FR3091660A1 - Process for the preparation of a selective hydrogenation catalyst comprising a step of forming a NiCu alloy in post-impregnation - Google Patents

Abstract

Process for preparing a selective hydrogenation catalyst comprising nickel, copper, and a support comprising at least one refractory oxide, comprising the following steps: - contacting the support with a solution comprising a nickel precursor; - drying the catalyst precursor at a temperature below 250 ° C; - Contacting the catalyst precursor with a solution containing at least one copper precursor and one nickel precursor; - step of drying the catalyst precursor at a temperature below 250 ° C; - reduction of the catalyst precursor by bringing said precursor into contact with a reducing gas at a temperature between 150 ° C and 250 ° C.

Description

Process for the preparation of a selective hydrogenation catalyst comprising a step of forming a NiCu alloy in post-impregnation

The present invention relates to a process for the preparation of a supported metal catalyst, comprising nickel and copper, intended particularly for the hydrogenation of unsaturated hydrocarbons.

The present invention also relates to the use of these catalysts in reactions for the hydrogenation of unsaturated hydrocarbons, and more particularly, for the selective hydrogenation of olefin cuts.

State of the art

Catalysts for the selective hydrogenation of polyunsaturated compounds are generally based on metals from group VIII of the periodic table of elements, such as nickel. The metal is in the form of nanometric metallic particles deposited on a support which may be a refractory oxide. The group VIII metal content, the possible presence of a second metallic element, the size of the metal particles and the distribution of the active phase in the support as well as the porous nature and distribution of the support are parameters which can have a importance on catalyst performance.

The rate of the hydrogenation reaction is governed by several criteria, such as the diffusion of the reactants towards the surface of the catalyst (external diffusional limitations), the diffusion of the reactants into the pores of the support towards the active sites (internal diffusional limitations) and the intrinsic properties of the active phase such as the size of the metal particles and the distribution of the active phase within the support.

The promotion of nickel-based catalyst has frequently been proposed in order to improve performance in selective hydrogenation. For example, it is known from US patent 5,208,405 to implement a catalyst based on nickel and silver for the selective hydrogenation of C4-C10 diolefins. On the other hand, it is known to promote nickel, present mainly, with group IB metals, in particular gold (FR 2,949,077) or tin (FR 2,949,078). Document FR 3,011,844 discloses a catalyst for implementing a selective hydrogenation process comprising a support and an active metallic phase deposited on the support, the active metallic phase comprising copper and at least one nickel or cobalt metal. in a Cu:(Ni and/or Co) molar ratio greater than 1.

Furthermore, prior to the use of such catalysts and their implementation in a hydrogenation process, a step of reducing treatment in the presence of a reducing gas is carried out so as to obtain a catalyst comprising an active phase at least partially in metallic form. This treatment activates the catalyst and forms metal particles. This treatment can be carried out in-situ or ex-situ, i.e. after or before loading the catalyst into the hydrogenation reactor.

Objects of the invention

Continuing its research in the field of hydrogenating catalysts, the Applicant has now surprisingly discovered that it is possible to prepare catalysts which are particularly active in the selective hydrogenation of polyunsaturated hydrocarbon cuts after reduction at low temperature, by carrying out a specific preparation process in which an alloy based on nickel and copper is formed on the support after having deposited on the support a precursor of the active phase (based on nickel) of the catalyst.

Without wishing to be bound by any theory, it has been observed by the Applicant that during the preparation of the catalyst, the performance of a step of bringing the support into contact with a solution containing simultaneously a metal precursor based on copper and a metal precursor based on nickel followed by a stage of drying and reduction in the presence of a reducing gas at low temperature (between 150°C and 250°C) makes it possible to obtain a nickel-copper alloy (in the form reduced) which unexpectedly makes it possible to greatly improve the reducibility of the active phase of nickel on the support, said active phase of nickel being supplied for the most part in a step prior to that of bringing said support into contact with said solution containing simultaneously a metal precursor of copper and nickel. The preparation process according to the invention thus makes it possible to carry out a stage of reduction of the metallic elements in the presence of a reducing gas at lower temperatures and shorter reaction times than those commonly used in the prior art. Advantageously, the use of less severe operating conditions than in the prior art makes it possible to carry out the reduction step directly within the reactor in which it is desired to carry out the selective hydrogenation of polyunsaturated cuts. Furthermore, the presence of copper in the catalyst makes it possible to maintain good activity and a longer life of the catalyst when the latter is brought into contact with a hydrocarbon feedstock comprising sulfur, in particular the C3 hydrocarbon cuts from steam cracking and /or catalytic cracking. Indeed, compared to nickel, the copper present in the catalyst more easily captures the sulfur compounds included in the charge, which greatly limits the irreversible poisoning of the most virulent active sites of nickel which exist on the new catalyst.

The subject of the present invention is a process for the preparation of a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising a metallic active phase based on nickel, at a rate of 1 and 35% by weight of nickel element relative to the weight total of the catalyst, and based on copper, in an amount of 0.5 to 15% by weight of copper element relative to the total weight of the catalyst, and a support comprising at least one refractory oxide chosen from silica, alumina and silica-alumina, which process comprises the following steps:

a) a step of bringing said support into contact with a solution comprising at least one nickel precursor is carried out;

b) at least one step of drying the catalyst precursor is carried out at the end of step a) at a temperature below 250° C.;

c) optionally, heat treatment of the catalyst precursor obtained at the end of step b) is carried out at a temperature of between 250 and 1000° C., in the presence or not of water;

d) a step is carried out for bringing the catalyst precursor obtained at the end of step b), optionally at the end of step c), into contact with at least one solution containing at least one copper precursor and a nickel precursor at a nickel concentration desired to obtain on the final catalyst a content of between 0.5 and 15% by weight of nickel element relative to the total weight of the final catalyst;

e) at least one stage of drying the catalyst precursor is carried out at the end of stage d) at a temperature below 250° C.;

f) optionally, heat treatment of the catalyst precursor obtained at the end of step e) is carried out at a temperature of between 250 and 1000° C., in the presence or not of water;

g) reducing the catalyst precursor from step e), optionally step f), by bringing said catalyst precursor into contact with a reducing gas at a temperature between 150 and 250°C.

Advantageously, in step d) the molar ratio between nickel and copper is between 0.5 and 5, preferably between 0.7 and 4.5, more preferably between 0.9 and 4.

Preferably, step g) is carried out at a temperature between 160 and 230°C.

More preferably, step g) is carried out at a temperature between 170 and 220°C.

Advantageously, step g) is carried out between 10 minutes and 110 minutes.

In one embodiment according to the invention, the method further comprises a step of passivation of the catalyst precursor by a sulfur compound after step g) of reduction.

Preferably, the passivation step is carried out at a temperature between 20 and 350° C. for 10 to 240 minutes.

Advantageously, said sulfur compound is chosen from thiophene, thiophane, dimethylsulphide, diethylsulphide, dipropylsulphide, propylmethylsulphide, di-thio-di-ethanol.

Advantageously, which copper precursor supplied during step d) is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulphate, copper chloride, copper bromide, copper iodide or copper fluoride.

Preferably, the copper precursor is copper nitrate.

Advantageously, the reducing gas of step g) is dihydrogen.

Preferably, the hydrogen flow rate, expressed in L/hour/gram of catalyst precursor, is between 0.01 and 100 L/hour/gram of catalyst precursor.

Preferably, the nickel precursor supplied during step a) and/or d) is chosen from nickel nitrate, nickel carbonate or nickel hydroxide.

Another object according to the invention relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and/or acetylenics and/or alkenylaromatics, contained in a charge of hydrocarbons having a final boiling point of less than or equal to 300°C, which process is carried out at a temperature of between 0 and 300°C, at a pressure of between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) of between 0.1 and 10 and at an hourly volume rate of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volume rate between 100 and 40,000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst obtained according to the preparation process according to the invention.

Another object according to the invention relates to a process for the preparation of a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising nickel, in an amount of 1 and 35% by weight of nickel element relative to the total weight of the catalyst, copper, in an amount of 0.5 to 15% by weight of copper element relative to the total weight of the catalyst, and a support comprising at least one refractory oxide chosen from silica, alumina and silica-alumina, which process including the following steps:

a) a step of bringing said support into contact with a solution comprising at least one nickel precursor is carried out;

b) at least one step of drying the catalyst precursor is carried out at the end of step a) at a temperature below 250° C.;

c) optionally, heat treatment of the catalyst precursor obtained at the end of step b) is carried out at a temperature of between 250 and 1000° C., in the presence or absence of water;

d) a step is carried out for bringing the catalyst precursor obtained at the end of step b), optionally at the end of step c), into contact with at least one solution containing at least one copper precursor at a rate of 0.5 to 15% by weight of copper element relative to the total weight of the final catalyst and at least one nickel precursor, the molar ratio between nickel and copper being between 0.5 and 5;

e) at least one stage of drying the catalyst precursor is carried out at the end of stage d) at a temperature below 250° C.;

f) optionally, heat treatment of the catalyst precursor obtained at the end of step e) is carried out at a temperature of between 250 and 1000° C., in the presence or not of water;

g) reducing the catalyst precursor from step e), optionally step f), by bringing said catalyst precursor into contact with a reducing gas at a temperature between 150 and 250°C.

Detailed description of the invention

1. 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 D.R. 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.

The degree of reduction (TR) of a metal M contained in the catalyst is defined as being the percentage of said metal M reduced after the step of reducing said catalyst. The reduction rate (TR) corresponds to the ratio between the quantity of reduced metal (M1) and the quantity of theoretically reducible metal present on the catalyst measured by Fluorescence X (M2), i.e. TR (%) = (M1/M2)x100 . In the context of the present invention, the rate of reduction of nickel (Ni) was measured by X-ray diffraction analysis (XRD or “ X-ray diffraction ” according to the English terminology). The description of the method for measuring the quantity of reducible metal on oxide catalysts is explained later in the description (cf. examples section).

By the specific surface of the catalyst or of the support used for the preparation of the catalyst according to the invention is meant the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical “The Journal of American Society”, 60, 309, (1938).

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 according to the invention is meant the volume measured by intrusion with a mercury porosimeter according to the ASTM D4284-83 standard 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 volume of macropores and mesopores is measured by mercury intrusion porosimetry according to 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 value from which the mercury fills all the intergranular voids is fixed at 0.2 MPa, and it is considered that beyond that the mercury penetrates into the pores of the sample.

The macroporous volume of the catalyst or of the support used for the preparation of the catalyst according to the invention is defined as being the cumulative volume of mercury introduced at a pressure of between 0.2 MPa and 30 MPa, corresponding to the volume contained in the pores of diameter apparent greater than 50 nm.

The mesoporous volume of the catalyst or of the support used for the preparation of the catalyst according to the invention is defined as being the cumulative volume of mercury introduced at a pressure of between 30 MPa and 400 MPa, corresponding to the volume contained in the pores of apparent diameter included between 2 and 50 nm.

The volume of the micropores is measured by nitrogen porosimetry. The quantitative analysis of the microporosity is carried out using the "t" method (method of Lippens-De Boer, 1965) which corresponds to a transformation of the initial adsorption isotherm as described in the work "Adsorption by powders and porous solids. Principles, methodology and applications” written by F. Rouquérol, J. Rouquérol and K. Sing, Academic Press, 1999.

The median mesoporous diameter is also defined as being the diameter such that all the pores, among all the pores constituting the mesoporous volume, of size less than this diameter constitute 50% of the total mesoporous volume determined by intrusion with a mercury porosimeter.

The median macroporous diameter is also defined as being the diameter such that all the pores, among all the pores constituting the macroporous volume, of size less than this diameter constitute 50% of the total macroporous volume determined by intrusion with a mercury porosimeter.

2. Detailed description

Catalyst Preparation Process

According to the invention, the process for preparing a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising a metal active phase based on nickel, at a rate of 1 and 35% by weight of nickel element relative to the total weight of the catalyst, and based on copper, in an amount of 0.5 to 15% by weight of copper element relative to the total weight of the catalyst, and a support comprising at least one refractory oxide chosen from silica, alumina and silica-alumina, includes the following steps:

a) a step of bringing said support into contact with a solution comprising at least one nickel precursor is carried out;

b) at least one step of drying the catalyst precursor is carried out at the end of step a) at a temperature below 250° C.;

c) optionally, heat treatment of the catalyst precursor obtained at the end of step b) is carried out at a temperature of between 250 and 1000° C., in the presence or not of water;

d) a step is carried out for bringing the catalyst precursor obtained at the end of step b), optionally at the end of step c), into contact with at least one solution containing at least one copper precursor and a nickel precursor at a nickel concentration desired to obtain on the final catalyst a content of between 0.5 and 15% by weight of nickel element relative to the total weight of the final catalyst;

e) at least one stage of drying the catalyst precursor is carried out at the end of stage d) at a temperature below 250° C.;

f) optionally, heat treatment of the catalyst precursor obtained at the end of step e) is carried out at a temperature of between 250 and 1000° C., in the presence or not of water;

g) reducing the catalyst precursor from step e), optionally step f), by bringing said catalyst precursor into contact with a reducing gas at a temperature between 150 and 250° C.;

h) optionally, a passivation step is carried out with a sulfur compound after the reducing treatment step g).

Steps a) to h) of said preparation process are described in detail below.

Step a) Bringing the support into contact with a solution comprising a nickel precursor

The deposition of nickel, in accordance with the implementation of step a), can be carried out by impregnation, dry or in excess, or by deposition-precipitation, according to methods well known to those skilled in the art.

Said step a) is preferably carried out by impregnating the support with a solution comprising a nickel precursor consisting for example of bringing the support into contact with at least one aqueous or organic solution (for example methanol or ethanol or phenol or acetone or toluene or dimethyl sulfoxide (DMSO)) or consisting of a mixture of water and at least one organic solvent, comprising, preferably consisting of, at least one nickel precursor at least partially the dissolved state, or even by bringing the support into contact with at least one colloidal solution comprising, preferably consisting of, at least one precursor of nickel, in oxidized form (nanoparticles of oxides, oxy(hydroxide) or nickel hydroxide) or in reduced form (metal nanoparticles of nickel in the reduced state). Preferably, the solution is aqueous. The pH of this solution may be modified by the possible addition of an acid or a base.

Preferably, said step a) is carried out by dry impregnation, which consists in bringing the support into contact with at least one solution, containing, preferably consisting of, at least one nickel precursor, the volume of the solution of which is between 0.25 and 1.5 times the porous volume of the support to be impregnated.

When the nickel precursor is introduced in aqueous solution, a nickel precursor is advantageously used in the form of nitrate, carbonate, chloride, sulphate, hydroxide, hydroxycarbonate, formate, acetate, oxalate , of complexes formed with acetylacetonates, or of tetrammine or hexammine complexes, or of any other inorganic derivative which is soluble in aqueous solution, which is brought into contact with said support. Advantageously used as nickel precursor, nickel nitrate, nickel carbonate, nickel chloride, nickel hydroxide, nickel hydroxycarbonate. Very preferably, the nickel precursor is nickel nitrate, nickel carbonate or nickel hydroxide.

The nickel precursor is supplied to step a) at a desired concentration to obtain on the final catalyst (ie obtained at the end of step h) reduction or step i) passivation if the latter is carried out) a content of between 0.5 and 34.5% by weight of nickel element relative to the total weight of the catalyst.

Step b) Drying of the impregnated support

Step b) of drying the impregnated support is carried out at a temperature below 250°C, preferably between 15 and 180°C, more preferably between 30 and 160°C, even more preferably between 50 and 150°C, and even more preferentially between 70 and 140° C., for a duration typically comprised between 10 minutes and 24 hours. Longer durations are not excluded, but do not necessarily bring improvement.

The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

Step c) Heat treatment of the dried catalyst (optional step)

The catalyst precursor obtained at the end of step b) can undergo an additional heat treatment step, before step d) of reduction, at a temperature between 250 and 1000° C. and preferably between 250 and 750 °C, for a period typically between 15 minutes and 10 hours, under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not. Longer treatment times are not excluded, but do not bring necessary improvement.

The term “heat treatment” is understood to mean the temperature treatment respectively without the presence or in the presence of water. In the latter case, contact with water vapor can take place at atmospheric pressure or at autogenous pressure. Several combined cycles without the presence or with the presence of water can be carried out.

In the event of the presence of water, the water content is preferably between 150 and 900 grams per kilogram of dry air, and even more preferably between 250 and 650 grams per kilogram of dry air.

Thus, after the drying step b), or after the optional heat treatment step c), the catalyst precursor comprises nickel in the oxide form, that is to say in the NiO form, and copper in the form oxide, i.e. in CuO form.

Step d) Bringing a nickel precursor and a copper precursor into contact with the support

The deposition of nickel and copper on said support, in accordance with the implementation of step d), can be carried out by impregnation, dry or in excess, or by deposition - precipitation, according to methods well known to the 'Man of the trade.

Said step d) is preferably carried out by impregnation of the catalyst precursor consisting for example of bringing said catalyst precursor into contact with at least one solution, aqueous or organic (for example methanol or ethanol or phenol or acetone or toluene or dimethyl sulfoxide (DMSO)) or consisting of a mixture of water and at least one organic solvent, comprising, preferably consisting of, at least one nickel precursor and at least one copper precursor at least partially in the dissolved state, or even by bringing said catalyst precursor into contact with at least one colloidal solution comprising, preferably consisting of, at least one nickel precursor and one copper precursor in oxidized form (nanoparticles of oxide, oxy(hydroxide) or hydroxide of nickel and copper) or in reduced form (metallic nanoparticles of nickel and copper in the reduced state). Preferably, the solution is aqueous. The pH of this solution can be modified by the possible addition of an acid or a base.

Preferably, said step d) is carried out by dry impregnation, which consists in bringing the catalyst precursor into contact with a solution, comprising, preferably consisting of, at least one nickel precursor and at least one copper precursor, the volume of the solution of which is between 0.25 and 1.5 times the pore volume of the catalyst precursor to be impregnated.

When the nickel precursor is introduced in aqueous solution, a nickel precursor is advantageously used in the form of nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, sulphate, formate , of complexes formed by a polyacid or an acid-alcohol and its salts, of complexes formed with acetylacetonates, of tetrammine or hexammine complexes, or of any other inorganic derivative which is soluble in aqueous solution, which is brought into contact with the said precursor of catalyst. Preferably, the nickel precursor used is advantageously nickel nitrate, nickel hydroxide, nickel carbonate, nickel chloride, or nickel hydroxycarbonate. Very preferably, the nickel precursor is nickel nitrate, nickel carbonate or nickel hydroxide.

When the copper precursor is introduced in aqueous solution, a copper precursor in mineral or organic form is advantageously used. In mineral form, the copper precursor can be chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulphate, copper chloride, copper bromide, copper iodide or copper fluoride. Very preferably, the copper precursor salt is copper nitrate.

According to the invention, the nickel precursor is supplied to stage d) at a desired concentration to obtain on the final catalyst (ie obtained at the end of stage g) of reduction or of stage h) of passivation if the latter is carried out) a content of between 0.5 and 15% by weight of nickel element relative to the total weight of the final catalyst, preferably between 0.5 and 10% by weight, more preferably between 1 and 8% by weight, even more preferably between 1 and 5% by weight.

The amounts of the copper precursor(s) introduced into the solution according to step d) are chosen such that the total copper content is between 0.5 and 15% by weight of copper element relative to the total weight of the catalyst. (ie obtained at the end of step g) of reduction or of step h) of passivation if the latter is carried out), preferably between 0.5 and 12% by weight, preferably between 0 75 and 10% by weight, and even more preferably between 1 and 9% by weight.

Step e) Drying of the impregnated support

Step e) of drying the impregnated support is carried out at a temperature below 250°C, preferably between 15 and 180°C, more preferably between 30 and 160°C, even more preferably between 50 and 150°C, and even more preferentially between 70 and 140° C., for a duration typically comprised between 10 minutes and 24 hours. Longer durations are not excluded, but do not necessarily bring improvement.

The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

f) Heat treatment of the dried catalyst (optional step)

The dried catalyst precursor can undergo an additional heat treatment step, before step g) of reduction, at a temperature between 250 and 1000° C. and preferably between 250 and 750° C., for a duration typically between 15 minutes and 10 hours, under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not. Longer treatment times are not excluded, but do not bring necessary improvement.

The term “heat treatment” is understood to mean the temperature treatment respectively without the presence or in the presence of water. In the latter case, contact with water vapor can take place at atmospheric pressure or at autogenous pressure. Several combined cycles without the presence or with the presence of water can be carried out. After this or these treatment(s), the catalyst precursor comprises nickel in oxide form, that is to say in NiO form.

In the event of the presence of water, the water content is preferably between 150 and 900 grams per kilogram of dry air, and even more preferably between 250 and 650 grams per kilogram of dry air.

Step g) Reduction with a reducing gas

Prior to the use of the catalyst in the catalytic reactor and the implementation of a hydrogenation process, a reducing treatment step g) is carried out in the presence of a reducing gas so as to obtain a catalyst comprising nickel in least partially in metallic form. This step is advantageously carried out in situ , that is to say after loading the catalyst into a reactor for the selective hydrogenation of polyunsaturated compounds. This treatment makes it possible to activate said catalyst and to form metallic particles, in particular nickel in the zero valent state. Performing the catalyst reduction treatment in situ makes it possible to dispense with an additional step of passivation of the catalyst by an oxygenated compound or by CO ₂ , which is necessarily the case when the catalyst is prepared by carrying out a reduction treatment. ex-situ, that is to say outside the reactor used for the selective hydrogenation. Indeed, when the reducing treatment is carried out ex-situ, it is necessary to carry out a passivation step in order to preserve the metallic phase of the catalyst in the presence of air (during transport and loading operations of the catalyst in the reactor of hydrogenation), then to carry out a new step of reduction of the catalyst.

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.

According to an essential aspect of the preparation process according to the invention, said reducing treatment is carried out at a temperature between 150° C. and 250° C., preferably between 160 and 230° C., and more preferably between 170 and 220° C. . The duration of the reducing treatment is between 5 minutes and less than 5 hours, preferably between 10 minutes and 4 hours, and even more preferably between 10 minutes and 110 minutes.

The presence of the nickel-copper alloy at least partially in reduced form makes it possible to use operating conditions for reducing the active phase of nickel that are much less severe than in the prior art and thus makes it possible to directly carry out the step of reduction within the reactor in which it is desired to carry out the selective hydrogenation of polyunsaturated cuts.

Furthermore, the presence of copper in the catalyst makes it possible to maintain good activity of the catalyst and good life of the catalyst when the latter is brought into contact with a hydrocarbon feedstock comprising sulfur, in particular the C3 hydrocarbon cuts from steam cracking. and/or catalytic cracking. Indeed, compared to nickel, the copper present in the catalyst more easily captures the sulfur compounds included in the charge, which limits the irreversible poisoning of the active sites.

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.

The hydrogen flow, expressed in L/hour/gram of catalyst precursor is between 0.01 and 100 L/hour/gram of catalyst, preferably between 0.05 and 10 L/hour/gram of catalyst precursor , even more preferably between 0.1 and 5 L/hour/gram of catalyst precursor.

Step h) Passivation (optional)

The catalyst prepared according to the process according to the invention can advantageously undergo a step of passivation by a sulfur compound which makes it possible to improve the selectivity of the catalysts and to avoid thermal runaways during the start-up of new catalysts (" run-away " according to Anglo-Saxon terminology). Passivation generally consists in irreversibly poisoning with the sulfur compound the most virulent active sites of nickel which exist on the new catalyst and therefore in attenuating the activity of the catalyst in favor of its selectivity. The passivation step is carried out by implementing methods known to those skilled in the art

The passivation step with a sulfur compound is generally carried out at a temperature of between 20 and 350° C., preferably between 40 and 200° C., for 10 to 240 minutes. The sulfur compound is for example chosen from the following compounds: thiophene, thiophane, alkylmonosulfides such as dimethylsulfide, diethylsulfide, dipropylsulfide and propylmethylsulfide or else an organic disulfide of formula HO-R ₁ -SSR ₂ -OH such as di-thio-di -ethanol of formula HO-C ₂ H ₄ -SSC ₂ H ₄ -OH (often called DEODS). The sulfur content is generally between 0.1 and 2% by weight of said element relative to the total weight of the catalyst.

Catalyst

The catalyst obtainable by the preparation process according to the invention comprises an active phase comprising nickel and copper, part of the nickel and copper of which is in the form of a nickel-copper alloy, corresponding advantageously in the formula Ni _x Cu _y with x between 0.1 and 0.9 and including between 0.1 and 0.9, and a support in the form of a refractory oxide chosen from silica, l alumina, silica-alumina.

The copper content is between 0.5 and 15% by weight of copper element relative to the total weight of the catalyst, preferably between 0.5 and 12% by weight, preferably between 0.75 and 10% by weight , and even more preferably between 1 and 9% by weight.

The total nickel content in the catalyst is between 1 and 35% by weight of nickel element relative to the total weight of the catalyst, preferably between 2 and 30% by weight, preferably between 3 and 27% by weight, and even more preferably between 4 and 18% by weight.

The nickel content included in the copper-nickel alloy formed by the preparation process according to the invention is between 0.5 and 15% by weight of copper element relative to the total weight of the catalyst, preferably between 1 and 12 % by weight, and more preferably between 1 and 10% by weight.

The porous support is selected from the group consisting of silica, alumina and silica-alumina. Even more preferably, the support is alumina. Alumina can be present in all possible crystallographic forms: alpha, delta, theta, chi, rho, eta, kappa, gamma, etc., taken alone or in a mixture. Preferably, the support is chosen from alpha, delta, theta, gamma alumina.

The specific surface of the porous support is generally greater than 5 m²/g, preferably between 30 and 400 m²/g, more preferably between 50 and 350 m²/g.

The total pore volume of the support is generally between 0.1 and 1.5 cm ³ /g, preferably between 0.35 and 1.2 cm ³ /g, and even more preferably between 0.4 and 1, 0 cm ³ /g, and even more preferably between 0.45 and 0.9 cm ³ /g.

Said catalyst is generally presented in all the forms known to those skilled in the art, for example in the form of beads (generally having a diameter of between 1 and 8 mm), extrudates, tablets, hollow cylinders. Preferably, it consists of extrudates with a diameter generally between 0.5 and 10 mm, preferably between 0.8 and 3.2 mm and very preferably between 1.0 and 2.5 mm and of average length between 0.5 and 20 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.

The specific surface of the catalyst is generally greater than 5 m²/g, preferably between 30 and 400 m²/g, more preferably between 50 and 350 m²/g.

The total pore volume of the catalyst is generally between 0.1 and 1.5 cm ³ /g, preferably between 0.35 and 1.2 cm ³ /g, and even more preferably between 0.4 and 1, 0 cm ³ /g, and even more preferably between 0.45 and 0.9 cm ³ /g.

The catalyst advantageously has a macropore volume less than or equal to 0.6 mL/g, preferably less than or equal to 0.5 mL/g, more preferably less than or equal to 0.4 mL/g, and even more preferably less than or equal to equal to 0.3 mL/g.

The mesoporous volume of the catalyst is generally at least 0.10 mL/g, preferably at least 0.20 mL/g, preferably between 0.25 mL/g and 0.80 mL/g, more preferably between 0.30 and 0.65 mL/g.

The median mesoporous diameter can be between 3 nm and 25 nm, and preferably between 6 and 20 nm, and particularly preferably between 8 and 18 nm.

The catalyst advantageously has a median macroporous diameter of between 50 and 1500 nm, preferably between 80 and 1000 nm, even more preferably between 250 and 800 nm.

Preferably, the catalyst has low microporosity, very preferably it has no microporosity.

Selective hydrogenation process

The present invention also relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and/or acetylenics and/or alkenylaromatics, also called styrenics, contained in a charge of hydrocarbons having a final boiling point of less than or equal to 300°C, which process is carried out at a temperature of between 0 and 300°C, at a pressure of between 0.1 and 10 MPa, at a hydrogen/ (polyunsaturated compounds to be hydrogenated) of between 0.1 and 10 and at an hourly volume rate of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a molar hydrogen/(polyunsaturated compounds to be hydrogenated ) between 0.5 and 1000 and at an hourly volume rate between 100 and 40,000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst obtained by the preparation process as described above in the describe option.

Monounsaturated organic compounds such as ethylene and propylene, for example, are the source of the manufacture of polymers, plastics and other value-added chemicals. These compounds are obtained from natural gas, naphtha or gas oil which have been treated by steam cracking or catalytic cracking processes. These processes are operated at high temperature and produce, in addition to the desired monounsaturated compounds, polyunsaturated organic compounds such as acetylene, propadiene and methylacetylene (or propyne), 1-2-butadiene and 1-3 -butadiene, vinylacetylene and ethylacetylene, and other polyunsaturated compounds whose boiling point corresponds to the C5+ cut (hydrocarbon compounds having at least 5 carbon atoms), in particular diolefinic or styrenic or indenic compounds. These polyunsaturated compounds are very reactive and lead to side reactions in the polymerization units. It is therefore necessary to eliminate them before recovering these cuts.

Selective hydrogenation is the main treatment developed to specifically remove unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatics while avoiding their total saturation and therefore the formation of the corresponding alkanes or naphthenes. In the case of steam cracked gasolines used as feed, selective hydrogenation also makes it possible to selectively hydrogenate alkenylaromatics into aromatics by avoiding the hydrogenation of aromatic rings.

The hydrocarbon feed treated in the selective hydrogenation process has a final boiling point less than or equal to 300°C and contains at least 2 carbon atoms per molecule and includes at least one polyunsaturated compound. The term “polyunsaturated compounds” means compounds comprising at least one acetylenic function and/or at least one diene function and/or at least one alkenylaromatic function.

More particularly, the feedstock is selected from the group consisting of a C2 steam cracking cut, a C2-C3 steam cracking cut, a C3 steam cracking cut, a C4 steam cracking cut, a C5 steam cracking cut and a steam cracking gasoline also called pyrolysis gasoline or C5+ cut.

The C2 cut from steam cracking, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following composition: between 40 and 95% by weight of ethylene relative to the total weight of the cut, of the order of 0.1 to 5% by weight of acetylene, the remainder being essentially ethane and methane. In certain C2 cuts from steam cracking, between 0.1 and 1% by weight of C3 compounds may also be present.

The C3 steam cracking cut, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following average composition: of the order of 90% by weight of propylene relative to the total weight of the cut , of the order of 1 to 8% by weight of propadiene and methylacetylene, the remainder being essentially propane. In some C3 cuts, between 0.1 and 2% by weight of C2 compounds and C4 compounds may also be present.

A C2-C3 cut can also be advantageously used for implementing the selective hydrogenation process according to the invention. It has for example the following composition: of the order of 0.1 to 5% by weight of acetylene relative to the total weight of the cut, of the order of 0.1 to 3% by weight of propadiene and methylacetylene, of the order of 30% by weight of ethylene, of the order of 5% by weight of propylene, the remainder being essentially methane, ethane and propane. This filler may also contain between 0.1 and 2% by weight of C4 compounds.

The C4 steam cracking cut, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following average mass composition: 1% weight of butane relative to the total weight of the cut, 46.5 wt% butene, 51 wt% butadiene, 1.3 wt% vinylacetylene and 0.2 wt% butyne. In some C4 cuts, between 0.1 and 2% by weight of C3 compounds and C5 compounds may also be present.

The C5 cut from steam cracking, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following composition: 21% weight of pentanes relative to the total weight of the cut, 45% weight of pentenes , 34% by weight of pentadienes.

The steam cracking gasoline or pyrolysis gasoline, advantageously used for the implementation of the selective hydrogenation process according to the invention, corresponds to a hydrocarbon cut whose boiling point is generally between 0 and 300° C., from preferably between 10 and 250°C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracked gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene, etc.), styrenic compounds (styrene, alpha-methylstyrene, etc.) and indene compounds (indene, etc.). ). Steam cracked gasoline generally comprises the C5-C12 cut with traces of C3, C4, C13, C14, C15 (for example between 0.1 and 3% by weight for each of these cuts). For example, a charge formed from pyrolysis gasoline generally has the following composition: 5 to 30% by weight of saturated compounds (paraffins and naphthenes), 40 to 80% by weight of aromatic compounds, 5 to 20% by weight of mono-olefins, 5 to 40% by weight of diolefins, 1 to 20% by weight of alkenylaromatic compounds, all the compounds forming 100%. It also contains from 0 to 1000 ppm by weight of sulphur, preferably from 0 to 500 ppm by weight of sulphur.

Preferably, the charge of polyunsaturated hydrocarbons treated in accordance with the selective hydrogenation process according to the invention is a C2 cut from steam cracking, or a C2-C3 cut from steam cracking, or a gasoline from steam cracking.

The selective hydrogenation process according to the invention aims to eliminate said polyunsaturated hydrocarbons present in said charge to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when said feed is a C2 cut, the selective hydrogenation process aims to selectively hydrogenate acetylene. When said feed is a C3 cut, the selective hydrogenation process aims to selectively hydrogenate propadiene and methylacetylene. In the case of a C4 cut, the aim is to eliminate butadiene, vinylacetylene (VAC) and butyne, in the case of a C5 cut, the aim is to eliminate the pentadienes. When said feedstock is a steam cracked gasoline, the selective hydrogenation process aims to selectively hydrogenate said polyunsaturated hydrocarbons present in said feedstock to be treated so that the diolefinic compounds are partially hydrogenated to mono-olefins and the styrenic and indenic compounds are partially hydrogenated to the corresponding aromatic compounds avoiding the hydrogenation of the aromatic rings.

The technological implementation of the selective hydrogenation process is for example carried out by injection, in ascending or descending current, of the charge of polyunsaturated hydrocarbons and hydrogen into at least one fixed-bed reactor. Said reactor can be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred. The charge of polyunsaturated hydrocarbons can advantageously be diluted by one or more re-injection(s) of the effluent, from said reactor where the selective hydrogenation reaction takes place, at various points of the reactor, located between the inlet and the outlet of the reactor in order to limit the temperature gradient in the reactor. The technological implementation of the selective hydrogenation process according to the invention can also be advantageously carried out by the implantation of at least said supported catalyst in a reactive distillation column or in reactors – exchangers or in a reactor of the slurry type. . The hydrogen flow can be introduced at the same time as the charge to be hydrogenated and/or at one or more different points of the reactor.

The selective hydrogenation of the C2, C2-C3, C3, C4, C5 and C5+ cuts from steam cracking can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5+ cuts and in the carbonated for C2 and C2-C3 cuts. A reaction in the liquid phase makes it possible to lower the energy cost and to increase the cycle time of the catalyst.

In general, the selective hydrogenation of a hydrocarbon charge containing polyunsaturated compounds containing at least 2 carbon atoms per molecule and having a final boiling point less than or equal to 300°C is carried out at a temperature between 0 and 300°C, at a pressure between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio between 0.1 and 10 and at an hourly volumetric speed VVH (defined as the ratio of the volume flow rate of charge to the volume of the catalyst) of between 0.1 and 200 h ^-1 for a process carried out in the liquid phase, or at a molar hydrogen/(polyunsaturated compounds to be hydrogenated) ratio of between 0.5 and 1000 and at an hourly volumetric speed VVH of between 100 and 40,000 h ^-1 for a process carried out in the gaseous phase.

In one embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the molar ratio (hydrogen)/(polyunsaturated compounds to be hydrogenated) is generally comprised between 0.5 and 10, preferably between 0.7 and 5.0 and even more preferably between 1.0 and 2.0, the temperature is between 0 and 200°C, preferably between 20 and 200° C and even more preferably between 30 and 180°C, the hourly volume velocity (VVH) is generally between 0.5 and 100 h ^-1 , preferably between 1 and 50 h ^-1 and the pressure is generally between 0.3 and 8.0 MPa, preferably between 1.0 and 7.0 MPa and even more preferably between 1.5 and 4.0 MPa.

More preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio is between 0.7 and 5.0, the temperature is between 20 and 200° C., the hourly volume velocity (VVH) is generally between 1 and 50 h ^-1 and the pressure is between 1.0 and 7.0 MPa.

Even more preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio is between 1.0 and 2.0, the temperature is between 30 and 180° C., the hourly volume velocity (VVH) is generally between 1 and 50 h ⁻¹ and the pressure is between 1.5 and 4.0 MPa.

The hydrogen flow is adjusted in order to have a sufficient quantity of it to theoretically hydrogenate all the polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

In another embodiment according to the invention, when a selective hydrogenation process is carried out in which the feed is a C2 cut from steam cracking and/or a C2-C3 cut from steam cracking comprising polyunsaturated compounds, the molar ratio ( hydrogen)/(polyunsaturated compounds to be hydrogenated) is generally between 0.5 and 1000, preferably between 0.7 and 800, the temperature is between 0 and 300°C, preferably between 15 and 280°C, the speed hourly volume (VVH) is generally between 100 and 40,000 h ^-1 , preferably between 500 and 30,000 h ^-1 and the pressure is generally between 0.1 and 6.0 MPa, preferably between 0.2 and 5, 0 MPa.

The invention will now be illustrated via the examples below which are in no way limiting.

Examples

For all the catalysts mentioned in the examples mentioned below, the support is an alumina A having a specific surface area of 80 m²/g, a pore volume of 0.7 mL/g (cm ³ /g) and a mesoporous median diameter of 12 nm.

Example 1: Preparation of an aqueous solution of Ni precursors

The aqueous solution of Ni precursors (solution S) used for the preparation of catalysts A to E is prepared by dissolving 43.5 g of nickel nitrate (NiNO ₃ , supplier Strem Chemicals®) in a volume of 13 mL of water distilled. The solution S is obtained, the Ni concentration of which is 350 g of Ni per liter of solution.

Example 2: Catalyst A - 15% by weight of Ni (comparative)

The solution S prepared in Example 1 is dry impregnated with 10 g of alumina A. The solid thus obtained is then dried in an oven overnight at 120° C., then calcined under an air flow of 1 L/ h/g of catalyst at 450° C. for 2 hours. The calcined catalyst thus prepared contains 15% by weight of the element nickel relative to the total weight of the catalyst supported on alumina.

The catalyst precursor is then reduced under the conditions as described in Example 8 below.

Example 3: Catalyst B - 15% by weight of Ni + Cu in co-impregnation with a Ni/Cu ratio=3 (comparative)

A solution of copper nitrate is prepared so as to obtain in the end a ratio Ni/Cu=3 on the final catalyst is co-impregnated dry with the solution S prepared in example 1 on 10 g of alumina A. The solid thus obtained is then dried in an oven overnight at 120°C. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor is then reduced under the conditions as described in Example 8 below.

Example 4: Catalyst C – Impregnation of 15% by weight of Ni followed by Impregnation of Ni + Cu (5% by weight Ni and molar ratio Ni/Cu=3) (according to the invention)

Solution S is impregnated dry on 10 g of alumina to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor C1 is obtained. A solution of copper nitrate is prepared so as to obtain in the end a ratio Ni/Cu=3 on the intermediate catalyst and is dry co-impregnated with the solution S prepared in example 1 on the catalyst precursor C1. The Ni content added at this stage is 5% by weight relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor is then reduced under the conditions as described in Example 8 below.

Example 5: Catalyst D - Impregnation of 15% by weight of Ni followed by Impregnation of Ni+Cu (2% by weight Ni and molar ratio Ni/Cu=3) (according to the invention)

Solution S is impregnated dry on 10 g of alumina to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor C1 is obtained. A solution of copper nitrate is prepared so as to obtain in the end a ratio Ni/Cu=3 on the intermediate catalyst and is dry co-impregnated with the solution S prepared in example 1 on the catalyst precursor C1. The Ni content added at this stage is 2% by weight relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor is then reduced under the conditions as described in Example 8 below.

Example 6: Catalyst E - Impregnation of 15% by weight of Ni followed by Impregnation of Ni+Cu (5% by weight Ni and molar ratio Ni/Cu=2) (according to the invention)

Solution S is impregnated dry on 10 g of alumina to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor C1 is obtained. A solution of copper nitrate is prepared so as to obtain in the end a Ni/Cu=2 ratio on the intermediate catalyst and is dry co-impregnated with the solution S prepared in example 1 on the catalyst precursor C1. The Ni content added at this stage is 5% by weight relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

The catalyst precursor is then reduced under the conditions as described in Example 8 below.

Example 7: Characterization

All the catalysts contain the contents targeted during impregnation, i.e. 15% of nickel element (characterized by X-ray fluorescence) relative to the total weight of the catalyst, and the % of added copper (characterized by X-ray fluorescence) .

The amount of alloy obtained after the calcination then reduction step was determined by X-ray diffraction (XRD) analysis on catalyst samples in powder form.

The amount of nickel in metallic form obtained after the reduction step was determined by X-ray diffraction (XRD) analysis on catalyst samples in powder form. Between the reduction stage and throughout the duration of characterization by XRD, the catalysts are never released into the open air. The diffraction diagrams are obtained by X-ray crystallographic analysis using a diffractometer using the conventional powder method with Kα1 radiation from copper (λ=1.5406 Å).

The reduction rate was calculated by calculating the area of the Ni ⁰ line located around 52°2θ, on all the diffractograms of each sample of catalyst analyzed, then by subtracting the signal present from room temperature under the line at 52° and which is due to the alumina.

Table 1 below summarizes the reduction rates or even the metallic nickel content Ni° (expressed in % weight relative to the total weight of Ni) for all the catalysts A to E characterized by XRD after a reduction step at 190 °C for 90 minutes under hydrogen flow. These values were also compared with the reduction rate obtained for catalyst A (Ni alone) after a conventional reduction step (i.e. at a temperature of 400°C for 15 hours under a flow of hydrogen) .

At room temperature on all catalysts, after calcination, containing copper and nickel, we detect alumina in delta and theta form, and large lines of NiO and CuO.

In order to evaluate the rate of reducibility and therefore the formation of Ni ⁰ , we measure the area of the Ni ⁰ line located around 52°2θ, on all the diffractograms, by subtracting the signal present from room temperature under the line at 52° and which is due to the alumina. It is thus possible to determine the relative percentage of Ni ⁰ crystallized after the reduction. We also detect after reduction a line corresponding to the alloy in the form of Ni _0.76 Cu _0.24.

Table 1 below summarizes the reducibility rates or the Ni° content for all the catalysts characterized by XRD after reduction at 190°C for 90 minutes under a hydrogen flow. These values were also compared with the reduction rate obtained for catalyst A (Ni alone) after a conventional reduction step (i.e. at a temperature of 400°C for 15 hours under a flow of hydrogen) . Catalyst Final reduction Ni content for the ^1st imp. (% wt) Ni content for the ^2nd imp. (% wt) Ni/Cu molar ratio for the 2nd imp. Percentage of Ni° alone (DRX) after reduction (%) A (comparative) 400°C, 3 p.m. 15 - - 80 A (comparative) 190°C, 90 mins 15 - - 0* B (comparative) 190°C, 90 mins - 15 3 0** C (invention) 190°C, 90 mins 15 5 3 100 D (invention) 190°C, 90 mins 15 2 3 90 E (invention) 190°C, 90 mins 15 5 2 80

*Nickel as NiO

**Nickel as an alloy

For catalyst A (15% Ni alone/alumina), the nickel reducibility rate is 0% after exactly the same reduction treatment under hydrogen as for catalysts B to E.

The post-impregnation of nickel (5% by weight of Ni) and copper with a Ni/Cu ratio of 2 makes it possible to obtain reduced Ni° of the order of 80% in the end on the catalyst. The post-impregnation of less NiCu alloy with a content of nickel composing the alloy of 2% by weight and of copper with a Ni/Cu ratio of 2 makes it possible to obtain Ni° reduced by around 90% ultimately on the catalyst. The post-impregnation of nickel (5% by weight of Ni) and copper with a Ni/Cu ratio of 3 allows obtaining 100% reduced Ni° from 190°C in the end on the catalyst

Example 8: Catalytic tests: performance in selective hydrogenation of a mixture containing styrene and isoprene (A _HYD1 )

Catalysts A to E described in the examples above are tested against the selective hydrogenation reaction of a mixture containing styrene and isoprene.

The composition of the charge to be selectively hydrogenated is as follows: 8% by weight styrene (Sigma Aldrich® supplier, purity 99%), 8% by weight isoprene (Sigma Aldrich® supplier, purity 99%), 84% by weight n-heptane (solvent ) (VWR® supplier, purity > 99% chromanorm HPLC). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis gasoline.

The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave, equipped with mechanical stirring with magnetic drive and able to operate under a maximum pressure of 100 bar (10 MPa) and temperatures between 5°C and 200°C.

In an autoclave are added 214 mL of n-heptane (supplier VWR®, purity> 99% chromanorm HPLC) and a quantity of 3 mL of catalyst. The autoclave is closed and purged. Then the autoclave is pressurized under 35 bar (3.5 MPa) of hydrogen. The catalyst is first reduced in situ , at 190°C for 90 minutes under hydrogen pressure (temperature rise ramp of 1°C/min) for catalysts A to E (which corresponds here to step h) of the preparation process according to the invention according to one embodiment). Then the autoclave is brought to the test temperature equal to 30°C. At time t=0, approximately 30 g of a mixture containing styrene, isoprene, n-heptane, pentanethiol and thiophene are introduced into the autoclave. The reaction mixture then has the composition described above and stirring is started at 1600 rpm. The pressure is kept constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle located upstream of the reactor.

Another test was carried out for catalyst A, but with a catalyst reduction temperature of 400° C. for 15 hours.

The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: the styrene is hydrogenated to ethylbenzene, without hydrogenation of the aromatic ring, and the isoprene is hydrogenated to methyl-butenes. If the reaction is prolonged longer than necessary, the methyl-butenes are in turn hydrogenated to isopentane. Hydrogen consumption is also monitored over time by the decrease in pressure in a reservoir bottle located upstream of the reactor. The catalytic activity is expressed in moles of H ₂ consumed per minute and per gram of Ni.

The catalytic activities measured for catalysts A to E are reported in Table 2 below. They are related to the catalytic activity (A_HYD1) measured for catalyst A prepared under conventional reduction conditions (at a temperature of 400°C for 15 hours under a flow of hydrogen). Catalyst Final reduction Ni content for the ^1st imp. (% wt) Ni content for the ^2nd imp. (% wt) Ni/Cu ratio for the 2nd imp. Percentage of Ni° (DRX) after reduction (%) A _HYD1 (%) A (comparative) 400°C, 3 p.m. 15 - - 80 100 A (comparative) 190°C, 90 mins 15 - - 0 0 B (comparative) 190°C, 90 mins - 15 3 0 30 C (invention) 190°C, 90 mins 15 5 3 100 180 D (invention) 190°C, 90 mins 15 2 3 90 130 E (invention) 190°C, 90 mins 15 5 2 80 100

This clearly shows the improved performance of catalysts C, D and E according to the invention, compared to the Ni catalyst alone on alumina reduced at 190° C. for 90 min, which is completely inactive. Furthermore, it should be noted that the NiCu alloy alone (catalyst B) has an activity that is much lower than the reference (of the order of 30%).

Claims (14)

Process for the preparation of a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising nickel, in an amount of 1 and 35% by weight of nickel element relative to the total weight of the catalyst, copper, in an amount of 0.5 to 15% by weight of copper element relative to the total weight of the catalyst, and a support comprising at least one refractory oxide chosen from silica, alumina and silica-alumina, which process comprises the following steps:
a) a step of bringing said support into contact with a solution comprising at least one nickel precursor is carried out;
b) at least one stage of drying the catalyst precursor is carried out at the end of stage a) at a temperature below 250° C.;
c) optionally, heat treatment of the catalyst precursor obtained at the end of step b) is carried out at a temperature of between 250 and 1000° C., in the presence or absence of water;
d) a step is carried out for bringing the catalyst precursor obtained at the end of step b), optionally at the end of step c), into contact with at least one solution containing at least one copper precursor and a nickel precursor at a nickel concentration desired to obtain on the final catalyst a content of between 0.5 and 15% by weight of nickel element relative to the total weight of the final catalyst;
e) at least one step of drying the catalyst precursor is carried out at the end of step d) at a temperature below 250° C.;
f) optionally, heat treatment of the catalyst precursor obtained at the end of step e) is carried out at a temperature of between 250 and 1000° C., in the presence or absence of water;
g) reducing the catalyst precursor from step e), optionally step f), by bringing said catalyst precursor into contact with a reducing gas at a temperature between 150 and 250°C. Process according to claim 1, in which in step d) the molar ratio between nickel and copper is between 0.5 and 5. Process according to one of Claims 1 or 2, in which step g) is carried out at a temperature of between 160 and 230°C. Process according to any one of Claims 1 to 3, in which step g) is carried out at a temperature of between 170 and 220°C. Process according to any one of Claims 1 to 4, in which step g) is carried out between 10 minutes and 110 minutes. Process according to any one of Claims 1 to 5, further comprising a stage of passivation of the catalyst precursor by a sulfur compound after stage g) of reduction. Process according to Claim 6, in which the passivation step is carried out at a temperature of between 20 and 350°C for 10 to 240 minutes. Process according to one of Claims 6 or 7, in which the said sulfur compound is chosen from thiophene, thiophane, dimethylsulphide, diethylsulphide, dipropylsulphide, propylmethylsulphide, di-thio-di-ethanol. Process according to any one of Claims 1 to 8, in which the copper precursor supplied during step d) is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulphate , copper chloride, copper bromide, copper iodide or copper fluoride. A method according to claim 9, wherein the copper precursor is copper nitrate. Process according to any one of Claims 1 to 10, in which the reducing gas in step g) is dihydrogen. Process according to Claim 11, in which the hydrogen flow rate, expressed in L/hour/gram of catalyst precursor, is between 0.01 and 100 L/hour/gram of catalyst precursor. Process according to any one of Claims 1 to 12, in which the nickel precursor supplied during stage a) and/or d) is chosen from nickel nitrate, nickel carbonate or nickel hydroxide. Process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and/or acetylenics and/or alkenylaromatics, contained in a hydrocarbon charge having a lower or equal final boiling point at 300°C, which process is carried out at a temperature of between 0 and 300°C, at a pressure of between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.1 and 10 and at an hourly volume rate of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at a speed hourly volume between 100 and 40,000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst obtained according to any one of claims 1 to 13.