METHOD FOR TREATMENT OF A PYROLYTIC GASOLINE

Abstract

A process for treating pyrolysis gasoline containing diolefins and sulfur compounds comprising: a) selective hydrogenation of the diolefins in said feedstock in the presence of hydrogen and a catalyst producing an effluent depleted in diolefins; b) selective weighting of the light sulfur compounds in the presence of hydrogen and a catalyst, said step b) being carried out after step a) or step c), or between two steps c), or during step e); c) separation of the effluent from step a) or step b) so as to obtain a gaseous stream and a liquid stream, said step c) being carried out before and / or after step b); d) recycling to step a) of a portion of the liquid stream from step c); e) a fractionation located downstream of steps a) and c), allowing the separation of a light gasoline cut having a sulfur content of less than 10 ppm by weight.

Description

Title of the invention: METHOD FOR TREATING A PYROLYSIS GASOLINE Technical field

[0001] The present invention relates to the treatment of a C5+ hydrocarbon feedstock containing diolefins and sulfur compounds. The method makes it possible to treat, in particular, gasoline-type hydrocarbon cuts in order to improve their quality so that they can be recovered, for example, in the gasoline pool or in an aromatic unit of the refinery. The method applies in particular to hydrocarbon feedstocks designated by the term "pyrolysis gasoline" which can be obtained by thermal conversion processes. Prior art

[0002] The various pyrolysis processes such as steam cracking, visbreaking or coking lead to the formation of gasolines, also called pyrolysis gasolines or “pygas” in English terminology, which do not meet the specifications.

[0003] Pyrolysis gasolines in fact contain gum-generating compounds which are diolefins mixed with monoolefinic compounds and aromatic compounds. For these gasolines it is therefore necessary to selectively hydrogenate these diolefins and possibly the alkenylaromatic compounds without hydrogenating the monoolefins and the aromatic nuclei through a step which is also called selective hydrogenation, before treating them catalytically in order to eliminate the other impurities (e.g. heavy metals and sulfur) contained.

[0004] For example, for a C5 - 200°C hydrocarbon cut, the operating conditions of this first stage are generally between 80 and 160°C (depending on the catalyst used) and under a total pressure of between 2 and 3.5 MPa. The most widespread catalysts for selective hydrogenation are based on palladium or nickel. This first stage produces a hydrocarbon cut free of diolefins but rich in aromatic compounds and monoolefinic compounds as well as sulfur compounds. It is advisable to treat the hydrocarbon cut in order to lower the content of monoolefinic and sulfur compounds before the aromatics extraction stage, for example. The hydrogenation of olefins and the decomposition of sulfur compounds generally involves two separate catalysts: the first to hydrogenate the monoolefins into paraffins, and the second to hydrogenolyze the sulfur compounds.For example, the hydrogenation of monoolefins uses supported catalysts with a bimetallic nickel / molybdenum or nickel / tungsten sulfide active phase. For the hydrogenolysis of sulfur compounds, generally- . ration of supported catalysts having a bimetallic cobalt / molybdenum sulfide active phase. The sulfur compounds include thiophenic products which are known to be refractory to the hydrogenolysis reaction, which makes it necessary to impose severe operating conditions (high temperature and hydrogen pressure). For example, for a C5 -200°C cut, the reaction takes place at an average temperature between 250 and 380°C, for a total pressure between 2.5 and 3.5 MPa.

[0005] This process also includes a step of separating the hydrogenated cuts to separate the C5 cut (intended for the gasoline pool) from the C6+ cut (intended for example for the extraction of aromatics). This step is carried out using a distillation column which is also called a "depentanizer" by those skilled in the art.

[0006] Patent FR3056598B1 describes a process for treating a pyrolysis gasoline containing monoolefinic, diolefinic and sulfur hydrocarbons improved in terms of energy consumption, comprising at least and in any order: a) a step in which the pyrolysis gasoline or a C6+ hydrocarbon cut from a pyrolysis gasoline is hydrotreated, in the presence of hydrogen and at least one hydrotreatment catalyst at a temperature between 220 and 380°C so as to produce a hydrotreated effluent;b) a step in which the pyrolysis gasoline or the hydrotreated effluent from step a) is separated when the latter is carried out before step b), in a separation column into a C5+ top hydrocarbon cut and a C6+ bottom hydrocarbon cut, said separation column comprising a reboiling section including two heat exchangers, at least one of the two exchangers being configured to carry out a heat exchange with a portion of the bottom cut which is recycled into the column via the reboiling section, and in which one of the two heat exchangers of the reboiling section is supplied with at least a portion of the hydrotreated effluent so as to provide a portion of the heat necessary for the operation of the reboiling section. ;

[0007] For economic reasons, refining units are increasingly required to process crude oils of lower quality, in particular with a high sulfur content (generally greater than 500 ppm by weight of sulfur) which generate products with high impurity contents which consequently condition the quality of the products obtained. Thus, the composition of sulfur compounds in the pyrolysis gasoline feedstock tends to increase. As a result, the C5 cut, also called light gasoline cut intended for the gasoline pool, sees its sulfur content increase and can no longer be directly integrated into this pool. This C5 cut must therefore be sent to a dedicated desulfurization unit before integrating it into the gasoline pool.

[0008] Thus, an aim of the present invention is to propose a method for treating a pyrolysis gasoline containing diolefinic compounds and concentrated in products sulfurs allowing the production of a desulfurized C5 cut, meeting the standards in terms of sulfur content which is generally less than or equal to 10 ppm by weight of sulfur while limiting the loss of research octane number, which can be directly integrated into the gasoline pool. Summary of the invention

[0009] The subject of the invention is a process for treating a pyrolysis gasoline feedstock containing diolefins and sulfur compounds, comprising the following steps: a) a step of selective hydrogenation of the diolefins of said feedstock in the presence of a flow comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element, carried out at an average temperature of between 40 and 200°C, a pressure of between 1 and 8 MPa, with a space velocity of between 0.5 and 100 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the flow rate of feedstock to be treated expressed in m3 per hour at standard conditions of between 100 Nm3 / m3 and 300 Nm3 / m3, producing an effluent depleted in diolefins;

[0010] b) a step of selectively weighting the light sulfur compounds in the presence of a flow comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element and a group VIB element, carried out at an average temperature of between 100 and 300°C, a pressure of between 1 and 8 MPa, with a space velocity of between 1 and 10 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the feed flow rate to be treated expressed in m3 per hour at standard conditions of between 5 Nm3 / m3 and 200 Nm3 / m3, producing an effluent comprising a light gasoline cut having a sulfur content of less than 10 ppm by weight; said step b) being carried out directly after step a), or directly after step c), or between two steps c), or even during step e);

[0011] c) a step of separating the effluent from step a) or from step b) so as to obtain a gaseous flow and a liquid flow, said step c) being carried out before and / or after step b);

[0012] d) a step of recycling to step a) a part of the liquid flow from step c);

[0013] e) a fractionation step in at least one fractionation column, located downstream of steps a) and c), allowing the separation of a light gasoline cut having a sulfur content of less than 10 ppm by weight and a heavy cut comprising products resulting from the weighting of the light sulfur compounds obtained by step b).

[0014] The process according to the invention thus makes it possible to produce a light C5 gasoline cut (comprising at least 90% by weight of hydrocarbons having 5 carbon atoms) with a sulfur content of less than 10 ppm by weight, while limiting the loss in research octane number (or RON for Research Octane Number according to Anglo-Saxon terminology) to 5 points at most, so that it can be directly integrated into a gasoline pool.

[0015] In the context of the invention, the term "selective weighting of light sulfur compounds" designates a catalytic reaction making it possible to selectively increase the boiling temperature of certain organosulfur compounds such as mercaptans boiling at the temperature of the C5 light gasoline cut, while limiting the hydrogenation of olefins. For example, mercaptans are converted into thioether-type compounds by reaction with monoolefinic compounds. Thus, the sulfur compounds initially boiling at the temperature of the C5 light gasoline cut are found after selective weighting in the heavier cut (C6+ cut). This makes it possible to obtain a C5 light gasoline cut freed from most of its sulfur compounds after separation (step c) and fractionation (step e).

[0016] Step a) of selective hydrogenation is carried out before steps b), c) or e).

[0017] Step b) of selective weighting can be carried out after or during different steps of the process according to the invention. It can in particular be carried out after step a) of selective hydrogenation, after step c) of separation, or even during step e) of fractionation.

[0018] The separation step c) can be carried out before step b), or after step b), or even before and after step b) (two separation steps c)).

[0019] These different variants are described below.

[0020] In a first variant of the method according to the invention, step a) is carried out, then steps b), c), d) and e) successively. According to this variant, step b) is thus carried out directly after step a), then step c) is carried out after step b).

[0021] More particularly, according to this first variant, the effluent from step a) of selective hydrogenation of diolefins is directed directly to step b) of selective weighting. The term "directly" means in the context of the invention that the effluent from step a) does not undergo any physical or chemical treatment, it being understood that a thermal treatment is however possible between said steps. The effluent from step b) is then separated (step c) into a gaseous stream and a liquid stream using any device known to those skilled in the art such as for example a separator drum or a distillation column. A portion of said liquid stream resulting from the separation carried out on the effluent from step b) is then recycled to step a) according to step d) while the other portion is sent to fractionation step e) where the light gasoline cut with a low sulfur content is produced.

[0022] In a second variant of the method according to the invention, step a) is carried out, then steps c), b), c) and e) successively. According to this variant, step c) is thus carried out twice: it is carried out before and after step b). As for step b), it is therefore carried out between two steps c). More particularly, according to this second variant, the effluent from step a) is separated (first step c) into a gaseous stream and a liquid stream using any device known to those skilled in the art, such as, for example, a separator flask or a distillation column. Part of said liquid stream thus obtained is then recycled to step a) according to step d) while the other part is sent to step b), preferably together with at least part of the gaseous stream from separation step c). The effluent from step b) is then separated (second step c)) into a gaseous stream and a liquid stream using any device known to those skilled in the art, such as, for example, a separator flask or a distillation column.The liquid stream produced by the second separation of the effluent from step b) is then sent to step e) where the low-sulfur light gasoline cut is produced.

[0023] In a third variant of the method according to the invention, step a) is carried out, then steps c), b) and e) successively. According to this variant, step b) is thus carried out directly after step c).

[0024] More particularly, according to this third variant, the effluent from step a) is separated into a gaseous stream and a liquid stream (according to step c) using any device known to those skilled in the art, such as, for example, a separator flask or a distillation column. A portion of said liquid stream resulting from the separation of the effluent produced in step c) is then recycled to step a) according to step d) while the other portion of said liquid stream is sent to step b). The effluent from step b) is then sent to step e) where the light gasoline cut with a low sulfur content is produced.

[0025] In a fourth variant of the method according to the invention, step a) is carried out, then steps c) and e) successively, then step b) is carried out during step e).

[0026] More particularly, according to this fourth variant, the effluent from step a) is separated according to step c) into a gaseous stream and a liquid stream using any device known to those skilled in the art, such as, for example, a separator flask or a distillation column. A portion of said liquid stream resulting from the separation of the effluent produced in step c) is then recycled to step a) according to step d) while the other portion of said liquid stream is fractionated according to step e) of the process. In this variant, an intermediate gasoline comprising C5 and C6 hydrocarbons is produced in fractionation step e) and is then sent to step b). The effluent produced in step b) is sent to step e), either directly into the fractionation column, or mixed with the portion of said liquid stream obtained in step c) which is treated in step e).In this embodiment, an intermediate gasoline is withdrawn from the fractionation column of step e) between the feed point of the column and the withdrawal tray of the low sulfur C5 light gasoline. This intermediate gasoline. (cut which contains C5 and C6 hydrocarbons) is sent to step b) generating an effluent which is returned to step e). Step e) is therefore supplied on the one hand by a liquid flow from separation step c) and on the other hand by the effluent from step b).

[0027] According to one embodiment, said fractionation column of step e) is operated with a pressure of between 0.2 and 1.0 MPa, and with a temperature at the bottom of the column of between 110 and 190°C.

[0028] According to one embodiment, the flow rate of the recycled liquid stream in step d) represents between 50% and 500% of the flow rate of the load.

[0029] According to one embodiment, the catalyst of step a) is a catalyst comprising nickel or palladium.

[0030] According to one embodiment, the catalyst of step b) is a catalyst comprising nickel and molybdenum.

[0031] According to one embodiment, the pyrolysis gasoline feedstock has a sulfur content greater than 500 ppm by weight.

[0032] According to one embodiment, the pyrolysis gasoline is a gasoline from a steam cracking unit.

[0033] According to one embodiment, fractionation step e) is carried out so as to produce a gas stream comprising hydrogen and light compounds C1 to C4, said light gasoline cut having a sulfur content of less than 10 ppm by weight and a heavy cut comprising products resulting from the weighting of the light sulfur compounds obtained by step b).

[0034] According to one embodiment, the heavy cut from step e) is separated in a rectification step into a heavy gasoline cut and a middle distillate cut, then a hydrotreatment step is carried out on said heavy gasoline cut.

[0035] According to one embodiment, said hydrotreated heavy gasoline cut is sent to an aromatic extraction unit.

[0036] According to one embodiment, fractionation step e) is carried out so as to additionally produce an intermediate gasoline cut comprising C5 and C6 hydrocarbons.

[0037] According to one embodiment, said intermediate gasoline cut comprising C5 and C6 hydrocarbons is introduced into step b) in a mixture with a stream comprising hydrogen, then the effluent from step b) is returned to step e).

[0038] According to one embodiment, when step b) is carried out directly after step c) or during step e), a flow comprising hydrogen is injected upstream of step b).

[0039] According to one embodiment, the method comprises a first and second separation step c) carried out respectively before and after step b), and the gas flow obtained in the first separation step c) carried out before step b) is at least partly introduced into step b).

[0040] Within the meaning of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.

[0041] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a preferred range of pressure values ​​can be combined with a preferred range of temperature values.

[0042] In the remainder of the text, the expressions "between ... and..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this were not the case and the limit values ​​were not included in the range described, such precision will be provided by the present invention.

[0043] In this description, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements that are not mentioned. It is understood that the term "comprise" includes the exclusive and closed term "consist".

[0044] According to the present invention, the pressures are absolute pressures, also noted abs., and are given in absolute MPa (or MPa abs.), unless otherwise indicated.

[0045] In the following text, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII (or VIIIB) according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUP AC classification, and group VIB to the metals of column 6.

[0046] The metal content is measured by X-ray fluorescence.

[0047] In the present description, the term "Cx hydrocarbons" designates hydrocarbon compounds containing x carbon atoms. The term "Cx+ hydrocarbons" designates hydrocarbon compounds containing at least x carbon atoms. The term "C6+" is thus understood to designate a fraction containing hydrocarbons containing at least 6 and more than 6 carbon atoms per hydrocarbon molecule.

[0048] The term "monoolefin" and its derivatives designate hydrocarbon molecules comprising a single carbon-carbon double bond. The term "diolefin" and its derivatives designate hydrocarbon molecules comprising two carbon-carbon double bonds. The term "olefin" (without a prefix) means monoolefin, unless otherwise indicated.

[0049] The term “selective weighting of light sulfur compounds” designates a catalytic reaction allowing the selective increase of the boiling temperature of certain sulfur compounds such as mercaptans boiling at the temperature of the C5 light gasoline cut, by limiting the hydrogenation of olefins.

[0050] Throughout this text, all metal contents in the catalysts are expressed by weight in oxide form, except for platinum and palladium which are in metallic form. For a calcined catalyst, the metal content by weight in oxide form corresponds to the metal oxide content on the catalyst itself. List of figures

[0051] [Fig.l]

[0052] [Fig.l] is a representation according to the prior art of a process for treating a C5+ pyrolysis gasoline type hydrocarbon feedstock containing monoolefinic, diolefinic and sulfur hydrocarbons.

[0053] [Fig.2]

[0054] [Fig.2] shows a diagram of the method according to a first variant of the invention.

[0055] [Fig.3]

[0056] [Fig.3] shows a diagram of the method according to a second variant of the invention.

[0057] [Fig.4]

[0058] [Fig.4] shows a diagram of the method according to a third variant of the invention.

[0059] [Fig.5]

[0060] [Fig.5] shows a diagram of the method according to a fourth variant of the invention. Detailed description

[0061] The process according to the invention makes it possible to treat any hydrocarbon feedstock of the C5+ pyrolysis gasoline type containing monoolefinic, diolefinic and sulfur compounds while producing a light C5 gasoline cut with a low sulfur content.

[0062] With reference to [Fig.l] (prior art), the pyrolysis gasoline feedstock, introduced via line 1, is brought into contact with a hydrogen-rich gas stream, supplied via line 2. It is then introduced into a selective hydrogenation unit 3 implementing at least one selective hydrogenation reactor. The effluent produced by the selective hydrogenation unit is then sent via line 4 to a separation unit 5 in order to separate a gas stream 6 and a liquid stream. All or part of the hydrogen-rich gas stream 6 is purged. A first part of the liquid stream is recycled into the selective hydrogenation unit 3 via line 7. A second part of the liquid stream is sent using line 8 to a fractionation step 9.The fractionation stage 9 is composed of at least one fractionation column, called a depentanizer, configured and operated to separate at the top of the column a gaseous product 10, composed mainly of light gases such as hydrogen (H2) and hydrocarbons comprising 4 carbons or less. A cut. Light gasoline, composed mainly of C5 hydrocarbons, is withdrawn laterally and sent, for example, to the gasoline pool via line 11. The additional heavy C6+ hydrocarbon cut withdrawn at the bottom of the column is, for example, exported via line 12 to a deep hydrotreatment stage.

[0063] With reference to [Fig. 2] which shows a first variant of treatment of the pyrolysis gasoline according to the invention, the effluent produced in the selective hydrogenation step (step a) in at least one selective hydrogenation reactor 3 is sent directly via line 4 to a selective weighting step (step b)) using at least one selective weighting reactor 13. The effluent from the selective weighting step 13 is sent via line 14 to the separation step c). The separator 5 (ega separator flask or a distillation column) provides a gaseous stream 6 and a liquid stream which is distributed into two streams 7, 8; the stream 7 is directed according to step d) to the selective hydrogenation step in the unit 3 and the stream 8 is sent to one or more fractionation columns 9 to carry out step e) of the process in order to recover a gasoline cut 11 consisting essentially of C5 (comprising at least 90% by weight of hydrocarbons having 5 carbon atoms) with a low sulfur content and high research octane number, as well as a gaseous product 10 and a heavy C6+ cut 12. .

[0064] With reference to [Fig. 3] which shows a second variant of treatment of the pyrolysis gasoline according to the invention, the effluent produced in step a) from the selective hydrogenation unit 3 is separated in unit 5 (step c)) into a gaseous stream and a liquid stream. The liquid stream is partly recycled according to step d) in unit 3 (via line 7) and the other part of the liquid stream (line 8) is sent to the selective weighting unit 13 (step b)). It is noted that in [Fig. 3], the non-recycled liquid stream 8 to the unit 13 is sent mixed with the gas stream 6. The effluent from the selective weighting stage is sent via the pipe 14 to a second separator 18. All or part of the gas stream 16 from the separator 18 is purged from the unit while the liquid stream 17 is sent to the fractionation stage in at least one column 9 according to stage e).

[0065] With reference to [Fig. 4] which shows a third variant of treatment of the pyrolysis gasoline according to the invention, a part 8 of the liquid flow withdrawn from the separator 5 which carries out step c) is mixed with a hydrogen-rich flow 15 before being introduced into the selective weighting unit 13 (step b)). The effluent from step b) is sent via the pipe 14 to the fractionation step e) using at least one fractionation column 9. As for the other part 7 of the liquid flow, it is recycled into the selective hydrogenation unit 3 in accordance with step d).

[0066] With reference to [Fig.5] which shows a fourth variant of treatment of pyrolysis gasoline according to the invention. This embodiment differs from those presented above- high in figures 2, 3 and 4 by the fact that in fractionation step e) a cut called intermediate gasoline (stream 16) comprising C5 and C6 hydrocarbons is withdrawn between the light C5 gasoline cut 11 and the C6+ hydrocarbon cut 12. Said stream 16 is mixed with a hydrogen-rich stream 15 before being introduced into a selective weighting unit 13 carrying out step b). The effluent from step b) is returned via line 14 to the fractionation column 9 either directly into the column (as shown in [Fig.5]) or mixed with the liquid stream 8 (not shown).

[0067] The fractionation step is therefore supplied on the one hand by a part 8 of the liquid flow from step c) and on the other hand by the flow 14 which is the effluent from step b).

[0068] According to this embodiment, the weighting step b) is thus carried out at the same time as the fractionation step e), for example by means of a catalytic distillation column in order to carry out a reactive distillation. Charge

[0069] The feedstock of the process according to the invention comprises a pyrolysis gasoline. Pyrolysis gasoline is understood to mean a gasoline resulting from various pyrolysis processes such as steam cracking, visbreaking, coking and / or catalytic cracking. Preferably, the pyrolysis gasoline is a steam cracking gasoline, optionally in a mixture with one or more gasoline cuts resulting from coking, visbreaking and / or catalytic cracking processes.

[0070] Pyrolysis gasoline corresponds to a hydrocarbon fraction whose boiling point is generally between 0°C and 250°C, preferably between 10°C and 220°C, and very preferably between 20°C and 200°C. The unsaturated hydrocarbons present in said pyrolysis gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene, etc.), alkenylaromatic compounds (styrene, methylstyrene, etc.) and indenics (indene, etc.).

[0071] The pyrolysis gasoline may be a C5-C12 cut, preferably C5-C10, with traces of C3, C4, C13, C14, C15 (for example between 0.1 and 3% by weight for each of these compounds). For example, a charge formed from pyrolysis gasoline generally has a composition, in % by weight relative to the weight of the composition, as follows: 5 to 15% by weight of paraffins, 30 to 65% by weight of aromatic compounds, 5 to 15% by weight of mono-olefins, 15 to 25% by weight of diolefins, 2 to 15% by weight of alkenylaromatic compounds, all of the compounds forming 100% by weight.

[0072] Preferably, the feedstock comprising the pyrolysis gasoline treated in the process according to the invention generally comprises between 5 and 35% by weight of diolefins and between 5 and 20% by weight of monoolefins.

[0073] The sulfur content of the feedstock comprising the pyrolysis gasoline treated in the process according to the invention is generally greater than 500 ppm by weight, often greater than 1000 ppm by weight, up to 2500 ppm by weight for certain difficult loads. Step a) of selective hydrogenation

[0074] According to the invention, the process comprises a step a) of selective hydrogenation of the diolefins of said feedstock in the presence of a stream comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element, carried out at an average temperature of between 40 and 200°C, a pressure of between 1 and 8 MPa, with a space velocity of between 0.5 and 100 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the flow rate of feedstock to be treated expressed in m3 per hour under standard conditions of between 100 Nm3 / m3 and 300 Nm3 / m3, producing an effluent depleted in diolefins.

[0075] The objective of selective hydrogenation step a) is to selectively hydrogenate the diolefins and optionally the alkenylaromatic compounds without hydrogenating the monoolefins and the aromatic nuclei. The diolefinic and alkenylaromatic compounds are thus transformed into the corresponding monoolefins and alkylaromatics.

[0076] It should be emphasized that step a) of selective hydrogenation does not carry out hydrodesulfurization reactions, the operating conditions being too mild.

[0077] Selective hydrogenation is generally carried out in at least one reactor, preferably a fixed bed reactor, at an average temperature of between 40 and 200°C, and preferably between 60 and 180°C. The pressure is between 1 and 8 MPa, and more preferably between 1.5 and 7 MPa. The overall hourly volumetric flow rate (WH), defined as the ratio of the volumetric flow rate of the fresh hydrocarbon feedstock at 15°C to the total volume of catalyst present in the selective hydrogenation reactor, is generally from 0.5 h 1 to 100 h 1, preferably from 1 h 1 to 50 h 1.

[0078] According to the invention, the “average temperature” corresponds to the Weight Average Bed Temperature (WABT) according to the established Anglo-Saxon term, well known to those skilled in the art. The average temperature is advantageously determined according to the catalytic systems, the equipment, and the configuration thereof, used. The average temperature (or WABT) is calculated as follows:

[0079] [Math 1]

[0080] WABT = (Tinput + 2 x Toutput) / 3

[0081] with Tinput: the temperature of the flow at the inlet of the reaction section and Toutput: the temperature of the effluent at the outlet of the reaction section. Unless otherwise indicated, the average temperature is given at start of cycle conditions.

[0082] Selective hydrogenation is generally carried out at a molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) of between 0.5 and 10, more preferably between 0.7 and 5, and preferably between 1 and 2. The hydrogen flow rate is adjusted in order to have sufficient quantity available to theoretically hydrogenate all of the polyunsaturated compounds with the exception of the aromatic nuclei.

[0083] The gas stream comprising hydrogen may consist of a hydrogen supplement and / or recycled hydrogen (for example contained in the gas stream resulting from step c)). The gas stream comprising hydrogen may come from a fossil source or a renewable source, for example from the gasification of plastic waste or produced by electrolysis.

[0084] Preferably, the selective hydrogenation is carried out at a molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) generally between 1 and 2, at an average temperature generally between 40 and 200°C, preferably between 60 and 180°C, at an hourly volumetric velocity (HVV) generally between 1 h 1 and 6 h 1 and at a pressure generally between 1.5 MPa and 7 MPa.

[0085] Taking into account the diolefin content of the feedstock from step a), the temperature T2 of the effluent at the outlet from step a) is higher than the temperature T1 of the feedstock which is introduced into step a) by at least 30°C, and more generally by at least 50°C. Indeed, the hydrogenation reactions of olefins and diolefins are highly exothermic.

[0086] The catalyst used for selective hydrogenation is a catalyst comprising at least one element from group VIII (CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001) corresponding to the metals of columns 8, 9 and 10 according to the new IUP AC classification), more preferably palladium, platinum or nickel. Preferably, the active phase of the selective hydrogenation catalyst consists of an element from group VIII.

[0087] When the group VIII element is palladium, the palladium content is between 0.01 and 2% by weight relative to the total weight of the catalyst, preferably 0.03 and 0.8% by weight.

[0088] When the group VIII element is platinum, the platinum content is between 0.01 and 2% by weight relative to the total weight of catalyst, preferably 0.03 and 0.8% by weight.

[0089] The "% weight" values ​​are based on the elemental form of the group VIII element in the case of palladium or platinum. These catalysts are used in metallic form (non-oxidized and non-sulfurized).

[0090] When the group VIII element is nickel, the nickel content is between 1 and 50% by weight relative to the total weight of catalyst, preferably between 5 and 40%. weight and more preferably between 7 and 30% by weight.

[0091] The "% weight" values ​​are based on the oxide form of the group VIII element in the case of a nickel-based catalyst. These catalysts are generally used in the sulfurized form.

[0092] The catalyst may also comprise phosphorus and / or an organic compound containing oxygen and / or nitrogen and / or sulfur before sulfurization.

[0093] The catalyst comprises in particular an oxide support chosen from alumina (A12O 3), silica (SiO2), titanium oxide (TiO2), ceria (CeO2) and zirconia (ZrO2). Preferably, said support is chosen from an alumina, a silica and a silica-alumina. The oxide support may in particular be in the form of extrudates (for example cylindrical, trilobed or quadrilobed), balls, pellets, or irregular and non-spherical agglomerates whose specific shape may result from a crushing step. Very advantageously, the support is in the form of extrudates.

[0094] The group VIII metal can be dispersed homogeneously within the support or it can be deposited in a crust at the periphery of the support (beads, extrudates). The crust distribution is well known to those skilled in the art and makes it possible to achieve better selectivity of the catalyst.

[0095] Preferably, a selective hydrogenation catalyst based on nickel or palladium is used.

[0096] After selective hydrogenation, the diolefin content, determined by means of the maleic anhydride index (MAV or Maleic Anhydride Value according to English terminology), according to the UOP 326 method, is generally reduced to less than 6 mg maleic anhydride / g, or even less than 4 mg AM / g and more preferably less than 2 mg AM / g. In certain cases, less than 1 mg AM / g can be obtained. Step b) selective weighting

[0097] According to the invention, the process comprises a step b) of selectively weighting the light sulfur compounds in the presence of a flow comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element and a group VIB element, carried out at an average temperature of between 100 and 300°C, a pressure of between 1 and 8 MPa, with a space velocity of between 1 and 10 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the feed flow rate to be treated expressed in m3 per hour at standard conditions of between 5 Nm3 / m3 and 200 Nm3 / m3, producing an effluent comprising a light gasoline cut having a sulfur content of less than 10 ppm by weight; said step b) being carried out directly after step a), or directly after step c), or between two steps c), or even during step e).

[0098] Step b) of selective weighting aims to increase, in a manner selective, the boiling temperature of certain sulfur compounds such as mercaptans boiling at the temperature of the C5 cut, while limiting the hydrogenation of olefins and therefore a loss of octane number. The increase in the boiling temperature is achieved by "heaviness" of sulfur compounds, for example by reaction of mercaptans RSH into thioether type compounds RSR by reaction with monoolefinic compounds. Thus, the sulfur compounds initially boiling at the temperature of the C5 cut are found after selective weighting in a heavier cut, in particular in the heavy C6+ cut. This makes it possible to obtain a C5 cut free of sulfur compounds after separation (step c) and fractionation (step e).

[0099] It should be emphasized that step b) of selective weighting does not carry out hydrodesulfurization reactions (formation of H2S by hydrogenolysis of sulfur compounds), the operating conditions being too mild.

[0100] Selective weighting is generally carried out in at least one reactor, preferably a fixed bed reactor, at an average temperature of between 100 and 300°C, and preferably between 120 and 200°C. The pressure is between 1 and 8 MPa, and more preferably between 1.5 and 7 MPa. The overall hourly volumetric flow rate (WH), defined as the ratio of the volumetric flow rate of the fresh hydrocarbon feedstock at 15°C to the total volume of catalyst present in the selective hydrogenation reactor, is generally from 1 h 1 to 10 h 1 , preferably from 1 h 1 to 6 h 1 . The quantity of the gas flow comprising hydrogen (H2) supplying step b), is advantageously such that the flow rate of hydrogen expressed in normal m3 per hour and the flow rate of charge to be treated expressed in m3 per hour under standard conditions is between 5 Nm3 / m3 and 200 Nm3 / m3, preferably between 5 Nm3 / m3 and 100 Nm3 / m3, or even preferably between 5 and 20 Nm3 / m3.

[0101] The gas stream comprising hydrogen, which feeds the selective weighting reaction section, may consist of a supply of fresh hydrogen and / or recycled hydrogen (for example contained in the gas stream from step c)) or even come directly from step a) of selective hydrogenation. The gas stream comprising hydrogen may come from a fossil source or a renewable source, for example from the gasification of plastic waste or produced by electrolysis.

[0102] When step b) is carried out directly after step a) of selective hydrogenation, an addition of hydrogen is generally not necessary.

[0103] When step b) is carried out after separation step c), hydrogen is added by injecting a stream comprising fresh or recycled hydrogen such as, for example, contained in the gas stream of the separation step of step c).

[0104] When step b) is carried out during fractionation step e), hydrogen is added by injecting a stream comprising fresh or recycled hydrogen such as that for example is contained in the gas flow of the separation step of step c).

[0105] Selective weighting is generally carried out at a molar ratio (hydrogen) / (sulfur compounds to be treated) of between 0.5 and 10, more preferably between 0.5 and 5, and preferably between 0.5 and 2.

[0106] The catalyst used in the selective weighting zone generally contains at least one group VIB element and at least one group VIII element on an oxide support.

[0107] The group VIB element is preferably molybdenum or tungsten and the group VIII element is preferably chosen from nickel or cobalt. The content of group VIII metal expressed as oxide (NiO or CoO) is generally between 0.5% and 15% by weight, preferably between 1% and 10% by weight relative to the total weight of the catalyst. The content of group VIB metal expressed as oxide (MoO3 or WO3) is generally between 1.5% and 60% by weight, preferably between 3% and 50% by weight relative to the total weight of the catalyst.

[0108] The catalyst support is usually an oxide solid, such as for example an alumina, a silica-alumina, magnesia, silica or titanium oxide, alone or in a mixture. Very preferably, the support is chosen from an alumina, a silica-alumina or a silica.

[0109] The oxide support may in particular be in the form of balls, extrudates (for example trilobed or quadrilobed), pellets, or irregular and non-spherical agglomerates whose specific shape may result from a crushing step. Very advantageously, the oxide support is in the form of balls or extrudates.

[0110] Preferably, a selective weighting catalyst based on nickel and molybdenum is used.

[0111] It is of course possible to use one or more successive beds of catalysts making it possible to carry out the desired catalytic reaction in steps a) and b).

[0112] Step b) of selective weighting thus makes it possible to produce an effluent comprising a light gasoline cut having a sulfur content of less than 10 ppm by weight. Step c) of separation

[0113] According to the invention, the process comprises a step c) of separating the effluent from step a) or b) so as to obtain a gaseous stream and a liquid stream, said step c) being carried out before and / or after step b).

[0114] According to step c) of the process according to the invention, the effluent from step a) or b) is separated so as to produce a gaseous stream comprising hydrogen (injected during step a) and / or b)) and light compounds C1 to C4 and a liquid stream comprising a light gasoline cut C5 which has been partially depleted in sulfur compounds (by selective weighting) and a heavy C6+ cut enriched in sulfur compounds.

[0115] This step is implemented in particular in order to separate the excess hydrogen which can be recycled in the process, possibly after purification and compression.

[0116] The separation step can be carried out by any means known to those skilled in the art, such as, for example, one or more separating flasks, a distillation column or a stripping column using an inert gas flow, for example hydrogen, nitrogen or steam. Step d) recycling

[0117] According to the invention, the method comprises a step d) of recycling to step a) a part of the liquid flow from step c).

[0118] The step of recycling the liquid flow from step c) can be carried out by any means known to those skilled in the art, such as, for example, a centrifugal pump or a reciprocating pump.

[0119] Preferably the flow rate of the recycled liquid stream represents between 50% and 500% of the flow rate of the load.

[0120] The recycling of a part of the liquid flow from step c) makes it possible on the one hand to dilute the impurities in the feedstock and on the other hand to control the temperature in step a) in which highly exothermic reactions (in particular the hydrogenation reactions of the diolefins) occur. Step e) of splitting

[0121] According to the invention, the process comprises a fractionation step in at least one fractionation column, located downstream of steps a) and c), allowing the separation of a light gasoline cut having a sulfur content of less than 10 ppm by weight.

[0122] The fractionation step comprises at least one fractionation column, called a depentanizer. This column is generally operated with an operating pressure of between 0.2 and 1.0 MPa, with a temperature at the bottom of the column varying between 110 and 190°C.

[0123] The fractionation column is thus supplied with at least part of the liquid flow from step c) when step c) is carried out after step b) (variants 1 or 2) and / or at least part of the effluent from step b) when step b) is carried out after step c) (variants 3 or 4).

[0124] According to a first embodiment, fractionation step e) is carried out so as to produce a gaseous stream comprising hydrogen and light compounds C1 to C4, said light gasoline cut having a sulfur content of less than 10 ppm by weight which has been partially depleted in sulfur compounds (by selective weighting) and a heavy cut enriched in sulfur compounds (by selective weighting).

[0125] According to a second embodiment, fractionation step e) is carried out so as to additionally produce an intermediate gasoline cut comprising C5 and C6 hydrocarbons.

[0126] The gas stream comprising hydrogen and light compounds Cl to C4 can be recycled in the process, possibly after purification and compression.

[0127] The light gasoline cut, also called C5 cut, comprises at least 90% by weight, preferably at least 95% by weight of hydrocarbons having 5 carbon atoms. It may comprise traces of C4 and C6 compounds.

[0128] The sulfur content of the light gasoline cut is less than 10 ppm by weight of sulfur, so that it can be directly integrated into a gasoline pool.

[0129] Despite step b) of selective weighting causing the reaction of olefins contained in the feedstock and thus leading to a loss of octane number, the loss of the research octane number (RON) is limited to 5 points at most in the light gasoline cut. Indeed, the light gasoline cut has an olefin content greater than 40% by weight.

[0130] The light gasoline cut generally comprises compounds having a boiling point between 20 and 80°C.

[0131] When an intermediate gasoline cut comprising C5 and C6 hydrocarbons is extracted, it generally comprises compounds having a boiling point between 30 and 100°C.

[0132] As for the heavy cut, also called C6+ cut, it generally includes compounds with a boiling point above 80°C. This cut generally undergoes additional treatments in order to send it to an aromatic compound extraction unit.

[0133] Thus, the heavy C6+ cut from step e) can be separated in a rectification step into a heavy gasoline cut and a middle distillate cut, then a hydrotreatment step is carried out on said heavy gasoline cut, thus producing a cut with a low sulfur and olefin content, which can, for example, be sent to an aromatic compound extraction unit.

[0134] The rectification step can be carried out in a rectification column so as to produce a heavy gasoline cut and a middle distillate cut. This column is generally operated with an operating pressure of between 0.2 and 1.0 MPa absolute, with a temperature at the bottom of the column varying between 110 and 190°C.

[0135] The heavy gasoline fraction generally comprises compounds having a boiling point between 80 and 175°C.

[0136] The middle distillate cut generally comprises compounds having a boiling point above 175°C.

[0137] Depending on the destination or use of the cuts from the grinding step, the person skilled in the art will adjust the cutting points in the grinding operations. For example, it may be necessary to adjust the end point of the heavy fuel cut to 150, 185 or 200°C.

[0138] In order to be able to send the heavy gasoline cut to an aromatic compound extraction unit, it must be hydrotreated in order to eliminate sulfur compounds in particular, and monoolefins. The hydrotreatment is carried out under operating conditions known to those skilled in the art.

[0139] Thus, in the hydrotreatment step, said heavy gasoline cut is brought into contact in at least one reactor, preferably in a fixed bed, with a stream comprising hydrogen and a hydrotreatment catalyst comprising an oxide support and an active phase comprising a group VIB element and a group VIII element, at a temperature of between 150 and 400°C, preferably between 200 and 400°C, at a pressure of between 1 and 8 MPa, preferably between 3 and 7 MPa, with a space velocity of between 0.1 and 80 h *, preferably between 0.4 and 40 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the feed flow rate to be treated expressed in m3 per hour at standard conditions of between 100 Nm3 / m3 and 600 Nm3 / m3, preferably between 200 and 500 Nm3 / m3.

[0140] The catalyst used in the hydrotreatment is a catalyst known to those skilled in the art. The hydrotreatment catalyst comprises an oxide support and an active phase comprising a group VIB element and a group VIII element and optionally phosphorus and / or an organic compound as described below.

[0141] The group VIB element present in the active phase of the catalyst is preferably chosen from molybdenum and tungsten. The group VIII element present in the active phase of the catalyst is preferably chosen from cobalt, nickel and the mixture of these two elements. The active phase of the catalyst is preferably chosen from the group formed by the combination of the elements nickel-molybdenum, cobalt-molybdenum and nickel-cobalt-molybdenum and very preferably the active phase consists of cobalt and molybdenum.

[0142] The content of group VIII element is between 0.1 and 10% by weight of oxide of the group VIII element relative to the total weight of the catalyst, preferably between 0.6 and 8% by weight, preferably between 2 and 7% by weight, very preferably between 2 and 6% by weight and even more preferably between 2.5 and 6% by weight.

[0143] The content of group VIB element is between 1 and 20% by weight of oxide of the group VIB element relative to the total weight of the catalyst, preferably between 2 and 18% by weight, very preferably between 3 and 16% by weight.

[0144] The molar ratio of group VIII element to group VIB element of the catalyst is generally between 0.1 and 0.8, preferably between 0.2 and 0.6.

[0145] Optionally, the catalyst may further have a phosphorus content generally comprised between 0.3 and 10% by weight of P2O5 relative to the total weight of catalyst, preferably between 0.5 and 5% by weight, very preferably between 1 and 3% by weight. For example, the phosphorus present in the catalyst is combined with the metal from group VIB and optionally also with the metal from group VIII in the form of heteropolyanions. Furthermore, the phosphorus / metal from group VIB molar ratio is generally comprised between 0.1 and 0.7, preferably between 0.2 and 0.6, when phosphorus is present.

[0146] The catalyst may also further comprise at least one organic compound containing oxygen and / or nitrogen and / or sulfur before sulfurization.

[0147] The catalyst comprises in particular an oxide support formed from at least one simple oxide chosen from alumina (A1203), silica (SiO2), titanium oxide (TiO2), ceria (CeO2) and zirconia (ZrO2). Preferably, said oxide support is chosen from an alumina, a silica and a silica-alumina.

[0148] The oxide support may in particular be in the form of balls, extrudates (for example trilobed or quadrilobed), pellets, or irregular and non-spherical agglomerates whose specific shape may result from a crushing step. Very advantageously, the support is in the form of balls or extrudates.

[0149] The preparation of the catalysts of steps a) and b) as well as the hydrotreatment catalyst is known and generally comprises a step of impregnation of the metals of group VIII and group VIB when present, and optionally of the phosphorus and / or of the organic compound on the oxide support, followed by drying, then by an optional calcination making it possible to obtain the active phase in their oxide forms. Before their use, these catalysts are generally subjected to sulfurization in order to form the active species with the exception of the palladium or platinum-based catalysts of step a) which are generally used in their reduced (metallic) form.

[0150] The heavy gasoline fraction thus hydrotreated has a low sulfur content (e.g. less than 10 ppm by weight of sulfur) and olefins (e.g. between 1 and 5% by weight of olefins), and can for example be sent to an aromatic compound extraction unit or to the refinery's gasoline pool. Examples

[0151] This example compares the properties of the light gasoline cut (stream 11 of the figures) for the prior art and the four variants of the invention. The properties of the feedstock and the operating conditions of the selective hydrogenation and recycling steps, common to the five configurations, are reported in Tables 1 to 3 below.

[0152] [Tables 1] Configuration IMts Yield* wo ppm 1600 Composition “® a” % aa -s. a-a? « fi O C4- C5 C6 C7 C8 C9 C10+ 0.0% 0.2% 0.0% 2.9% 8.7% 12.4% 0.0% 3.1% 4.0% 5.8% 0.0% 15.8% 4.1% 0.0% 3.3% 0.1% 1.5% 3.8% 0.0% 0.0% 0.1% 6.5% 2.3% 1.1% 0.0% 0.0% 0.0% 0.6% 7.1% 0.0% 0.0% 2.8% 0.0% 1.7% 2.0% ü 2% 24.0% 28.6% 19.0% 12.7% 8.8% 6.6% Total 15.0% 12.9% 24.3% 0.2% 36.2% 11.4% 100.0% 1: Efficiency Flow rate / discharged unit load

[0153] Table 1: property of the charge (flow 1)

[0154] [Tables2] Configuration All Inlet temperature Tl °C 60 Outlet temperature T2 °C 120 Pressure MPa 3.5 H2 / HC NmVm3 118

[0155] Table 2: operating conditions of step a) of selective hydrogenation

[0156] The operating conditions of step d) of recycling, common to all confi gurations, are presented in Table 3.

[0157] [Tables3] Configuration All Temperature °C 120 Yield 1% weight 360

[0158] 1: Efficiency = Flow rate / Unit load rate

[0159] Table 3: operating conditions of recycling step d)

[0160] The operating conditions of step b) of selective weighting, which is implemented in all the variants of the invention, are presented in table 4.

[0161] [Tables4] Configuration Prior Art Invention Figure Number 1 2 3 4 5 Temperature T3 °C - 120 120 120 120 Pressure MPa - 3.3 3.3 3.3 3.3 H2 / HC NmVm3 - 32 32 8 8

[0162] Table 4: operating conditions of step b) of selective weighting

[0163] The properties of the light gasoline cut, resulting from each of the configurations, are presented in Table 5.

[0164] [Tables5] Configuration Prior Art Invention Figure Number 1 2 3 4 5 Yield2 % weight 22.6 22.6 22.6 22.3 21.7 Research Octane Number (RON) - 88.1 86.9 87.7 87.6 87.3 Sulfur Content PPm weight 48 3 8 9 7 Sp gr1 - ASTM D4052 0.667 0.665 0.666 0.667 0.666 Paraffin Content % weight 27.3 35.0 29.8 29.9 31.6 Olefin Content % weight 59.5 50.5 56.4 56.0 52.3 Naphthene Content % weight 13.0 14.3 13.6 13.9 15.9 Aromatic Content % weight 0.2 0.2 0.2 0.2 0.2

[0165] 1: Relative density (specifies gravity according to Anglo-Saxon terminology) Sp Gr= p sample at 20°C / pH2o at 4°C where p is the density expressed in g / cm3

[0166] 2: Efficiency = Flow rate / Unit load rate

[0167] Table 5: properties of the light gasoline cut (flow 11)

[0168] It can therefore be seen that the process variants according to the invention make it possible to produce a light C5 gasoline cut whose sulfur content is less than 10 ppm by weight of sulfur, without significant loss of research octane number (RON), nor of mono-olefin compounds.

Claims

Claims

1. Process for treating a pyrolysis gasoline feedstock containing diolefins and sulfur compounds, comprising the following steps: a) a step of selective hydrogenation of the diolefins of said feedstock in the presence of a stream comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element, carried out at an average temperature of between 40 and 200°C, a pressure of between 1 and 8 MPa, with a space velocity of between 0.5 and 100 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the flow rate of feedstock to be treated expressed in m3 per hour at standard conditions of between 100 Nm3 / m3 and 300 Nm3 / m3, producing an effluent depleted in diolefins; b) a step of selectively weighting the light sulfur compounds in the presence of a flow comprising hydrogen and a catalyst comprising an oxide support and an active phase comprising a group VIII element and a group VIB element, carried out at an average temperature of between 50 and 320°C, a pressure of between 1 and 8 MPa, with a space velocity of between 1 and 10 h 1 and a ratio between the hydrogen flow rate expressed in normal m3 per hour and the feed flow rate to be treated expressed in m3 per hour at standard conditions of between 5 Nm3 / m3 and 200 Nm3 / m3, producing an effluent comprising a light gasoline cut having a sulfur content of less than 10 ppm by weight; said step b) being carried out directly after step a), or directly after step c), or between two steps c), or during step e); c) a step of separating the effluent from step a) or step b) so as to obtain a gaseous stream and a liquid stream, said step c) being carried out before and / or after step b); d) a step of recycling to step a) a part of the liquid flow from step c); e) a fractionation step in at least one fractionation column, located downstream of steps a) and c), allowing the separation of a light gasoline cut having a sulfur content of less than 10 ppm by weight and a heavy cut comprising products resulting from the weighting of the light sulfur compounds obtained by step b).

2. The method of claim 1, wherein said frac- operation of step e) is carried out with a pressure of between 0.2 and 1.0 MPa, and with a temperature at the bottom of the column of between 110 and 190°C.

3. Method according to one of the preceding claims, in which the flow rate of the liquid stream recycled in step d) represents between 50% and 500% of the flow rate of the load.

4. Method according to one of the preceding claims, in which the catalyst of step a) is a catalyst comprising nickel or palladium.

5. Method according to one of the preceding claims, in which the catalyst of step b) is a catalyst comprising nickel and molybdenum.

6. A method according to any preceding claim, wherein the pyrolysis gasoline feedstock has a sulfur content greater than 500 ppm by weight.

7. Method according to one of the preceding claims, in which the pyrolysis gasoline is a gasoline from a steam cracking unit.

8. Process according to one of the preceding claims, in which the fractionation step e) is carried out so as to produce a gaseous stream comprising hydrogen and light compounds C1 to C4, said light gasoline cut having a sulfur content of less than 10 ppm by weight, and a heavy cut comprising products resulting from the weighting of the light sulfur compounds obtained by step b).

9. Method according to the preceding claim, in which the heavy cut from step e) is separated in a rectification step into a heavy gasoline cut and a middle distillate cut, then a hydrotreatment step is carried out on said heavy gasoline cut.

10. Method according to the preceding claim, in which said hydrotreated heavy gasoline cut is sent to an aromatic extraction unit.

11. Process according to one of the preceding claims, in which the fractionation step e) is carried out so as to additionally produce an intermediate gasoline cut comprising C5 and C6 hydrocarbons.

12. Process according to the preceding claim, in which said intermediate gasoline cut comprising C5 and C6 hydrocarbons is introduced into step b) in a mixture with a stream comprising hydrogen, then the effluent from step b) is returned to step e).

13. A method according to any preceding claim, wherein when step b) is carried out directly after step c) or during step e), a flow comprising hydrogen is injected upstream of step b).

14. Method according to one of claims 1 to 13, comprising a first and second separation step c) carried out respectively before and after step b), and the gas flow obtained in the first separation step c) carried out before step b) is at least partly introduced into step b).

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