FR3116740A1 - Process for the preparation of a catalyst for the hydrodesulphurization of a gasoline cut comprising a metal from group VIB, a metal from group VIII and graphitic carbon - Google Patents

Abstract

The invention relates to a process for the preparation of a catalyst comprising an active phase comprising a group VIB metal and a group VIII metal, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen, said preparation process comprising the following steps:a) bringing a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound into contact with an oxide support so as to carry out carbonization,b) then brings a compound comprising a metal from group VIB and a compound comprising a metal from group VIII into contact with the mixed support obtained in step a), c), drying is carried out at a temperature below 200° C. without subsequent calcination. The invention also relates to the catalyst obtained by this process and its use in a process for the hydrodesulphurization of a gasoline cut.

Description

Process for the preparation of a catalyst for the hydrodesulphurization of a gasoline cut comprising a metal from group VIB, a metal from group VIII and graphitic carbon

Field of invention

The present invention relates to a process for the preparation of a catalyst for the hydrodesulphurization of a gasoline cut, the catalyst obtained by this process and its use in the field of the hydrodesulphurization of a gasoline cut.

State of the art

Sulfur is a naturally occurring element in crude oil and is therefore present in gasoline and diesel if not removed during refining. However, sulfur in gasoline impairs the efficiency of emission reduction systems (catalytic converters) and contributes to air pollution. In order to fight against environmental pollution, all countries are therefore gradually adopting strict sulfur specifications, the specifications being, for example, 10 ppm (weight) of sulfur in commercial gasoline in Europe, China, the United States. and in Japan. The problem of reducing sulfur content essentially focuses on gasolines obtained by cracking, whether catalytic (FCC Fluid Catalytic Cracking according to Anglo-Saxon terminology) or non-catalytic (coking, visbreaking, steam cracking), the main precursors of sulfur in gasoline pools.

A solution, well known to those skilled in the art, for reducing the sulfur content consists in carrying out a hydrotreatment (or hydrodesulphurization) of the hydrocarbon cuts (and in particular gasolines from catalytic cracking) in the presence of hydrogen and a heterogeneous catalyst. . However, this process has the major drawback of causing a very significant drop in the octane number if the catalyst used is not selective enough. This decrease in the octane number is in particular linked to the hydrogenation of the olefins present in this type of gasoline concomitantly with the hydrodesulphurization.

Unlike other hydrotreating processes, in particular those for diesel-type feedstocks, the hydrodesulphurization of gasolines must therefore make it possible to respond to a double antagonistic constraint: to ensure deep hydrodesulphurization of gasolines and to limit the hydrogenation of the unsaturated compounds present .

The way most used to respond to the double problem mentioned above consists in using processes whose sequence of unit steps makes it possible both to maximize hydrodesulphurization while limiting the hydrogenation of olefins. Thus, the most recent processes, such as the Prime G+ process (trademark), make it possible to desulphurize cracked gasolines rich in olefins, while limiting the hydrogenation of mono-olefins and consequently the loss of octane and the resulting high hydrogen consumption. Such processes are for example described in patent applications EP 1 077 247 and EP 1 174 485.

Obtaining the desired reaction selectivity (ratio between hydrodesulfurization and hydrogenation of olefins) may therefore be partly due to the choice of process, but in all cases the use of an intrinsically selective catalytic system is very often a key factor. In general, the catalysts used for this type of application are sulfide type catalysts containing a group VIB element (Cr, Mo, W) and a group VIII element (Fe, Ru, Os, Co, Rh , Ir, Pd, Ni, Pt). Such catalysts are for example disclosed in documents US 5,985,136, US 4,140,626, US 4,774,220, US 8,637,423 and EP 1,892,039 which describe selective hydrodesulfurization catalysts.

It is known that the presence of carbon in a gasoline cut hydrodesulphurization catalyst can improve selectivity. Various processes for the preparation of such a catalyst containing carbon are known in the state of the art.

Document US 2,793,170 describes a process for the hydrodesulfurization of a cracked gasoline in the presence of a catalyst containing between 0.2 and 6% by weight of carbon. The catalyst is prepared by regenerating spent catalyst.

The document US2009/0258780 for its part describes that a catalyst containing a group VIII metal, molybdenum (Mo), phosphorus and sulfur supported on a porous inorganic oxide support comprising a carbonaceous material makes it possible to observe an increase selectivity in a gasoline hydrodesulfurization process. The carbonaceous material must contain oxygen and is characterized by a carbon content of between 5 and 20% by weight relative to the weight of the support, an atomic ratio of the amount of hydrogen to the amount of carbon H/C of 0.4 to 1.0, and an atomic ratio of the amount of oxygen to the amount of carbon O/C of 0.1 to 0.6. It is prepared by introducing an oxygen-containing organic compound, preferably a saccharide, into the carrier.

The document Hatanaka et al. (Ind. Eng. Chem. Res. 1998, 37, 1748-1754) describes the preparation of a carbon catalyst for selective hydrodesulphurization by introducing the carbon by a pretreatment involving a mixture of 1-methylnaphthalene and cyclohexane before or after the sulfurization.

Document EP0745660 describes a process for the preparation of a catalyst containing carbon for the hydrodesulphurization of a gasoline. The carbon is introduced by a hydrocarbon oil in the presence of hydrogen at a temperature between 200 and 350°C, said hydrocarbon oil having a composition in which olefinic components are contained in an amount not exceeding 10% by volume, a content in dienes not exceeding 0.1% by volume, a content of bicyclic aromatics not exceeding 5% by volume, and a content of tricyclic aromatics not exceeding 1% by volume, and having a boiling point less than or equal to 300°C.

Finally, document FR 2 850 299 describes a process for the hydrodesulfurization of an olefinic gasoline cut using a catalyst previously carbonized on the surface, with a carbon content less than or equal to 2.8% by weight relative to the weight of the catalyst. The carbon is introduced by at least one hydrocarbon compound chosen from olefins, naphthenes, aromatics and paraffins.

The invention proposes a preparation process making it possible to obtain a selective hydrodesulphurization catalyst which exhibits maintained catalytic performances in terms of catalytic activity while significantly improving the selectivity.

Objects of the invention

The invention relates to a process for the preparation of a catalyst comprising an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen, said preparation process comprising the following steps:

a) a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound is brought into contact with an oxide support at a temperature of between 300 and 500° C., an hourly volumetric speed of between 1 and 10 h ^-1 and a total pressure of between 0.05 and 10 MPa, so as to obtain a mixed support comprising said oxide support and a graphitic material containing carbon and hydrogen, and sulfur,

b) then a compound comprising at least one metal from group VIB and at least one compound comprising a metal from group VIII, and optionally phosphorus and/or at least one organic compound comprising oxygen and/or nitrogen and/or sulfur with said mixed support obtained in step a), so as to obtain a catalytic precursor,

c) said catalytic precursor is dried at a temperature below 200° C. without subsequent calcination, so as to obtain a dried catalyst,

d) the dried catalyst is optionally activated in the presence of a sulfurizing agent.

It has in fact been observed that the introduction of carbon into the catalyst by the use of a specific compound, in particular aromatic, and in the presence of a sulfur compound, makes it possible to obtain a catalyst which has catalytic performances maintained in terms of catalytic activity while significantly improving selectivity.

Without being bound to any theory, it seems that the nature of the carbonaceous precursor, in particular its aromatic nature, has an influence on the nature of the graphitic material after the carbonization inducing a better selectivity towards the hydrodesulphurization reaction compared to the reaction of hydrogenation. In addition, a synergistic effect is observed for the selectivity when the carbonization is carried out in the presence of a sulfur compound.

Similarly, it seems important that the carbonization (step a) be carried out before the introduction of the metals (step b). Indeed, without being bound to any theory, it seems that the deposition of carbon on the oxide support facilitates the dispersion of metals within the support by making it possible to avoid the phenomena of rise in pH classically observed in the absence of deposition of carbon during the impregnation of the solution containing the metal precursors. Maintaining a fairly low pH thus allows the presence of heteropolyanions to the detriment of monomolybdate and polymolybdate species, said heteropolyanions favoring the sulphidation of metal species and the formation of more selective sulphide phases.

According to a variant, said aromatic compound is a monoaromatic compound chosen from benzene, toluene, xylenes, styrene, tetraline and divinylbenzene.

According to a variant, the carbon content is between 5 and 20% by weight expressed as carbon element relative to the weight of the catalyst, and the H/C atomic ratio is less than 1.4.

According to a variant, said sulfur compound is chosen from dimethyl disulphide, di-tert-butyl disulphide or di-tert-butyl polysulphide.

According to a variant, the sulfur content is between 1 and 8% by weight expressed as sulfur element relative to the weight of the catalyst.

According to a variant, said aliphatic compound is an alkane chosen from hexane, heptane and octane.

According to a variant, the oxide support is chosen from an alumina, a silica and a silica-alumina.

According to a variant, the group VIB metal is chosen from molybdenum and tungsten, and the group VIII metal is chosen from cobalt, nickel and a mixture of these two elements.

Alternatively, the group VIB metal content is between 5 and 40% by weight, expressed as group VIB metal oxide, relative to the total weight of the catalyst and the group VIII metal content is between 1 and 10 % by weight, expressed as group VIII metal oxide, relative to the total weight of the catalyst.

According to one variant, the catalyst also comprises phosphorus at a content of between 0.1 and 20% by weight, expressed as P ₂ O ₅ relative to the total weight of the catalyst.

According to a variant, the catalyst also comprises an organic compound containing oxygen and/or nitrogen and/or sulfur.

According to this variant, the organic compound is chosen from a compound comprising one or more chemical functions chosen from a carboxylic, alcohol, thiol, thioether, sulphone, sulphoxide, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea, amide, or a compound including a furan cycle or even a sugar, and more particularly the organic compound is chosen from γ-valerolactone, 2-acetylbutyrolactone, triethylene glycol, diethylene glycol, ethylene glycol, acid ethylenediaminetetraacetic acid (EDTA), maleic acid, malonic acid, citric acid, acetic acid, oxalic acid, gluconic acid, glucose, fructose, sucrose, sorbitol, xylitol, γ-ketovaleric acid, a C1-C4 dialkyl succinate and more particularly dimethyl succinate, dimethylformamide, 1-methyl-2-pyrrolidinone, propylene carbonate, 2-methoxyethyl 3-oxobutanoate, bicine, tricine, 2- furaldehyde (also known as furfural), 5-hydroxymethylfurfural, 2-acetylfuran, 5-methyl-2-furaldehyde, ascorbic acid, butyl lactate, ethyl lactate, butyl butyryllactate, ethyl 3-hydroxybutanoate, ethyl 3-ethoxypropanoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, 2-hydroxyethyl acrylate, 1-vinyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, 1,5-pentanediol, 1-(2-hydroxyethyl)-2-pyrrolidinone, 1-(2-hydroxyethyl)-2,5-pyrrolidinedione, 5-methyl-2 (3H)-furanone, 1-methyl-2-piperidinone, 4-aminobutanoic acid, butyl glycolate, ethyl 2-mercaptopropanoate, ethyl 4-oxopentanoate, diethyl maleate, maleate dimethyl fumarate, diethyl fumarate, dimethyl adipate and dimethyl 3-oxoglutarate.

The invention also relates to the catalyst obtained according to the preparation process according to the invention and its use in a process for the hydrodesulphurization of a gasoline cut containing sulfur compounds and olefins in which said gasoline cut is brought into contact with hydrogen and said catalyst, said process being carried out at a temperature of between 200 and 400°C, a total pressure of between 1 and 3 MPa, an hourly volume rate, defined as being the volume flow rate of charge relative to the volume of catalyst, between 1 and 10 h ^-1 , and a hydrogen/gasoline charge volume ratio between 100 and 1200 NL/L.

Definitions

In the following, 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 according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

By specific surface area is meant the BET specific surface area (S _BET in m ² /g) determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established from the BRUNAUER-EMMETT-TELLER method described in the periodical " The Journal of American Society ", 1938, 60, 309.

By total pore volume of the catalyst or of the support used for the preparation of the catalyst is meant the volume measured by intrusion with a mercury porosimeter according to standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°. The wetting angle was taken as equal to 140° by following the recommendations of the work “Engineering techniques, treatise on analysis and characterization”, pages 1050-1055, written by Jean Charpin and Bernard Rasneur. In order to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the sample minus the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the same sample for a pressure corresponding to 30 psi (about 0.2 MPa).

The contents of group VIII and group VIB metals are measured by X-ray fluorescence.

The contents of group VIB metal, group VIII metal and phosphorus in the catalyst are expressed in oxides after correction of the loss on ignition of the catalyst sample at 550°C for two hours in a muffle furnace. Loss on ignition is due to moisture loss. It is determined according to ASTM D7348.

Detailed description of the invention

Catalyst Preparation Process

The invention relates to a process for the preparation of a catalyst comprising an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material. containing carbon and hydrogen, said method of preparation comprising the following steps:

a) a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound is brought into contact with an oxide support at a temperature of between 300 and 500° C., an hourly volumetric speed of between 1 and 10 h ^-1 and a total pressure of between 0.05 and 10 MPa, so as to obtain a mixed support comprising said oxide support and a graphitic material containing carbon and hydrogen, and sulfur,

b) then a compound comprising at least one metal from group VIB and at least one compound comprising a metal from group VIII, and optionally phosphorus and/or at least one organic compound comprising oxygen and/or nitrogen and/or sulfur with said mixed support obtained in step a), so as to obtain a catalytic precursor,

c) said catalytic precursor is dried at a temperature below 200° C. without subsequent calcination, so as to obtain a dried catalyst,

d) the dried catalyst is optionally activated in the presence of a sulfurizing agent.

The various preparation steps will be described in detail below.

Step a): Bringing an aromatic compound/aliphatic compound/sulfur compound mixture into contact with the oxide support (carbonization)

According to step a) of the preparation process according to the invention, a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound is brought into contact with an oxide support at a temperature between 300 and 500° C., an hourly volumetric velocity comprised between 1 and 10 h ^-1 and a total pressure comprised between 0.05 and 10 MPa, so as to obtain a mixed support comprising said oxide support and a graphitic material containing carbon and hydrogen , and sulfur.

Preferably, the mixture consists of an aromatic compound, an aliphatic compound and a sulfur compound.

The duration of the contacting is generally between 1 and 12 hours.

According to a variant, the contacting is carried out in the presence of a gas stream comprising nitrogen or hydrogen, preferably hydrogen, an aromatic compound, an aliphatic compound and a sulfur compound, at a temperature comprised between 300 and 500° C., an hourly volumetric velocity of between 1 and 10 h ^-1 , a pressure of between 0.05 and 10 MPa and a gas flow/charge ratio of between 50 and 500 NL/L.

Under the effect of temperature and pressure, the aromatic compound carbonizes and forms a graphitic material containing carbon and hydrogen on the oxide support. Similarly, under the effect of temperature and pressure, the sulfur compound decomposes into H ₂ S which is deposited at least partially in the form of sulfur on the oxide support and/or in the graphitic material containing carbon. and hydrogen.

By graphitic material containing carbon and hydrogen is meant a material resulting from the carbonization of the aromatic compound. It will be noted that the term "graphitic material" in the present application means an aromatic hydrocarbon-based substance deposited on the surface of the oxide support, strongly cyclized and condensed and having an appearance similar to graphite.

It is important to emphasize that the carbon and hydrogen of the graphitic material are not (or no longer) in the form of an aromatic molecule. However, the catalyst may contain, in addition to the graphitic material containing carbon and hydrogen, an organic compound (additive) as described below.

Said aromatic compound is advantageously a monoaromatic compound such as benzene, toluene, xylenes (ortho, para or meta), styrene, tetralin, and divinylbenzene, preferably benzene, toluene and xylenes, and very preferably toluene.

The amount of carbon introduced during step a) is such that the carbon content, expressed as carbon element, is between 5 and 20% by weight, preferably between 7 and 18% by weight and very preferably between 10 and 15 % weight relative to the total weight of the catalyst.

The hydrogen to carbon atomic ratio, also called H/C ratio, is less than 1.4, preferably between 0.7 and 1.35 and preferably between 0.8 and 1.2.

The carbon content of the catalyst according to the invention refers to the carbon content of the catalyst resulting from the carbonization of the aromatic compound without taking into account the carbon contained in any organic additive introduced in step b). To this end, the carbon content and the H/C atomic ratio are determined according to the ASTM D5373 method after pretreatment of the catalyst under a flow of dry air at 300°C for 2 hours and a flow rate of 2 L/h/g.

Said aliphatic compound is an alkane chosen from hexane, heptane and octane, and preferably hexane. The aliphatic compound acts as a solvent. Its content in the mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound is generally greater than 50% by weight, preferably greater than 60% by weight.

Said sulfur compound is an organic molecule capable of decomposing into H ₂ S and chosen from the families of disulfides and polysulfides, preferably dimethyldisulfide, di-tert-butyl disulfide or di-tert-butyl polysulfide, so very preferred is dimethyldisulfide.

The amount of sulfur compound introduced during step a) is such that the sulfur content in said catalyst is between 1 and 8% by weight expressed as sulfur element, relative to the total weight of the catalyst, preferably between 1 and 6%, and very preferably between 2 and 5% by weight.

The sulfur content of the catalyst refers to the total sulfur content of the catalyst introduced during the formation of the graphitic material (carbonization), taking into account the sulfur contained in any organic additive contained in said catalyst or introduced by a possible activation. (sulfidation). For this purpose, the sulfur content is determined according to the ASTM D5373 method (conventional, i.e. without the said pretreatment of the catalyst carried out for the measurement of the carbon content).

The oxide support of said catalyst of the process according to the invention is usually a porous solid chosen from the group consisting of: aluminas, silica, silica alumina or even titanium or magnesium oxides used alone or mixed with the alumina or silica alumina.

The oxide support advantageously has a total pore volume of between 0.1 and 1.5 mL/g, preferably between 0.4 and 1.1 mL/g.

The oxide support advantageously has a specific surface of between 5 and 400 m ² .g ^-1 , preferably between 10 and 350 m ² .g ^-1 , more preferably between 40 and 350 m ² .g ^-1 .

It is preferably chosen from the group consisting of: silica, the family of transition aluminas and alumina silicas, very preferably, the oxide support consists essentially of at least one transition alumina, i.e. that is to say that it comprises at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, or even at least 90% by weight of transition alumina. It preferably consists solely of a transition alumina. Preferably, the oxide support of said catalyst of the process according to the invention is a gamma phase alumina.

In another preferred case, the oxide present in the support of said catalyst of the process according to the invention is a silica-alumina containing at least 50% by weight of alumina relative to the total weight of the composite support. The silica content in the support is at most 50% by weight relative to the total weight of the support, usually less than or equal to 45% by weight, preferably less than or equal to 40%.

Silicon sources are well known to those skilled in the art. Mention may be made, by way of example, of silicic acid, silica in powder form or in colloidal form (silica sol), tetraethylorthosilicate Si(OEt) ₄ .

When the support of said catalyst is based on silica, it contains more than 50% by weight of silica relative to the total weight of the support and, in general, it contains only silica.

According to a particularly preferred variant, the support consists of alumina, silica or silica-alumina.

The support is advantageously in the form of beads, extrudates, pellets or irregular and non-spherical agglomerates, the specific shape of which may result from a crushing step.

Step b): Introduction of metals

According to step b) of the preparation process according to the invention, at least one compound comprising a metal from group VIB and at least one compound comprising a metal from group VIII, and optionally phosphorus and/or at least an organic compound comprising oxygen and/or nitrogen and/or sulfur with said mixed support obtained in step a), so as to obtain a catalytic precursor.

Bringing at least one compound comprising a group VIB metal and at least one compound comprising a group VIII metal into contact with said mixed support obtained in step a) can advantageously be carried out by any known technique of I Those skilled in the art, such as for example ion exchange, dry impregnation, excess impregnation, vapor phase deposition, etc. The bringing into contact can take place in one step or in several successive steps. According to a preferred embodiment, said contacting step(s) is (are) carried out by the so-called "dry" impregnation method well known to those skilled in the art by bringing into contact an impregnation solution containing a compound comprising a group VIII metal and a compound comprising a group VIB metal with said mixed support obtained in step a).

The active phase of the catalyst comprises at least one metal from group VIB and at least one metal from group VIII. The group VIB metal present in the active phase of the catalyst is preferably chosen from molybdenum and tungsten. The group VIII metal present in the active phase of the catalyst is preferably chosen from cobalt, nickel and a 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.

The bringing into contact advantageously involves a precursor of said metals.

By way of example, among the sources of molybdenum, use may be made of oxides and hydroxides, molybdic acids and their salts, in particular ammonium salts such as ammonium molybdate, ammonium heptamolybdate, phosphomolybdic acid (H ₃ PMo ₁₂ O ₄₀ ), and their salts, and optionally silicomolybdic acid (H ₄ SiMo ₁₂ O ₄₀ ) and its salts. The sources of molybdenum can also be any heteropolycompound of Keggin, lacunary Keggin, substituted Keggin, Dawson, Anderson, Strandberg type, for example. Preferably, molybdenum trioxide and the heteropolycompounds of Keggin, lacunary Keggin, substituted Keggin and Strandberg type are used.

The tungsten precursors which can be used are also well known to those skilled in the art. For example, among the sources of tungsten, it is possible to use oxides and hydroxides, tungstic acids and their salts, in particular ammonium salts such as ammonium tungstate, ammonium metatungstate, phosphotungstic acid and their salts, and optionally silicotungstic acid (H ₄ SiW ₁₂ O ₄₀ ) and its salts. The tungsten sources can also be any heteropolycompound of Keggin, lacunary Keggin, substituted Keggin, Dawson type, for example. Preferably, ammonium oxides and salts are used, such as ammonium metatungstate or heteropolyanions of Keggin, lacunary Keggin or substituted Keggin type.

The cobalt precursors which can be used are advantageously chosen from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example. Cobalt hydroxide and cobalt carbonate are preferably used.

The nickel precursors which can be used are advantageously chosen from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example.

The amount of group VIB metal introduced in step b) is such that the content of group VIB metal is between 5 and 40% by weight, expressed as group VIB metal oxide relative to the total weight of the catalyst, preferably between 8 and 35% by weight, very preferably between 10 and 30% by weight. When the metal is molybdenum or tungsten, the metal content is expressed as MoO ₃ or WO ₃ respectively.

The amount of group VIII metal introduced in step b) is such that the content of group VIII metal is between 1 and 10% by weight, expressed as group VIII metal oxide relative to the total weight of the catalyst, preferably between 1.5 and 9% by weight, and preferably between 2 and 8% by weight. When the metal is cobalt or nickel, the metal content is expressed as CoO or NiO respectively.

The molar ratio of group VIII metal to group VIB metal in the catalyst is preferably between 0.1 and 0.8, preferably between 0.15 and 0.6 and even more preferably between 0.15 and 0.45.

Any impregnation solution described in the present invention can comprise any polar protic solvent known to those skilled in the art. Preferably, a polar protic solvent is used, for example chosen from the group formed by methanol, ethanol and water. Preferably, the impregnation solution comprises a water-ethanol or water-methanol mixture as solvents in order to facilitate the impregnation of the compound containing a metal from group VIB and of the compound containing a metal from group VIII (and optionally the phosphorus and/or an organic compound as described below) on the mixed support containing the graphitic material and which is therefore partly hydrophobic. Preferably, the solvent used in the impregnation solution consists of a water-ethanol or water-methanol mixture.

The catalyst of the process according to the invention can also comprise phosphorus as a dopant. The dopant is an added element which in itself has no catalytic character but which increases the catalytic activity of the active phase.

Thus, according to another variant, the contacting step b) can also comprise bringing the mixed support obtained in step a) into contact with an impregnation solution containing phosphorus, in addition to the compound comprising a metal from group VIB and the compound comprising a metal from group VIII.

In this case, the molar ratio of added phosphorus per group VIB metal is between 0.1 and 2.5 mol/mol, preferably between 0.1 and 2.0 mol/mol, and even more preferably between 0.1 and 1.0 mol/mol.

The phosphorus content in said catalyst is preferably between 0.1 and 20% by weight, expressed as P ₂ O ₅ relative to the total weight of the catalyst, preferably between 0.2 and 15% by weight, and very preferably between 0.3 and 6% by weight.

The preferred phosphorus precursor is orthophosphoric acid H ₃ PO ₄ , but its salts and esters such as ammonium phosphates are also suitable. The phosphorus can also be introduced at the same time as the element(s) of group VIB in the form of heteropolyanions of Keggin, lacunary Keggin, substituted Keggin or of the Strandberg type.

The catalyst may also further comprise at least one organic compound containing oxygen and/or nitrogen and/or sulfur before sulfurization. Such additives are described below.

Thus, according to yet another variant, the contacting step b) can also comprise bringing the mixed support obtained in step a) into contact with an impregnation solution containing an organic compound containing oxygen and / or nitrogen and / or sulfur, in addition to the compound comprising a metal from group VIB, the compound comprising a metal from group VIII and optionally phosphorus. The function of additives or organic compounds is to increase the catalytic activity compared to catalysts without additives. Said organic compound is preferentially impregnated on said catalyst after solubilization in aqueous or non-aqueous solution.

In this case, the molar ratio of the organic compound added per group VIB metal in solution is between 0.01 and 5 mol/mol, preferably between 0.05 and 3 mol/mol, preferably between 0. 05 and 2 mol/mol and very preferably between 0.1 and 1.5 mol/mol.

When more than one organic compound is present, the different molar ratios apply for each of the organic compounds present.

Generally, the organic compound is chosen from a compound comprising one or more chemical functions chosen from a carboxylic function, alcohol, thiol, thioether, sulphone, sulphoxide, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and amide, or a compound including a furan ring or even a sugar.

The organic compound containing oxygen can be one or more chosen from compounds comprising one or more chemical functions chosen from a carboxylic, alcohol, ether, aldehyde, ketone, ester or carbonate function or else compounds including a furan cycle. or sugars. Here, an organic compound containing oxygen is understood to mean a compound containing no other heteroatom. By way of example, the organic compound containing oxygen can be one or more chosen from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, a polyethylene glycol (with a molecular weight of between 200 and 1500 g /mol), propylene glycol, 2-butoxyethanol, 2-(2-butoxyethoxy)ethanol, 2-(2-methoxyethoxy)ethanol, triethyleneglycoldimethylether, glycerol, acetophenone, 2,4-pentanedione, pentanone, acetic acid, oxalic acid, maleic acid, malic acid, malonic acid, oxalic acid, gluconic acid, tartaric acid, citric acid, γ- acid ketovaleric, a dialkyl C1-C4 succinate and more particularly dimethyl succinate, methyl acetoacetate, ethyl acetoacetate, 2-methoxyethyl 3-oxobutanoate, 2-methacryloyloxyethyl 3-oxobutanoate, dibenzofuran , a crown ether, orthophthalic acid, glucose, fructose, sucrose, sorbitol, xylitol, γ-valerolactone, 2-acetylbutyrolactone, propylene carbonate, 2-furaldehyde (also known as furfural), 5-hydroxymethylfurfural (also known as 5-(hydroxymethyl)-2-furaldehyde or 5- HMF), 2-acetylfuran, 5-methyl-2-furaldehyde, methyl 2-furoate, furfuryl alcohol (also known as furfuranol), furfuryl acetate, ascorbic acid, lactate ethyl lactate, butyl butyryllactate, ethyl 3-hydroxybutanoate, ethyl 3-ethoxypropanoate, methyl 3-methoxypropanoate, 2-ethoxyethyl acetate, 2- butoxyethyl, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,5-hexanediol, 3-ethyl-1,5 -pentanediol, 2,4-diethyl-1,5-pentanediol, 5-methyl-2(3H)-furanone, butyl glycolate, ethyl 4-oxo-pentanoate, diethyl maleate, maleate dimethyl, dimethyl fumarate, diethyl fumarate , dimethyl adipate, dimethyl 3-oxoglutarate, dimethyl tartrate, diethyl tartrate, diisopropyl tartrate, di-tert-butyl tartrate, dimethyl malate, diethyl malate, malate diisopropyl and dibutyl malate.

The organic compound containing nitrogen can be one or more chosen from compounds comprising one or more chemical functions chosen from an amine or nitrile function. Here, an organic compound containing nitrogen is understood to mean a compound containing no other heteroatom. By way of example, the organic compound containing nitrogen can be one or more selected from the group consisting of ethylenediamine, diethylenetriamine, hexamethylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, acetonitrile , octylamine, guanidine or a carbazole.

The organic compound containing oxygen and nitrogen can be one or more chosen from compounds comprising one or more chemical functions chosen from a carboxylic acid, alcohol, ether, aldehyde, ketone, ester, carbonate, amine function. , nitrile, imide, amide, urea or oxime. Here, an organic compound containing oxygen and nitrogen is understood to mean a compound containing no other heteroatom. By way of example, the organic compound containing oxygen and nitrogen can be one or more chosen from the group consisting of 1,2-cyclohexanediaminetetraacetic acid, monoethanolamine (MEA), 1- methyl-2-pyrrolidinone, dimethylformamide, ethylenediaminetetraacetic acid (EDTA), alanine, glycine, nitrilotriacetic acid (NTA), N-(2-hydroxyethyl)ethylenediamine-N,N′,N acid ′-triacetic acid (HEDTA), diethylene-triaminepentaacetic acid (DTPA), tetramethylurea, glutamic acid, dimethylglyoxime, bicine, tricine, 2-methoxyethyl cyanoacetate, 1-ethyl-2-pyrrolidinone, 1-vinyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, 1-(2-hydroxyethyl)-2-pyrrolidinone, 1-(2-hydroxyethyl)-2,5-pyrrolidinedione, 1 -methyl-2-piperidinone, 1-acetyl-2-azepanone, 1-vinyl-2-azepanone and 4-aminobutanoic acid.

The organic compound containing sulfur can be one or more chosen from compounds comprising one or more chemical functions chosen from a thiol, thioether, sulphone or sulphoxide function. By way of example, the organic compound containing sulfur can be one or more selected from the group consisting of thioglycolic acid, 2,2'-thiodiethanol, 2-hydroxy-4-methylthiobutanoic acid, a sulfonated derivative of a benzothiophene or a sulfoxide derivative of a benzothiophene, ethyl 2-mercaptopropanoate, methyl 3-(methylthio)propanoate and ethyl 3-(methylthio)propanoate.

Preferably, the organic compound contains oxygen, preferably it is chosen from γ-valerolactone, 2-acetylbutyrolactone, triethylene glycol, diethylene glycol, ethylene glycol, ethylenediaminetetraacetic acid (EDTA), l maleic acid, malonic acid, citric acid, acetic acid, oxalic acid, gluconic acid, glucose, fructose, sucrose, sorbitol, xylitol, γ-ketovaleric acid , a C1-C4 dialkyl succinate and more particularly dimethyl succinate, dimethylformamide, 1-methyl-2-pyrrolidinone, propylene carbonate, 2-methoxyethyl 3-oxobutanoate, bicine, tricine, 2 -furaldehyde (also known as furfural), 5-hydroxymethylfurfural (also known as 5-(hydroxymethyl)-2-furaldehyde or 5-HMF), 2-acetylfuran, 5-methyl-2-furaldehyde, ascorbic acid, butyl lactate, ethyl lactate, butyl butyryllactate, ethyl 3-hydroxybutanoate, 3-ethyl ethyl hoxypropanoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, 2-hydroxyethyl acrylate, 1-vinyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, 1,5-pentanediol, 1-(2-hydroxyethyl)-2-pyrrolidinone, 1-(2-hydroxyethyl)-2,5-pyrrolidinedione, 5-methyl-2(3H)-furanone, 1-methyl- 2-piperidinone, 4-aminobutanoic acid, butyl glycolate, ethyl 2-mercaptopropanoate, ethyl 4-oxopentanoate, diethyl maleate, dimethyl maleate, dimethyl fumarate, diethyl, dimethyl adipate and dimethyl 3-oxoglutarate.

The impregnation step includes several modes of implementation. They are distinguished in particular by the moment of introduction of the organic compound when it is present and which can be carried out either at the same time as the impregnation of the metals (co-impregnation), or after (post-impregnation), or before (pre-impregnation). In addition, the modes of implementation can be combined.

When the organic compound is present, the total content of organic compound(s) containing oxygen and/or nitrogen and/or sulfur present in the catalyst is generally between 1 and 30 % by weight, preferably between 1.5 and 25% by weight, and more preferably between 2 and 20% by weight relative to the total weight of the catalyst.

Advantageously, after each impregnation step, the impregnated support is allowed to mature. Curing allows the impregnation solution to disperse evenly within the support.

Any maturation step described in the present invention is advantageously carried out at atmospheric pressure, in an atmosphere saturated with water and at a temperature between 17° C. and 50° C., and preferably at ambient temperature. Generally, a maturation period of between ten minutes and forty-eight hours, and preferably between thirty minutes and six hours, is sufficient.

After step b), a catalytic precursor is thus obtained which comprises an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen, and optionally phosphorus and/or an organic compound containing oxygen and/or nitrogen and/or sulphur.

Step c) drying

According to step c) of the preparation process according to the invention, said catalytic precursor is dried at a temperature below 200° C., advantageously between 50° C. and 180° C., preferably between 70° C. and 150° C. , very preferably between 75° C. and 130° C., without subsequent calcination, so as to obtain a dried catalyst.

The drying step is preferably carried out under an inert atmosphere, typically under a nitrogen atmosphere.

The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure. It is advantageously carried out in a traversed bed using any hot inert gas. Preferably, when the drying is carried out in a fixed bed, the gas used is argon or nitrogen. Very preferably, the drying is carried out in a traversed bed in the presence of nitrogen. Preferably, the drying step lasts between 5 minutes and 15 hours, preferably between 30 minutes and 12 hours.

According to a variant and advantageously when an organic compound is present, the drying is carried out so as to preferably retain at least 30% by weight of the organic compound introduced during an impregnation step, preferably this quantity is greater than 50% weight and even more preferably, greater than 70% by weight, calculated on the basis of the carbon remaining on the catalyst.

The carbon content originating from the organic compound can be determined by taking the difference between the carbon content measured according to ASTM D5373 with and without pretreatment of the catalyst dried under a flow of dry air at 300°C for 2 hours and a flow rate of 2 L /h/g. Indeed, the carbon of the graphitic material has a significantly higher decomposition temperature (generally around 400 to 450°C) than that of the organic compound (generally around 100 to 200°C).

It is important to emphasize that the catalyst during its preparation process does not undergo calcination in order to preserve the graphitic material and, when it is present, at least in part the organic compound in the catalyst. Here, calcination means a heat treatment under a gas containing air or oxygen at a temperature greater than or equal to 200°C.

At the end of the drying step, a dried catalyst is then obtained, which will be subjected to an optional activation step (sulphurization) for its subsequent implementation in a gasoline hydrodesulphurization process.

Step d) optional activation (sulfidation)

According to step d) of the preparation process according to the invention, the dried catalyst is optionally activated in the presence of a sulfurizing agent.

Sulphidation is preferably carried out in a sulphur-reducing medium, that is to say in the presence of H ₂ S and hydrogen, in order to form sulphide metal species. Sulfurization is carried out by injecting onto the catalyst a stream containing H ₂ S and hydrogen, or else a sulfur compound capable of decomposing into H ₂ S in the presence of the catalyst and hydrogen. Polysulphides such as dimethyldisulphide (DMDS) are H ₂ S precursors commonly used to sulphide catalysts. The temperature is adjusted so that the H ₂ S reacts with the dried catalyst to form metal sulphides such as, for example, MoS ₂ and Co ₉ S ₈ . This sulfurization can be carried out in situ or ex situ (inside or outside the reactor) of the reactor of the process according to the invention at temperatures between 200 and 600°C and more preferably between 300 and 500°C.

To be active, metals must be substantially sulfurized. An element is considered to be substantially sulfurized when the molar ratio between the sulfur (S) present on the catalyst and said element is at least equal to 50% of the theoretical molar ratio corresponding to the total sulfurization of the element considered. The overall sulfurization rate is defined by the following equation:

with :

(S/element) _catalyst molar ratio between the sulfur (S) and the element present on the catalyst

(S/element) _theoretical molar ratio between sulfur and the element corresponding to the total sulphidation of the element in sulphide.

This theoretical molar ratio varies according to the element considered:

- (S/Co) _theoretical = 8/9

- (S/Ni) _theoretical = 1/1

- (S/Mo) _theoretical =2/1

- (S/W) _theoretical =2/1

The catalyst comprising several metals, the molar ratio between the S present on the catalyst and all the elements must also be at least equal to 50% of the theoretical molar ratio corresponding to the total sulfurization of each element in sulphide, the calculation being carried out in proportion to the relative molar fractions of each element.

For example, for a catalyst comprising molybdenum and nickel with a respective molar fraction of 0.7 and 0.3, the minimum molar ratio (S/Mo+Ni) is given by the following relationship:

Very preferably, the sulfurization rate of the metals will be greater than 70%.

According to another variant of the invention, the catalyst of the process according to the invention does not undergo a sulfurization step, that is to say that the catalyst is not brought into contact with a sulfurizing agent, before injection of the load. In this case, the catalyst is activated (sulphurized) by the sulfur contained in the charge to be desulphurized.

Catalyst

The catalyst obtained by the process according to the invention comprises an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen. It may additionally comprise phosphorus and/or an organic compound as described above.

The catalyst of the process according to the invention has a total pore volume greater than or equal to 0.15 mL/g, preferably greater than or equal to 0.18 mL/g, and particularly preferably between 0.2 and 0, 5mL/g.

The catalyst of the process according to the invention is characterized by a specific surface comprised between 20 and 200 m²/g, preferably comprised between 30 and 180 m²/g, preferably comprised between 40 and 160 m²/g, very preferably comprised between 50 and 150 m²/g.

The catalyst of the process according to the invention is in the form of grains having an average diameter of between 0.5 and 10 mm. The grains can have any shape known to those skilled in the art, for example the shape of beads (preferably having a diameter of between 1 and 6 mm), extrudates, tablets, hollow cylinders. Preferably, the catalyst (and the support used for the preparation of the catalyst) are either in the form of extrudates with an average diameter of between 0.5 and 10 mm, preferably between 0.8 and 3.2 mm and of average length between 0.5 and 20 mm, or in the form of beads with an average diameter of between 0.5 and 10 mm, preferably between 1.4 and 4 mm. The term "average diameter" of the extrudates means the average diameter of the circle circumscribed to the cross section of these extrudates. The catalyst can advantageously be presented in the form of cylindrical, multi-lobed, tri-lobed or quadri-lobed extrudates. Preferably, its shape will be trilobed or quadrilobed. The shape of the lobes can be adjusted according to all known methods of the prior art.

Gasoline hydrodesulphurization process

The invention also relates to the use of the catalyst prepared according to the process of the invention in a process for the hydrodesulfurization of a gasoline cut containing sulfur compounds and olefins.

The hydrodesulphurization process makes it possible to transform the organosulfur compounds of a gasoline cut into hydrogen sulphide (H ₂ S) while limiting as much as possible the hydrogenation of the olefins present in said cut.

The hydrodesulphurization process is implemented by bringing said gasoline cut, hydrogen and said catalyst into contact, said process being carried out at a temperature of between 200 and 400° C., a total pressure of between 1 and 3 MPa, an hourly volume rate, defined as being the volume flow rate of charge relative to the volume of catalyst, of between 1 and 10 h ^-1 , and a volume ratio of hydrogen/gasoline charge of between 100 and 1200 NL/L.

More specifically, the hydrodesulfurization process comprises bringing the gasoline cut containing sulfur compounds and olefins into contact with the catalyst and hydrogen under the following conditions:

- a temperature between 200 and 400°C, preferably between 230 and 330°C;

- at a total pressure of between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa;

- an Hourly Volume Velocity (VVH), defined as being the volume flow rate of charge relative to the volume of catalyst, between 1 and 10 h^-1, preferably between 2 and 6 hours^-1;

- a hydrogen/petrol feedstock ratio of between 100 and 1200 NL/L, preferably between 150 and 400 NL/L.

The catalytic hydrodesulphurization process can be carried out in one or more reactors in series of the fixed bed type or of the bubbling bed type. If the method is implemented by means of at least two reactors in series, it is possible to provide a device for removing H ₂ S from the effluent from the first hydrodesulphurization reactor before treating said effluent in the second hydrodesulfurization reactor. The operating conditions in the two reactors may or may not be identical.

Load to be processed

The hydrodesulphurization process makes it possible to treat any type of gasoline cut containing sulfur compounds and olefins, such as for example a cut from a coking unit (coking according to the Anglo-Saxon terminology), visbreaking (visbreaking according to the Anglo-Saxon terminology), steam cracking (steam cracking according to Anglo-Saxon terminology) or catalytic cracking (FCC, Fluid Catalytic Cracking according to Anglo-Saxon terminology). This gasoline may optionally be composed of a significant fraction of gasoline from other production processes such as atmospheric distillation (gasoline from direct distillation (or straight run gasoline according to Anglo-Saxon terminology) or from conversion (gasoline from coking or steam cracking) Said feed preferably consists of a gasoline cut from a catalytic cracking unit.

The feed is advantageously a gasoline cut containing sulfur compounds and olefins and has a boiling point of between 30 and less than 250°C, preferably between 35°C and 240°C, and preferably between 40°C and 220°C.

The sulfur content of gasoline cuts produced by catalytic cracking (FCC) depends on the sulfur content of the FCC-treated feedstock, the presence or not of a pretreatment of the FCC feedstock, as well as the end point of the chopped off. Generally, the sulfur contents of an entire gasoline cut, in particular those coming from the FCC, are above 100 ppm by weight and most of the time above 500 ppm by weight. For gasolines having end points higher than 200° C., the sulfur contents are often higher than 1000 ppm by weight, they can even in certain cases reach values of the order of 4000 to 5000 ppm by weight.

In addition, gasolines 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% weight of sulfur of which generally less than 300 ppm of mercaptans. Mercaptans are generally concentrated in the light fractions of gasoline and more specifically in the fraction whose boiling point is below 120°C.

It should be noted that the sulfur compounds present in gasoline can also comprise heterocyclic sulfur compounds, such as for example thiophenes, alkylthiophenes or benzothiophenes.

Preferably, the gasoline treated by the process according to the invention is a heavy gasoline (or HCN for Heavy Cracked Naphtha according to the Anglo-Saxon terminology) resulting from a distillation step aimed at separating a large cut from the gasoline resulting a cracking process (or FRCN for Full Range Cracked Naphtha according to the Anglo-Saxon terminology) into a light gasoline (LCN for Light Cracked Naphtha according to the Anglo-Saxon terminology) and a heavy gasoline HCN. The cut point of light gasoline and heavy gasoline is determined in order to limit the sulfur content of light gasoline and to allow its use in the gasoline pool preferably without additional post-treatment.

Advantageously, the large FRCN cut is subjected to a selective hydrogenation step described below before the distillation step so as to at least partially hydrogenate the diolefins and carry out a reaction of weighting down part of the sulfur compounds. .

To this end, the large FRCN cut is sent to a selective hydrogenation catalytic reactor containing at least one fixed or moving bed of catalyst for the selective hydrogenation of the diolefins and for the weighting down of the mercaptans. The reaction of selective hydrogenation of the diolefins and weighting of the mercaptans is preferably carried out on a sulfur catalyst comprising at least one element from group VIII and optionally at least one element from group VIB and an oxide support. The group VIII element is preferably chosen from nickel and cobalt and in particular nickel. The element of group VIB, when it is present, is preferably chosen from molybdenum and tungsten and very preferably molybdenum. The oxide support of the selective hydrogenation catalyst is preferably chosen from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Preferably, alumina is used and even more preferably, high purity alumina. According to a preferred embodiment, the selective hydrogenation catalyst contains nickel at a content by weight of nickel oxide (in NiO form) of between 1 and 12%, and molybdenum at a content by weight of molybdenum oxide (in MoO ₃ form) of between 6% and 18% and a nickel/molybdenum molar ratio of between 0.3 and 2.5, the metals being deposited on a support consisting of alumina and of which the rate of sulfurization of the metals constituting the catalyst being greater than 50%.

During the optional selective hydrogenation step, the gasoline is 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 more preferably between 90°C and 200°C, with a liquid space velocity (LHSV) 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 selective hydrogenation step is typically carried out with an H ₂ /petrol feed ratio of between 2 and 100 Nm ³ of hydrogen per m ³ of feed, preferably between 3 and 30 Nm ³ of hydrogen per m ³ dump.

Examples

The following examples show the catalytic performance in terms of activity and selectivity in a hydrodesulfurization process for a gasoline cut of a catalyst prepared by:

- bringing an oxide support into contact with a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound before the introduction of the metals (catalyst A according to the invention),

- bringing an oxide support into contact with a mixture comprising an aromatic compound, an aliphatic compound without sulfur compound before the introduction of the metals (comparative catalyst B),

- bringing an oxide support into contact with a mixture comprising an olefinic compound, an aliphatic compound and a sulfur compound before the introduction of the metals (comparative catalyst C),

- introduction of metals before bringing an oxide support into contact with a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound (comparative catalyst D).

Example 1 - Preparation of a catalyst A (according to the invention)

50 cm ³ of an alumina support having a BET surface area of 230 m ² /g, a pore volume measured by mercury porosimetry of 0.78 ml/g and an average pore diameter of 11.5 nm defined as the median diameter by volume by mercury porosimetry and which is in the “extruded” form is loaded into a crossed-bed type reactor. The carbonization of the support is carried out with a charge composed of 20% by weight of toluene, 5.9% by weight of dimethyldisulphide and 74.1% by weight of hexane under the following conditions: T = 350° C., VVH = 4.5 h ^-1 _, P _tot = 60 bar (6 MPa), volume ratio H ₂ /load = 150 NL/L.

The mixed support has a water uptake volume of 0.5 mL/g. Cobalt, molybdenum and phosphorus are then added. The impregnation solution is prepared by dissolving at 90°C molybdenum oxide (2.2 g, MoO ₃ >99.5%, Merck™), cobalt hydroxide (0.57 g, (Co (OH) ₂ 95%, Merck™), 85% weight phosphoric acid in water (0.46 g, Merck™) in 4.7 mL of distilled water After dry impregnation of 10 grams of mixed support, the extrudates are left to mature in a water-saturated atmosphere for 24 hours at room temperature, then they are dried at 90° C. for 16 hours. The dried catalyst thus obtained is denoted A. The final metal composition of the catalyst expressed in the form of oxides and related to the weight of the dry catalyst is then the following: MoO ₃ = 17.1 +/- 0.2% by weight, CoO = 3.4 +/- 0.1% by weight and P ₂ O ₅ = 2.2 +/- 0.1% by weight The catalyst has 4.3% by weight S based on the weight of the catalyst analyzed by CHNS analysis according to ASTM D5373, and 10.7% by weight C based on the weight of the catalyst with an H/C ratio = 1.05 analyzed by CHNS analysis according to ASTM D5373 after pretreatment of the catalyst under a flow of dry air at 300° C. for 2 hours and a flow rate of 2 L/h/g.

Example 2 – Preparation of a catalyst B (non-compliant)

50 cm ³ of the same support as described in Example 1 is loaded into a crossed-bed type reactor. The carbonization of the support is carried out with a charge composed of 20% by weight of toluene and 80% by weight of hexane under the following conditions: T = 350° C., VVH = 4.5 h ^-1 _, P _tot = 60 bar (6 MPa), H ₂ /filler volume ratio = 150 NL/L.

The mixed support has a water uptake volume of 0.75 mL/g. Cobalt, molybdenum and phosphorus are then added. The impregnation solution is prepared by dissolving at 90°C molybdenum oxide (2.2 g), cobalt hydroxide (0.57 g), 85% weight phosphoric acid in water (0.46 g) in 7.2 mL of distilled water. After dry impregnation of 10 grams of mixed support, the extrudates are left to mature in an atmosphere saturated with water for 24 hours at ambient temperature, then they are dried at 90° C. for 16 hours. The dried catalyst thus obtained is denoted B. The final metal composition of the catalyst, expressed in the form of oxides and related to the weight of the dry catalyst, is then as follows: MoO ₃ = 17.1 +/- 0.2% by weight, CoO = 3.4 +/- 0.1% by weight and P ₂ O ₅ = 2.2 +/- 0.1% by weight. The catalyst has 0.15% weight C relative to the weight of the catalyst with an H/C ratio = 2.8 analyzed by CHNS analysis according to ASTM D5373 after pretreatment of the catalyst under a stream of dry air at 300°C for 2 hours and a flow rate of 2 L/h/g.

Example 3 – Preparation of a catalyst C (non-compliant)

50 cm ³ of the same support as described in Example 1 is loaded into a crossed-bed type reactor. The carbonization of the support is carried out with a charge composed of 20% by weight of cyclohexene and 5.9% by weight of dimethyldisulphide and 74.1% by weight of hexane under the following conditions: T = 350° C., VVH = 4.5 h ^-1 _, P _tot = 60 bar (6 MPa), volume ratio H ₂ /load = 150 NL/L.

The mixed support has a water uptake volume of 0.74 mL/g. Cobalt, molybdenum and phosphorus are then added. The impregnation solution is prepared by dissolving at 90°C molybdenum oxide (2.2 g), cobalt hydroxide (0.57 g) and 85% weight phosphoric acid in water (0.46 g) in 7.1 mL of distilled water. After dry impregnation of 10 grams of mixed support, the extrudates are left to mature in an atmosphere saturated with water for 24 hours at ambient temperature, then they are dried at 90° C. for 16 hours. The dried catalyst thus obtained is denoted C. The final metal composition of the catalyst, expressed in the form of oxides and related to the weight of the dry catalyst, is then as follows: MoO ₃ = 17.1 +/- 0.2% by weight, CoO = 3.4 +/- 0.1% by weight and P ₂ O ₅ = 2.2 +/- 0.1% by weight. The catalyst has 0.9% weight S based on the weight of the catalyst analyzed by CHNS analysis according to ASTM D5373, and 1.4% weight C based on the weight of the catalyst with an H/C ratio = 1.12 analyzed by analysis CHNS according to ASTM D5373 after pretreatment of the catalyst under a stream of dry air at 300° C. for 2 hours and a flow rate of 2 L/h/g.

Example 4 – Preparation of a catalyst D (non-compliant)

An impregnation solution is prepared by dissolving at 90°C molybdenum oxide (2.2 g, MoO ₃ >99.5%, Merck™), cobalt hydroxide (0.57 g, (Co (OH) ₂ 95%, Merck™), 85 wt% phosphoric acid in water (0.46 g, Merck™) in 4.7 mL of distilled water 10 grams of the same oxide carrier that used in example 1 is impregnated dry with this impregnation solution. The final metal composition of the catalyst, expressed in the form of oxides and relative to the weight of the dry catalyst, is then as follows: MoO ₃ = 17.1 +/- 0.2% by weight, CoO = 3.4 +/- 0.1% by weight and P ₂ O ₅ = 2.2 +/- 0.1% by weight.
The catalyst is then loaded into a traversed bed type reactor. The carbonization of the catalyst is carried out with a charge composed of 20% by weight of toluene, 5.9% by weight of dimethyldisulphide and 74.1% by weight of hexane under the following conditions: T = 335° C., VVH = 3 h ^-1 _, P _tot = 60 bar (6 MPa), volume ratio H ₂ /charge = 150 NL/L. The carbonized catalyst thus obtained is denoted D. After 12 hours, the carbonized catalyst is analyzed by CHNS analysis according to ASTM D5373. The catalyst has 4.4% weight S based on the weight of the catalyst analyzed by CHNS analysis according to ASTM D5373, and 10.9% weight C based on the weight of the catalyst with an H/C ratio = 1.14 analyzed by analysis CHNS according to ASTM D5373 after pretreatment of the catalyst under a stream of dry air at 300° C. for 2 hours and a flow rate of 2 L/h/g.

Example 5 - Evaluation of the catalytic performance of catalysts A, B, C and D

A representative model charge of a catalytic cracked gasoline containing 10% by weight of 2,3-dimethylbut-2-ene and 0.33% by weight of 3-methylthiophene (i.e. 1000 ppm by weight of sulfur in the charge) is used for the evaluation of the catalytic performances of the different catalysts. The solvent used is heptane.

The hydrodesulfurization reaction (HDS) is carried out in a fixed bed reactor passed through under a total pressure of 1.5 MPa, at 210° C., at VVH = 6 h ^-1 (VVH = volume flow rate of charge/volume of catalyst ), and an H ₂ /feed volume ratio of 300 NL/L, in the presence of 4 mL of catalyst. Prior to the HDS reaction, the catalyst is sulfurized in-situ at 350° C. for 2 hours under a stream of hydrogen containing 15 mol% of H ₂ S at atmospheric pressure.

Each of the catalysts is successively placed in said reactor. Samples are taken at different time intervals and are analyzed by gas phase chromatography in order to observe the disappearance of the reagents and the formation of the products.

The catalytic performances of the catalysts are evaluated in terms of catalytic activity and selectivity. The hydrodesulphurization (HDS) activity is expressed from the rate constant for the HDS reaction of 3-methylthiophene (kHDS), normalized by the volume of catalyst introduced and assuming first-order kinetics with respect to the sulfur compound. The hydrogenation activity of olefins (HydO) is expressed from the rate constant of the hydrogenation reaction of 2,3-dimethylbut-2-ene, normalized by the volume of catalyst introduced and assuming a kinetics of order 1 with respect to the olefin.

The selectivity of the catalyst is expressed by the normalized rate constant ratio kHDS/kHydO. The kHDS/kHydO ratio will be higher the more selective the catalyst. The values obtained are normalized by taking catalyst B as reference (relative HDS activity and relative selectivity equal to 100). The performances are therefore the relative HDS activity and the relative selectivity.

Catalysts Relative HDS activity Relative selectivity A (according to the invention) 101 134 B (comparative) 100 100 C (comparative) 90 111 D (comparative) 50 121

Among the 3 catalysts A, C and D and taking catalyst B as a reference, only catalyst A prepared according to the invention has both a maintained activity in hydrodesulfurization and an increased selectivity in hydrogenation of olefins.

This improvement in the selectivity of the catalysts is particularly advantageous in the case of an implementation in a process for the hydrodesulphurization of gasoline containing olefins for which it is sought to limit as much as possible the loss of octane due to the hydrogenation of the olefins.

Claims (15)

Process for the preparation of a catalyst comprising an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen, said preparation process comprising the following steps:
a) a mixture comprising an aromatic compound, an aliphatic compound and a sulfur compound is brought into contact with an oxide support at a temperature of between 300 and 500° C., an hourly volumetric speed of between 1 and 10 h ^-1 and a total pressure of between 0.05 and 10 MPa, so as to obtain a mixed support comprising said oxide support and a graphitic material containing carbon and hydrogen, and sulfur,
b) then a compound comprising at least one metal from group VIB and at least one compound comprising a metal from group VIII, and optionally phosphorus and/or at least one organic compound comprising oxygen and/or nitrogen and/or sulfur with said mixed support obtained in step a), so as to obtain a catalytic precursor,
c) said catalytic precursor is dried at a temperature below 200° C. without subsequent calcination, so as to obtain a dried catalyst,
d) the dried catalyst is optionally activated in the presence of a sulfurizing agent. Process according to the preceding claim, in which the said aromatic compound is a monoaromatic compound chosen from benzene, toluene, xylenes, styrene, tetraline and divinylbenzene. Process according to one of the preceding claims, in which the carbon content is between 5 and 20% by weight expressed as carbon element relative to the weight of the catalyst, and the H/C atomic ratio is less than 1.4. Process according to one of the preceding claims, in which the said sulfur compound is chosen from dimethyl disulphide, di-tert-butyl disulphide or di-tert-butyl polysulphide. Process according to one of the preceding claims, in which the sulfur content is between 1 and 8% by weight, expressed as sulfur element relative to the weight of the catalyst. Process according to one of the preceding claims, in which the said aliphatic compound is an alkane chosen from hexane, heptane and octane. Process according to one of the preceding claims, in which the oxide support is chosen from an alumina, a silica and a silica-alumina. Process according to one of the preceding claims, in which the group VIB metal is chosen from molybdenum and tungsten, and the group VIII metal is chosen from cobalt, nickel and the mixture of these two elements. Process according to one of the preceding claims, in which the group VIB metal content is between 5 and 40% by weight, expressed as group VIB metal oxide, relative to the total weight of the catalyst and the group VIB metal content. VIII is between 1 and 10% by weight, expressed as group VIII metal oxide, relative to the total weight of the catalyst. Process according to one of the preceding claims, in which the catalyst also comprises phosphorus at a content of between 0.1 and 20% by weight, expressed as P ₂ O ₅ relative to the total weight of the catalyst. Process according to one of the preceding claims, in which the catalyst additionally comprises an organic compound containing oxygen and/or nitrogen and/or sulphur. Process according to the preceding claim, in which the organic compound is chosen from a compound comprising one or more chemical functions chosen from a carboxylic, alcohol, thiol, thioether, sulphone, sulphoxide, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea, amide, or a compound including a furan ring or even a sugar. Process according to Claim 12, in which the organic compound is chosen from γ-valerolactone, 2-acetylbutyrolactone, triethylene glycol, diethylene glycol, ethylene glycol, ethylenediaminetetraacetic acid (EDTA), maleic acid, malonic acid, citric acid, acetic acid, oxalic acid, gluconic acid, glucose, fructose, sucrose, sorbitol, xylitol, γ-ketovaleric acid, dialkyl succinate C1-C4 and more particularly dimethyl succinate, dimethylformamide, 1-methyl-2-pyrrolidinone, propylene carbonate, 2-methoxyethyl 3-oxobutanoate, bicine, tricine, 2-furaldehyde (also known as furfural), 5-hydroxymethylfurfural, 2-acetylfuran, 5-methyl-2-furaldehyde, ascorbic acid, butyl lactate, ethyl lactate, butyl butyryllactate, 3-hydroxybutanoate ethyl acetate, ethyl 3-ethoxypropanoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate e, 2-hydroxyethyl acrylate, 1-vinyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, 1,5-pentanediol, 1-(2-hydroxyethyl)-2-pyrrolidinone, 1-(2-hydroxyethyl)-2,5-pyrrolidinedione, 5-methyl-2(3H)-furanone, 1-methyl-2-piperidinone, 4-aminobutanoic acid, butyl glycolate, 2- ethyl mercaptopropanoate, ethyl 4-oxopentanoate, diethyl maleate, dimethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl adipate and dimethyl 3-oxoglutarate. Catalyst comprising an active phase comprising at least one metal from group VIB and at least one metal from group VIII, sulfur and a mixed support comprising an oxide support and a graphitic material containing carbon and hydrogen, said catalyst being obtained according to the preparation process according to one of Claims 1 to 13. Use of the catalyst prepared according to the process according to one of Claims 1 to 13 in a process for the hydrodesulfurization of a gasoline cut containing sulfur compounds and olefins, in which said gasoline cut is brought into contact with hydrogen and said catalyst, said process being carried out at a temperature of between 200 and 400°C, a total pressure of between 1 and 3 MPa, an hourly volumetric speed, defined as being the volume flow rate of charge relative to the volume of catalyst, of between 1 and 10 h ^-1 , and a hydrogen/gasoline charge volume ratio of between 100 and 1200 NL/L.