FR3104602A1 - Finishing hydrodesulfurization process in the presence of a catalyst obtained by the molten salt route - Google Patents

Abstract

Process for treating a partially desulfurized, sulfur-containing hydrocarbon feedstock resulting from a preliminary catalytic hydrodesulfurization step in the presence of a catalyst prepared by at least the following steps: a) said porous oxide support is brought into contact with at least one metal salt comprising at least one group VIII metal at a temperature below the melting point of said metal salt to form a solid mixture; b) the solid mixture obtained at the end of step a) is heated with stirring to a temperature above the melting point of said metal salt and below 200 ° C; c) the catalyst precursor obtained at the end of step b) is sulfided.

Description

Finishing hydrodesulfurization process in the presence of a catalyst obtained by the molten salt route

Field of the invention

The present invention relates to the field of hydrotreating gasoline cuts, in particular gasoline cuts from fluidized bed catalytic cracking units. More particularly, the present invention relates to the implementation of a catalyst in a process for the production of gasoline with a low sulfur content as well as its method of manufacture. The invention applies most particularly to the treatment of gasoline cuts containing olefins and sulfur, such as gasolines resulting from catalytic cracking, for which it is sought to reduce the content of sulfur compounds, without hydrogenating the olefins and the aromatics.

State of the art

The specifications for automotive fuels provide for a sharp reduction in the sulfur content in these fuels, and in particular in gasolines. This reduction is intended to limit, in particular, the sulfur and nitrogen oxide content in automobile exhaust gases. The specifications currently in force in Europe since 2009 for gasoline fuels set a maximum sulfur content of 10 ppm by weight (parts per million). Such specifications are also in force in other countries such as the United States and China, for example, where the same maximum sulfur content has been required since January 2017. To achieve these specifications, it is necessary to treat gasoline with desulfurization processes.

The main sources of sulfur in gasoline bases are so-called cracked gasolines, and mainly the gasoline fraction resulting from a catalytic cracking process of a residue from the atmospheric or vacuum distillation of a crude oil. The fraction of gasoline resulting from catalytic cracking, which represents on average 40% of the gasoline bases, in fact contributes for more than 90% to the contribution of sulfur in gasolines. Consequently, the production of low-sulphur gasolines requires a stage of desulphurization of catalytic cracking gasolines. Other sources of gasoline that may contain sulfur include coker and visbreaker gasoline or, to a lesser extent, gasoline from atmospheric distillation or steam cracked gasoline.

The elimination of sulfur in gasoline cuts consists of specifically treating these sulfur-rich gasolines by desulfurization processes in the presence of hydrogen. This is referred to as hydrodesulphurization (HDS) processes. However, these gasoline cuts and more particularly the gasolines from the FCC contain a significant proportion of unsaturated compounds in the form of mono-olefins (approximately 20 to 50% by weight) which contribute to a good octane number, diolefins (0.5 at 5% by weight) and aromatics. These unsaturated compounds are unstable and react during the hydrodesulfurization treatment. Diolefins form gums by polymerization during hydrodesulfurization treatments. This formation of gums leads to progressive deactivation of the hydrodesulphurization catalysts or progressive clogging of the reactor. Consequently, the diolefins must be eliminated by hydrogenation before any treatment of these gasolines. Traditional treatment processes desulphurize gasoline in a non-selective manner by hydrogenating a large part of the mono-olefins, which leads to a high loss in octane number and high hydrogen consumption. The most recent hydrodesulphurization processes make it possible to desulphurize cracked gasolines rich in mono-olefins, while limiting the hydrogenation of mono-olefins and consequently the loss of octane. Such methods are for example described in the documents EP-A-1077247 and EP-A-1174485.

However, in the case where the cracking gasolines must be desulphurized very deeply, part of the olefins present in the cracking gasolines is hydrogenated on the one hand and recombines with the H ₂ S to form mercaptans d other hand. This family of compounds, of chemical formula R-SH where R is an alkyl group, are generally called recombinant mercaptans, and generally represent between 20% by weight and 80% by weight of the residual sulfur in desulphurized gasolines. Recombinant mercaptan content can be reduced by catalytic hydrodesulphurization, but this leads to the hydrogenation of a large part of the mono-olefins present in the gasoline, which then leads to a sharp reduction in the index of gasoline octane as well as an overconsumption of hydrogen. It is also known that the loss of octane linked to the hydrogenation of mono-olefins during the hydrodesulphurization step is greater the lower the sulfur content targeted, that is to say that one seeks to eliminate in depth the sulfur compounds present in the load.

It is thus possible to treat the gasoline by a sequence of two reactors as described in the document EP1077247, the first stage, also called the stage of selective HDS, generally aims to carry out a deep desulphurization of the gasoline. with minimal olefin saturation (and no aromatic loss) leading to maximum octane retention. The catalyst used is generally a CoMo type catalyst. During this step, new sulfur compounds are formed by recombination of the H ₂ S resulting from the desulphurization and the olefins: the recombination mercaptans.

The second step generally has the role of minimizing the quantity of recombinant mercaptans. For this, the gasoline is then treated in a hydrodesulfurization reactor, also called a finishing reactor, with a catalyst generally based on nickel which has practically no olefin hydrogenation activity and is capable of reducing the quantity of recombination mercaptans. The temperature is generally higher in the finishing reactor in order to thermodynamically promote the elimination of mercaptans. In practice, a furnace is therefore placed between the two reactors in order to be able to raise the temperature of the second reactor to a temperature higher than that of the first. Usually the nickel-based catalyst used has only a low activity in hydrodesulfurization of sulfur compounds excluding mercaptans.

Different solutions are proposed in the literature to reduce the content of sulfur compounds at the outlet of the finishing reactor for two-step processes.

For example, patent applications WO02/28988 or WO01/79391 describe a treatment of partially desulfurized gasolines to extract said recombinant mercaptans therefrom.

Other solutions are described in the literature for desulphurizing cracked gasolines using a combination of hydrodesulphurization steps and elimination of recombinant mercaptans by reaction to thioethers or disulphides (also called sweetening or " sweetening " according to Anglo-Saxon terminology) (see for example US7799210, US6960291, US2007114156, EP2861094).

Patent application US20030188992 describes how to desulphurize olefinic gasolines by treating the gasoline in a first hydrodesulphurization step, then eliminating sulfur compounds of the mercaptan type during a finishing step. This finishing step mainly consists of an extraction of the mercaptans by solvent by washing.

The patent US5866749 proposes a solution for eliminating the elemental sulfur and the mercaptans contained in an olefinic cut by passing the mixture to be treated over a reduced metal chosen from groups IB, IIB, IIIA of the periodic table and implemented at a lower temperature. at 37°C.

Finally, patent FR2785833 describes a supported catalyst comprising between 1 and 80% by weight of nickel relative to the total weight of the catalyst, the nickel being partly sulphurized, making it possible to reduce the total sulfur and mercaptan contents of gasoline hydrocarbon cuts at very low residual sulfur levels. The catalyst was obtained by a conventional process of dry impregnation of the support with a precursor of the active phase of nickel.

It has now been surprisingly discovered that the implementation in a finishing step of a two-step hydrodesulphurization process of a catalyst prepared in a specific manner makes it possible to convert refractory sulfur compounds other than mercaptans more efficiently, while limiting the degree of hydrogenation of the olefins to values generally lower than 15%, preferentially lower than 10%, and even more preferably lower than 5%. The method for preparing this catalyst implemented in the context of the method according to the invention allows, without addition of solvent and therefore in a very limited number of steps and above all less than the conventional preparation method (i.e. by impregnation), the Obtaining a catalyst whose catalytic performances are at least as good or even superior to conventional catalysts.

Objects of the invention

The present invention relates to a method for treating a partially desulphurized sulfur-containing hydrocarbon feed resulting from a preliminary stage of catalytic hydrodesulphurization, said process being carried out at a temperature of between 200°C and 400°C, a pressure of between between 0.2 and 5 MPa, at an hourly volume rate, defined as the volume flow rate of inlet feed per volume of catalyst used, of between 1 h ^-1 and 10 h ^-1 , in the presence of a catalyst comprising, preferably consisting of an active phase comprising at least one group VIII metal, said active phase being in sulphide form, and a porous support chosen from the group consisting of aluminas, silica, alumina silicas, or even titanium oxides or magnesium used alone or mixed with alumina or silica alumina, said catalyst being prepared by at least the following steps:

a) said porous oxide support is brought into contact with at least one metal salt comprising at least one group VIII metal at a temperature below the melting point of said metal salt to form a solid mixture;

b) the solid mixture obtained at the end of step a) is heated with stirring to a temperature above the melting point of said metallic salt and below 200° C.;

c) optionally, the solid obtained at the end of step b) is dried at a temperature below 200° C. to obtain a dried catalyst precursor;

d) optionally, the solid obtained at the end of step b) or c) is calcined at a temperature greater than 200° C. and less than or equal to 1100° C. under an inert atmosphere or under an atmosphere containing oxygen to obtaining a calcined catalyst precursor;

e) optionally, the catalyst precursor obtained at the end of step c) or d) is reduced to obtain a reduced catalyst precursor;

f) the catalyst precursor obtained at the end of step b), optionally c), d) or e) is sulphided.

Preferably, the metal salt has a melting point between 20 and 150°C.

Preferably, the metal salt is a hydrated nitrate salt.

Preferably, said Group VIII metal is nickel.

Preferably, said metal salt is nickel nitrate hexahydrate.

Preferably, the mass ratio between said metal salt and the porous support is between 0.1 and 2.5.

Preferably, step a) is carried out for 5 minutes to 12 hours.

Preferably, the drying time of step c) is less than 16 hours.

Preferably, the group VIII metal content, expressed as group VIII element, is between 5 and 65% by weight relative to the total weight of the catalyst.

Preferably, the active phase of said catalyst consists of group VIII metal sulphide particles of size less than or equal to 20 nm.

In one embodiment according to the invention, a step a′) of bringing the porous support into contact with an organic compound comprising oxygen and/or nitrogen is carried out.

In one embodiment according to the invention, steps a) and a′) are carried out simultaneously, said organic compound being in solid form to form a solid mixture.

In one embodiment according to the invention, step a′) is carried out after the sequence of steps a) and b).

Preferably, the molar ratio of said organic compound introduced during step a′) relative to the group VIII element introduced in step a) is between 0.01 and 5.0 mol/mol.

Detailed description of the invention

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.

In this application, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open-ended and does not exclude other non-recited material. It is understood that the term “include” includes the exclusive and closed term “consist”.

By “macropores”, we mean pores whose opening is greater than 50 nm.

By "mesopores", we mean pores whose opening is between 2 nm and 50 nm, limits included.

By “micropores”, we mean pores whose opening is less than 2 nm.

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 book "Engineering techniques, analysis and characterization treatise", 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 term “size of the group VIII metal sulphide (nano)particles” is understood to mean the size of the coherence domain of the crystallites of the group VIII metals in sulphide form. This coherence domain size of group VIII metal crystallites in sulphide form is determined by X-ray diffraction, from the width of the most intense diffraction line using the Scherrer relationship. This method, used in X-ray diffraction on powders or polycrystalline samples which links the width at mid-height of the diffraction peaks to the size of the particles, is described in detail in the reference: J. Appl. Crystal. (1978), 11, 102-113 "Scherrer after sixty years: A survey and some new results in the determination of crystallite size", J. I. Langford and A. J. C. Wilson. The size measurement of each species of nickel sulphide present is carried out by decomposition of the line of interest using functions of the Pseudo-Voigt type with a contribution of the Gaussian and Lorentzian forms equal to 0.5. This treatment is conventionally used by those skilled in the art.

Where multiple Group VIII sulfide species are present, "Group VIII metal sulfide particle size" is the weighted average of the sizes of each Group VIII sulfide species, the amount of each of the phases being determined by refinement of structure by the Rietveld method.

Group VIII metal content is measured by X-ray fluorescence.

Finishing hydrodesulfurization process

The present invention relates to a process for treating a hydrocarbon feedstock containing sulfur and partially desulphurized, resulting from a preliminary stage of catalytic hydrodesulphurization, in which said feedstock to be treated is brought into contact with a so-called finishing catalyst. The hydrodesulfurization step, known as finishing (or " polishing " according to the Anglo-Saxon terminology), is mainly implemented to at least partially decompose the recombination mercaptans into olefins and H ₂ S, but it also allows to hydrodesulphurize the more refractory sulfur compounds whereas the first stage of hydrodesulphurization is mainly implemented to transform a large part of the sulfur compounds into H ₂ S. The remaining sulfur compounds are essentially refractory sulfur compounds and the recombination mercaptans derived from the addition of the H ₂ S formed.

The finishing hydrodesulfurization process is generally carried out at a temperature between 280°C and 400°C, preferably between 300°C and 380°C, more preferably between 310°C and 370°C. The temperature of this finishing stage is generally at least 5° C., preferably at least 10° C. and very preferably at least 30° C. higher than the temperature of the first hydrodesulphurization stage.

The process is generally implemented at an hourly volume rate (which is defined as the volume flow rate of inlet feed per volume of catalyst used) of between 1 h ^-1 and 10 h ^-1 , preferably between 1 h ^-1 and 8:00 ^a.m.

The process is generally implemented with a hydrogen flow rate such that the ratio between the hydrogen flow rate expressed in normal m ³ per hour (Nm ³ /h) and the feed flow rate to be treated expressed in m ³ per hour at standard conditions is between 10 Nm ³ /m ³ and 4000 Nm ³ /m ³ , preferably between 50 Nm ³ /m ³ and 1000 Nm ³ /m ³ .

The process is generally implemented at a pressure of between 0.5 MPa and 5 MPa, preferably between 1 MPa and 3 MPa.

The hydrocarbon feedstock containing sulfur and partially desulphurized is preferably a gasoline containing olefinic compounds, preferably a gasoline cut resulting from a catalytic cracking process. The treated hydrocarbon charge generally has a boiling point below 350°C, preferably below 300°C and very preferably below 250°C. Preferably, the hydrocarbon feed contains less than 100 ppm by weight of sulfur derived from organic compounds and preferably less than 50 ppm by weight of sulfur derived from organic compounds, in particular in the form of recombinant mercaptans and refractory sulfur compounds.

The charge to be treated undergoes a partial desulfurization treatment before said finishing step. This preliminary treatment consists in bringing the hydrocarbon feed containing sulfur into contact with hydrogen, in one or more hydrodesulphurization reactors in series, containing one or more catalysts suitable for carrying out the hydrodesulphurization. Preferably, the operating pressure of this step is generally between 0.5 MPa and 5 MPa, and very preferably between 1 MPa and 3 MPa, and the temperature is generally between 200° C. and 400° C. , and very preferably between 220°C and 380°C. Preferably, the quantity of catalyst used in each reactor is generally such that the ratio between the flow rate of gasoline to be treated, expressed in m ³ per hour at standard conditions, per m ³ of catalyst is between 0.5 h ^-1 and 8:00 ^p.m. , and very preferably between ^1:01 a.m. and 10:00 ^a.m. Preferably, the hydrogen flow rate is generally such that the ratio between the hydrogen flow rate expressed in normal m ³ per hour (Nm ³ /h) and the flow rate to be treated expressed in m ³ per hour at standard conditions is comprised between 50 Nm ³ /hm ³ and 1000 Nm ³ /m ³ , very preferably between 70 Nm ³ /m ³ and 800 Nm ³ /m ³ . Preferably, this step will be implemented with the aim of carrying out hydrodesulphurization selectively, that is to say with a hydrogenation rate of the mono-olefins of less than 80% by weight, preferably less than 70% weight and very preferably less than 60% weight.

The desulfurization rate reached during this hydrodesulfurization step is generally greater than 50% and preferably greater than 70%, such that the hydrocarbon fraction used in the mercaptan capture process contains less than 100 ppm by weight of sulfur and preferably less than 50 ppm by weight of sulfur.

Any hydrodesulfurization catalyst can be used in the preliminary hydrodesulfurization step. Preferably, catalysts are used which exhibit a high selectivity with respect to hydrodesulphurization reactions relative to the hydrogenation reactions of olefins. Such catalysts comprise at least one amorphous and porous mineral support, a group VIB metal, a group VIII metal. The group VIB metal is preferably molybdenum or tungsten and the group VIII metal is preferably nickel or cobalt. The support is generally selected from the group consisting of aluminas, silica, silica-aluminas, silicon carbide, titanium oxides alone or mixed with alumina or silica alumina, magnesium oxides alone or as a mixture with alumina or silica alumina. Preferably, the support is selected from the group consisting of aluminas, silica and silica-aluminas. Preferably, the hydrodesulphurization catalyst used in the additional hydrodesulphurization stage or stages has the following characteristics:

- the content of group VIB elements is between 1 and 20% by weight of oxides of group VIB elements relative to the total weight of the catalyst;

- the content of group VIII elements is between 0.1 and 20% by weight of oxides of group VIII elements relative to the total weight of the catalyst;

- the molar ratio (group VIII elements/group VIB elements) is between 0.1 and 0.8.

A very preferred hydrodesulfurization catalyst comprises cobalt and molybdenum and has the characteristics mentioned above. Furthermore, the hydrodesulphurization catalyst may comprise phosphorus. In this case, the phosphorus content is preferably between 0.1 and 10% by weight of P ₂ O ₅ relative to the total weight of catalyst and the phosphorus to group VIB elements molar ratio is greater than or equal to 0.25 , preferably greater than or equal to 0.27.

At the end of the hydrodesulphurization stage, the effluent can undergo a stage of separation of hydrogen and H ₂ S by any method known to those skilled in the art (separation drum, stabilization column, etc.). .

Characteristics of the finishing catalyst

The catalyst used in the context of the process according to the invention comprises, preferably consists of, an active phase based on at least one group VIII metal, said active phase being partly in sulphide form, and a support porous material chosen from the group consisting of aluminas, silica, alumina silicas, or alternatively titanium or magnesium oxides used alone or as a mixture with alumina or alumina silica. Preferably, the Group VIII metal is nickel. Preferably, said active phase does not comprise any group VIB metal. Very preferably, the catalyst consists of an active phase of sulfurized nickel and an alumina support.

When the Group VIII metal is nickel, the phase diagram of nickel sulfide exhibits a large number of sulfur-rich and nickel-rich phases at low temperatures. Different phases and stoichiometries of nickel sulphide are therefore possible, ranging from nickel-rich compounds such as Ni ₃ S ₂ , Ni ₆ S ₅ , Ni ₇ S ₆ , Ni ₉ S ₈ and NiS to sulfur-rich compounds such as Ni ₃ S ₄ and NiS ₂ . Note that NiS is also known to exist in two main phases, namely the hexagonal α-NiS, which is stable at high temperatures, and the rhombohedral β-NiS which is stable at low temperatures. The existence of these numerous phases makes the synthesis of nickel sulphide in the form of a single phase complex, the products therefore often being mixtures of two or more phases.

The active phase of at least one group VIII metal in sulphide form designates in the present application chemical compounds of the M _x S _y type, where M is a group VIII metal with 0.5 ≤ x/y ≤ 2 , preferably x = 1 and y = 1 or else x= 3 and y = 2. When the group VIII metal is nickel, the compounds most present are NiS in hexagonal or rhombohedral form or else Ni ₃ S ₂ .

Advantageously, the active phase of the group VIII metal in sulphide form is in the form of group VIII sulphide nanoparticles deposited on the oxide support. The size of the group VIII sulfide nanoparticles in the catalyst is preferably less than or equal to 20 nm, preferably less than or equal to 15 nm, more preferably between 1 and 12 nm.

The group VIII metal content, expressed as group VIII element, is preferably between 5 and 65% by weight relative to the total weight of the catalyst, preferably between 8 and 55% by weight, even more preferably between 12 and 40% by weight, and particularly preferably between 12 and 34% by weight.

The catalyst preferably has a total pore volume greater than or equal to 0.3 mL/g, preferably greater than or equal to 0.4 mL/g, and particularly preferably between 0.5 and 1.1 mL/g .

The catalyst has a BET specific surface of at least 40 m ² /g, preferably of at least 50 m ² /g, and even more preferably between 55 and 250 m ² /g, preferably between 60 and 225 m ² /g.

Said catalyst 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. “Average diameter” of the extrudates is understood to mean the average diameter of the circle circumscribed to the cross section of these extrudates. Said 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.

The catalyst support is a mineral support selected from the group consisting of aluminas, silica, silica-aluminas, titanium oxides alone or mixed with alumina or silica alumina, magnesium oxides alone or in mixture with alumina or silica alumina. Preferably, the support is selected from the group consisting of aluminas, silica and silica-aluminas. Very preferably, the support consists essentially of at least one alumina, that is to say 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 alumina relative to the total weight of said support. Preferably, said support has an alumina content greater than or equal to 90% by weight relative to the total weight of said support, optionally supplemented by silica and/or phosphorus at a total content of at most 10% by weight in equivalent SiO ₂ and/or P ₂ O ₅ , preferably less than 5% by weight, and very preferably less than 2% by weight relative to the total weight of the support. The silica and/or the phosphorus can be introduced by any technique known to those skilled in the art, during the synthesis of the alumina gel or by impregnation of the support used for the preparation of the catalyst.

Even more preferably, the support consists of alumina. Preferably, the alumina present in said support is a transition alumina such as a gamma, delta, theta, chi, rho or eta alumina, alone or as a mixture. More preferably, the alumina is a gamma, delta or theta transition alumina, alone or as a mixture.

The following characteristics of the support correspond to the characteristics of the support used for the preparation of the catalyst before introduction of the active phase.

The support used for the preparation of the catalyst preferably has a total pore volume greater than or equal to 0.45 mL/g, preferably greater than or equal to 0.60 mL/g, and particularly preferably between 0.60 and 1.3mL/g.

The support used for the preparation of the catalyst has a BET specific surface of at least 40 m ² /g, preferably at least 50 m ² /g, and even more preferably between 60 and 300 m ² /g , preferably between 80 and 250 m ² /g.

Catalyst Preparation Process

The catalyst used in the context of the finishing hydrodesulfurization process according to the invention could be obtained by a preparation process comprising at least the following steps:

a) said porous oxide support is brought into contact with at least one metal salt comprising at least one group VIII metal at a temperature below the melting point of said metal salt to form a solid mixture;

b) the solid mixture obtained at the end of step a) is heated with stirring to a temperature above the melting point of said metallic salt and below 200° C.;

c) optionally, the solid obtained at the end of step b) is dried at a temperature below 200° C. to obtain a dried catalyst precursor;

d) optionally, the solid obtained at the end of step b) or c) is calcined at a temperature greater than 200° C. and less than or equal to 1100° C. under an inert atmosphere or under an atmosphere containing oxygen to obtaining a calcined catalyst precursor;

e) optionally, the catalyst precursor obtained at the end of step c) or d) is reduced to obtain a reduced catalyst precursor;

f) the catalyst precursor obtained at the end of step b), c), d) or e) is sulphided.

The process for preparing the catalyst may also comprise a step a′) of bringing the support into contact with an organic compound, optionally followed by a step a′′) of drying said impregnated support at a temperature below 250°C.

The steps of the catalyst preparation process are described in detail below.

Step a)

According to step a), a porous support of the oxide type is brought into contact with a metal salt comprising at least one group VIII metal to form a solid mixture. Preferably, the melting point of said metal salt is between 20 and 150°C. The contact time is generally between 5 minutes to 12 hours. Preferably, the mass ratio between said metal salt and said porous oxide support is between 0.1 and 2.5, preferably between 0.3 and 2. In this step, the metal salt is in solid form, it is that is to say that the bringing into contact between said porous support and said metal salt is carried out at a temperature below the melting point of said metal salt.

According to step a), at least one metal salt comprising at least one metal belonging to group VIII is provided. Preferably, the melting point of said metal salt is between 20 and 150°C. Preferably the metal is Ni. Preferably the metal salt is hydrated. Preferably, the metal salt is a hydrated nitrate salt. Preferably, the metal salt is hexahydrated nickel nitrate (Ni(NO ₃ ) ₂ .6H ₂ O, T _{melting point} =56.7° C.).

According to step a), the contacting of said porous oxide support and the metal salt can be done by any method known to those skilled in the art. Preferably, the bringing into contact of said porous support and of the metal salt is carried out with contact means chosen from among convective mixers, drum mixers or static mixers. Step a) is preferably carried out for a period of between 5 minutes to 5 hours depending on the type of mixer used, preferably between 10 minutes and 4 hours, and even more preferably between 15 minutes and 3 hours.

Step b)

According to step b), the mixture obtained at the end of step a) is heated with stirring to a temperature above the melting point of the metal salt. Preferably, the temperature is between the melting temperature of the metal salt and 200° C., very preferably between the melting temperature of the metal salt and 150° C., and at atmospheric pressure. The residence time is generally between 5 minutes and 12 hours, preferably between 5 minutes and 4 hours.

According to step b), the mechanical homogenization of the mixture can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used.

Step c) (optional step)

According to optional step c), the drying of the solid obtained in step b) is carried out at a temperature below 200° C., advantageously between 50 and 180° C., preferably between 70 and 150° C., so very preferred between 75 and 130°C.

The drying step is preferably carried out for a maximum duration of 4 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen.

The optional 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 using air or any other hot gas. Preferably, the gas used is either air or an inert gas such as argon or nitrogen. Very preferably, the drying is carried out in the presence of nitrogen and/or air. Unlike step b), the drying step c) is preferably not carried out with stirring. A dried catalyst precursor is obtained.

Step d) (optional step)

According to step d), the solid obtained in step b) or c) undergoes a calcination treatment at a temperature above 200° C. and less than or equal to 1100° C., preferably between 250° C. and 650° C. ° C, and very preferably between 300° C. and 500° C., under an inert atmosphere (nitrogen for example) or under an atmosphere containing oxygen (air for example). The duration of this heat treatment is generally less than 16 hours, preferably less than 5 hours. After this treatment, the group VIII element is in oxide form and the solid no longer contains or contains very few counterions and water of crystallization initially present in the metallic salt. The calcination step can be carried out by any technique known to those skilled in the art. It is advantageously carried out in a traversed bed or in a fluidized bed using air or any other hot gas. A calcined catalyst precursor is obtained.

Step e) (optional step)

Prior to the sulfurization of the catalyst, at least one step of reducing treatment is optionally carried out in the presence of a reducing gas after steps b), c) or d) so as to obtain a catalyst comprising at least one metal from group VIII in least partially in metallic form. This treatment makes it possible to form metallic particles, in particular of group VIII in the zero valent state. The reducing gas is preferably hydrogen. The hydrogen can be used pure or in a mixture (for example a hydrogen/nitrogen, hydrogen/argon, hydrogen/methane mixture). In the case where the hydrogen is used as a mixture, all the proportions are possible.

Said reducing treatment is preferably carried out at a temperature of between 120 and 500°C, preferably between 150 and 450°C. The duration of the reducing treatment is generally between 2 and 40 hours, preferably between 3 and 30 hours. The rise in temperature up to the desired reduction temperature is generally slow, for example fixed between 0.1 and 10° C./min, preferably between 0.3 and 7° C./min. A reduced catalyst precursor is obtained.

Step f)

After stage b), or after optional stages c) d) or e), the product obtained (dried, calcined or reduced catalyst) must be sulfurized so as to form the group VIII sulphide. This sulfurization is carried out by methods well known to those skilled in the art, and advantageously under a sulfo-reducing atmosphere in the presence of hydrogen and hydrogen sulfide. 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 are precursors of H ₂ S commonly used to sulphide the catalyst. The temperature is adjusted so that the H ₂ S reacts with group VIII to form group VIII sulfide. This sulfurization can be carried out in situ or ex situ (inside or outside the reactor of the capture process). Advantageously, it is carried out ex-situ. Generally it is carried out at temperatures between 200 and 600°C and more preferably between 250 and 500°C. To be active, Group VIII should preferably be substantially sulfurized. The operating conditions of the sulfurization, in particular the nature of the sulfurizing agent, the H ₂ S/hydrogen ratio, the temperature and the duration of the sulfurization will preferably be adapted according to the product obtained after step b) or after the optional steps c) d) or e), so as to obtain a good sulphidation of the metal of group VIII, that is to say that the metal of group VIII is largely and preferably entirely sulphurized.

The degree of sulfurization of the metals constituting the active phase of said catalyst is advantageously at least equal to 60%, preferably at least equal to 80%. The sulfur content in the sulphide material is measured by elemental analysis according to ASTM D5373. A metal is considered to be sulfurized when the overall sulfurization rate defined by the molar ratio between the sulfur (S) present on said catalyst and said metal is at least equal to 60% of the theoretical molar ratio corresponding to the total sulfurization of the metal(s) considered. The overall sulfurization rate is defined by the following equation:

in which :

(S/metal) _catalyst is the molar ratio between the sulfur (S) and the metal present on the catalyst;

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

This theoretical molar ratio varies according to the metal considered:

(S/Ni) _theoretical = 2/3

V ariante: P repair catalyst using an organic compound

The process for preparing the catalyst may also optionally comprise a stage a') of bringing the support into contact with an organic compound comprising oxygen and/or nitrogen, optionally followed by a stage a'') of drying said impregnated support at a temperature below 250°C.

The molar ratio of said organic compound relative to the group VIII element is advantageously between 0.01 and 5.0 mol/mol, preferably between 0.05 and 2.0 mol/mol.

Generally, the organic compound comprising oxygen and/or nitrogen is chosen from a compound comprising one or more chemical functions chosen from a carboxylic acid, alcohol, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and amide. Preferably, the organic compound is chosen from a compound comprising at least one carboxylic acid function, or at least one alcohol function, or at least one ester function, or at least one amide function.

In one embodiment according to the invention, said organic compound comprises at least one carboxylic acid function. Preferably, said organic compound is chosen from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids. In this case, the organic compound is more preferably chosen from oxalic acid, malonic acid, glutaric acid, glycolic acid, lactic acid, succinic acid, tartronic acid, citric acid, tartaric acid, pyruvic acid and γ-ketovaleric acid.

In one embodiment according to the invention, said organic compound comprises at least one alcohol function. Preferably, said organic compound is chosen from:

- organic compounds comprising a single alcohol function;

- organic compounds comprising two alcohol functions;

- organic compounds chosen from diethylene glycol, triethylene glycol, tetraethylene glycol, or a polyethylene glycol corresponding to the formula H(OC ₂ H ₄ ) _n OH with n greater than 4 and having an average molar mass of less than 20,000 g /mol;

- monosaccharides of molecular formula C _n (H ₂ O) _p with n between 3 and 12;

- disaccharides, trisaccharides, or monosaccharide derivatives.

In this case, the organic compound is more preferably chosen from methanol, ethanol, phenol, ethylene glycol, propane-1,3-diol, butane-1,4-diol, pentane-1, 5-diol, hexane-1,6-diol, glycerol, xylitol, mannitol, sorbitol, pyrocatechol, resorcinol, hydroquinol, diethylene glycol, triethylene glycol, polyethylene glycols having a mass average molar less than 600 g/mol, glucose, mannose, fructose, sucrose, maltose, lactose, in any one of their isomeric forms.

In one embodiment according to the invention, said organic compound comprises at least one ester function.

Preferably, said organic compound is chosen from:

- linear or cyclic or cyclic unsaturated carboxylic acid esters;

- organic compounds comprising at least two carboxylic acid ester functions;

- organic compounds comprising at least one carboxylic acid ester function and at least one second functional group chosen from alcohols, ethers, ketones, aldehydes;

- cyclic or linear esters of carbonic acid;

- linear carbonic acid diesters.

In this case, the organic compound is more preferably chosen from γ-valerolactone, methyl laurate, C1-C4 dialkyl succinate and more particularly dimethyl succinate, dimethyl malate, an acetoacid and propylene carbonate.

In one embodiment according to the invention, said organic compound comprises at least one amide function.

Preferably, said organic compound is chosen from:

- acyclic amides comprising one or two amide functions;

- cyclic amides or lactams;

- organic compounds comprising at least one amide function and one carboxylic acid function or one alcohol function;

- organic compounds comprising at least one amide function and one additional nitrogen heteroatom.

In this case, the organic compound is more preferably chosen from formamide, N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, acetamide, N-methylacetamide, N ,N-dimethylmethanamide, N,N-diethylacetamide, N,N-dimethylpropionamide, propanamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, γ-lactam, caprolactam, acetylleucine, N-acetylaspartic acid, aminohippuric acid, N-acetylglutamic acid, 4-acetamidobenzoic acid, lactamide, glycolamide, urea, N-methylurea, N,N′-dimethylurea, 1,1- dimethylurea, tetramethylurea according to any of their isomeric forms.

Mode of introduction of the organic compound

The variant of the catalyst preparation process implementing step a′), possibly a′′) comprises several modes of implementation when it is desired to add the organic compound. They are distinguished in particular by the order of introduction of the organic compound and of the precursor of the group VIII metal, the bringing into contact of the organic compound with the support which can be carried out either after the bringing into contact of the precursor of the group VIII metal with the support, or during contacting of the Group VIII metal precursor with the support.

In one embodiment according to the invention, step a′) is carried out at the same time as step a), that is to say that the contacting of the support is carried out in the presence of at least a metal salt comprising at least one Group VIII metal and at least one organic compound to form a solid mixture. In this variant embodiment, the organic additive must be in solid form to form a solid mixture.

In another embodiment according to the invention, step a′) is carried out after the sequence of steps a) and b). In this embodiment, step a′) can be carried out by impregnation, according to methods well known to those skilled in the art. Preferably, said step a′) is carried out by dry impregnation, which consists in bringing the catalyst support into contact with a volume of said solution of between 0.25 and 1.5 times the porous volume of the support. Said solution containing at least one organic compound may be aqueous or organic (for example methanol or ethanol or phenol or acetone or toluene or dimethyl sulfoxide (DMSO)) or else consist of a mixture of water and at least one organic solvent. Said organic compound is previously at least partially dissolved in said solution at the desired concentration. Preferably, said solution is aqueous or contains ethanol. Even more preferably, said solution is aqueous. The pH of said solution may be modified by the possible addition of an acid or a base. In another possible embodiment, the solvent may be absent from the impregnation solution. In the embodiment in which step a′) is carried out by impregnation, dry or in excess, preferably dry, the impregnation of the support with at least one solution containing at least said organic compound can be advantageously carried out via at least two impregnation cycles, using identical or different organic compounds for each cycle. In this case, each impregnation is advantageously followed by drying and possibly by heat treatment. In this variant embodiment, after the step of bringing the organic compound into contact with the support, the impregnated support can advantageously be allowed to mature, optionally before an intermediate drying step. When a maturation step is carried out, said step is advantageously carried out at atmospheric pressure or at reduced pressure, under an inert atmosphere or under an atmosphere containing oxygen or under an atmosphere containing water, and at a temperature between between 10°C and 50°C, and preferably at room temperature. Generally, a maturation period of less than forty-eight hours and preferably between five minutes and five hours is sufficient.

In the embodiment in which step a') is carried out after the sequence of steps a) and b), step a') is followed by a step a'') of drying at a temperature below 250°C, preferably between 15 and 240°C, more preferably between 30 and 220°C, even more preferably between 50 and 200°C, and even more preferably between 70 and 180°C.

Each step a), b) and a') (optionally a'') can be carried out several times, optionally in the presence of a group VIII precursor and/or an identical or different organic compound(s). at each step a) and b) and/or a') respectively, all possible combinations of implementations of steps a) and b) and/or a') being included within the scope of the invention.

The invention is illustrated by the examples which follow.

Examples

Example 1: Catalyst AT containing nickel prepared by impregnation according to the state of the art ( improper )

In this example, catalyst A is prepared by double dry impregnation of the alumina support (S_BET= 116 m²/g; V_total = 0.82 mL/g) via an aqueous solution of nickel nitrate hexahydrate. Drying at 120°C for 12 hours followed by calcination at 450°C for 6 hours is carried out after each impregnation. The solid is then sulfurized according to the protocol described. Catalyst A contains 23.6% by weight of nickel relative to the total weight of the catalyst.

Example 2 : Catalyst B containing nickel (compliant)

An alumina alumina support (S_BET= 116 m²/g; V_total = 0.82 mL/g) in the form of beads and a hexahydrated nickel nitrate salt (Aldrich®, >98%). The homogenization stage is a drum mixer inclined at 45° and equipped with counter-blades to ensure a cascading movement when mixing the solids. The mixer is stirred at 60 revolutions per minute for 1 hour at ambient temperature and pressure. The solid mixture obtained is then sent to a heating capacity with stirring in which the temperature is increased at 5°C/min up to 80°C and left for 1 hour. The solid obtained is then calcined at 450° C. for 6 hours in a traversed bed, then sulfurized according to the protocol described. Catalyst B obtained containing 23.5% by weight of Ni relative to the weight of the catalyst.

Example 3 : Evaluation of the performance of catalysts implemented in a finishing reactor of a desulfurization process .

The evaluation of the catalytic performance of nickel-based solids A (non-conforming) and B (according to the invention) is carried out using a model charge representative of a partially desulfurized catalytic cracking gasoline from a preliminary stage of catalytic hydrodesulfurization, containing 10% by weight of 2,3-dimethylbut-2-ene and 70 ppmS (including 42 ppmS of hexanethiol-1 and 28 ppmS of 3-methylthiophene). The solvent used is heptane.

The finishing reaction is carried out in a fixed-bed reactor passed through under a total pressure of 1.5 MPa, at 270° C., at VVH = 6 h ^-1 (VVH = volume flow rate of charge/volume of catalyst), and a H ₂ /feed volume ratio of 300 Nl/l, in the presence of 4 mL of catalyst. Prior to the finishing 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. 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 conversion of 3-methylthiophene and hexanethiol-1.

Catalyst AT
(comparative) B (according to the invention ) S _BET catalyst (m ² .g ^-1 ) 116 116 V _porous catalyst (mL.g ^-1 ) 0.82 0.82 Ni content (wt%) 23.6 23.5 Hexanethiol-1 conversion (% wt) 88% 89% Conversion 3 methylthiophene (% wt) 50% 65% 2,3-dimethylbut-2-ene conversion (% wt) 5% 5%

The conversions of 3-methylthiophene observed with catalyst B are greater than those observed with comparative catalyst A, the conversions to hexanethiol-1 and 2,3-dimethylbut-2-ene being moreover substantially equivalent. This improvement in the conversion of the catalysts to sulfur compound excluding mercaptan 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 ensure deep desulphurization and to limit as much as possible octane loss due to hydrogenation of olefins.

Claims (14)

Process for treating a partially desulphurized sulfur-containing hydrocarbon feed resulting from a preliminary stage of catalytic hydrodesulphurization, said process being carried out at a temperature of between 200°C and 400°C, a pressure of between 0.2 and 5 MPa, at an hourly volume rate, defined as the volume flow rate of inlet feed per volume of catalyst used, between 0.1 h ^-1 and 20 h ^-1 , in the presence of a catalyst comprising, preferably consisting of , an active phase comprising at least one group VIII metal, said active phase being partly in sulphide form, and a porous support chosen from the group consisting of aluminas, silica, alumina silicas, or titanium oxides or magnesium used alone or mixed with alumina or silica alumina, said catalyst being prepared by at least the following steps:
a) said porous oxide support is brought into contact with at least one metal salt comprising at least one group VIII metal at a temperature below the melting point of said metal salt to form a solid mixture;
b) the solid mixture obtained at the end of step a) is heated with stirring to a temperature above the melting point of said metal salt and below 200° C.;
c) optionally, the solid obtained at the end of step b) is dried at a temperature below 200° C. to obtain a dried catalyst precursor;
d) optionally, the solid obtained at the end of step b) or c) is calcined at a temperature greater than 200° C. and less than or equal to 1100° C. under an inert atmosphere or under an atmosphere containing oxygen to obtaining a calcined catalyst precursor;
e) optionally, the catalyst precursor obtained at the end of step c) or d) is reduced to obtain a reduced catalyst precursor;
f) the catalyst precursor obtained at the end of step b), optionally c), d) or e) is sulphided. Process according to Claim 1, in which the metal salt has a melting temperature of between 20 and 150°C. A method according to claim 1 or 2, wherein the metal salt is a hydrated nitrate salt. A method according to any of claims 1 to 3, wherein said Group VIII metal is nickel. A method according to claim 4, wherein said metal salt is nickel nitrate hexahydrate. Process according to any one of Claims 1 to 5, in which the mass ratio between the said metallic salt and the porous support is between 0.1 and 2.5. Process according to any one of claims 1 to 6, in which step a) is carried out for 5 minutes to 12 hours. Process according to any one of Claims 1 to 7, in which the drying time in step c) is less than 16 hours. Process according to any one of Claims 1 to 8, in which the content of group VIII metal, expressed as group VIII element, is between 5 and 65% by weight relative to the total weight of the catalyst Process according to any one of Claims 1 to 9, in which the active phase of the said catalyst consists of group VIII metal sulphide particles of a size less than or equal to 20 nm. Process according to any one of Claims 1 to 10, in which a step a′) of bringing the porous support into contact with an organic compound comprising oxygen and/or nitrogen is carried out. Process according to claim 11, in which steps a) and a') are carried out simultaneously, said organic compound being in solid form to form a solid mixture. Process according to Claim 12, in which step a') is carried out after the sequence of steps a) and b). Process according to any one of Claims 11 to 13, in which the molar ratio of the said organic compound introduced during stage a') relative to the group VIII element introduced in stage a) is between 0.01 and 5.0 mol/mol.