EP3911439A1

EP3911439A1 - Process for preparing a selective hydrogenation catalyst, comprising a step of forming a ni-cu alloy in pre-impregnation

Info

Publication number: EP3911439A1
Application number: EP20700054.8A
Authority: EP
Inventors: Malika Boualleg; Anne-Agathe Quoineaud
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2019-01-15
Filing date: 2020-01-08
Publication date: 2021-11-24
Also published as: US20220062886A1; JP2022517360A; FR3091657A1; JP7449945B2; FR3091657B1; WO2020148131A1; US11779915B2; CN113646087B; CN113646087A

Abstract

The invention relates to a process for preparing a selective hydrogenation catalyst comprising nickel, copper and a support having at least one refractory oxide, said process comprising the following steps: - contacting the support with a solution containing at least one copper precursor and a nickel precursor; - drying the catalyst precursor at a temperature of less than 250°C; - reduction of the catalyst precursor by contacting said precursor with a reduction gas at a temperature of between 150°C and 250°C; - contacting the catalyst precursor with a solution comprising a nickel precursor; - step of drying the catalyst precursor at a temperature of less than 250°C; - reduction of the catalyst precursor by contacting said precursor with a reduction gas at a temperature of between 150°C and 250°C.

Description

PROCESS FOR PREPARING A SELECTIVE HYDROGENATION CATALYST INCLUDING A STEP FOR FORMING AN ALLOY OF

NI-CU IN PRE-IMPREGNATION

Technical field The present invention relates to a process for preparing 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 olefinic fractions.

State of the art

The catalysts for the selective hydrogenation of polyunsaturated compounds are generally based on metals from group VIII of the Periodic Table of the 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 nature and pore distribution of the support are parameters which may have an impact. 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 in the porosity 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 a nickel-based catalyst has frequently been proposed in order to improve the performance in selective hydrogenation. For example, it is known from US Pat. No. 5,208,405 to use a nickel and silver-based catalyst for the selective hydrogenation of C4-C10 diolefins. On the other hand, it is known to promote nickel, present predominantly, with metals from group IB, in particular gold (FR 2,949,077) or tin (FR 2,949,078). Document FR 3,011, 844 discloses a catalyst for the implementation of 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 molar ratio: ( Ni and / or Co) greater than 1.

Furthermore, prior to the use of such catalysts and their implementation in a hydrogenation process, a reducing treatment step in the presence of a reducing gas is carried out so as to obtain a catalyst comprising an at least partially active phase. in metallic form. This treatment activates the catalyst and forms metal particles. This treatment can be carried out in-situ or ex-situ, that is to say 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 cuts of polyunsaturated hydrocarbons 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 before depositing on the support the 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, carrying out a step of bringing the support into contact with a solution simultaneously containing a copper-based metal precursor and a nickel-based metal precursor followed by a drying and reduction step 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 of 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 subsequent to the formation of the nickel-copper alloy (under reduced form). The preparation process according to the invention thus makes it possible to carry out a step 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 allows the reduction step to be carried out directly within the reactor in which it is desired to carry out the hydrogenation. selective polyunsaturated sections. Furthermore, the presence of copper in the catalyst makes it possible to maintain good activity and a longer lifespan of the catalyst when the latter is brought into contact with a hydrocarbon feed comprising sulfur, in particular the C3 hydrocarbon cuts from steam cracking and / or catalytic cracking. In fact, compared with nickel, the copper present in the catalyst more easily captures the sulfur compounds included in the feed, which therefore avoids irreversibly poisoning the most virulent active sites of the nickel which exist on the new catalyst.

The present invention relates to a process for preparing a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising a metallic active phase based on nickel, in an amount of 1 and 35% by weight of nickel element relative to the weight. total catalyst, and copper-based, 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 is carried out of bringing the support into contact with at least one solution containing at least one copper precursor and one nickel precursor at a desired nickel concentration in order to obtain a content of between 0.5 and 15 on the final catalyst % by weight of nickel element relative to the total weight of the final catalyst;

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

d) the catalyst precursor resulting from step b), optionally step c), is reduced by contacting said catalyst precursor with a reducing gas at a temperature between 150 and 250 ° C;

e) a step of bringing the catalyst precursor obtained at the end of step d) into contact with a solution comprising at least one nickel precursor;

f) at least one step of drying the catalyst precursor is carried out at the end of step e) at a temperature below 250 ° C .; g) optionally, a heat treatment of the catalyst precursor obtained at the end of step f) is carried out at a temperature between 250 and 1000 ° C., in the presence or absence of water;

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

Advantageously, in step a) the molar ratio between nickel and copper is between 0.5 and 5.

Preferably, step d) and / or h) is (are) carried out at a temperature between 160 and 230 ° C.

More preferably, step d) and / or h) is (are) carried out at a temperature between 170 and 220 ° C.

Advantageously, steps d) and / or h) is (are) carried out between 10 minutes and 110 minutes. Advantageously, the preparation process further comprises a step of passivation of the catalyst precursor with a sulfur compound after step d) of reduction but before step e), and / or after step h) of reduction.

Preferably, the passivation step (s) is (are) carried out at a temperature of between 20 and 350 ° C for 10 to 240 minutes. Advantageously, said sulfur compound is chosen from thiophene, thiophane, dimethylsulfide, diethylsulfide, dipropylsulfide, propylmethylsulfide, di-thio-di-ethanol.

Advantageously, the copper precursor is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or fluoride. copper.

Advantageously, the copper precursor is copper nitrate.

Advantageously, the reducing gas of step d) and / or h) is dihydrogen. Advantageously, the hydrogen flow rate, expressed in L / hour / gram of catalyst precursor is between 0.01 and 100 L / hour / gram of catalyst precursor.

Advantageously, the nickel precursor supplied during step a) and / or e) 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 less than or equal to 300 ° C, which process being carried out at a temperature between 0 and 300 ° C, at a pressure between 0.1 and 10 MPa, at a hydrogen / (polyunsaturated compounds) molar ratio to be hydrogenated) between 0.1 and 10 and at an hourly volume speed 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 speed 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.

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, editor 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 reduction rate (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 degree 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 amount 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 BET specific surface determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established using the BRUNAUER-EMMETT method. -TELLER described in "The Journal of American Society", 60, 309, (1938).

In this application, the term "understand" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other unrequited elements. It is understood that the term "to understand" includes the exclusive and closed term "to consist".

By "macropores" we mean pores with an opening greater than 50 nm.

By "mesopores" is meant pores with an opening between 2 nm and 50 nm, limits included.

By "micropores" is meant pores with an opening of 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 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 equal to 140 ° by following the recommendations of the book “Engineering techniques, analysis and characterization treaty”, 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 (approximately 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 this 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 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 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 transform of the starting adsorption isotherm as described in the book "Adsorption by powders and porous solids. Principles, methodology and applications ”written by F. Rouquérol, J. Rouquérol and K. Sing, Academie Press, 1999.

The mesoporous median 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 macroporous median 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

Process for preparing the catalyst

According to the invention, the process for preparing a catalyst for the selective hydrogenation of polyunsaturated hydrocarbon cuts comprising, preferably consisting of, a metallic active phase based on nickel, in an amount of 1 and 35% by weight in element nickel relative to the total weight of the catalyst, and copper-based, 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, preferably comprises the following steps: a) a step is carried out of bringing the support into contact with at least one solution containing at least, preferably consisting of, a copper precursor and a nickel precursor at a desired nickel concentration in order to obtain a content on the final catalyst of between 0.5 and 15% by weight of nickel element relative to the total weight of the final catalyst;

e) a step of bringing the catalyst precursor obtained at the end of step d) into contact with a solution comprising at least, preferably consisting of, a nickel precursor;

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

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

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

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

Steps a) to i) of said preparation process are described in detail below. Step a) 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 a), can be carried out by impregnation, dry or in excess, or alternatively by deposition - precipitation, according to well known methods of 'Man skilled in the art.

Said step a) is preferably carried out by impregnation of the support consisting for example in bringing said support into contact with at least one solution, aqueous or organic (for example methanol or ethanol or phenol or acetone or toluene or dimethylsulfoxide (DMSO)) or else consisting of a mixture of water and at least one organic solvent, comprising, preferably consisting of, at least one precursor of nickel and at least one precursor of at least partially copper. the dissolved state, or also by bringing said support into contact with at least one colloidal solution comprising, preferably consisting of, at least one precursor of nickel and of a precursor of copper in oxidized form (oxide nanoparticles, oxide (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 optional addition of an acid or a base.

Preferably, said step a) is carried out by dry impregnation, which consists in bringing the catalyst support into contact with a solution, comprising, preferably consisting of, at least one nickel precursor and at least one copper precursor, in which the volume of the solution is between 0.25 and 1.5 times the pore 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, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, sulfate, 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 soluble in aqueous solution, which is brought into contact with said support. Preferably, as nickel precursor, nickel nitrate, nickel hydroxide, nickel carbonate, nickel chloride or nickel hydroxycarbonate are used advantageously. 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 sulfate, 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 step a) at a desired concentration to obtain on the final catalyst (ie obtained at the end of step h) reduction or step i) 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 weight, even more preferably between 1 and 5% by weight.

The quantities of the copper precursor (s) introduced into the solution according to step a) 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 final (ie obtained at the end of step h) of reduction or of step i) 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 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 preferably between 70 and 140 ° C, for a period typically 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 reduction step d), 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 durations of treatment are not excluded, but do not necessarily bring improvement.

The term “heat treatment” is understood to mean treatment at temperature respectively without the presence or in the presence of water. In the latter case, the contact with the 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 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 oxide form, that is to say in NiO form, and copper in oxide form. oxide, that is to say in CuO form.

Step d) Reduction by reducing gas

According to the invention, a step of reducing treatment d) of the dried catalyst obtained at the end of step b) or of the catalyst obtained at the end of step c) is carried out in the presence of a reducing gas of so as to form on the catalyst support a nickel-copper alloy at least partially in metallic form. The reducing gas is preferably hydrogen. The hydrogen can be used pure or as a mixture (eg a mixture of hydrogen / nitrogen, hydrogen / argon, hydrogen / methane). In the case where the hydrogen is used as a mixture, all the proportions can be envisaged.

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. It has been observed by the Applicant that step d) of reduction with a reducing gas makes it possible to form a nickel-copper alloy at least partially in metallic form. The nickel-copper alloy has the formula Ni _x Cu _y with x ranging between 0.1 and 0.9 and including between 0.1 and 0.9.

The rise in temperature to the desired reduction temperature is generally slow, for example set between 0.1 and 10 ° C / min, preferably between 0.3 and 7 ° C / min.

The hydrogen flow rate, 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.

Passivation (optional step)

The catalyst precursor obtained at the end of reduction step d) can advantageously be passivated before carrying out the step of bringing said catalyst precursor into contact with a solution comprising, preferably consisting of, at least one precursor of nickel (step e).

When carried out, the step of passivation of the catalyst precursor obtained at the end of step d) is carried out with a sulfur compound which makes it possible to improve the selectivity of the catalysts and to avoid thermal runaways during catalyst start-ups. new ("run away" according to the 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 step of passivation with a sulfur compound is generally carried out at a temperature 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 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. Step e) Contacting the catalyst precursor with a solution comprising a nickel precursor

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

Said step e) is preferably carried out by impregnating the catalyst precursor obtained at the end of step d) (or after the optional passivation step) consisting for example in bringing the catalyst precursor into contact with at least one solution, aqueous or organic (for example methanol or ethanol or phenol or acetone or toluene or dimethylsulfoxide (DMSO)) or else consisting of a mixture of water and at least one organic solvent, comprising, preferably consisting of, at least one nickel precursor at least partially in the dissolved state, or alternatively by bringing the catalyst precursor into contact with at least one colloidal solution comprising, preferably consisting of, at least one precursor nickel, in oxidized form (nanoparticles of oxides, oxy (hydroxide) or nickel hydroxide) or in reduced form (metallic nanoparticles of nickel 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 e) is carried out by dry impregnation, which consists in bringing the catalyst precursor into contact with at least one solution, containing, preferably consisting of, at least one precursor of nickel, the volume of which is solution is between 0.25 and 1.5 times the pore volume of the support 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, chloride, sulfate, hydroxide, hydroxycarbonate, formate, acetate, oxalate , complexes formed with acetylacetonates, or else tetrammine or hexammine complexes, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said catalyst precursor. Nickel nitrate, nickel carbonate, nickel chloride, nickel hydroxide and nickel hydroxycarbonate are advantageously used as nickel precursor. Very preferably, the nickel precursor is nickel nitrate, nickel carbonate or nickel hydroxide. The nickel precursor is supplied to step e) at a desired concentration to obtain on the final catalyst (ie obtained at the end of step h) of reduction or of step i) of 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 f) Drying of the impregnated support

Step f) 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 preferably between 70 and 140 ° C, for a period typically 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. g) Heat treatment of the dried catalyst (optional step)

The dried catalyst precursor can undergo an additional heat treatment step, before reduction step h), 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 durations of treatment are not excluded, but do not necessarily bring improvement.

The term “heat treatment” is understood to mean treatment at temperature respectively without the presence or in the presence of water. In the latter case, the contact with the 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 case 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 h) Reduction by reducing gas

Prior to the use of the catalyst in the catalytic reactor and the implementation of a hydrogenation process, a reducing treatment step h) is carried out in the presence of a reducing gas so as to obtain a catalyst comprising nickel in less 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 metal particles, in particular nickel in the zero valent state. Carrying out in situ the reducing treatment of the catalyst eliminates the need for an additional step of passivation of the catalyst with an oxygen-containing compound or with C0 ₂ , which is necessarily the case when the catalyst is prepared by performing a reducing 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 the operations of transporting and loading the catalyst into the reactor d. 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 as a mixture (eg a mixture of hydrogen / nitrogen, hydrogen / argon, hydrogen / methane). In the case where the hydrogen is used as a mixture, all the proportions can be envisaged.

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 ° vs. 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 resort to operating conditions for reducing the active phase of nickel which are less severe than in the prior art and thus 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 fractions.

Furthermore, the presence of copper in the catalyst makes it possible to maintain good activity of the catalyst and a good lifetime of the catalyst when the latter is brought into contact with a hydrocarbon feed comprising sulfur, in particular the C3 hydrocarbon cuts from steam cracking. and / or catalytic cracking. In fact, compared to nickel, the copper present in the catalyst more easily captures the sulfur compounds included in the feed, which therefore avoids irreversibly poisoning the most virulent active sites of nickel which exist on the new catalyst.

Step i) Passivation (optional)

The catalyst prepared according to the process according to the invention can advantageously undergo a passivation step with a sulfur compound which makes it possible to improve the selectivity of the catalysts and to avoid thermal runaways during the start-ups 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 step of passivation with a sulfur compound is generally carried out at a temperature 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 SSR ₂ -OH such as di-thio-di-ethanol of formula HO-C ₂ H ₄ -SSC ₂ H ₄ -OH (often called DEODS). Content sulfur is generally between 0.1 and 2% by weight of said element relative to the total weight of the catalyst.

Catalyst

The catalyst that can be obtained 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 to advantageously of the formula Ni _x Cu _y with x ranging 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, 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, more 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 nickel 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 chosen 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 as a mixture. Preferably, the support is chosen from alpha, delta, theta and gamma alumina.

The specific surface of the porous support is generally greater than 5 m ² / g, preferably between 30 and 400 m ² / g, preferably between 50 and 350 m ² / 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), of extrudates, of tablets, of 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 is understood to mean the average diameter of the circle circumscribing the cross section of these extrudates. The catalyst can advantageously be presented in the form of cylindrical, multilobed, trilobal or quadrilobed extrudates. Preferably its shape will be trilobed or quadrilobed. The shape of the lobes can be adjusted according to all the methods known from the prior art.

The specific surface of the catalyst is generally greater than 5 m ² / g, preferably between 30 and 400 m ² / g, preferably between 50 and 350 m ² / 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 macroporous 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 or 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 mesoporous median diameter may 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 macroporous median 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 a low microporosity, very preferably it does not have any microporosity. Selective hydrogenation process

A subject of the present invention is also 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 less than or equal to 300 ° C, which process being carried out at a temperature between 0 and 300 ° C, at a pressure between 0.1 and 10 MPa, at a hydrogen / molar ratio (polyunsaturated compounds to be hydrogenated) between 0.1 and 10 and at an hourly volume speed 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 between 0.5 and 1000 and at an hourly volume speed 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 description ption.

Monounsaturated organic compounds, such as ethylene and propylene, are the source of the manufacturing 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 indene compounds. These polyunsaturated compounds are very reactive and lead to side reactions in the polymerization units. It is therefore necessary to eliminate them before upgrading these cuts.

Selective hydrogenation is the main treatment developed to specifically remove unwanted polyunsaturated compounds from these hydrocarbon feeds. It allows the conversion of the 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 cracking gasolines used as feed, the selective hydrogenation also makes it possible to selectively hydrogenate the alkenylaromatics into aromatics while avoiding the hydrogenation of the aromatic rings. The hydrocarbon feed treated in the selective hydrogenation process has a final boiling point of 300 ° C or less and contains at least 2 carbon atoms per molecule and comprises 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 feed 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 steam cracking cut, advantageously used for carrying out 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 said cut, of the order of 0.1 to 5% by weight of acetylene, the remainder being essentially ethane and methane. In certain C2 steam cracking cuts, between 0.1 and 1% by weight of C3 compounds can also be present.

The steam cracking C3 cut, advantageously used for carrying out 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 said cut , of the order of 1 to 8% by weight of propadiene and methylacetylene, the remainder being essentially propane. In certain C3 cuts, between 0.1 and 2% by weight of C2 compounds and C4 compounds can also be present.

A C2 - C3 cut can also be advantageously used for carrying out 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 said 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 charge can also contain between 0.1 and 2% by weight of C4 compounds.

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

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

The gasoline of steam cracking or gasoline of pyrolysis, 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, of preferably between 10 and 250 ° C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracking gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene, etc.), styrene compounds (styrene, alpha-methylstyrene, etc.) and indene compounds (indene, etc.) ). Steam cracking 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 of the compounds forming 100%. It also contains 0 to 1000 ppm by weight of sulfur, preferably 0 to 500 ppm by weight of sulfur.

Preferably, the polyunsaturated hydrocarbon feed treated in accordance with the selective hydrogenation process according to the invention is a C2 steam cracking cut, or a C2-C3 steam cracking cut, or a steam cracked gasoline.

The selective hydrogenation process according to the invention aims to eliminate said polyunsaturated hydrocarbons present in said feed to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when said feedstock is a C2 cut, the selective hydrogenation process aims to selectively hydrogenate acetylene. When said feedstock 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 the butadiene, vinylacetylene (VAC) and butyne, in the case of a C5 cut, the aim is to eliminate the pentadienes. When said feed is a steam cracked gasoline, the selective hydrogenation process aims to selectively hydrogenate said polyunsaturated hydrocarbons present in said feed to be treated so that the compounds diolefins are partially hydrogenated to mono-olefins and the styrenic and indene compounds are partially hydrogenated to the corresponding aromatic compounds avoiding 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 feed of polyunsaturated hydrocarbons and of hydrogen in 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 polyunsaturated hydrocarbon feed can advantageously be diluted by one or more re-injections of the effluent, coming 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. 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 slurry type reactor. . The hydrogen flow can be introduced at the same time as the feed 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 gas phase or in the liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5 + cuts and in the carbonated for cuts C2 and C2-C3. A liquid phase reaction lowers the energy cost and increases the cycle time of the catalyst.

In general, the selective hydrogenation of a hydrocarbon feed 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 of between 0.1 and 10 and at an hourly volume speed VVH (defined such as the ratio of the volume flow rate of feed 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 hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volume speed VVH of between 100 and 40,000 h ¹ for a process carried out in the gas phase.

In one embodiment according to the invention, when carrying out a selective hydrogenation process in which the feed is a steam cracked gasoline comprising polyunsaturated compounds, the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally 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 speed (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 feed is a steam cracking 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 speed (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 feed 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 speed (VVH) is generally between 1 and 50 h ¹ and the pressure is between 1, 5 and 4.0 MPa.

The hydrogen flow rate is adjusted in order to have enough 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 carrying out a selective hydrogenation process in which the feed is a C2 steam cracking cut and / or a C2-C3 steam cracking cut 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 m ² / g, a pore volume of 0.7 mL / g (cm ³ / g) and a median diameter 12 nm mesoporous.

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 (NiN0 ₃ , supplier Strem Chemicals®) in a volume of 13 mL of water distilled. 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)

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 ratio

Ni / Cu = 3 (comparative)

A copper nitrate solution is prepared so as to finally obtain a Ni / Cu ratio = 3 on the final catalyst and dry co-impregnated 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.

Example 4: Catalyst C - Impregnation of Ni + Cu (5% by weight Ni and molar ratio

Ni / Cu = 3) followed by an impregnation of 15% by weight of Ni (according to the invention)

A copper nitrate solution is prepared so as to finally obtain a Ni / Cu ratio = 3 on the intermediate catalyst is dry co-impregnated with the solution S prepared in Example 1 on 10 g of alumina A. The Ni content 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. This is then reduced under hydrogen pressure at 190 ° C. for 4 h then returned to air. The catalyst precursor C1 is obtained.

The solution S is then dry impregnated on the precursor of catalyst C1 to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst (which does not contribute to the alloy). 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.

Example 5: Catalyst D - Ni + Cu impregnation (2% by weight of Ni and molar ratio

A copper nitrate solution is prepared so as to finally obtain a Ni / Cu ratio = 3 on the intermediate catalyst is dry co-impregnated with the solution S prepared in Example 1 on 10 g of alumina A. The Ni content 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. This is then reduced under a stream of hydrogen at 190 ° C for 4 hours and then returned to air. The catalyst precursor D1 is obtained.

The solution S is then dry impregnated on the catalyst precursor D1 to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst (which does not contribute to the alloy). 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.

Example 6: Catalyst E - Impregnation of Ni + Cu (5% by weight of Ni and molar ratio

Ni / Cu = 2) followed by an impregnation of 15% by weight of Ni (according to the invention)

A solution of copper nitrate is prepared so as to finally obtain a Ni / Cu ratio = 2 on the intermediate catalyst is dry co-impregnated with the solution S prepared in Example 1 on 10 g of alumina A. The Ni content 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. This is then reduced under a flow of hydrogen at 190 ° C. for 4 h then returned to air. The catalyst precursor E1 is obtained.

The solution S is then dry impregnated on the catalyst precursor E1 to obtain 15% by weight of Ni alone relative to the total weight of the final catalyst (which does not contribute to the alloy). 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.

Example 7: Characterization

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

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

The amount of metallic nickel obtained after the reduction step was determined by X-ray diffraction (XRD) analysis on samples of the catalyst in powder form. Between the reduction step and throughout the duration of the XRD characterization, the catalysts are never vented. The diffraction patterns are obtained by radiocrystallographic analysis using a diffractometer using the classical powder method with the Ka1 radiation of copper (l = 1, 5406

AT).

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

Table 1 below collates the reduction rates or even the metallic nickel content Ni ° (expressed in% by weight relative to the total weight of Ni) for all the catalysts A to E characterized by DRX after a reduction step at 190 ° C for 90 minutes under a flow of hydrogen. These values were also compared with the reduction rate obtained for catalyst A (Ni alone) after a conventional reduction step (that is to say at a temperature of 400 ° C for 15 hours under a flow of hydrogen) . At room temperature on all the catalysts, after calcination, containing copper and nickel, we detect alumina in delta and theta form, and large lines of NiO and CuO.

We also detect after reduction a line corresponding to the alloy in the form NÎO, 76CUO, 24.

In order to evaluate the degree of reducibility and therefore the formation of Ni ⁰ , the area of the Ni ^{0 line} located at around 52 ° 2Q is measured, on all the diffractograms, by subtracting the signal present from ambient 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 reduction.

Table 1 below summarizes the levels of reducibility or even the Ni ° content for all the catalysts characterized by DRX after reduction at 190 ° C for 90 minutes under a flow of hydrogen. These values were also compared with the reduction rate obtained for catalyst A (Ni alone) after a conventional reduction step (that is to say at a temperature of 400 ° C for 15 hours under a flow of hydrogen) .

Table 1

* Nickel in the form of NiO

** Nickel as an alloy

For catalyst A (15% Ni alone / alumina), the degree of nickel reducibility is 0% after exactly the same reduction treatment in hydrogen as for catalysts B to E. The pre-impregnation of nickel (5% by weight of Ni) and of copper with a Ni / Cu ratio of 2 makes it possible to obtain a reduced Ni ° of the order of 70% in the end on the catalyst. The pre-impregnation of less NiCu alloy with a nickel content composing the alloy of 2% by weight and copper with a Ni / Cu ratio of 3 makes it possible to obtain Ni ° reduced in the order of 90% at final on the catalyst. The pre-impregnation of nickel (5% by weight of Ni) and of copper with a Ni / Cu ratio of 3 makes it possible to obtain 100% of Ni ° reduced from 170 ° C. in the end on the catalyst.

Example 8: Catalytic test: performance in selective hydrogenation of a mixture containing styrene and isoprene (A _Hy m)

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 feed to be selectively hydrogenated is as follows: 8% wt styrene (supplier Sigma Aldrich®, purity 99%), 8% wt isoprene (supplier Sigma Aldrich®, purity 99%), 84% wt 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 essence.

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

214 mL of n-heptane (supplier VWR®, purity> 99% chromanorm HPLC) and a quantity of 3 mL of catalyst are added in an autoclave. 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 followed by taking samples of the reaction medium at regular time intervals: the styrene is hydrogenated to ethylbenzene, without hydrogenation of the aromatic ring, and isoprene is hydrogenated to methyl-butenes. If the reaction is prolonged longer than necessary, the methyl-butenes are in turn hydrogenated to isopentane. The consumption of hydrogen 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 _H YDI) measured for catalyst A prepared under conventional reduction conditions (at a temperature of 400 ° C. for 15 hours under a flow of hydrogen). Table 2

This clearly shows the improved performance of catalysts C, D and E according to the invention, compared to the catalyst Ni alone on alumina (catalyst A) 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 significantly lower than the reference (of the order of 30%).

Claims

1. Process for preparing 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 comprising the following steps:

a) a step is carried out of bringing the support into contact with at least one solution containing at least one copper precursor and one nickel precursor at a desired nickel concentration in order to obtain a content of between 0.5 and 15 on the final catalyst % by weight of nickel element relative to the total weight of the final catalyst; 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;

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

2. Method according to claim 1, wherein in step a) 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.

3. Method according to one of claims 1 or 2, wherein step d) and / or h) is (are) carried out at a temperature between 160 and 230 ° C.

4. Method according to any one of claims 1 to 3, wherein step d) and / or h) is (are) carried out at a temperature between 170 and 220 ° C.

5. Method according to any one of claims 1 to 4, in steps d) and / or h) is (are) carried out between 10 minutes and 110 minutes.

6. Method according to any one of claims 1 to 5 further comprising a step of passivation of the catalyst precursor with a sulfur-containing compound after reduction step d) but before step e), and / or after the reduction. step h) reduction.

7. The method of claim 6, wherein the passivation step (s) is (are) carried out at a temperature between 20 and 350 ° C for 10 to 240 minutes.

8. Method according to one of claims 6 or 7, wherein said sulfur compound is selected from thiophene, thiophane, dimethylsulfide, diethylsulfide, dipropylsulfide, propylmethylsulfide, di-thio-di-ethanol.

9. A method according to any one of claims 1 to 8, wherein the copper precursor is selected from copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or copper fluoride.

10. The method of claim 9, wherein the copper precursor is copper nitrate.

11. A method according to any one of claims 1 to 10, wherein the reducing gas of step d) and / or h) is dihydrogen.

12. The method of claim 11, wherein the hydrogen flow rate, expressed in L / hour / gram of catalyst precursor is between 0.01 and 100 L / hour / gram of catalyst precursor.

13. Method according to any one of claims 1 to 12, in which the nickel precursor supplied during step a) and / or e) is chosen from nickel nitrate, nickel carbonate or nickel hydroxide. .

14. Process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and / or acetylenics and / or alkenyl aromatics, contained in a hydrocarbon feedstock having a lower final boiling point. or equal to 300 ° C, which process being 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 of between 0, 1 and 10 and at an hourly volume speed 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 hourly volume speed 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.