METHOD FOR PREPARING A CATALYST COMPRISING AN ACTIVE PHASE OF NICKEL DISTRIBUTED INTO A CRUMBLE VIA IMPREGNATION WITH HEXANOL

Abstract

A process for preparing a catalyst comprising an active nickel phase and an alumina support, said catalyst comprising between 1 and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, which process comprises the following steps: a) impregnating said support with a volume V1 of a hexanol solution of between 0.2 and 0.8 times the total porous volume VPT of said support to obtain an impregnated support; b) impregnating the impregnated support obtained at the end of step a) with a solution comprising a precursor of the active nickel phase to obtain a catalyst precursor; c) drying the catalyst precursor obtained at the end of step b) at a temperature below 250°C.

Description

Title of the invention: METHOD FOR PREPARING A CATALYST COMPRISING AN ACTIVE PHASE OF NICKEL DISTRIBUTED IN A CRUMBLING VIA IMPREGNATION WITH HEXANOL technical field

[0001] The present invention relates to a process for preparing a supported nickel-based metal catalyst particularly intended for the hydrogenation of unsaturated hydrocarbons, and more particularly, for the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatics. State of the art

[0002] Monounsaturated organic compounds, such as ethylene and propylene, are the basis for the manufacture of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or diesel fuel that has been treated by steam cracking or catalytic cracking processes. These processes are carried out at high temperatures 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+ gasoline fraction (gasoline containing hydrocarbon compounds having 5 or more carbon atoms), in particular styrenic or indenic compounds.These polyunsaturated compounds are highly reactive and lead to unwanted reactions in the polymerization units. It is therefore necessary to remove them before processing these fractions. Selective hydrogenation is the main treatment developed to specifically remove undesirable polyunsaturated compounds from these hydrocarbon feedstocks. It allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatics, preventing their complete saturation and thus the formation of the corresponding alkanes or naphthenes.

[0003] Selective hydrogenation catalysts are generally based on metals from group VIII of the periodic table, preferably palladium or nickel. The metal is in the form of metallic particles deposited on a support. The metal content, the size of the metal particles, and the distribution of the active phase within the support are among the criteria that are important for the activity and selectivity of the catalysts.

[0004] The macroscopic distribution of metallic particles in the support is an important criterion, particularly in the context of rapid and consecutive reactions. such as selective hydrogenations. It is generally desirable for these elements to be located in a crust at the periphery of the support to avoid intragranular mass transfer problems that can lead to activity defects and a loss of selectivity. Such catalysts are also called "eggshell" catalysts in Anglo-Saxon terminology.

[0005] Such catalysts are widely known in the case of palladium-based selective hydrogenation catalysts. Indeed, thanks to the low palladium content (generally less than 1 wt% of palladium relative to the catalyst) and suitable preparation processes, a thin palladium crust can be obtained at the periphery of the support grains (FR2922784, US2010 / 217052).

[0006] It is often proposed to substitute nickel for palladium, a metal less active than palladium, which therefore needs to be present in a larger quantity in the catalyst. Thus, nickel-based catalysts generally have a nickel content of between 5 and 50 wt% relative to the catalyst. In these catalysts, the nickel is generally distributed homogeneously within the support. One possible way to improve the activity and selectivity of these catalysts is to control the distribution of nickel within the support by depositing the nickel in a more concentrated manner on a crust at the periphery of the support. Such catalysts are known from the prior art.

[0007] US patent 4,519,951 describes an eggshell-type catalyst with nickel on a porous support having a pore volume of at least 0.2 ml / g for pores smaller than 11.7 nm and a pore volume of at least 0.1 ml / g for pores larger than 11.7 nm. More than 50% of the nickel is contained in a crust whose thickness is equal to 0.15 times the radius of the support. This catalyst is used for the hydrogenation of fats.

[0008] Document CN101890351 describes a supported nickel catalyst in which more than 90% of the nickel is contained within a crust 700 µm thick. The catalyst is prepared using an ammonia solution to dissolve the nickel salt. These catalysts are used in a selective hydrogenation application.

[0009] US2012 / 0065442 describes a supported nickel catalyst distributed both on a crust with a thickness of 3 to 15% of the diameter and in the core, the nickel concentration ratio between the crust and the core being between 3.0:1 and 1.3:1. The deposition of the active nickel phase is carried out by spraying ("spray coating" according to Anglo-Saxon terminology) an ammoniacal solution of a nickel salt onto the support.

[0010] Document FR3099387 describes a process for preparing a nickel-based catalyst on an alumina support obtained according to a very specific method, the nickel being distributed both on a crust on the periphery of the support, and in the core of the support, The thickness of said crust being between 2% and 15% of the catalyst diameter. The process for preparing such a catalyst requires, on the one hand, the use of a specific alumina support that has undergone hydrothermal treatment in the presence of an acidic solution, and on the other hand, carrying out a hydrothermal treatment step after the addition of a specific organic additive to the catalyst precursor. Objects of the invention

[0011] Surprisingly, the Applicant discovered that carrying out a specific step of impregnating a porous alumina support, regardless of its origin, with a hexanol solution, without performing an intermediate drying step between the hexanol impregnation and the impregnation of the nickel active phase precursor, makes it possible to obtain a catalyst in which at least some of the nickel is distributed over a crust at the periphery of the support, the other part of the nickel being distributed in the core of the catalyst. Without wishing to be bound by any particular theory, the presence of hexanol prevents the migration of the nickel active phase into the core of the support. Indeed, only a portion of the porosity is occupied by the hexanol. Moreover, since hexanol and water are only slightly miscible, the hexanol layer constitutes a barrier to the diffusion of nickel into the core of the support.

[0012] The present invention thus relates to a new process for preparing a catalyst which makes it possible to obtain a catalyst comprising performance at least as good, or even better, in terms of activity and selectivity in the context of the selective hydrogenation reactions of polyunsaturated compounds or the hydrogenation of aromatics, while using a lower quantity of effective nickel phase (i.e. a quantity of nickel which is in the end found in a crust on the periphery of the support allowing the performance of the selective hydrogenation reactions or the hydrogenation of aromatics) than that typically used in the prior art, which is due to a better distribution of the active nickel phase in the support, making the latter more accessible to the reactants.

[0013] The present invention relates to a process for preparing a catalyst comprising a nickel-based active phase and an alumina support, said catalyst comprising between 1 and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust on the periphery of the support and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst, the size of the nickel particles in the catalyst, measured in oxide form, being less than 15 nm, which process comprises the following steps:

[0014] a) said support is impregnated with a volume VI of a hexanol solution between 0.2 and 0.8 times the total porous volume VPT of said support to obtain an impregnated support;

[0015] b) the impregnated support obtained at the end of step a) is impregnated with a solution comprising at least one precursor of the active nickel phase to obtain a catalyst precursor;

[0016] c) the catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C.

[0017] According to one or more embodiments, in step b) the volume V2 of the solution comprising at least one precursor of the active nickel phase impregnated on the impregnated support obtained at the end of step a) is such that V2 = VPT - VI.

[0018] According to one or more embodiments, step c) is carried out for a time between 0.5 hours and 12 hours.

[0019] According to one or more embodiments, said process further comprises a step d) in which the catalyst obtained at the end of step c) is calcined at a temperature between 250°C and 600°C.

[0020] According to one or more embodiments, step d) is carried out for 0.5 hours to 24 hours.

[0021] According to one or more embodiments, in step a) said volume VI of said hexanol solution is between 0.25 and 0.75 times the total porous volume VPT of said support.

[0022] According to one or more embodiments, in step a) an n-hexanol solution is used.

[0023] According to one or more embodiments, said process further includes a step bl) in which either the impregnated support obtained at the end of step a), or the catalyst precursor obtained at the end of step b), is impregnated with at least one solution containing at least one organic compound comprising at least one carboxylic acid function, or at least one alcohol function, or at least one ester function, or at least one amide function, or at least one amine function, steps b) and bl) being carried out in any order, or simultaneously.

[0024] According to one or more embodiments, the volume V2 of the solution comprising at least one precursor of the active nickel phase and the volume V3 of the solution comprising at least one organic compound impregnated on the impregnated support obtained at the end of step a) are such that V2 + V3 = VPT - VI.

[0025] According to one or more embodiments, steps b) and bl) are carried out simultaneously.

[0026] According to one or more embodiments, the volume V2' of the solution comprising at least one precursor of the active nickel phase and at least one organic compound impregnated on the impregnated support obtained at the end of step a) is such that V2' = VPT-VI.

[0027] According to one or more embodiments, the molar ratio between said compound organic introduced in step bl) and the element nickel also introduced in step b) is between 0.01 and 5.0 mol / mol.

[0028] According to one or more embodiments, the organic compound of step bl) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, tartronic acid, citric acid, tartaric acid, pyruvic acid, levulinic acid, ethylene glycol, propane-1,3-diol, butane-1,4-diol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, gamma-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylmethanamide, 2-pyrrolidone, γ-lactam, lactamide, urea, alanine, arginine, lysine, the proline, serine, EDTA.

[0029] According to one or more embodiments, a step a1) is carried out in which the impregnated support obtained at the end of step a) is allowed to mature for 0.5 hours to 40 hours.

[0030] According to one or more embodiments, the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm. Description of the figure

[0031] [Fig-1] Fig. 1 is a diagram representing the distribution of nickel in the ca catalyst. The x-axis represents the catalyst thickness, measured from the catalyst edge (in µm). The y-axis represents the nickel density (in grams of Ni / mm³). The nickel is distributed both on a crust at the periphery of the support, with a thickness of epl, and in the core of the support. The nickel density on the crust is greater than the nickel density in the core of the support. The transition interval between the core and the crust of the catalyst has a thickness denoted ep²-epl. Detailed description of the invention 1. Definitions

[0032] In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUP AC classification.

[0033] In the present description, according to the IUP AC convention, micropores are pores whose diameter is less than 2 nm, i.e. 0.002 pm; mesopores are pores whose diameter is greater than or equal to 2 nm, i.e. 0.002 pm and less than or equal to 50 nm, i.e. 0.05 pm; and macropores are pores whose diameter is greater than 50 nm, i.e. 0.05 pm.

[0034] In order to analyze the distribution of the metallic phase on the support, a measurement is taken Crust thickness by Castaing microprobe (or electron microprobe microanalysis). The instrument used is a CAMECA XS100, equipped with four monochromator crystals allowing the simultaneous analysis of four elements. The Castaing microprobe analysis technique consists of detecting X-rays emitted by a solid after its elements have been excited by a high-energy electron beam. For the purposes of this characterization, catalyst grains are embedded in epoxy resin pads. These pads are polished to a cross-section the same diameter as the beads or extruded particles, then metallized by carbon deposition in a metal evaporator. The electron probe is scanned along the diameter of five beads or extruded particles to obtain the average distribution profile of the constituent elements of the solids. This method, well known to those skilled in the art, is defined in the publication by L. Sorbier et al.“Measurement of palladium crust thickness on catalyst by EPMA” Materials Science and Engineering 32 (2012). This method allows us to establish the distribution profile of a given element, in this case nickel, within the grain. Furthermore, the Ni concentration is defined for each measurement and therefore for each analysis step. The Ni density within the grain is thus defined as the Ni concentration per mm³.

[0035] The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore III™ device from Microméritics™.

[0036] The specific surface area BET is measured by nitrogen physisorption according to ASTM D3663-03, a method described in the book Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academy Press, 1999.

[0037] The term "nickel particle size" refers to the diameter of nickel crystallites in the oxide form. The diameter of nickel crystallites in the oxide form is determined by X-ray diffraction, from the width of the diffraction line located at the angle 2θ = 43° (i.e., along the crystallographic direction

[200] ) using Scherrer's relation. This method, used in X-ray diffraction on powders or polycrystalline samples, which relates the full width at half maximum (FWHM) of the diffraction peaks to the particle size, is described in detail in the reference: Appl. Cryst. (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.

[0038] The nickel content is measured by X-ray fluorescence. 2. Process for preparing the catalyst

[0039] The steps of said preparation process are described in detail below. Step a)

[0040] According to step a) of the process, the alumina support is impregnated with a volume VI of a hexanol solution between 0.2 and 0.8 times the total porous volume (also called here VPT) of said support to be impregnated, preferably between 0.25 and 0.75.

[0041] Hexanol is defined as organic compounds comprising an alcohol functional group with the molecular formula C6Hi4O. Hexanol thus includes the following family of organic compounds: hexan-1-ol (or n-hexanol), hexan-2-ol, and their isomers. Preferably, step a) is carried out in the presence of hexan-1-ol. Step a1) (optional)

[0042] After step a), the impregnated support can be cured in a moist state for 0.5 to 40 hours, preferably for 1 to 30 hours. The curing step a1) is preferably carried out at a temperature of 60°C or lower, and more preferably at room temperature. This step allows the hexanol solution to migrate into the core of the support. When carried out, the curing step a1) allows the hexanol solution to enhance the migration into the core of the support and to release a "corona of free pores" at the periphery of the support, accessible to nickel during the impregnation step of the active phase precursor. Step b)

[0043] In step b) of the process, the porous support of impregnated alumina obtained at the end of step a) (or the matured impregnated support obtained at the end of step a1)) is impregnated with a solution comprising at least one precursor of the nickel active phase to obtain a catalyst precursor. The impregnation step can be carried out by dry or excess impregnation according to methods well known to those skilled in the art.

[0044] The pH of said solution comprising at least one precursor of the active phase of impregnated nickel can be modified by the possible addition of an acid or a base.

[0045] Preferably, said nickel precursor is introduced in aqueous solution, for example in the form of nitrate, carbonate, acetate, chloride, oxalate, complexes formed by a polyacid or an acid-alcohol and its salts, complexes formed with acetylacetonates, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said support. Preferably, nickel nitrate, nickel chloride, nickel acetate, or nickel hydroxycarbonate are advantageously used as nickel precursors. Most preferably, the nickel precursor is nickel nitrate.

[0046] The concentration of nickel in solution is adjusted according to the porous volume of the support still available so as to obtain for the supported catalyst, a nickel content of between 1 and 50% by weight in nickel element relative to the total weight of the catalyst, more preferably between 2 and 40% by weight and even more preferably between 3 and 35% by weight and even more preferably between 5 and 25% by weight. Step bl) (optional)

[0047] When step bl) is carried out, the porous support of impregnated alumina obtained at the end of step a) (or matured impregnated support obtained at the end of step a1)) or the catalyst precursor obtained at the end of step b) is impregnated with a solution containing at least one organic compound comprising at least one carboxylic acid function, or at least one alcohol function, or at least one ester function, or at least one amide function, or at least one amine function, said steps b) and bl) being carried out in any order, or simultaneously.

[0048] The impregnation step can be carried out by dry or excess impregnation using methods well known to those skilled in the art. Indeed, it has also been observed that catalysts prepared in the presence of an organic compound (listed below) are more active than catalysts prepared in the absence of this type of organic compound. This effect is linked to the reduction in the size of the nickel particles.

[0049] Said solution, containing at least one organic compound comprising at least one carboxylic acid functional group, is preferably aqueous. Said organic compound is pre-dissolved at least partially in said solution at the desired concentration. The pH of said solution may be modified by the optional addition of an acid or a base.

[0050] Advantageously, the molar ratio between said organic compound introduced in step bl) and the nickel element also introduced in step b) is between 0.01 and 5.0 mol / mol, preferably between 0.05 and 2.0 mol / mol, more preferably between 0.1 and 1.5 mol / mol and even more preferably between 0.3 and 1.2 mol / mol.

[0051] Said organic compound comprising at least one carboxylic acid function may be an aliphatic organic compound, saturated or unsaturated, or an aromatic organic compound. Preferably, the aliphatic organic compound, saturated or unsaturated, comprises between 1 and 9 carbon atoms, preferably between 2 and 7 carbon atoms. Preferably, the aromatic organic compound comprises between 7 and 10 carbon atoms, preferably between 7 and 9 carbon atoms.

[0052] Said aliphatic organic compound, saturated or unsaturated, or said aromatic organic compound, comprising at least one carboxylic acid function, may be selected from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids.

[0053] Advantageously, the organic compound comprising at least one carboxylic acid function is selected from ethanedioic acid (oxalic acid), propanedioic acid (malonic acid), pentanedioic acid (glutaric acid), hydroxyacetic acid (glycolic acid), 2-hydroxypropanoic acid (lactic acid), 2-hydroxypropanedioic acid (tartronic acid), 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), acid 2,3-Dihydroxybutanedioic acid (tartaric acid), 2-oxopropanoic acid (pyruvic acid), 4-oxopentanoic acid (levulinic acid). Implementation of steps b) and bl)

[0054] The process for preparing the nickel catalyst can include several modes of implementation if step bl) is carried out. They are distinguished in particular by the order of introduction of the organic compound and the nickel precursor, the contacting of the organic compound with the support being carried out either after the contacting of the nickel precursor with the impregnated support obtained at the end of step a) (or a1)), or before the contacting of the nickel precursor with the impregnated support obtained at the end of step a) (or a1)), or at the same time as the contacting of the nickel with the impregnated support obtained at the end of step a) (or a1)).

[0055] A first method of implementation consists of carrying out said step b) prior to said step bl) (post-impregnation).

[0056] A second mode of implementation consists of carrying out said step bl) prior to said step b) (pre-impregnation).

[0057] Each step b) and bl) of impregnating the impregnated support with the nickel precursor, and of impregnating the impregnated support, possibly matured, with at least one solution containing at least one organic compound comprising at least one carboxylic acid function is carried out at least once and may advantageously be carried out several times, possibly in the presence of a nickel precursor and / or an identical or different organic compound at each step b) and / or bl) respectively, all possible combinations of implementations of steps b) and bl) being included in the scope of the invention.

[0058] Preferably, the volume V2 of the solution comprising at least one precursor of the active nickel phase and the volume V3 of the solution comprising at least one organic compound impregnated on the impregnated support, possibly matured, obtained at the end of step a) are such that V2 + V3 = VPT - VI.

[0059] A third embodiment consists of carrying out said step b) and said step bl) simultaneously (co-impregnation). This embodiment may advantageously include carrying out one or more steps b), optionally with the same or different nickel precursor in each step b). In particular, one or more steps b) advantageously precede(s) and / or follow said co-impregnation step, optionally with the same or different nickel precursor in each step. This embodiment may also include several co-impregnation steps: steps b) and bl) are carried out simultaneously on several occasions, optionally in the presence of the same or different nickel precursor and / or organic compound in each co-impregnation step.

[0060] Preferably, steps b) and bl) are carried out simultaneously. Preferably, the volume V2' of the solution comprising at least one precursor of the active nickel phase and at least one organic compound impregnated on the support obtained at the end of step a) (or a1)) is such that V2' = VPT - VI. Step c)

[0061] Step c) of drying is advantageously carried out at a temperature below 250°C, preferably between 15°C and 180°C, more preferably between 30°C and 160°C, even more preferably between 50°C and 150°C, and even more preferably between 70°C and 140°C, for a period typically between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 5 hours. Longer periods are not excluded, but do not necessarily provide any improvement.

[0062] 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.

[0063] At the end of step c), the total, partial, or absence of the hexanol solution in the catalyst does not affect the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds. Step d) (optional)

[0064] Step d) of calcination can be carried out at a temperature between 250°C and 600°C, preferably between 350°C and 550°C, for a period typically between 0.5 hours and 24 hours, preferably between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 10 hours, preferably under an inert atmosphere or an atmosphere containing oxygen. Longer durations are not excluded, but do not necessarily provide any improvement.

[0065] At the end of step d), the total, partial, or absence of the hexanol solution in the catalyst does not affect the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds. Step e) (optional)

[0066] Prior to using the catalyst in the catalytic reactor and implementing a hydrogenation process, advantageously at least one step is carried out of reducing treatment e) in the presence of a reducing gas after steps c) or d) so as to obtain a catalyst comprising nickel at least partially in metallic form.

[0067] This treatment activates the catalyst and forms metallic particles, in particular nickel in its zero-valent state. This reduction treatment can be carried out in-situ or ex-situ, that is, after or before loading the catalyst into the hydrogenation reactor.

[0068] The reducing gas is preferably hydrogen. Hydrogen can be used pure or in a mixture (for example, a hydrogen / nitrogen, hydrogen / argon, or hydrogen / methane mixture). When hydrogen is used in a mixture, any proportion is possible.

[0069] Said reduction treatment is carried out at a temperature between 120°C and 500°C, preferably between 150°C and 450°C. When the catalyst does not undergo passivation, or undergoes a reduction treatment before passivation, the reduction treatment is carried out at a temperature between 180°C and 500°C, preferably between 200°C and 450°C, and even more preferably between 350°C and 450°C. When the catalyst has previously undergone passivation, the reduction treatment is generally carried out at a temperature between 120°C and 350°C, preferably between 150°C and 350°C.

[0070] The duration of the reduction treatment is generally between 2 and 40 hours, preferably between 3 and 30 hours. The temperature rise to the desired reduction temperature is generally slow, for example set between 0.1°C / min and 10°C / min, preferably between 0.3°C / min and 7°C / min.

[0071] The hydrogen flow rate, expressed in L / hour / gram of catalyst, is between 0.01 and 100 L / hour / gram of catalyst, preferably between 0.05 and 10 L / hour / gram of catalyst, even more preferably between 0.1 and 5 L / hour / gram of catalyst. 3. Catalyst

[0072] The preparation process according to the invention makes it possible to obtain a catalyst comprising an active phase based on nickel and an alumina support, said catalyst comprising between 1 and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust on the periphery of the support, and in the core of the support, the thickness of said crust (also called epl) being between 2% and 15% of the diameter of the catalyst, the size of the nickel particles, measured in oxide form, in the catalyst being less than 15 nm.

[0073] Preferably, the nickel is distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust (also called epl) being between 2% and 15% of the diameter of the catalyst, preferably between 2.5% and 12% of the diameter of the catalyst, more preferably between 3% and 10% of the diameter of the catalyst, and more preferably between 3% and 7.5% of the diameter of the catalyst.

[0074] Preferably, the nickel density ratio between the crust and the core (also referred to here as dcrust / dcore) is strictly greater than 3, preferably greater than 3.5, and preferably between 3.8 and 15;

[0075] Preferably, said crust comprises more than 25% by weight of nickel element relative to the total weight of nickel element contained in the catalyst, preferably more than 40% by weight, more preferably between 45% and 90% by weight, and even more preferably between 60% and 90% by weight.

[0076] Advantageously, the transition interval between the core and the crust of the catalyst (also referred to herein as the core / crust transition interval, or ep2-epl according to the notation in [Fig. 1]), related to the variation in nickel density measured along the thickness of the catalyst from the edge of the catalyst to the center of the catalyst, is very abrupt. Preferably, the core / crust transition interval is between 0.05% and 3% of the catalyst diameter, preferably between 0.5% and 2.5% of the catalyst diameter.

[0077] The nickel content in said catalyst is advantageously between 1 and 50% by weight relative to the total weight of the catalyst, more preferably between 2 and 40% by weight, and even more preferably between 3 and 35% by weight, and even more preferably between 5 and 25% by weight relative to the total weight of the catalyst. The "% by weight" values ​​are based on the elemental form of nickel.

[0078] The catalyst can be described as a “semi egg-shell” catalyst, i.e. the concentration of nickel is higher at the periphery of the support than in the core of the support, said concentration of nickel in the core of the support being non-zero.

[0079] The specific surface area of ​​the catalyst is generally between 10 m2 / g and 350 m2 / g, preferably between 25 m2 / g and 300 m2 / g, more preferably between 40 m2 / g and 250 m2 / g.

[0080] The total porous volume of the catalyst is generally between 0.1 ml / g and 1 ml / g, preferably between 0.2 ml / g and 0.8 ml / g, and particularly preferably between 0.3 ml / g and 0.7 ml / g.

[0081] The size of the nickel particles, measured in oxide form, in the catalyst is advantageously less than 15 nm, preferably less than 13 nm, preferably less than 10 nm. When step bl) of the process according to the invention is carried out, then the size of the nickel particles, measured in oxide form, in the catalyst is advantageously less than 7 nm, preferably less than 5 nm, more preferably less than 4 nm, and even more preferably less than 3 nm.

[0082] The active phase of the catalyst does not include any metal from group VIB. In particular, it does not include molybdenum or tungsten.

[0083] Said catalyst (and the support used for preparing the catalyst) is in the form of grains advantageously having a diameter of between 0.5 mm and 10 mm. The grains can have any shape known to those skilled in the art, for example, the form of beads (preferably having a diameter of between 1 mm and 8 mm), extrudates, tablets, or hollow cylinders. Preferably, the catalyst (and the support used for preparing the catalyst) is in the form of extrudates with a diameter of between 0.5 mm and 10 mm, preferably between 0.8 mm and 3.2 mm, and most preferably between 1.0 mm and 2.5 mm, and a length of between 0.5 mm and 20 mm. The "diameter" of the extrudates is understood to mean the diameter of the circle circumscribed about the cross-section of these extrudates. The catalyst can advantageously be in the form of cylindrical, multilobed, trilobed, or quadrilobed extrudates. Preferably its shape is trilobed or quadrilobed.The shape of the lobes can be adjusted according to all methods known in the prior art. 4. Support

[0084] The characteristics of alumina, mentioned in this section, correspond to the characteristics of alumina before the implementation of step a) of the preparation process according to the invention.

[0085] The support is alumina, that is to say, the support comprises at least 95%, preferably at least 98%, and particularly preferably at least 99% by weight of alumina relative to the weight of the support. The alumina generally has a crystallographic structure of the delta, gamma, or theta alumina type, alone or in mixtures.

[0086] The alumina support may include impurities such as metal oxides of groups IIA, IIIB, IVB, IIB, IIIA, IVA according to the CAS classification, for example silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alkali metals, for example lithium, sodium or potassium, and / or alkaline earth metals, for example magnesium, calcium, strontium or barium or sulfur.

[0087] The specific surface area BET of alumina is generally between 10 m2 / g and 400 m2 / g, preferably between 30 m2 / g and 350 m2 / g, more preferably between 50 m2 / g and 300 m2 / g.

[0088] The total pore volume of alumina is generally between 0.1 ml / g and 1.2 ml / g, preferably between 0.3 ml / g and 0.9 ml / g, and most preferably between 0.5 ml / g and 0.9 ml / g. 5. Selective hydrogenation process

[0089] 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 that diolefins and / or acetylenic and / or alkenylaromatic compounds, also called styrenics, contained in a hydrocarbon feedstock having a final boiling point of 300°C or less, which process is carried out at a temperature between 0 and 300°C, at a pressure between 0.1 MPa and 10 MPa, at a molar ratio of hydrogen to (polyunsaturated compounds to be hydrogenated) between 0.1 and 10, and at a volumetric flow rate between 0.1 and 200 h⁻¹ when the process is carried out in the liquid phase, or at a molar ratio of hydrogen to (polyunsaturated compounds to be hydrogenated) between 0.5 and 1000 and at a volumetric flow rate between 100 h⁻¹ 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 as described above.

[0090] Monounsaturated organic compounds, such as ethylene and propylene, are the basis for the manufacture of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or diesel fuel that has been treated by steam cracking or catalytic cracking processes. These processes are carried out at high temperatures 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+ fraction (hydrocarbon compounds having at least 5 carbon atoms), in particular diolefinic, styrenic, or indenic compounds.These polyunsaturated compounds are highly reactive and lead to unwanted reactions in the polymerization units. It is therefore necessary to remove them before processing these fragments.

[0091] Selective hydrogenation is the main treatment developed to specifically remove undesirable polyunsaturated compounds from these hydrocarbon feedstocks. It allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatics while avoiding their complete saturation and thus the formation of the corresponding alkanes or naphthenes. In the case of steam cracking gasoline used as feedstock, selective hydrogenation also allows the selective hydrogenation of alkenyl-aromatics into aromatics while avoiding the hydrogenation of the aromatic rings.

[0092] The hydrocarbon feedstock 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. "Polyunsaturated compounds" are defined as compounds having at least one acetylenic group and / or at least one dienic group and / or at least one alkenyl-romatic group.

[0093] More specifically, the charge is selected from the group consisting of a C2 steam cracker cut, a C2-C3 steam cracker cut, a C3 steam- pocraquage, a C4 cut of vapocraquage, a C5 cut of vapocraquage and a vapocraquage essence also called pyrolysis essence or C5+ cut.

[0094] The C2 steam cracker cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following composition: between 40 and 95 wt% ethylene, approximately 0.1 to 5 wt% acetylene, the remainder being essentially ethane and methane. In some C2 steam cracker cuts, between 0.1 and 1 wt% of C3 compounds may also be present.

[0095] The C3 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following average composition: approximately 90% by weight of propylene, approximately 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.

[0096] A C2-C3 fraction can also be advantageously used for implementing the selective hydrogenation process according to the invention. For example, it has the following composition: approximately 0.1 to 5 wt% acetylene, approximately 0.1 to 3 wt% propadiene and methylacetylene, approximately 30 wt% ethylene, approximately 5 wt% propylene, the remainder being essentially methane, ethane, and propane. This feed can also contain between 0.1 and 2 wt% C4 compounds.

[0097] The C4 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following average mass composition: 1 wt% butane, 46.5 wt% butene, 51 wt% butadiene, 1.3 wt% vinylacetylene, and 0.2 wt% butyne. In some C4 cuts, between 0.1 and 2 wt% of C3 and C5 compounds may also be present.

[0098] The C5 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has for example the following composition: 21% weight of pentanes, 45% weight of pentenes, 34% weight of pentadienes.

[0099] The steam cracking gasoline or pyrolysis gasoline, advantageously used for implementing the selective hydrogenation process according to the invention, corresponds to a hydrocarbon fraction whose boiling point is generally between 0 and 300°C, preferably between 10°C and 250°C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracking gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene...), styrenic compounds (styrene, alpha-methylstyrene...) and indenic compounds (indene...). Steam cracking gasoline typically comprises the C5-C12 fraction with traces of C3, C4, C13, C14, and C15 fractions (e.g., between 0.1 and 3 wt% of each). For example, a pyrolysis gasoline feedstock typically has the following composition: 5 to 30 wt% saturated compounds (paraffins and naphthenes), 40 to 80 wt% aromatic compounds, 5 to 20 wt% monoolefins, 5 to 40 wt% diolefins, and 1 to 20 wt% alkenylaromatic compounds, with all compounds totaling 100%. It also contains 0 to 1000 wt ppm of sulfur, preferably 0 to 500 wt ppm.

[0100] Preferably, the polyunsaturated hydrocarbon feed treated according to the selective hydrogenation process according to the invention is a C2 steam cracking cut, or a C2-C3 steam cracking cut, or a steam cracking gasoline.

[0101] The selective hydrogenation process according to the invention aims to eliminate the polyunsaturated hydrocarbons present in the feedstock to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when the feedstock is a C2 cut, the selective hydrogenation process aims to selectively hydrogenate acetylene. When the 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 butadiene, vinylacetylene (VAC), and butyne; in the case of a C5 cut, the aim is to eliminate pentadienes.When said feedstock is steam cracking gasoline, the selective hydrogenation process aims to selectively hydrogenate said polyunsaturated hydrocarbons present in said feedstock to be treated in such a way that diolefinic compounds are partially hydrogenated into mono-olefins and that styrenic and indenic compounds are partially hydrogenated into corresponding aromatic compounds while avoiding the hydrogenation of aromatic rings.

[0102] The technological implementation of the selective hydrogenation process is, for example, carried out by injecting, in an upward or downward flow, the polyunsaturated hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor. This reactor may be isothermal or adiabatic. An adiabatic reactor is preferred. The polyunsaturated hydrocarbon feedstock may advantageously be diluted by one or more reinjections of the effluent from said reactor, where the selective hydrogenation reaction takes place, at various points in the reactor located between the inlet and outlet, in order to limit the temperature gradient within the reactor. The technological implementation of the selective hydrogenation process according to the invention may also advantageously be carried out by installing at least one of said supported catalysts in a reactive distillation column, in heat exchanger reactors, or in a slurry 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 in the reactor.

[0103] The selective hydrogenation of C2, C2-C3, C3, C4, C5 and C5+ steam cracking cuts can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase for C3, C4, C5 and C5+ cuts and in the gas phase for C2 and C2-C3 cuts. A reaction in the liquid phase reduces the energy cost and increases the catalyst cycle time.

[0104] Generally, the selective hydrogenation of a hydrocarbon feedstock containing polyunsaturated compounds with at least two carbon atoms per molecule and a final boiling point of 300°C or less is carried out at a temperature between 0°C and 300°C, at a pressure between 0.1 MPa and 10 MPa, at a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio between 0.1 and 10, and at an hourly volumetric rate (defined as the ratio of the feed volume flow rate to the catalyst volume) between 0.1 h⁻¹ and 200 h⁻¹ for a liquid-phase process, or at a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio between 0.5 and 1000 and an hourly volumetric rate between 100 and 40,000 h⁻¹ for a process carried out in gaseous phase.

[0105] In an embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a steam cracking 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°C and 200°C, preferably between 20°C and 200°C, and even more preferably between 30°C and 180°C; the volumetric velocity per hour (VVH) is generally between 0.5 h₁ and 100 h₁, preferably between 1 and 50 h₁; and the pressure is generally between 0.3 MPa and 8.0 MPa, preferably between 1.0 MPa and 7.0 MPa, and even more preferably between 1.0 and 2.0. preferred between 1.5 MPa and 4.0 MPa.

[0106] More preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the molar ratio hydrogen / (polyunsaturated compounds to be hydrogenated) is between 0.7 and 5.0, the temperature is between 20°C and 200°C, the hourly volumetric velocity (VVH) is generally between 1 h 1 and 50 h 1 and the pressure is between 1.0 MPa and 7.0 MPa.

[0107] Even more preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the molar ratio hydrogen / (polyunsaturated compounds to be hydrogenated) is between 1.0 and 2.0, the temperature is between 30°C and 180°C, the volumetric hourly velocity (VVH) is generally between 1 h 1 and 50 h 1 and the pressure is between 1.5 MPa and 4.0 MPa.

[0108] The hydrogen flow rate is adjusted to ensure sufficient quantity is available for hy- theoretically, to drogenate all polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

[0109] In another embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a C2 steam cracker cut and / or a C2-C3 steam cracker 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°C and 300°C, preferably between 15°C and 280°C, the hourly volumetric velocity (VVH) is generally between 100 h₁ and 40,000 h₁, preferably between 500 h₁ and 30,000 h₁ and the pressure is generally between 0.1 MPa and 6.0 MPa, preferably between 0.2 MPa and 5.0 MPa. 6. Hydrogenation process for aromatics

[0110] The present invention also relates to a process for hydrogenating at least one aromatic or polyaromatic compound contained in a hydrocarbon feedstock having a final boiling point less than or equal to 650°C, generally between 20°C and 650°C, and preferably between 20°C and 450°C. Said hydrocarbon feedstock containing at least one aromatic or polyaromatic compound may be selected from the following petroleum or petrochemical cuts: catalytic reforming reformate, kerosene, light diesel, heavy diesel, cracking distillates, such as FCC recycled oil, coking unit diesel, hydrocracking distillates.

[0111] The content of aromatic or polyaromatic compounds in the hydrocarbon feed treated in the hydrogenation process according to the invention is generally between 0.1% and 80% by weight, preferably between 1% and 50% by weight, and particularly preferably between 2% and 35% by weight, the percentage being based on the total weight of the hydrocarbon feed. The aromatic compounds present in said hydrocarbon feed are, for example, benzene or alkylaromatics such as toluene, ethylbenzene, o-xylene, m-xylene, or p-xylene, or even aromatics having several aromatic rings (polyaromatics) such as naphthalene.

[0112] The sulfur or chlorine content of the feed is generally less than 5000 ppm by weight of sulfur or chlorine, preferably less than 100 ppm by weight, and particularly preferably less than 10 ppm by weight.

[0113] The technological implementation of the process for hydrogenating aromatic or polyaromatic compounds is, for example, carried out by injecting, in an upward or downward flow, the hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor. This reactor may be isothermal or adiabatic. An adiabatic reactor is preferred. The hydrocarbon feedstock may be... The solution can be diluted by one or more reinjections of the effluent from the reactor where the aromatic hydrogenation reaction takes place, at various points in the reactor located between the inlet and outlet, in order to limit the temperature gradient within the reactor. The technological implementation of the aromatic hydrogenation process according to the invention can also advantageously be achieved by installing at least one of the supported catalysts in a reactive distillation column, in heat exchanger reactors, or in a slurry reactor. The hydrogen flow can be introduced simultaneously with the feed to be hydrogenated and / or at one or more different points in the reactor.

[0114] The hydrogenation of aromatic or polyaromatic compounds can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase. In general, the hydrogenation of aromatic or polyaromatic compounds is carried out at a temperature between 30°C and 350°C, preferably between 50°C and 325°C, at a pressure between 0.1 MPa and 20 MPa, preferably between 0.5 MPa and 10 MPa, at a molar ratio of hydrogen / (aromatic compounds to be hydrogenated) between 0.1 and 10 and at an hourly volumetric rate between 0.05 h 1 and 50 h 1, preferably between 0.1 h 1 and 10 h 1 of a hydrocarbon feed containing aromatic or polyaromatic compounds and having a final boiling point less than or equal to 650°C, generally between 20°C and 650°C, and preferably between 20°C and 450°C.

[0115] The hydrogen flow rate is adjusted to ensure sufficient quantity is available to theoretically hydrogenate all aromatic compounds and to maintain an excess of hydrogen at the reactor outlet.

[0116] The conversion of aromatic or polyaromatic compounds is generally greater than 20% by mole, preferably greater than 40% by mole, more preferably greater than 80% by mole, and particularly preferably greater than 90% by mole of the aromatic or polyaromatic compounds contained in the hydrocarbon feed. The conversion is calculated by dividing the difference between the total moles of aromatic or polyaromatic compounds in the hydrocarbon feed and in the product by the total moles of aromatic or polyaromatic compounds in the hydrocarbon feed.

[0117] According to a particular embodiment of the process according to the invention, a process for hydrogenating benzene from a hydrocarbon feedstock, such as reformate from a catalytic reforming unit, is carried out. The benzene content in said hydrocarbon feedstock is generally between 0.1 and 40 wt%, preferably between 0.5 and 35 wt%, and particularly preferably between 2 and 30 wt%, the wt% being based on the total weight of the hydrocarbon feedstock.

[0118] The sulfur or chlorine content of the feed is generally less than 10 ppm by weight of sulfur or chlorine respectively, and preferably less than 2 ppm by weight.

[0119] The hydrogenation of benzene contained in the hydrocarbon feedstock can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase. When carried out in the liquid phase, a solvent may be present, such as cyclohexane, heptane, or octane. Generally, the hydrogenation of benzene is carried out at a temperature between 30°C and 250°C, preferably between 50°C and 200°C, and more preferably between 80°C and 180°C, at a pressure between 0.1 MPa and 10 MPa, preferably between 0.5 MPa and 4 MPa, at a hydrogen / (benzene) molar ratio between 0.1 and 10, and at an hourly volumetric rate between 0.05 h₁ and 50 h₁, preferably between 0.5 h₁ and 10 h₁.

[0120] The conversion of benzene is generally greater than 50% by mole, preferably greater than 80% by mole, more preferably greater than 90% by mole and particularly preferred greater than 98% by mole.

[0121] The invention will now be illustrated by means of the following examples, which are in no way limiting. Examples

[0122] For all catalysts mentioned in the examples below, the support is an alumina A having a specific surface area of ​​80 m2 / g, a total pore volume (TPV) of 0.7 mL / g and a mesoporous median diameter of 12 nm.

[0123] Example 1: Preparation of an aqueous Ni precursor solution with additive

[0124] The aqueous solution S used for the preparation of catalysts B to H is prepared by dissolving 43.5 g of nickel nitrate (NiNO3, supplier Strem Chemicals®) and 7.69 g of malonic acid (CAS 141-82-2; supplier Fluka®) in 13 mL of distilled water. The molar ratio of additive to Ni is set at 0.5. The resulting solution S has a Ni concentration of 350 g per liter of solution.

[0125] Example Ibis: Preparation of an aqueous solution of Ni precursor without additives

[0126] The aqueous solution S' used for the preparation of catalyst A is prepared by dissolving 43.5 g of nickel nitrate (NiNO3, supplier Strem Chemicals®) in 13 mL of distilled water. This yields solution S' with a Ni concentration of 350 g per liter of solution.

[0127] Example 2: Preparation of a catalyst A according to the invention 110% wt. of Ni-hexanol 25% VRE as pre-impregnation]

[0128] 10 g of alumina A are impregnated with 2.4 ml of n-hexanol added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Next, 7.1 ml of the solution S' prepared according to example Ibis is drip-applied to the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C, and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0129] Catalyst A is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0130] The characteristics of the catalyst A thus obtained are shown in Table 1 below.

[0131] Example 3: Preparation of a catalyst B according to the invention [10% by weight of Ni-hexanol 25% VRE as pre-impregnation + additive]

[0132] 10 g of alumina A are impregnated with 2.4 ml of n-hexanol added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Next, 7.1 ml of solution S prepared in Example 1 is drip-dipped onto the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0133] Catalyst B is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0134] The characteristics of the catalyst B thus obtained are shown in Table 1 below.

[0135] Example 4: Preparation of a catalyst C according to the invention 15% wt of Ni-hexanol 25%VRE as pre-impregnation + additive]

[0136] 10 g of alumina A are impregnated with 2.4 ml of n-hexanol added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Next, 3.55 ml of solution S prepared in Example 1, diluted with water to bring the total volume to 7.1 ml, is impregnated dropwise onto the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C, and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0137] Catalyst C is obtained containing 5% by weight of the element nickel relative to the total weight of the catalyst.

[0138] The characteristics of the catalyst C thus obtained are shown in Table 1 below.

[0139]

[0140] Example 5: Preparation of a catalyst D according to the invention [10% by weight of Ni-hexanol 75% of the VRE in pre-impregnation + additive]

[0141] 10 g of alumina A are impregnated with 7.2 ml of n-hexanol added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Next, 2.4 ml of solution S prepared in Example 1 is drip-dipped onto the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0142] Catalyst D is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0143] The characteristics of the catalyst D thus obtained are shown in Table 1 below.

[0144] Example 6: Preparation of a catalyst E not according to the invention [conventional impregnation 10%Ni+ additive]

[0145] The solution S prepared in Example 1 is impregnated dry, by adding it dropwise, onto 10 g of alumina. The catalyst precursor thus obtained is then dried in an oven for 12 hours at 120°C, and then calcined under a flow of dry air of 1 L / h / g of catalyst at 450°C for 2 hours.

[0146] Catalyst E is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0147] The characteristics of the catalyst E thus obtained are shown in Table 1 below.

[0148] Example 7: Preparation of a non-conforming F catalyst [ 10% wt. of Ni-hexanol 25%VRE in post-impregnation!

[0149] 7.1 ml of the solution S prepared in example 1 is impregnated dry, by adding drop by drop, onto 10 g of alumina. The 10 g of prepared catalyst precursor are impregnated with 2.4 ml of n-hexanol added drop by drop. The solid is then left to mature for 30 min at 60°C.

[0150] The solid thus obtained is then dried in an oven for 12 hours at 120°C, then calcined under a flow of dry air of 1 L / h / g of catalyst at 450°C for 2 hours.

[0151] Catalyst F is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0152] The characteristics of the catalyst F thus obtained are shown in Table 1 below.

[0153] Example 8: Preparation of a non-conforming G catalyst [10 wt% Ni - toluene 25%VRE as pre-impregnation]

[0154] 10 g of alumina A are impregnated with 2.4 ml of toluene added dropwise. The The impregnated support is then left to mature for 30 min at 60°C. Next, 7.1 ml of the solution S prepared in Example 1 is drip-dipped onto the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0155] Catalyst G is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0156] The characteristics of the catalyst G thus obtained are shown in Table 1 below.

[0157] Example 9: Preparation of a non-conforming H catalyst F10% by weight of Ni - n- propanol 25% VRE in pre-impregnation]

[0158] 10 g of alumina A are impregnated with 2.4 ml of n-propanol added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Next, 7.1 ml of solution S prepared in Example 1 is drip-dipped onto the impregnated support. The resulting catalyst precursor is then oven-dried for 12 hours at 120°C and subsequently calcined under a stream of dry air at a rate of 1 L / h / g of catalyst at 450°C for 2 hours.

[0159] Catalyst H is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0160] The characteristics of the H catalyst thus obtained are shown in Table 1 below.

[0161] [Tables 1] Ni solvent catalyst (% wt) Particle size (nm) Crust thickness / grain diameter (%) Crust thickness / core diameter Ni content in crust / total Ni (%) A (compliant) 25% n-hexanol pre-impregnation 10 8 6.8 6 68 B (compliant) 25% n-hexanol pre-impregnation 10 2.3 6.8 6 65 C (compliant) 25% n-hexanol pre-impregnation 5 2 3.8 14 73 D (compliant) 75% n-hexanol pre-impregnation 10 2.3 4.7 12 71 E (non-compliant) - 10 2.3 <1% 1.5 7 F (non-compliant) 25% n-hexanol post-impregnation 10 2.3 Homogeneous distribution - - G (non-compliant) 25% toluene pre-impregnation n 10 2.3 Homogeneous distribution - - H (non-compliant) 25% n-propanol pre-impregnation 10 2.3 Homogeneous distribution - -

[0162] Table 1: Characteristics of catalysts A to H

[0163] Example 10: Catalytic tests: performance in selective hydrogenation of a mixture containing styrene and isoprene (AHydi)

[0164] The catalysts A to H described in the examples above are tested with respect to the selective hydrogenation reaction of a mixture containing styrene and isoprene.

[0165] The composition of the feedstock to be selectively hydrogenated is as follows: 8 wt% styrene (supplier Sigma Aldrich®, 99% purity), 8 wt% isoprene (supplier Sigma Aldrich®, 99% purity), 84 wt% n-heptane (solvent) (supplier VWR®, purity > 99% chromanorm HPLC). This feedstock also contains sulfur compounds in very small amounts: 10 ppm wt of sulfur introduced as pentanethiol (supplier Fluka®, purity > 97%) and 100 ppm wt of sulfur introduced as thiophene (supplier Merck®, 99% purity). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis fuel.

[0166] The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave, equipped with magnetically driven mechanical stirring and capable of operating under a maximum pressure of 100 bar (10 MPa) and temperatures between 5°C and 200°C.

[0167] Prior to its introduction into the autoclave, a 3 mL quantity of catalyst is reduced ex situ under a hydrogen flow of 1 L / h / g of catalyst at 400 °C for 16 hours (temperature ramp of 1 °C / min), and then transferred into the autoclave, protected from air. After adding 214 mL of n-heptane (supplier VWR®, purity > 99% chromanorm HPLC), the autoclave is closed, purged, and then pressurized to 35 bar (3.5 MPa) of hydrogen and brought to the test temperature of 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 maintained constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle located upstream of the reactor.

[0168] The progress of the reaction is monitored by taking samples of the reaction medium at regular time intervals: styrene is hydrogenated to ethylbenzene, without hydrogenation of the aromatic ring, and isoprene is hydrogenated to methyl butene. If the reaction is prolonged longer than necessary, the methyl butene is 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 H2 consumed per minute per gram of Ni.

[0169] The catalytic activities measured for catalysts A to H are reported in Table 2 below. They are related to the catalytic activity (AHydi) measured for catalyst E.

[0170] Example 11: Catalytic tests: performance in hydrogenation of toluene (AhydA

[0171] The catalysts A to H described in the examples above are also tested vis- regarding the hydrogenation reaction of toluene.

[0172] The selective hydrogenation reaction is carried out in the same autoclave as that described in Example 9.

[0173] Prior to its introduction into the autoclave, a 2 mL quantity of catalyst is reduced ex situ under a hydrogen flow of 1 L / h / g of catalyst, at 400°C for 16 hours (temperature ramp of 1°C / min), then transferred into the autoclave, protected from air. After adding 216 mL of n-heptane (supplier VWR®, purity > 99% chromanorm HPLC), the autoclave is closed, purged, then pressurized under 35 bar (3.5 MPa) of hydrogen, and brought to the test temperature of 80°C. At time t=0, approximately 26 g of toluene (SDS® supplier, purity > 99.8%) are introduced into the autoclave (the initial composition of the reaction mixture is then toluene 6 wt% / n-heptane 94 wt%) and agitation is started at 1600 rpm. The pressure is maintained constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle located upstream of the reactor.

[0174] The progress of the reaction is monitored by taking samples of the reaction medium at regular time intervals: the toluene is completely hydrogenated to methylcyclohexane. 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 H2 consumed per minute per gram of Ni.

[0175] The catalytic activities measured for catalysts A to H are reported in Table 2 below. They are related to the catalytic activity (AHYD2) measured for catalyst E.

[0176] [Tables2] Catalyst Ni° content (%) AhyDI (%) AhyD2 (%) A (compliant) 10 105 110 B (compliant) 10 195 220 C (compliant) 5 120 140 D (compliant) 10 200 240 E (non-compliant) 10 100 100 F (non-compliant) 10 50 50 G (non-compliant) 10 70 80 H (non-compliant) 10 95 98

[0177] Table 2: Comparison of the performance of catalysts A to H in hydrogenation selective for a mixture containing styrene and isoprene (AHYDi) and for the hydrogenation of toluene (AHYD2)

[0178] These examples clearly demonstrate the improved performance of catalysts A, B, C, and D according to the invention, compared to the non-conforming catalysts E, F, G, and H. This is due to the crust-like distribution of nickel on catalysts A, B, C, and D, which gives them significantly improved activity, particularly in rapid hydrogenation reactions. Catalyst A, despite its larger particle size (8 nm) due to the absence of malonic acid, remains quite efficient because the nickel is well distributed in a crust and therefore highly accessible. Catalyst E exhibits reduced activity due to the conventional impregnation process implemented without pre-impregnation with hexanol. Catalyst F underwent post-impregnation with hexanol, which prevents the nickel from forming a crust. Catalyst G is prepared with a pre-impregnation step using toluene.Thus, although toluene is poorly miscible with water, as in the case of hexanol, the absence of -OH groups in the molecule prevents it from interacting strongly with the -OH groups of the alumina support. This may explain the migration of toluene by the water contained in the nickel nitrate solution during the nickel impregnation step. In the case of propanol, the -OH groups appear to allow it to both penetrate the core of the support and interact with it. However, since water and n-propanol are highly miscible, unlike the hexanol / water pair, diffusion into the core of the aqueous nickel nitrate solution seems to occur, considering both the physicochemical characteristics of the final catalyst obtained and the results of catalytic tests. Thus, for catalysts F, G, and H, the nickel is distributed homogeneously throughout the catalyst grain.Catalysts F and G therefore have a significantly lower activity than catalyst A in AHYDi and AHYD2. Catalyst G is even more reduced due to the presence of toluene, which disrupts the impregnation of the nickel nitrate solution.

Claims

Demands

1. A process for preparing a catalyst comprising a nickel-based active phase and an alumina support, said catalyst comprising between 1 and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst, the size of the nickel particles in the catalyst, measured in oxide form, being less than 15 nm, which process comprises the following steps: a) impregnating said support with a volume VI of a hexanol solution of between 0.2 and 0.8 times the total pore volume VPT of said support to obtain an impregnated support; b) impregnating the impregnated support obtained at the end of step a) with a solution comprising at least one precursor of the nickel active phase to obtain a catalyst precursor;c) the catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C.;

2. A method according to claim 1, wherein in step b) the volume V2 of the solution comprising at least one precursor of the active nickel phase impregnated on the impregnated support obtained at the end of step a) is such that V2 = VPT - VI.

3. A method according to claims 1 or 2, characterized in that step c) is carried out for a time between 0.5 hours and 12 hours.

4. A process according to any one of claims 1 to 3, characterized in that it further comprises a step d) in which the catalyst obtained at the end of step c) is calcined at a temperature between 250°C and 600°C.

5. A method according to claim 4, wherein step d) is carried out for 0.5 hours to 24 hours.

6. A method according to any one of claims 1 to 5, wherein in step a) said volume VI of said hexanol solution is between 0.25 and 0.75 times the total porous volume VPT of said support.

7. A method according to any one of claims 1 to 6, wherein in step a) an n-hexanol solution is used.

8. A method according to any one of claims 1 to 7, wherein a step bl) is carried out in which either the impregnated support obtained at the end of step a) or the catalyst precursor obtained at the outcome of step b), with at least one solution containing at least one organic compound comprising at least one carboxylic acid function, or at least one alcohol function, or at least one ester function, or at least one amide function, or at least one amine function, steps b) and bl) being carried out in any order, or simultaneously.

9. A process according to claim 8, wherein the volume V2 of the solution comprising at least one precursor of the nickel active phase and the volume V3 of the solution comprising at least one organic compound impregnated on the impregnated support obtained at the end of step a) are such that V2 + V3 = VPT - VI.

10. A method according to any one of claims 8 or 9, wherein steps b) and b1) are carried out simultaneously.

11. A process according to claim 10, wherein the volume V2' of the solution comprising at least one precursor of the nickel active phase and at least one organic compound impregnated on the impregnated support obtained at the end of step a) is such that V2' = VPT - VI.

12. A process according to any one of claims 8 to 11, wherein the molar ratio between said organic compound introduced in step bl) and the nickel element also introduced in step b) is between 0.01 and 5.0 mol / mol.

13. A process according to any one of claims 8 to 12, wherein the organic compound of step 1b) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, tartaric acid, citric acid, tartaric acid, pyruvic acid, levulinic acid, ethylene glycol, propane-1,3-diol, butane-1,4-diol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, gamma-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylmethanamide, 2-pyrrolidone, γ-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, EDTA.

14. A method according to any one of claims 1 to 13, wherein a step a1 is carried out in which the impregnated support obtained at the end of step a) is allowed to mature for 0.5 hours to 40 hours.

15. A method according to any one of claims 8 to 14, wherein the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm.

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