, sec-butyl mercaptan, iso-amyl mercaptan, n-amyl mercaptan, α-methylbutyl mercaptan, α-ethylpropyl mercaptan, n-hexyl mercaptan 2-mercaptohexane.

For this purpose, the FRCN gasoline feedstock is sent via line 1 to a selective hydrogenation catalytic reactor 2 containing at least one fixed or mobile bed of a catalyst for the selective hydrogenation of diolefins and for increasing the mercaptans.

The reaction for selective hydrogenation of the diolefins and for increasing the weight of the mercaptans is preferably carried out on a sulfurized catalyst comprising at least one group VIII element (groups 8, 9 and 10 of the new periodic table). Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and possibly at least one element of group Vlb (group 6 of the new periodic Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and a support. The group VIII element is preferably chosen from nickel and cobalt and in particular nickel. The group VIb element, when present, is preferably selected from molybdenum and tungsten and very preferably molybdenum.

The catalyst support is preferably selected from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Alumina and, more preferably, high purity alumina are preferably used.

According to a preferred embodiment, the selective hydrogenation catalyst contains nickel with a content by weight of nickel oxide (in NiO form) of between 4 and 12%, and molybdenum with a content by weight of molybdenum oxide. (in MoO3 form) of between 6% and 18% and a nickel / molybdenum molar ratio of between 1 and 2.5, the metals being deposited on a support consisting of alumina and whose sulphidation rate of the metals constituting the catalyst being greater than 80%.

In the optional step of selective hydrogenation, the gasoline to be treated is typically brought into contact with the catalyst at a temperature of between 50 ° C. and 250 ° C., and preferably between 80 ° C. and 220 ° C., and even more preferably between 90 ° C and 200 ° C, with a liquid space velocity (LHSV) of between 0.5 h ^-1 and 20 h ^-1 , the unit of the liquid space velocity being the liter of charge per liter of catalyst and per hour (l / lh). The pressure is between 0.4 MPa and 5 MPa, preferably between 0.6 and 4 MPa and even more preferably between 1 and 2 MPa. The optional step of selective hydrogenation is typically carried out with an H2 / HC ratio of between 2 and 100 Nm ³ of hydrogen per m ³ of filler, preferably between 3 and 30 Nm ³ of hydrogen per m ³ of filler.

The entire charge is usually injected at the reactor inlet. However, it may be advantageous in some cases to inject a fraction or the entire charge between two consecutive catalytic beds placed in the reactor. This embodiment makes it possible in particular to continue operating the reactor if the inlet of the reactor is clogged by deposits of polymers, particles, or gums present in the load.

With reference to the example of figure 1 , an effluent with low levels of diolefins and mercaptans is withdrawn from the reactor 2 by the line 3 and is sent, according to step a), in a fractionation column 4 (or splitter according to the English terminology) configured to separate the gasoline in two sections: a light gasoline cut LCN (or light gasoline) and an intermediate heavy cut (or intermediate heavy gasoline) HCN which is constituted by the heavy fraction complementary to the light gasoline. The final boiling point of the light cut is chosen so as to provide a light gasoline cut with a low sulfur content (total sulfur content typically less than 30 ppm by weight and preferably less than 10 ppm by weight) without requiring a step of subsequent hydrodesulfurization. Thus, preferably, the LCN light gasoline cut is a C 5 ^- hydrocarbon cut (ie containing hydrocarbons having 5 and less than 5 carbon atoms per molecule).

The intermediate heavy gasoline cut HCN 6 which is preferably a C6 ⁺ cut (ie containing hydrocarbons having 6 and more than 6 carbon atoms per molecule) is, according to step a) of the process, sent to a fractionation column. 7 configured to separate an intermediate gasoline fraction MCN characterized by a narrow distillation range, that is to say for which the difference of temperatures corresponding to 5% and 95% of the distilled mass (determined according to the simulated distillation method "CSD" described in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) is less than or equal to 60 ° C, preferably between 20 ° C and 60 ° C and even more preferably between 25 ° C and 40 ° C. In a preferred embodiment, the temperature corresponding to 5% of the distilled mass of the intermediate gasoline fraction MCN is between 50 ° C. and 68 ° C. and the temperature corresponding to 95% of the distilled mass of the intermediate gasoline fraction CMN. is between 88 ° C and 110 ° C. The intermediate gasoline fraction MCN, for example has temperatures corresponding to 5% and 95% of the distilled mass of respectively 60 ° C and 100 ° C or respectively 65 ° C and 100 ° C or respectively 55 ° C and 90 ° C. The intermediate gasoline fraction MCN may contain hydrocarbons having from 5 to 7 carbon atoms and predominantly hydrocarbons with 6 carbon atoms.

As shown on the figure 1 the intermediate gasoline cut MCN is withdrawn by the line 8 while the complementary heavy bottom cut, called HHCN is extracted from the fractionation column 7 by the line 10.

• le 2-méthyl-2-propanethiol (Température normale d'ébullition = 64°C),
• le méthyl-ethyl-sulfure (Température normale d'ébullition = 67°C),
• le propanethiol (Température normale d'ébullition = 68°C),
• le thiophène (Température normale d'ébullition = 84°C),
• le 2 méthyl-1-propanethiol (Température normale d'ébullition = 88°C)
• le di-éthyl-sulfure (Température normale d'ébullition = 92°C),
• le thiacyclobutane (Température normale d'ébullition = 95°C),
• le 1-butanethiol (Température normale d'ébullition = 98°C),
• le 2 méthyl-2-butanethiol (Température normale d'ébullition = 99°C)

The head section 8 (intermediate gasoline section MCN) still contains sulfur compounds of the mercaptan, sulphide and thiophene type. Depending on the cutting points chosen, these sulfur compounds may be, for example:

• 2-methyl-2-propanethiol (normal boiling point = 64 ° C),
• methyl ethyl sulfide (normal boiling temperature = 67 ° C),
• propanethiol (normal boiling temperature = 68 ° C),
• thiophene (normal boiling temperature = 84 ° C),
• 2-methyl-1-propanethiol (normal boiling point = 88 ° C)
• diethyl sulfide (normal boiling temperature = 92 ° C),
• thiacyclobutane (normal boiling temperature = 95 ° C),
• 1-butanethiol (normal boiling temperature = 98 ° C),
• 2-methyl-2-butanethiol (normal boiling temperature = 99 ° C)

According to the invention, the head cut 8 (intermediate cut MCN) is treated in a step b) selective hydrodesulfurization (selective HDS). This step aims, using a catalyst described below and hydrogen, to convert into H ₂ S and hydrocarbons the sulfur compounds of the intermediate gasoline section MCN.

The hydrocarbon cut 8 (intermediate essence cut MCN) is brought into contact with the hydrogen supplied by the line 9 and a selective HDS catalyst in at least one hydrodesulfurization unit 11 which comprises at least one bed reactor stationary or mobile catalyst. The hydrodesulfurization reaction is generally carried out at a temperature of between 160 ° C. and 450 ° C. under a pressure of between 0.5 and 8 MPa. The liquid space velocity is generally between 0.5 and 20 h ^-1 (expressed in volume of liquid per volume of catalyst and per hour), preferably between 1 and 8 h ^-1 . The H ₂ / intermediate gasoline MCN ratio is adjusted according to the desired hydrodesulphurization rates in the range of 50 to 1000 normal m ³ per m ³ at standard conditions. Preferably, the mixture of the intermediate gasoline fraction MCN with the hydrogen brought into contact with the catalyst in step b) is entirely in the vapor phase. Preferably the temperature is between 200 ° C and 400 ° C, and very preferably between 200 ° C and 350 ° C. Preferably the pressure is between 1 and 3 MPa.

The selective HDS catalyst used in sulphide form, comprises at least one element of group VIII (groups 8, 9 and 10 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ), at least one element of group Vlb (group 6 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and a support. The group VIII element is preferably chosen from nickel and cobalt and in particular cobalt. The group VIb element is preferably selected from molybdenum and tungsten and very preferably molybdenum. The catalyst may for example be a catalyst as described in the patents FR2840315 , FR2840316 , FR2904242 or FR3023184 .

The catalyst support is preferably selected from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Alumina is preferably used.

It should be noted that the hydrogen provided by the line 9 may be fresh hydrogen (make-up according to English terminology), or hydrogen said "recycle" from a process step, in particular of step d). Preferably the hydrogen of line 9 is fresh hydrogen.

The hydrodesulfurization step b) generates in the reactor 11 hydrogen sulphide (H ₂ S) which reacts with the olefins of the intermediate cut MCN to form so-called recombinant mercaptans which, when they are not removed, are responsible for the presence of residual sulfur in the partially desulphurized intermediate CMN cut. This reduction in the content of recombinant mercaptans could be achieved by catalytic hydrodesulphurization by means of an additional reactor or by employing a second catalytic bed but at the cost of hydrogenation of the mono-olefins present in the intermediate cut MCN and which would then have as a result a sharp decrease in the octane number of said cut and a surplus of hydrogen consumption.

According to stage c) of the process according to the invention, the effluent resulting from stage b) is sent to a fractionation column 13 designed and operated to separate at the top of the column an intermediate gasoline 14 with a low sulfur content and low mercaptans content (recombinant), that is to say with a sulfur content typically less than 30 ppm by weight and a mercaptan content typically less than 15 ppm by weight and a bottom section which contains sulfur compounds mercaptans type generated in step b) and whose boiling point is higher than the boiling point of the intermediate gasoline section MCN from the fractionation step a).

Preferably, the head cut 14 withdrawn from the column 13 has a narrow distillation interval corresponding to that of the intermediate gasoline section MCN recovered in step a), that is to say characterized by a difference in temperature (ΔT) (difference between the temperatures corresponding to 5% and 95% of the distilled mass determined according to the simulated distillation method "CSD" described in document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) which is substantially equal to the temperature difference (ΔT) of the intermediate gasoline section MCN from step a).

According to another operating mode, the head cut withdrawn at the top of the column 13 is characterized by a temperature corresponding to 95% of the distilled mass (determined according to the simulated distillation method "CSD" described in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ) which is less than the maximum of 10 ° C relative to the temperature corresponding to 95% of the distilled mass of the intermediate gasoline section MCN from step a).

Thus, when the head section has a temperature difference (ΔT) which is substantially equal to or less than that of the MCN section from which it is derived, said head section contains a very low content of recombinant mercaptans because the latter, which have usually a boiling temperature higher than the final temperature of the head cut, are trained in the bottom cut.

As stated in the figure 1 step c) can be carried out by employing a so-called redistillation column (Rerun Column according to the English terminology) which is operated at total reflux in the bottom and with a discontinuous withdrawal of the bottom section containing the recombinant mercaptans. . Note also that in the example of figure 1 the fractionation column 13 is designed and operated to concomitantly carry out the degassing of the H ₂ (unreacted) and the H ₂ S which are withdrawn (via the line 14 ') from the top of the fractionation column and the separation of the intermediate gasoline at low sulfur and mercaptan contents which is withdrawn by a near side withdrawal, typically a few theoretical trays below the head of this same column.

Alternatively, as also represented in figure 1 a heavier cut than the intermediate essence cut MCN can also be used in step c) to facilitate the training of the recombinant mercaptans at the bottom of the column. This heavier cut 25 may either be mixed with the partially desulfurized intermediate cut from step b) or may be directly injected into column 13 below the point of entry of the partially desulfurized intermediate cut 12. Preferably the heavier cut will be part of the desulphurized HHCN cut, stabilized or not, recycled by line 25.

The stream withdrawn from the bottom of the column 13 (via the line 15) can either directly feed the reactor 16 of the selective hydrodesulfurization unit or be mixed with the HHCN section. (from step a) and the mixture being sent to the selective hydrodesulfurization unit.

When the stream withdrawn from the bottom of the column 13 is sent directly into the hydrodesulfurization reactor, it can be injected between two catalytic beds of the reactor 16 so that it is used as a quenching fluid (Quench according to the English terminology). ). This step d) of selective hydrodesulphurization thus makes it possible to convert the sulfur compounds of the HHCN section and the recombination mercaptans formed in the hydrodesulfurization step b) into H ₂ S and hydrocarbons. The selective hydrodesulphurization step d) is carried out in the presence of hydrogen brought by line 17 and a selective hydrodesulfurization catalyst which comprises at least one element of group VIII (groups 8, 9 and 10 of the new classification periodic Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ), at least one element of group Vlb (group 6 of the new periodic table Handbook of Chemistry and Physics, 76th Edition, 1995-1996 ) and a support. The group VIII element is preferably chosen from nickel and cobalt and in particular cobalt.

The group VIb element is preferably selected from molybdenum and tungsten and very preferably molybdenum. The catalyst may for example be a catalyst as described in the patents FR2840315 , FR2840316 , FR2904242 or FR3023184 .

The hydrodesulfurization reaction is generally carried out at a temperature of between 200 ° C. and 450 ° C. under a pressure of between 0.5 and 8 MPa. The liquid space velocity is generally between 0.5 and 20 h ^-1 (expressed in volume of liquid per volume of catalyst and per hour), preferably between 1 and 8 h ^-1 . The H2 / HHCN cut ratio which is adjusted according to the desired hydrodesulphurization rates is in the range of between 50 and 1000 normal m ³ per m ³ at standard conditions.

Preferably the temperature is between 200 ° C and 400 ° C, and very preferably between 200 ° C and 350 ° C. Preferably the pressure is between 0.5 and 3 MPa.

At the end of step d), a hydrocarbon fraction HHCN desulphurized, which typically has a total sulfur content of less than 30 ppm by weight, is withdrawn from the selective hydrodesulfurization unit via line 18, preferably less than 15 ppm by weight.

This desulfurized HHCN hydrocarbon fraction advantageously constitutes a base for the formulation of gasoline type fuel alone or mixed with the LCN light gasoline fraction and / or the intermediate gasoline with low levels of sulfur and mercaptans.

The figure 2 represents another embodiment of the method according to the invention which differs from that of the figure 1 by the implementation of an optional step of intermediate hydrodesulfurization when step a) makes it possible to separate the gasoline feed into three hydrocarbon cuts by means of the two fractionations in two cuts. In this case, a first fractionation is carried out in such a way that two cuts are obtained: the LCN light petrol cut and an HCN heavy gasoline intermediate cut. The HCN heavy intermediate cut is then at least partially desulphurized in the optional hydrodesulphurization step and then fractionated in the second fractionation column to obtain the intermediate gasoline fraction MCN and the HHCN heavy gasoline fraction at the bottom of this same column.

This mode of operation has the advantage of partially desulphurizing the heavy gasoline HCN intermediate cut and thus to operate the hydrodesulphurization steps b) and d) under operating conditions less severe than those required in the same reactors in the case of the Figure 1 so as to limit the hydrogenation of the olefins.

With reference to the figure 2 the HCN intermediate heavy gasoline fraction is treated in a hydrodesulfurization unit which comprises at least one reactor 19 equipped with a fixed or mobile bed of hydrodesulfurization catalyst. As with any hydrodesulfurization treatment, the HCN cut is contacted with hydrogen and the catalyst.

The effluent HCN withdrawn from the reactor 19 is then, in accordance with step a) of the process according to the invention, fractionated in column 7 to produce the intermediate gasoline fraction MCN and the heavy fraction HHCN. Steps b) to d) are identical to those described with reference to the figure 1 .

The figure 3 represents another exemplary embodiment of the process according to the invention wherein step d) is carried out in a selective hydrodesulfurization unit comprising two reactors 16 and 24 arranged in series. Such a unit can be operated with or without an intermediate degassing step of the H ₂ S formed in the first reactor 16 of the series. Preferably step d) is carried out with an intermediate degassing step of H ₂ S.

As stated in figure 3 , the effluent 18 withdrawn from the first hydrodesulphurization reactor 16 is sent to a unit 20 configured to separate the H ₂ S from the effluent 18. In the example of the figure 3 the effluent 18 is brought into contact with a gas such as hydrogen (supplied via line 26) in a stripping column of the H ₂ S from which a gas stream 21 containing hydrogen and H ₂ S and at the bottom of column an effluent 22 purified H ₂ S. It should be noted that the gas stream 21 can be advantageously treated to separate hydrogen from H ₂ S so to produce a stream of purified hydrogen which can be recycled to a hydrodesulfurization unit, for example in the first hydrodesulphurization reactor 16. For the H ₂ S removal step it is also possible to use in place of a stripping unit, an absorption device using, for example, amines.

The H ₂ S purified effluent 22 is then sent to a second hydrodesulfurization reactor 24 in which it is brought into contact with hydrogen (line 23) and a selective hydrodesulfurization catalyst as already described above. to produce a HHCN hydrocarbon fraction with a very low sulfur content. It should be noted that the bottom section of the fractionation column described in step c) can be sent either to the inlet of the reactor 16 or to the inlet of the reactor 24 to be desulfurized.

It should be emphasized that step d) can of course employ a selective hydrodesulfurization unit comprising more than two reactors arranged in series, which is implemented with or without the H ₂ S elimination step of the effluent between two successive stages of hydrodesulfurization.

The figure 4 shows another embodiment of the process according to the invention in which the step a) of fractionation of the gasoline in three sections is carried out in a single fractionation step, by means of a divided wall distillation column or " Divided Wall Column "according to Anglo-Saxon terminology. This type of column is well described in the literature for example in the publication Chemical Engineering and Processing, 49 (2010) pp 559-580 . By way of example, this type of column makes it possible to separate three products of different volatility in a single fractionation column instead of using two columns in series, which saves energy and investment costs. . Licences US 2003/0116474 A1 , US 6,927,314 B1 and US 7,947,860 B2 illustrate applications of this type of column for splitting species into at least 3 sections.

The principle of a divided wall column is to install inside a fractionation column, a vertical wall in a vertical median part of the column. This partition wall extends between opposite sides of the inner surface of the column. A seal installed between the vertical wall and the inner surface of the column seals the divided wall so that the fluids can not pass horizontally from one side of the column to the other. The inner vertical wall divides the central portion of the column into two parallel zones or fractionation chambers (equivalent to two fractionation columns). Each fractionation zone may contain conventional vapor-liquid contact equipment such as trays, packings or both, depending on the design of the column.

In the embodiment of the figure 4 the column 27 comprises two fractionating chambers 28 and 28 'separated by a vertical partition wall 29 arranged in a central section of the column which extends over both a portion of the rectification section and a portion of the section of exhaustion of the column. From the column of divided-wall distillation 27, the LCN light gasoline cut 5 at the head of the column is withdrawn directly, the heavy gasoline cut HHCN 10 at the bottom of the column and the intermediate gasoline cutter MCN 8 by means of a side withdrawal located in a fractionating chamber. 28.

The figure 5 represents an alternative embodiment of the process in which the three-slice fractionation step a) is carried out in two stages with two fractionation columns, the second column of which is a divided-wall distillation column and in which step c) Fractionation of the MCN cut containing recombinant mercaptans is also performed in the split-wall distillation column.

With reference to the figure 5 , the gasoline charge 1, after the optional selective hydrogenation step is fractionated in a first column 4 configured to separate the LCN light gasoline cut 4 at the head of the column and the HCN 6 heavy gasoline intermediate cut at the bottom of the column. The intermediate heavy gasoline cut HCN 6 is then sent to a divided wall distillation column 30 which comprises two fractionating chambers 31 and 31 'which are separated by a vertical wall 32 which extends both over the entire rectification section and possibly also on a portion of the depletion section of the column. Examples of principle of this type of column are illustrated in the patents US 5,755,933 , US 3,314,879 , US 3,412,016 .

As indicated on the figure 5 , the HCN charge 6 is sent into the fractionation chamber 31 from which the intermediate gasoline fraction MCN 8 is extracted at the head of said chamber 31. The intermediate gasoline fraction MCN 8 is then desulphurized in the hydrodesulphurization reactor 11, according to step b). The effluent 12 from the reactor 11 is sent via the line 33 into the second fractionation chamber 31 'of the column 30 which is operated to separate the mercaptan-type sulfur compounds so as to produce a low-sulfur intermediate gasoline MCN. and in mercaptans which is withdrawn at the top of the fractionation chamber 31 '. The mercaptans are then drawn into the exhaustion section of the chamber 31 'and withdrawn mixed with the HHCN cut at the bottom of the column via line 29. The heavy gasoline cut HHCN loaded with sulfur compounds is, according to step d) , hydrodesulphurized to provide a low sulfur HHCN cut.

Example : Hydrodesulfurization of an FCC gasoline according to the example of Figure 1

Table 1 presents the characteristics of an FCC gasoline processed by the process according to figure 1 of the present invention. In this example results are presented without the implementation of the selective hydrogenation reactor 2.

An FRCN gasoline is fractionated to obtain a light LCN gasoline cut and an HCN heavy gasoline cut. The HCN intermediate heavy gasoline fraction is then fractionated, as proposed according to the invention, into an intermediate gasoline fraction MCN and a heavy gasoline HHCN. The methods of analysis used to characterize the charges and effluents are as follows:
• Density according to the method NF EN ISO 12185
• Sulfur content according to ASTM D2622 for contents greater than 10 ppm S and ISO 20846 for contents less than 10 ppm S.
• Distillation according to CSD simulated distilling method "CSD" described in the document Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 .
• The high octane content of olefins is measured indirectly by ASTM D1159, the so-called bromine number. Table 1: Characteristics of FCC HCN, CMN and HHCN sections of Figure 1 Line 6 HCN Line 8 CMN Line 10 HHCN Density at 15 ° C (g / cm ³ ) 0791 0711 0.82 Organic sulfur content (ppm S) 1279 481 1543 Mercaptans content (ppm S) Simulated Distillation 13 23 10 5% distilled mass (° C) 69 58 100 10% distilled mass (° C) 74 62 111 30% distilled mass (° C) 113 72 140 50% distilled mass (° C) 143 75 162 70% distilled mass (° C) 172 83 182 90% distilled mass (° C) 207 96 208 95% distilled mass (° C) 220 100 218 99.5% distilled mass (° C) 235 104 233

According to the example of the figure 1 the intermediate gasoline cut MCN is a cut whose temperature at 5% of distilled mass is 58 ° C. and the temperature at 95% of distilled mass is 100 ° C. (points determined according to the simulated distillation method "CSD" described in the scientific literature ( Oil Gas Sci. Technol. Flight. 54 (1999), No. 4, pp. 431-438 ).

For this intermediate gasoline fraction MCN, the temperature difference between the points at 5% and 95% distilled mass is therefore 42 ° C.

As shown in the example of the figure 1 the intermediate gasoline fraction MCN is mixed with hydrogen and treated in a selective hydrodesulphurization unit (reactor 11) in the presence of a CoMo catalyst supported on alumina (HR806 sold by the company Axens). The temperature is 240 ° C, the pressure is 2 MPa, the liquid space velocity (expressed in volume of liquid per volume of catalyst and per hour) is 4 h ^-1 , the ratio H2 / cut MCN is 360 normal liters per liter under standard conditions. The characteristics of the partly desulphurized intermediate gasoline MCN cut are shown in Table 2.

The HHCN heavy gasoline cut is mixed with hydrogen and treated in a selective hydrodesulfurization unit (reactor 16) in the presence of a CoMo catalyst supported on alumina (HR806 sold by the company Axens). The temperature is 298 ° C, the pressure is 2 MPa, the liquid space velocity (expressed in volume of liquid per volume of catalyst and per hour) is 4 h ^-1 , the ratio H2 / cutting intermediate gasoline MCN is 360 normal m ³ per m ³ under standard conditions. The characteristics of the partially desulfurized HHCN section are shown in Table 2.

The partially desulphurized intermediate gasoline fraction MCN (line 12) is mixed with a fraction of the desulfurized HHCN heavy gasoline fraction and sent to a fractionation column (13) (according to step c) of the invention), the cutting point at 100 ° C.

Partially desulfurized MCN gasoline with a low recombinant mercaptan content (line 14) is recovered at the top of fractionator 13. The characteristics of intermediate gasoline (line 14) after stabilization are shown in Table 2 . Table 2: Characteristics of CMN, intermediate gasoline and HHCN cuts according to Figure 1 MCN Line 12 partially desulphurized Line 14 Stabilized intermediate gas and desulfurized Line 18 partially desulfurized HHCN Total organic sulfur content (ppm S) 104 10 10 Mercaptan content (ppm S) 98 4 8 Bromine index (g / 100g) 87 87 19

The process according to the invention thus makes it possible to produce an intermediate gasoline after the hydrodesulphurization (step b) and fractionation (step c) stages with a low total sulfur content and with a mercaptan content of less than 10 ppm weight expressed in equivalent. sulfur and this by limiting the hydrogenation of olefins.

It is noted that before the hydrodesulphurization stage, the intermediate gasoline fraction MCN has a total organic sulfur content of 481 ppm by weight sulfur, of which 13 ppm by weight sulfur of mercaptans. The MCN effluent after the desulfurization step has a total organic sulfur content of 104 ppm sulfur, the major part of which is below recombinant mercaptans (98 ppm sulfur).

Thanks to fractionation step c), which is carried out judiciously so as to recover an intermediate gasoline with a narrow distillation range, an intermediate gasoline is obtained which is at the same time low in total organic sulfur (10 ppm sulfur weight). ) and mercaptans (4 ppm sulfur weight). The method according to the invention thus makes it possible to respond to two constraints namely to provide a gasoline cut with low mercaptan content (recombination) and with a loss of limited octane number.

Claims (15)

A process for treating a gasoline containing sulfur compounds, olefins and diolefins, the process comprising the steps of: a) the gasoline is fractionated so as to recover at least one intermediate gasoline fraction MCN comprising hydrocarbons and whose temperature difference (ΔT) between the points at 5% and at 95% of distilled mass is less than or equal to 60 ° VS; b) the intermediate gasoline fraction MCN is desulfurized alone and in the presence of a hydrodesulfurization catalyst and hydrogen, at a temperature of between 160 and 450 ° C., at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio of the flow rate of hydrogen expressed in normal m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 and Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce a partially desulphurized intermediate gasoline fraction MCN; and c) fractionating in a fractionation column the partly desulfurized intermediate gasoline fraction MCN that has not undergone catalytic treatment subsequent to step b) so as to recover at the column head an intermediate gasoline with low sulfur contents and mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans. The method of claim 1, wherein: a) the gasoline is split into at least: • a light LCN petrol cut; • an intermediate gasoline cut MCN comprising hydrocarbons and whose temperature difference (ΔT) between the points at 5% and 95% of distilled mass is less than or equal to 60 ° C; and • a HHCN heavy gasoline cutter containing hydrocarbons; b) the intermediate gasoline fraction MCN is desulfurized alone and in the presence of a hydrodesulfurization catalyst and hydrogen, at a temperature of between 160 and 450 ° C., at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio of the flow rate of hydrogen expressed in normal m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 and Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce an at least partially desulphurized intermediate gasoline fraction MCN; c) fractionating in a fractionation column the partly desulfurized intermediate gasoline fraction MCN that has not undergone catalytic treatment subsequent to step b) so as to recover at the column head an intermediate gasoline with low sulfur contents and mercaptans and at the bottom of the column a hydrocarbon cut containing sulfur compounds including mercaptans; d) the heavy gasoline fraction HHCN is desulphurized alone or in admixture with the bottom hydrocarbon fraction resulting from stage c) in the presence of a hydrodesulphurization catalyst and with hydrogen, at a temperature of between 200 and 400 ° C. , at a pressure of between 0.5 and 8 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in normal m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 50 Nm ³ / m ³ and 1000 Nm ³ / m ³ so as to produce a heavy cut HHCN at least partially desulfurized. Process according to claims 1 or 2, wherein the intermediate gasoline fraction MCN has a temperature difference (ΔT) between the temperatures corresponding to 5% and 95% of the distilled mass, which is between 20 ° C and 60 ° C and more preferably between 25 and 40 ° C. Process according to one of Claims 2 and 3, in which step a) is carried out in two fractionation steps: a1) the gasoline is split into a light LCN gasoline cut and an HCN heavy gasoline intermediate cut; a2) the HCN intermediate heavy gasoline fraction is fractionated into at least one intermediate gasoline fraction MCN and a heavy gasoline fraction HHCN. The process according to claim 4, wherein the HCN heavy gasoline intermediate cut from step a1) is desulphurized prior to the fractionation step a2). Method according to one of claims 2 to 3, wherein step a) is carried out in a single fractionation step. The process of claim 6 wherein step a) is carried out in a divided wall distillation column. A process according to claim 4, wherein step a2) is carried out in a divided wall distillation column and wherein the partially desulfurized intermediate gasoline fraction CMN from step b) is fractionated in said divided wall distillation column . Method according to one of the preceding claims, wherein the intermediate gasoline fraction MCN of step a) has temperatures corresponding to 5% and 95% of the distilled mass which are respectively between 50 and 68 ° C and between 88 and 110 ° C. Process according to one of the preceding claims, in which the intermediate gasoline with low sulfur and mercaptan content resulting from stage c) has a temperature difference (ΔT) between the temperatures corresponding to 5% and 95% of the distilled mass which is equal to the difference in temperature (ΔT) of the intermediate gasoline fraction MCN from step a). Process according to one of Claims 1 to 9, in which the intermediate gasoline with low sulfur and mercaptan content resulting from stage c) has a temperature corresponding to 95% of the distilled mass which is less than the maximum of 10%. ° C relative to the temperature corresponding to 95% of the distilled mass of the intermediate gasoline section MCN of step a). Process according to one of Claims 2 to 11, in which step d) uses a first and a second hydrodesulfurization reactor arranged in series. The process according to claim 12, wherein the effluent from the first hydrodesulfurization reactor is stripped of the H ₂ S before being treated in the second hydrodesulfurization reactor. Process according to one of Claims 2 to 13, in which a portion of the heavy gasoline HHCN desulfurized cut obtained from step d) is recycled to stage c). Process according to one of the preceding claims, wherein before step a) the gasoline is treated in the presence of hydrogen and of a selective hydrogenation catalyst so as to hydrogenate diolefins and carry out an increase reaction of a part of the sulfur compounds, step a) being carried out at a temperature of between 50 and 250 ° C., at a pressure of between 1 and 5 MPa, with a liquid space velocity of between 0.5 and 20 h ^-1 and with a ratio between the flow rate of hydrogen expressed in m ³ per hour and the charge rate to be treated expressed in m ³ per hour at standard conditions of between 2 Nm ³ / m ³ and 100 Nm ³ / m ³ .

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