FR3112088A1 - PROCESS FOR THE PREPARATION OF A SELECTIVE HYDROGENATION CATALYST OBTAINED FROM MELTED SALTS AND A NICKEL COPPER ALLOY - Google Patents

Abstract

Process for the preparation of a selective hydrogenation catalyst comprising the following steps:- bringing the support into contact with an organic additive comprising oxygen and/or nitrogen;- bringing the support into contact with a metal salt of nickel, at a temperature below the melting temperature of said metal salt of nickel, to form a solid mixture; - heating, with stirring, of the solid mixture to a temperature between the melting temperature of said metal salt and 200°C; contact of the support with a solution containing at least one copper precursor and one nickel precursor at a copper concentration desired to obtain on the final catalyst a content of between 0.5 and 15% by weight of copper element relative to the total weight of the final catalyst.

Description

METHOD FOR PREPARING A CATALYST FOR SELECTIVE HYDROGENATION OBTAINED FROM MOLTEN SALTS AND A NICKEL-COPPER ALLOY

The present invention relates to a process for the preparation of a supported metal catalyst based on nickel intended particularly for the selective hydrogenation of polyunsaturated compounds.

State of the art

Many synthesis processes are known from the prior art to improve the reducibility of the metallic phase or to control the particle sizes. Among these methods, the use of molten salts as precursors of the active phase of a catalyst or of a capture mass is known from the literature.

For example, document US 5,036,032 discloses a method for preparing a supported catalyst based on cobalt by bringing a support into contact (of the order of a few tens of seconds) in a bath of molten salt of cobalt nitrate, followed by a step of drying and reduction without intermediate calcination. This method allows the preferential localization of the cobalt phase at the periphery of the support. Nevertheless, the method does not allow precise control of the amount of active phase (here cobalt) deposited due to the very short contact time and on the other hand the type of catalyst obtained is not suitable for implementation. in a reactor operating in the liquid phase with a catalyst in suspension (called a "slurry reactor" or "slurry" according to English terminology) due to the excessive loss of metal by attrition. On the other hand, the absence of a calcination step is risky since the reaction between the reducing element and the nitrates in the solid is very exothermic. Finally, this method requires the manipulation of large quantities of cobalt nitrate (toxic) in liquid form and at temperature, with ratios of approximately 4 grams of active phase precursors for 1 gram of support. The catalysts obtained by this preparation route are used for the synthesis of Fischer-Tropsch hydrocarbons.

It is known to Chem. Mater., 1999, 11, p.1999-2007 to prepare mixed phosphates by a molten salt type route. The reaction mixture contains a metal precursor salt (in particular Ni(NO ₃ ) ₂ or Co(No ₃ ) ₂ ), a source of phosphorus (NH ₄ HPO ₄ ), and an alkali metal nitrate (Na or K). These preparations are carried out at high temperatures of the order of 400 to 450°C. Solids of the mixed phosphate type are obtained, for example Na ₃ Ni ₂ (P ₂ O ₇ )PO ₄ , K ₂ Ni ₄ (PO ₄ ) ₂ P ₂ O ₇ or Na ₉ Co ₃ (PO ₄ ) ₅ . These solids can find applications in ion exchange, high temperature ionic conduction or in catalysis.

Document GB 191308864 discloses a process for synthesizing a mass catalyst based on nickel or cobalt for the production of hydrogen by steam reforming (“ steam-reforming ” according to the Anglo-Saxon terminology). These catalysts can be obtained by liquefaction of metallic salts at moderate temperatures then poured into a mold before calcining heat treatment.

The publication by J.-Y. Tilquin entitled “ Intercalation of CoCl ₂ into graphite: Mixing method vs molten salt method ” published in Carbon, 35(2), p. 299-306, 1997, proposes the use in the form of molten salt of a CoCl ₂ -NaCl mixture at high temperature (450-580° C.) for the intercalation between sheets of graphite. These graphite intercalation compounds find applications in catalysis for oxygen reduction in polymer electrolyte fuel cells.

Document EP 2921227 discloses a Fischer-Tropsch catalyst based on a group VIIIB metal deposited on an oxide support comprising alumina, silica, spinel and phosphorus as well as its method of manufacture. This process includes the preparation of the oxide support as well as the impregnation of this support with an aqueous solution of a metal precursor followed by drying and calcination. In the case of high metal contents, the impregnation/drying/calcination of the active phase in several stages is preferred.

Objects of the invention

The present invention thus relates to a new process for the preparation of a catalyst for selective hydrogenation comprising performances at least as good, or even better than the catalysts according to the prior art, while using a quantity of active phase based on nickel in less equal, or even less than that typically used in the state of the art.

The present invention therefore relates, according to a first aspect, to a process for the preparation of a selective hydrogenation catalyst comprising an active phase of nickel, a nickel-copper alloy, and an alumina support, said catalyst comprising a nickel element content comprised in the active phase greater than or equal to 1% by weight and less than 20% by weight relative to the total weight of the catalyst, and a copper element content of between 0.5 to 15% by weight relative to the total weight of the catalyst, the size of the nickel particles of the active phase of the catalyst, measured in oxide form, being less than 18 nm, which method comprises at least the following steps:

a) the sequence of the following sub-steps is carried out:

a1) the alumina support or the catalyst precursor obtained at the end of step b) is brought into contact with at least one organic additive comprising oxygen and/or nitrogen, the molar ratio between the organic additive and the nickel being greater than 0.05 mol/mol;

a2) the alumina support is brought into contact with at least one nickel metal salt, at a temperature below the melting point of said nickel metal salt, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3,

steps a1) and a2) being carried out either successively in this order, or simultaneously;

a3) the solid mixture obtained at the end of steps a1) and a2) is heated with stirring to a temperature between the melting point of said metal salt and 200° C., to obtain a catalyst precursor;

a4) optionally, the catalyst precursor is dried at the end of step a3) at a temperature below 250° C. to obtain a dried catalyst precursor;

b) the sequence of the following sub-steps is carried out:

b1) either the porous support, or the catalyst precursor obtained at the end of step a), is impregnated with at least one solution containing at least one copper precursor and one nickel precursor at a predetermined copper concentration for obtain on the final catalyst a content of between 0.5 and 15% by weight of copper element relative to the total weight of the final catalyst;

b2) the catalyst precursor obtained at the end of step b1) is dried at a temperature below 250° C.;

said step b) being carried out either before step a) or after step a), it being understood that when step b) is carried out before step a), then sub-step a4) is OBLIGATORY.

The process for preparing the catalyst according to the invention leads to a catalyst having a nickel particle size of less than 18 nm, conferring a high intrinsic activity of the nickel active phase. Also, the process for preparing the catalyst used in the context of the present invention makes it possible to introduce the precursor of the active phase of nickel without adding solvent and therefore makes it possible, in a very limited number of steps and above all less to the conventional preparation process (ie by conventional impregnation of the precursor of the active phase on the support), obtaining a catalyst whose catalytic performances are at least as good or even superior to conventional catalysts. In addition, the presence on the catalyst of a NiCu alloy allows said catalyst to be reduced in situ in the reactor before hydrogenation and this at very low temperatures compared to the conventional reduction temperature which thus takes place ex situ and which therefore requires an additional passivation step.

In one embodiment according to the invention, said process comprises a step c) in which the catalyst precursor resulting from the sequence of steps a) + b), or b) + a), is reduced by bringing said catalyst precursor with a reducing gas at a temperature greater than or equal to 150°C and less than 250°C.

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

In one embodiment according to the invention, said process further comprises a step c5) in which the catalyst obtained at the end of step c4) is calcined at a temperature of between 250°C and 600°C.

Advantageously, the melting point of said metal salt is between 20°C and 150°C.

Advantageously, the molar ratio between said organic additive introduced in step a1) and the nickel element introduced in step a2) is between 0.1 and 5.0 mol/mol.

Advantageously, steps a1) and a2) are carried out simultaneously.

Advantageously, the organic additive of step a1) is chosen from aldehydes containing 1 to 14 carbon atoms per molecule, ketones or polyketones containing 3 to 18 carbon atoms per molecule, ethers and esters containing 2 to 14 carbon atoms per molecule, alcohols or polyalcohols containing 1 to 14 carbon atoms per molecule and carboxylic acids or polycarboxylic acids containing 1 to 14 carbon atoms per molecule, or a combination of the various compound groups referenced above.

Advantageously, said organic additive from step a1) is chosen from formic acid, formaldehyde, acetic acid, citric acid, oxalic acid, glycolic acid, malonic acid, levulinic acid, ethanol, methanol, ethyl formate, methyl formate, paraldehyde, acetaldehyde, gamma-valerolactone acid, glucose and sorbitol.

Advantageously, the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid.

Advantageously, the organic additive is citric acid.

Advantageously, step a3) is carried out by means of a drum operating at a speed of between 4 and 70 revolutions per minute.

Advantageously, in step a2) the mass ratio between said metal salt and the alumina support is between 0.2 and 2.

Advantageously, the nickel precursor content supplied in step b1) is at a predetermined concentration to obtain on the catalyst a nickel content comprised in the copper-nickel alloy comprised between 0.5 and 15% by weight of nickel element relative to the total weight of the catalyst.

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 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 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 volumetric speed 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 40000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst obtained by the process according to the first aspect.

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.

In the present description, according to the IUPAC convention, micropores are understood to mean pores whose diameter is less than 2 nm, that is to say 0.002 μm; by mesopores pores whose diameter is greater than or equal to 2 nm, i.e. 0.002 µm and less than or equal to 50 nm, i.e. 0.05 µm and by macropores pores whose diameter is greater than 50 nm, i.e. 0.05 µm.

The total pore volume is measured by mercury porosimetry according to the ASTM D4284-92 standard with a wetting angle of 140°, for example by means of an Autopore III™ model device from the Micromeritics™ brand.

The BET specific surface is measured by physisorption with nitrogen according to standard ASTM D3663-03, method described in the work Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, 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 term "nickel particle size" means the diameter of the nickel crystallites included in the active phase of the catalyst in oxide form. The diameter of nickel crystallites in oxide form is determined by X-ray diffraction, from the width of the diffraction line located at the angle 2theta=43° (i.e. along the crystallographic direction [200 ]) using the Scherrer relation. This method, used in X-ray diffraction on powders or polycrystalline samples which links the width at mid-height of the diffraction peaks to the size of the particles, is described in detail in the reference: Appl. Crystal. (1978), 11, 102-113 "Scherrer after sixty years: A survey and some new results in the determination of crystallite size", J. I. Langford and A. J. C. Wilson.

The nickel and copper content is measured by X-ray fluorescence.

2. Catalyst preparation process

The steps of said preparation process are described in detail below.

Step a)

Step a) includes the following sub-steps:

Step a1)

According to step a1) of the process for preparing the catalyst, the porous support or the catalyst precursor obtained at the end of step b) is brought into contact with at least one organic additive comprising oxygen and/or nitrogen, preferably chosen from aldehydes containing from 1 to 14 carbon atoms per molecule (preferably from 2 to 12), ketones or polyketones containing from 3 to 18 (preferably from 3 to 12) carbon atoms per molecule, ethers or esters containing from 2 to 14 (preferably from 3 to 12) carbon atoms per molecule, alcohols or polyalcohols containing from 1 to 14 (preferably from 2 to 12) carbon atoms per molecule and carboxylic acids or polycarboxylic acids containing from 1 to 14 (preferably from 1 to 12) carbon atoms per molecule. The organic additive can be composed of a combination of the various compound groups mentioned above.

Preferably, the organic additive is chosen from formic acid HCOOH, formaldehyde CH ₂ O, acetic acid CH ₃ COOH, citric acid, oxalic acid, glycolic acid (HOOC-CH ₂ - OH), malonic acid (HOOC-CH ₂ -COOH), levulinic acid (CH ₃ CCH ₂ CH ₂ CO ₂ H), ethanol, methanol, ethyl formate HCOOC ₂ H ₅ , HCOOCH ₃ methyl formate, paraldehyde (CH ₃ -CHO) ₃ , acetaldehyde C ₂ H ₄ O, gamma-valerolactone acid (C ₅ H ₈ O ₂ ), glucose and sorbitol.

Particularly preferably, the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid.

In one embodiment according to the invention, said step a1) is carried out by bringing the support into contact with at least one organic additive in the form of a powder.

In another embodiment according to the invention, said step a1) is carried out by bringing the support into contact with at least one organic additive in the form of a powder dissolved in a minimum amount of water. The term “minimum quantity of water” means the quantity of water allowing the at least partial dissolution of said organic additive in water. This minimum quantity of water cannot be assimilated to a solvent. In this case, and, when the step of introducing the additive is carried out separately from the introduction of the precursor of the active phase of the catalyst (i.e. steps a1) and a2) are carried out separately) the step of setting in contact with the support with the organic additive is advantageously followed by drying at a temperature below 250°C, preferably between 15 and 240°C, more preferably between 30 and 220°C.

The bringing into contact according to step a1) is generally carried out at a temperature between 0 and 70° C., preferably between 10 and 60° C., and in a particularly preferred manner at room temperature.

According to step a1), the contacting of said porous support or of the catalyst precursor obtained at the end of step b) with the organic additive can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Step a1) is advantageously carried out for a period of between 5 minutes to 5 hours depending on the type of mixer used, preferably between 10 minutes and 4 hours.

According to the invention, the molar ratio between the organic additive and the nickel is greater than 0.05 mol/mol, preferably between 0.1 and 5 mol/mol, more preferably between 0.12 and 3 mol/ mol, and even more preferably between 0.15 and 2.5 mol/mol.

Step a2)

According to step a2), the alumina support, optionally obtained at the end of step a1), is brought into contact with at least one nickel metal salt, at a temperature below the melting temperature of the salt metal, optionally for a period of between 5 minutes to 5 hours, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3, preferably between 0.2 and 2.

Preferably, the melting point of said metal salt is between 20°C and 150°C. Preferably the metal salt is hydrated. Preferably, the metal salt is hexahydrated nickel nitrate (Ni(NO ₃ ) ₂ .6H ₂ O, T _{melting point} =56.7° C.).

According to step a2), the bringing into contact of said porous alumina support and the nickel metal salt can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Step a2) is advantageously carried out for a period of between 5 minutes to 5 hours depending on the type of mixer used, preferably between 10 minutes and 4 hours.

Implementation of steps a1) and a2)

According to the invention:

- steps a1) a2) are carried out successively in this order, or

- Steps a) and a2) are carried out simultaneously.

In a preferred embodiment, step a1) is performed before performing step a2).

Step a3)

According to step a3), the mixture obtained at the end of steps a1) and a2) is heated with stirring to a temperature between the melting temperature of the metal salt and 200° C., and optionally under atmospheric pressure. Preferably, the temperature is between 50 and 100°C.

Advantageously, step a3) is carried out for a period of between 5 minutes and 12 hours, preferably between 5 minutes and 4 hours.

According to step a3), the mechanical homogenization of the mixture can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Even more preferentially, step a3) is carried out by means of a drum mixer whose speed of rotation is between 4 and 70 revolutions/minute, preferably between 10 and 60 revolutions/minute. Indeed, if the rotation of the drum is too high, the active phase of the catalyst may be less well distributed in the grain of the support.

Step a4) (optional)

In one embodiment according to the invention, step a4) of drying is advantageously 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, optionally for a period of between 0.5 and 12 hours, and even more preferably for a period of 0.5 to 5 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 a5) (optional)

Calcination step a5) can be carried out after step a3) or after optional step a4) at a temperature between 250°C and 600°C, preferably between 350°C and 550°C, for a duration typically comprised between 0.5 to 24 hours, preferably for a duration of 0.5 to 12 hours, and even more preferably for a duration of 0.5 to 10 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen. Longer durations are not excluded, but do not necessarily bring improvement.

Step b)

Step b) includes the following sub-steps.

Step b1)

During step b1) of the process, either the porous support or the catalyst precursor obtained at the end of step a) is impregnated with at least one solution containing at least one copper precursor and one nickel precursor. at a predetermined copper concentration to obtain on the final catalyst a content of between 0.5 and 15% by weight of copper element relative to the total weight of the final catalyst.

The pH of said solution comprising at least one nickel precursor and one impregnated copper precursor may be modified by the possible addition of an acid or a base.

Preferably, said nickel precursor and the copper precursor are introduced in aqueous solution.

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.

Preferably, the nickel precursor is supplied to step b1) at a predetermined concentration to obtain on the final catalyst (i.e. obtained at the end of steps a) + b) or b) + a)) a nickel content comprised in the copper-nickel alloy comprised 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 quantities of the copper precursor(s) introduced into the solution according to step b1) 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 (i.e. obtained at the end of steps a) + b) or b) + a)), 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 b2)

A step b2) of drying the catalyst precursor obtained at the end of step b1) is carried out. Step b2) of drying is advantageously 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., optionally for a period of between 0.5 hour and 12 hours, and even more preferably for a period of 0.5 hour to 5 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 b2’)

In one embodiment according to the invention, a step b2′) of calcining the catalyst precursor obtained at the end of step b2) is carried out at a temperature of between 250°C and 600°C. Step b2′) of calcination can be carried out at a temperature of between 250° C. and 600° C., preferably between 350° C. and 550° C., optionally for a period of between 0.5 and 24 hours, so as preferably for a period of 0.5 to 12 hours, and even more preferably for a period of 0.5 to 10 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen. Longer durations are not excluded, but do not necessarily bring improvement.

Implementation of steps a) and b)

The process for preparing the catalyst comprises several modes of implementation. They are distinguished in particular by the order of introduction of the solution comprising the precursor of the active phase of nickel and of the solution based on nickel and copper to obtain the NiCu alloy.

Step b) can be carried out either before step a), or after step a) of the preparation process.

When performing step b) before step a), then sub-step a4) is mandatory. Preferably, steps a5) and/or b2′) are also carried out.

Step c) Reduction by 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 c) 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 hydrogenation reactor. 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 hydrogenation of aromatic or polyaromatic compounds. 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 one or more embodiments of the preparation process according to the invention, said reducing treatment is carried out at a temperature greater than or equal to 150° C. and less than 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 less severe operating conditions for reducing the active phase of nickel than in the prior art and thus makes it possible to directly carry out the reduction step within the reactor in which it is desired to carry out the hydrogenation of unsaturated or aromatic compounds.

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. 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 d) Passivation (optional)

The process according to the invention can advantageously comprise 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 the English terminology). Saxon). 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.

In one embodiment according to the invention, the preparation of the catalyst is carried out ex-situ, that is to say before loading the catalyst into the reaction unit of the selective hydrogenation or aromatics hydrogenation process.

Catalyst

The nickel content included in the active phase of the catalyst obtained according to the preparation process according to the invention is greater than or equal to 1% by weight and less than 20% by weight of nickel element relative to the total weight of the catalyst, more preferably between 2 and 19% by weight and even more preferably between 3 and 19% by weight and even more preferably 5 and 18% by weight relative to the total weight of the catalyst.

The copper content included in the alloy of the catalyst obtained according to 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 0.5 and 12% by weight, preferably between 0.75 and 10% by weight, and even more preferably between 1 and 9% by weight.

Part of the nickel and copper included in the catalyst is in the form of a nickel-copper alloy, advantageously corresponding to the formula Ni _x Cu _y with x between 0.1 and 0.9 and including between 0 .1 and 0.9. Preferably, the nickel content included in the copper-nickel alloy obtained 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.

Preferably, the molar ratio between the nickel of the alloy and the copper is between 0.5 and 5, preferably between 0.7 and 4.5, more preferably between 0.9 and 4.

Advantageously, the active phase of the catalyst does not comprise any group VIB metal. In particular, it does not include molybdenum or tungsten.

The size of the nickel particles in the catalyst, measured in oxide form, is less than 18 nm, preferably less than 15 nm, more preferably between 0.5 and 12 nm, preferably between 1 and 8 nm, even more preferably between 1 and 6 nm, and even more preferably between 1 and 5 nm.

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 or equal to 30 m ² /g, preferably greater than or equal to 50 m ² /g, more preferentially comprised between 60 m ² /g and 500 m ² /g, and even more preferentially comprised between 70 m ² /g and 400 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 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 of the catalyst is advantageously between 3 nm and 25 nm, and preferably between 6 and 20 nm, and in a particularly preferred manner 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 a microporosity of less than 0.05 ml/g, very preferably it has no microporosity.

Support

The support is an alumina, that is to say that the support comprises at least 95%, preferably at least 98%, and in a particularly preferred manner at least 99% by weight of alumina relative to the weight of the support. Alumina generally has a crystallographic structure of the delta, gamma or theta alumina type, alone or in a mixture.

According to the invention, the alumina support may comprise impurities such as metal oxides of groups IIA, IIIB, IVB, IIB, IIIA, IVA according to the CAS classification, preferably silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alternatively alkali metals, preferably lithium, sodium or potassium, and/or alkaline earth metals, preferably magnesium, calcium, strontium or barium or sulfur.

The specific surface of the support is generally greater than or equal to 30 m ² /g, preferably greater than or equal to 50 m ² /g, more preferentially comprised between 60 m ² /g and 500 m ² /g, and even more preferentially comprised between 70 m ² /g and 400 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.

The support 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 support 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 of the support is advantageously between 3 nm and 25 nm, and preferably between 6 and 20 nm, and in a particularly preferred manner between 8 and 18 nm.

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

Preferably, the catalyst has a microporosity of less than 0.05 ml/g, 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 less than or equal to 300°C. The process can be 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 a hourly volume rate 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 rate between 100 and 40,000 h ⁻¹ when the process is carried out in the gas phase, in the presence of the catalyst obtained by the preparation process as described above in the description.

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, has for example the following composition: between 40 and 95% by weight of ethylene, 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, has for example the following average composition: of the order of 90% by weight of propylene, 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 carrying out the selective hydrogenation process. It has for example the following composition: of the order of 0.1 to 5% by weight of acetylene, 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, has for example the following average mass composition: 1% weight of butane, 46.5% weight of butene, 51% weight of butadiene, 1 3% by weight of vinylacetylene and 0.2% by weight of 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 carrying out the selective hydrogenation process, has for example the following composition: 21% by weight of pentanes, 45% by 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, corresponds to a hydrocarbon cut whose boiling point is generally between 0 and 300° C., 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 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 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 the butadiene, vinylacetylene (VAC) and the 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 diolefinic compounds are partially hydrogenated into mono-olefins and that 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 can also be advantageously carried out by installing the catalyst in a reactive distillation column or in reactor-exchangers or in a slurry-type reactor. 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 one embodiment, 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 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 so 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, 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 hourly volume velocity (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 AL-1 alumina having a specific surface area of 80 m²/g, a pore volume of 0.7 mL/g.

Example 1: Preparation of an aqueous solution of the precursors of the NiCu alloy (5% Ni)

The aqueous solution of Ni precursors (used for the preparation of catalysts containing NiCu) is prepared by dissolving 14.5 g of nickel nitrate (NiNO ₃ , supplier Strem Chemicals®) in a volume of 13 mL of distilled water. a solution is obtained whose Ni concentration is 116.6 g of Ni per liter of solution.The copper nitrate precursor is then added in order to have a Ni/Cu molar ratio of 1 (catalysts A to E). obtains the solution S. It makes it possible to introduce the precursors of the NiCu alloy with a mass content of Ni relative to the final catalyst of approximately 5% by weight.

Example 2 (compliant, 15% weight of molten salt nickel + citric acid (Ac) + NiCu in pre-impregnation, ratio Ac / Ni=0.2)

The solution prepared in Example 1 is added over 10 grams (g) of AL-1 alumina. The Ni/Cu ratio is 1. The nickel content at the end of this stage is 5% by weight relative to the total weight of the 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.

10 g of alumina impregnated with NiCu are brought into contact with 2.38 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Then, the support is brought into contact with 11.37 g of hexahydrated nickel nitrate in a drum at 25° C. which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes. The molar ratio between citric acid and nickel is 0.2.

The nickel content targeted for this second impregnation step is 15% by weight of nickel 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.

Catalyst A containing 20% by weight of the element nickel relative to the total weight of the catalyst is obtained (15% by weight in Ni in the active phase and 5% by weight in Ni in the nickel-copper alloy). The characteristics of catalyst A thus obtained are reported in Table 1 below.

Example 3: (compliant, 15% weight of molten salt nickel + citric acid (Ac) + NiCu in pre-impregnation, ratio Ac / Ni=0.4)

The solution prepared in Example 1 is added to 10 g of alumina. The Ni/Cu ratio is 1. The Ni content at the end of this stage is 5% by weight. 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.

10 g of alumina impregnated with NiCu are brought into contact with 4.78 g of citric acid dissolved in 10 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C. Then, the support is brought into contact with 11.37 g of hexahydrated nickel nitrate in a drum at 25° C. which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes. The citric acid to Ni molar ratio is 0.4. 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. Catalyst B containing 20% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst B thus obtained are reported in Table 1 below.

Example 4 (compliant with 15% by weight of molten salt nickel + citric acid (Ac) + NiCu in post impregnation, ratio Ac / Ni=0.2)

10 g of AL-1 alumina support are brought into contact with 2.38 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C. Then, the support is brought into contact with 11.37 g of hexahydrated nickel nitrate in a drum at 25° C. which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes. The citric acid to Ni molar ratio is 0.2. The nickel content aimed at in this stage is 15% by weight of Ni 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 precursor of catalyst C′ is obtained, containing 15% by weight of the element nickel relative to the total weight of the catalyst. The solution prepared in Example 1 is added to 10 g of the catalyst precursor prepared above. The Ni/Cu ratio is 1. 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. .

Catalyst C containing 20% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst C thus obtained are reported in Table 1 below.

Example 5 (compliant with 15% by weight of molten salt nickel + glycolic acid (Ag) + NiCu in post-impregnation, Ag / Ni ratio = 0.2)

10 g of AL-1 alumina support are brought into contact with 0.93 g of glycolic acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Then, the support is brought into contact with 11.37 g of hexahydrated nickel nitrate in a drum at 25° C. which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes. The glycolic acid to Ni molar ratio is 0.2.

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 D′ is obtained, containing 15% by weight of the element nickel relative to the total weight of the catalyst.

The solution prepared in Example 1 is then added over 10 grams of the catalyst precursor prepared above. The Ni/Cu ratio is 1.

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.

Catalyst D containing 20% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst D thus obtained are reported in Table 1 below.

Example 6 (non-compliant without citric acid but with NiCu in post impregnation)

10 g of AL-1 alumina support are dry impregnated with 11.37 g of hexahydrated nickel nitrate in a drum at 25°C which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes.

The nickel content aimed at in this stage is 15% by weight of Ni 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 E′ is obtained, containing 15% by weight of the element nickel relative to the total weight of the catalyst.

The solution prepared in Example 1 is then added over 10 grams of the catalyst precursor prepared above. The Ni/Cu ratio is 1. 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. .

Catalyst E containing 20% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst E thus obtained are reported in Table 1 below.

Example 7 (non-compliant, 15% weight of molten salt nickel + Citric Acid (Ac) + without NiCu, ratio Ac / Ni=0.2)

10 g of AL-1 alumina support are brought into contact with 2.38 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Then, the support is brought into contact with 11.37 g of hexahydrated nickel nitrate in a drum at 25° C. which rotates at a speed of 40 to 50 revolutions per minute. The drum is then heated to 62°C and rotates at a speed of 40 to 50 revolutions per minute for 15 minutes. The molar ratio by weight between citric acid and nickel is 0.2.

The nickel content aimed at in this stage is 15% by weight of Ni 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.

Catalyst F containing 15% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst F thus obtained are reported in Table 1 below.

Example 8: Characterization

All the catalysts contain the contents targeted during the impregnation, i.e. 20% by weight of nickel element for catalysts A to E and 15% by weight for catalyst F (characterized by X-ray fluorescence) relative to the total weight of the catalyst, and the % of copper added (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 % by weight relative to the total weight of "active" Ni which does not make up the alloy) for all catalysts A to F characterized by XRD after a reduction step at 170° 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 (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.

We also detect after reduction a line corresponding to the alloy in the form of Ni _0.76 Cu _0.24.

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.

Table 1 below summarizes the reducibility rates or the Ni° content for all the catalysts characterized by XRD after reduction at 170°C for 90 minutes under a hydrogen flow. These values were also compared with the reduction rate obtained for catalyst F (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/Cu Particle size
(m) Percentage of Ni° alone (DRX) after reduction (%) A (compliant) 170°C, 90 mins Yes 4 90 B (compliant) 170°C, 90 mins Yes 4 92 C (compliant) 170°C, 90 mins Yes 4 90 D (compliant) 170°C, 90 mins Yes 4 90 E
(improper) 170°C, 90 mins Yes 20 90 F
(improper) 170°C, 90 mins No 2 0* F
(improper) 400°C, 3 p.m. No 2 80

Example 9: Catalytic tests: performance in selective hydrogenation of a mixture containing styrene and isoprene (A _HYD1 )

Catalysts A to F 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 170°C for 90 minutes under a hydrogen flow of 1 L/h/g (temperature rise ramp of 1°C/min) for catalysts A to F ( which here corresponds to step g) 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 F, 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 F are reported in Table 2 below. They are related to the catalytic activity (A _HYD1 ) measured for catalyst F prepared under conventional reduction conditions (at a temperature of 400° C. for 15 hours under a flow of hydrogen).

Catalyst Ni content
(%) Ni° particle size
(m) A _HYD1 (%) A (compliant) 20 4 220 B (compliant) 20 4 250 C (compliant) 20 4 250 D (compliant) 20 4 220 E (not compliant) 20 20 50 F(not compliant) 20 2 20 F reduced at 400°C 20 2 200

Catalysts A, B, C and D according to the invention lead to very high selective hydrogenation activities. In Example 6, the additive was not added, which leads to catalyst E with a very low activity due to the size of the nickel particles of 20 nm, ie 10 times greater than for the catalysts. In Example 7, the NiCu was not added, which leads after reduction at 170° C. to a catalyst having only Ni atoms in the oxide form which is not active in hydrogenation.

Claims (15)

Process for the preparation of a selective hydrogenation catalyst comprising an active phase of nickel, a nickel-copper alloy, and an alumina support, said catalyst comprising a nickel element content comprised in the active phase greater than or equal to 1% by weight and less than 20% by weight relative to the total weight of the catalyst, and a copper element content of between 0.5 and 15% by weight relative to the total weight of the catalyst, the size of the nickel particles of the active phase of the catalyst, measured in oxide form, being less than 18 nm, which method comprises at least the following steps:
a) the sequence of the following sub-steps is carried out:
a1) the alumina support or the catalyst precursor obtained at the end of step b) is brought into contact with at least one organic additive comprising oxygen and/or nitrogen, the molar ratio between the organic additive and the nickel being greater than 0.05 mol/mol;
a2) the alumina support is brought into contact with at least one nickel metal salt, at a temperature below the melting point of said nickel metal salt, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3,
steps a1) and a2) being carried out either successively in this order, or simultaneously;
a3) the solid mixture obtained at the end of steps a1) and a2) is heated with stirring to a temperature between the melting point of said metal salt and 200° C., to obtain a catalyst precursor;
a4) optionally, the catalyst precursor is dried at the end of step a3) at a temperature below 250° C. to obtain a dried catalyst precursor;
b) the sequence of the following sub-steps is carried out:
b1) either the alumina support, or the catalyst precursor obtained at the end of step a), is impregnated with at least one solution containing at least one copper precursor and one nickel precursor at a copper concentration predetermined to obtain on the final catalyst a content of between 0.5 and 15% by weight of copper element relative to the total weight of the final catalyst;
b2) the catalyst precursor obtained at the end of step b1) is dried at a temperature below 250° C.;
said step b) being carried out either before step a) or after step a), it being understood that when step b) is carried out before step a), then sub-step a4) is OBLIGATORY. Process according to Claim 1, characterized in that it comprises a stage c) in which the catalyst precursor resulting from the sequence of stages a) + b), or b) + a), is reduced by bringing said catalyst precursor with a reducing gas at a temperature greater than or equal to 150°C and less than 250°C. Process according to one of Claims 1 or 2, in which the copper precursor is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulphate, copper chloride, copper bromide, copper, copper iodide and copper fluoride. Process according to any one of Claims 1 to 3, characterized in that it also comprises a stage a5) in which the catalyst precursor obtained at the end of stage a4) is calcined at a temperature of between 250 °C and 600°C. Process according to any one of claims 1 to 4, in which the melting temperature of said metal salt is between 20°C and 150°C. Process according to any one of Claims 1 to 5, in which the molar ratio between the said organic additive introduced in step a1) and the nickel element introduced in step a2) is between 0.1 and 5.0 mol/mol. Process according to any one of Claims 1 to 6, in which steps a1) and a2) are carried out simultaneously. Process according to any one of Claims 1 to 7, in which the organic additive of step a1) is chosen from aldehydes containing 1 to 14 carbon atoms per molecule, ketones or polyketones containing 3 to 18 carbon atoms per molecule, ethers and esters containing 2 to 14 carbon atoms per molecule, alcohols or polyalcohols containing 1 to 14 carbon atoms per molecule and carboxylic acids or polycarboxylic acids containing 1 to 14 carbon atoms per molecule, or a combination of the various compounds referenced above. Process according to any one of Claims 1 to 8, in which the said organic additive of step a1) is chosen from formic acid, formaldehyde, acetic acid, citric acid, oxalic acid, glycolic acid, malonic acid, levulinic acid, ethanol, methanol, ethyl formate, methyl formate, paraldehyde, acetaldehyde, gamma-valerolactone acid, glucose and sorbitol. Process according to Claim 9, in which the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid. A method according to claim 10, wherein the organic additive is citric acid. Process according to any one of Claims 1 to 11, in which step a3) is carried out by means of a drum operating at a speed of between 4 and 70 revolutions per minute. Process according to any one of Claims 1 to 12, in which in step a2) the mass ratio between the said metal salt and the alumina support is between 0.2 and 2. Process according to any one of Claims 1 to 13, in which the content of nickel precursor supplied in stage b1) is at a concentration desired to obtain on the catalyst a nickel content comprised in the copper-nickel alloy comprised between 0.5 and 15% by weight of nickel element relative to the total weight of the catalyst. Process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule contained in a charge of hydrocarbons having a final boiling point less than or equal to 300°C, which process is carried out at a temperature 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 1,000 and at an hourly volume rate between 100 and 40,000 h ^-1 when the process is carried out in the gas, in the presence of a catalyst obtained by the process according to any one of claims 1 to 14.