Method for preparing a catalyst containing a nickel active phase dispersed in a crust via impregnation with heptanol

Abstract

A method for preparing a catalyst comprising a nickel active phase and an alumina support, said catalyst comprising 1-50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust around the support and in the core of the support, said method comprising the following steps: a) impregnating said support with a heptanol solution having a volume V1 between 0.2 and 0.8 times the total pore volume TPV of said support to obtain an impregnated support; b) impregnating the impregnated support obtained at the end of step a) with a solution containing a precursor of the nickel active 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

[Technical field]

[0001] The present invention relates to a process for preparing supported metal catalysts based on nickel, in particular intended for the hydrogenation of unsaturated hydrocarbons, more particularly the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds. [Background technology]

[0002] Monounsaturated organic compounds, such as ethylene and propylene, are the backbone for the production of polymers, plastics and other value-added chemical products. These compounds are obtained from natural gas, naphtha, or gas oils processed 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 points correspond to the C5+ gasoline fraction (gasoline containing hydrocarbon compounds with 5 or more carbon atoms), in particular styrene or indene compounds. These polyunsaturated compounds are highly reactive and cause side reactions in the polymerization unit. It is thus necessary to remove them before making economical use of these fractions. Selective hydrogenation is the main process developed to specifically remove the undesired polyunsaturated compounds from these hydrocarbon feedstocks. This allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatic compounds while avoiding their complete saturation and thus the formation of the corresponding alkanes or naphthenes.

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

[0004] The macroscopic distribution of metal particles in the support constitutes an important criterion, primarily in the context of rapid and continuous reactions, such as selective hydrogenation. It is generally desirable for these elements to be located in a crust around the support, to avoid intragranular mass transport problems that can lead to activity defects and loss of selectivity. Such catalysts are also called "eggshell" catalysts.

[0005] Such catalysts are widely known in the case of palladium-based selective hydrogenation catalysts: indeed, with low palladium contents (generally less than 1% by weight (wt%) of palladium relative to the catalyst) and appropriate preparation methods, a thin crust of palladium around the support granules can be obtained (Patent Documents 1 and 2).

[0006] It is often proposed to replace palladium with nickel, but this metal is less active than palladium and therefore needs to be present in larger amounts in the catalyst. The metal content of nickel-based catalysts is therefore generally between 5% and 50% by weight of nickel relative to the catalyst. In these catalysts, the nickel is generally distributed homogeneously within the support. One possible way to improve these catalysts in terms of activity and selectivity is to control the distribution of nickel within the support by depositing it more intensively on the crust and around the support. Such catalysts are known from the prior art.

[0007] US Patent No. 5,399,633 describes an "eggshell" catalyst with nickel on a porous support, the pore volume of which is at least 0.2 mL / g for pores with a size of less than 11.7 nm and at least 0.1 mL / g for pores with a size of more than 11.7 nm. More than 50% of the nickel is found in the crust, the thickness of which is equal to 0.15 times the radius of the support. This catalyst is used for the hydrogenation of fats.

[0008] US Patent No. 5,399,633 describes supported nickel catalysts in which more than 90% of the nickel is found in a crust 700 μm thick. The catalysts are prepared using an ammonia solution that dissolves nickel salts. These catalysts are used in selective hydrogenation applications.

[0009] Patent Document 5 describes a supported nickel catalyst having nickel distributed both on a crust having a thickness of 3% to 15% of the diameter and in a core, with the nickel concentration ratio between the crust and the core being 3.0:1 to 1.3:1. The nickel active phase is deposited on the support by spray coating of an ammoniacal solution of nickel salts.

[0010] Patent document 6 describes a method for preparing a nickel-based catalyst on an alumina support obtained according to a very specific method, in which nickel is distributed both on a crust around 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 method for preparing such a catalyst requires, firstly, the use of a specific alumina support that has been subjected to a hydrothermal treatment in the presence of an acidic solution, and, secondly, the implementation of a step of hydrothermal treatment after the addition of specific organic additives to the catalyst precursor. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] French Patent No. 2922784 [Patent Document 2] US Patent Application Publication No. 2010 / 217052 [Patent Document 3] U.S. Pat. No. 4,519,951 [Patent Document 4] China Patent Application Publication No. 101890351 [Patent Document 5] US Patent Application Publication No. 2012 / 0065442 [Patent Document 6] French Patent No. 3099387 Summary of the Invention [Means for solving the problem]

[0012] (Summary of the invention) Surprisingly, the applicant has discovered that the specific step of impregnating a heptanol solution on a porous alumina support, regardless of its origin, without an intermediate drying step between the impregnation of the heptanol and the impregnation of the precursor of the active nickel phase, makes it possible to obtain a catalyst in which at least a portion of the nickel is distributed throughout the crust around the support, and another portion of the nickel is distributed in the core of the catalyst. Without wishing to be bound by any theory, the presence of heptanol prevents the migration of the active nickel phase into the core of the support, since only a portion of the porosity is occupied by heptanol. Furthermore, since heptanol and water are poorly miscible, the heptanol layer constitutes a barrier to the diffusion of nickel into the core of the support.

[0013] The invention therefore relates to a novel method for preparing a catalyst, which makes it possible to obtain catalysts comprising at least as good, and even better, performance qualities in terms of activity and selectivity in the context of the selective hydrogenation reaction of polyunsaturated compounds or the hydrogenation reaction of aromatic compounds, while using a lower effective amount of nickel phase (i.e. the amount of nickel finally located in a crust around the support that makes it possible to carry out the selective hydrogenation reaction or the hydrogenation reaction of aromatic compounds) than is typically used in the prior art, which is due in particular to a better distribution of the active nickel phase in the support, making it more accessible to the reagents.

[0014] One subject of the invention is a method for preparing 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 around 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, and the size of the nickel particles in the catalyst, measured in the form of the oxide, being less than 15 nm, said method comprising the following steps: a) impregnating the carrier with a heptanol solution having a volume V1 that is 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) impregnating the impregnated support obtained at the end of step a) with a solution containing at least one precursor of a nickel active phase to obtain a catalyst precursor; c) drying the catalyst precursor obtained at the end of step b) at a temperature below 250° C.

[0015] According to one or more embodiments, in step b), the volume V2 of the solution comprising at least one precursor of the nickel active phase impregnated on the impregnated support obtained at the end of step a) is such that V2=TPV-V1.

[0016] According to one or more embodiments, step c) is carried out for a period of 0.5 hours to 12 hours.

[0017] According to one or more embodiments, the method 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.

[0018] According to one or more embodiments, step d) is carried out for a period of between 0.5 hours and 24 hours.

[0019] According to one or more embodiments, in step a), the volume V1 of the heptanol solution is 0.25 to 0.75 times the total pore volume TPV of the support.

[0020] According to one or more embodiments, in step a) a solution of n-heptanol is used.

[0021] According to one or more embodiments, the method further comprises a step b1), 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 group, or at least one alcohol group, or at least one ester group, or at least one amide group, or at least one amine group, steps b) and b1) being carried out in any order or simultaneously.

[0022] According to one or more embodiments, the volume V2 of the solution containing at least one precursor of the active nickel phase and the volume V3 of the solution containing at least one organic compound impregnated on the impregnated support obtained at the end of step a) are such that V2+V3=TPV-V1.

[0023] According to one or more embodiments, steps b) and b1) are carried out 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 at least one organic compound impregnated on the impregnated support obtained at the end of step a) is such that V2'=TPV-V1.

[0025] According to one or more embodiments, the molar ratio of said organic compound introduced in step b1) to elemental nickel also introduced in step b) is between 0.01 and 5.0 mol / mol.

[0026] According to one or more embodiments, the organic compound of step b1) 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, γ-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.

[0027] 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 subjected to static aging for a period ranging from 0.5 h to 40 h.

[0028] 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 subjected to static aging for a period ranging from 0.5 h to 40 h.

[0029] According to one or more embodiments, the size of the nickel particles in the catalyst, measured in the oxide form, is less than 13 nm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Description of the drawings FIG. 1 shows the distribution of nickel in the catalyst. The X-axis corresponds to the thickness of the catalyst (μm), measured from the edge of the catalyst. The Y-axis corresponds to the nickel density (grams of Ni / mm 3 ) Nickel is distributed both on the crust around the support with a thickness of ep1 and in the core of the support. The nickel density on the crust d crust is the nickel density in the core of the support, d core The transition interval between the catalyst core and the crust has a thickness denoted ep2-ep1.

[0031] Detailed Description of the Invention (1.Definition) In the following text, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, published by CRC Press, editor DR Lide, 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals in columns 8, 9 and 10 according to the new IUPAC classification.

[0032] In the present description, in accordance with the IUPAC convention, "micropores" are understood to mean pores whose diameter is less than 2 nm, i.e. less than 0.002 μm; "mesopores" are understood to mean pores whose diameter is greater than or equal to 2 nm, i.e. greater than or equal to 0.002 μm, and less than 50 nm, i.e. less than 0.05 μm, and "macropores" are understood to mean pores whose diameter is greater than or equal to 50 nm, i.e. greater than or equal to 0.05 μm.

[0033] To analyze the distribution of the metallic phases on the support, the crust thickness is measured by Castaing microprobe (or electron microprobe microanalysis). The device used is a CAMECA XS100, equipped with four monochromator crystals that allow the simultaneous analysis of four elements. The Castaing microprobe analysis technique consists of the detection of X-rays emitted by a solid after excitation of its elements by a high-energy electron beam. For the purpose of this characterization, the catalyst granules are coated in blocks of epoxy resin. These blocks are polished until a cross section through the diameter of the bead or extrudate is reached, then metallized by carbon deposition in a metal evaporator. The electron probe is scanned along the diameter of five beads or extrudates to obtain an average distribution profile of the constituent elements of the solid. This method is well known to the skilled person and is defined in the publication "Measurement of palladium crust thickness on catalyst by EPMA" by L. Sorbier et al., Materials Science and Engineering 32 (2012). It is thereby possible to establish a distribution profile within the grains of a given element, here nickel. Furthermore, the Ni concentration is defined for each measurement and therefore for each analytical step. The density of Ni within the grains is therefore given by the volume (mm 3 ) is defined as the concentration of Ni per unit area.

[0034] The total pore volume is measured by mercury porosimetry according to standard ASTM D4284-92 at a wetting angle of 140°, for example using an Autopore III® model device from the brand Micromeritics®.

[0035] The BET specific surface area is measured by nitrogen physical adsorption according to standard ASTM D3663-03. The method is described in the study by Rouquerol F., Rouquerol J. and Singh K. "Adsorption by Powders & Porous Solids: Principles, Methodology and Applications, Academic Press, 1999."

[0036] The term "nickel particle size" is understood to mean the diameter of the nickel crystallites in the oxide form. The diameter of the 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

[0200] ) using the Scherrer relation. This method, used in X-ray diffraction on polycrystalline samples or powders, connects the full width at half maximum of the diffraction peak to the size of the particles, and is described in detail in the following reference: Appl. Cryst. (1978), 11, 102-113, "Scherrer after sixty years: A survey and some new results in the determination of crystallite size", JI Langford and AJC Wilson.

[0037] The nickel content is measured by X-ray fluorescence.

[0038] 2. Methods for Preparing the Catalyst The steps of the preparation method are described in detail below.

[0039] (Step a)) According to step a) of the process, the alumina support is impregnated with a heptanol solution of a volume V1 between 0.2 and 0.8 times, preferably between 0.25 and 0.75 times, the total pore volume (herein also called TPV) of said support to be impregnated.

[0040] Heptanol contains an alcohol group and has the empirical chemical formula CH 16 O. Heptanol is therefore understood to mean the family of organic compounds: heptan-1-ol (or n-heptanol), heptan-2-ol and their isomers. Preferably, step a) is carried out in the presence of heptan-1-ol.

[0041] (Step a1) (optional) After step a), the impregnated support can be aged in wet conditions for 0.5 h to 40 h, preferably 1 h to 30 h. The temperature at which the aging step a1) is preferably carried out is below 60° C., more preferentially at ambient temperature. This step allows the heptanol solution to migrate to the core of the support. If it is carried out, the aging step a1) allows the heptanol solution to enhance its migration to the core of the support and to free up a “ring of free pores” around the support accessible by nickel during the step of impregnation of the precursor of the active phase.

[0042] (Step b)) During step b) of the process, the impregnated porous alumina support obtained at the end of step a) (or the aged impregnated porous alumina support obtained at the end of step a1)) is impregnated with a solution containing at least one precursor of the nickel active phase to obtain the catalyst precursor. The impregnation step can be carried out by dry impregnation or excess impregnation according to methods well known to those skilled in the art.

[0043] The pH of the solution containing at least one precursor of the impregnated nickel active phase may be modified by the optional addition of an acid or a base.

[0044] Preferably, the nickel precursor is introduced into an aqueous solution and brought into contact with the support, for example in the form of a nitrate, carbonate, acetate, chloride or oxalate, in the form of a complex formed with a polyacid or an acid alcohol and its salt, in the form of a complex formed with an acetylacetonate or in the form of any other inorganic derivative soluble in an aqueous solution. Preferably, nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate are advantageously used as nickel precursor. Highly preferably, the nickel precursor is nickel nitrate.

[0045] The concentration of nickel in the solution is adjusted depending on the pore volume of the support still available in order to obtain, for the supported catalyst, a nickel content of 1% to 50% by weight, more preferentially 2% to 40% by weight, even more preferentially 3% to 35% by weight, even more preferentially 5% to 25% by weight, by weight of elemental nickel relative to the total weight of the catalyst.

[0046] (Step b1) (optional) When step b1) is carried out, the impregnated porous alumina support obtained at the end of step a) (or the aged impregnated porous alumina 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 group, or at least one alcohol group, or at least one ester group, or at least one amide group, or at least one amine group, said steps b) and b1) being carried out in any order or simultaneously.

[0047] The impregnation step can be carried out by dry impregnation or by excess impregnation according to methods well known to those skilled in the art. This is because it is further noted that catalysts prepared in the presence of organic compounds (described below) are more active than those prepared in the absence of this type of organic compound. This effect is associated with the reduction in the size of the nickel particles.

[0048] The solution containing at least one organic compound containing at least one carboxylic acid group is preferably aqueous. The organic compound is at least partially dissolved in the solution beforehand at a desired concentration. The pH of the solution can be modified by the optional addition of an acid or a base.

[0049] Advantageously, the molar ratio of said organic compound introduced in step b1) to elemental nickel also introduced in step b) is between 0.01 and 5.0 mol / mol, preferably between 0.05 and 2.0 mol / mol, more preferentially between 0.1 and 1.5 mol / mol and even more preferentially between 0.3 and 1.2 mol / mol.

[0050] The organic compound containing at least one carboxylic acid group may be a saturated or unsaturated aliphatic organic compound or an aromatic organic compound. Preferably, the saturated or unsaturated aliphatic organic compound contains 1 to 9 carbon atoms, preferably 2 to 7 carbon atoms. Preferably, the aromatic organic compound contains 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms.

[0051] The saturated or unsaturated aliphatic organic compound or the aromatic organic compound containing at least one carboxylic acid group may be selected from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids.

[0052] Advantageously, the organic compound containing at least one carboxylic acid group is chosen 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), 2,3-dihydroxybutanedioic acid (tartaric acid), 2-oxopropanoic acid (pyruvic acid) or 4-oxopentanoic acid (levulinic acid).

[0053] (Implementation of steps b) and b1) The method for preparing a nickel catalyst, if step b1) is carried out, may comprise several embodiments, which differ in particular in the order of introduction of the organic compound and the nickel precursor, the organic compound being able to be contacted with the support either after the nickel precursor has been contacted with the impregnated support obtained at the end of step a) (or a1)), or before the nickel precursor has been contacted with the impregnated support obtained at the end of step a) (or a1)), or at the same time that the nickel is contacted with the impregnated support obtained at the end of step a) (or a1)).

[0054] A first embodiment consists in carrying out said step b) before said step b1) (post-impregnation).

[0055] A second embodiment consists in carrying out said step b1) before said step b) (pre-impregnation).

[0056] Each step b) and b1) of impregnating the impregnated support with a nickel precursor and impregnating the impregnated and optionally aged support with at least one solution containing at least one organic compound comprising at least one carboxylic acid group may be carried out at least once and advantageously several times, possibly in the presence of a nickel precursor and / or an organic compound, which (these) may be the same or different in each of the steps b) and / or b1), all possible combinations of the implementation of steps b) and b1) being included within the scope of the present invention.

[0057] Preferably, the volume V2 of the solution containing at least one precursor of the active nickel phase and the volume V3 of the solution containing at least one organic compound impregnated on the impregnated, optionally aged, support obtained at the end of step a) are such that V2+V3=TPV-V1.

[0058] A third embodiment consists in carrying out said step b) and said step b1) simultaneously (co-impregnation). This embodiment may advantageously comprise carrying out step b) one or more times, possibly with the same or different nickel precursor in each step b). In particular, one or more steps b) precede and / or advantageously follow said co-impregnation step, possibly with the same or different nickel precursor in each step. This embodiment may comprise several co-impregnation steps: steps b) and b1) are carried out several times simultaneously, possibly in the presence of the same or different nickel precursors and / or organic compounds in each co-impregnation step.

[0059] Preferably, steps b) and b1) 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'=TPV-V1.

[0060] (Step c)) Drying step c) is advantageously carried out at a temperature below 250° C., preferably between 15° C. and 180° C., more preferentially between 30° C. and 160° C., even more preferentially between 50° C. and 150° C., even more preferentially between 70° C. and 140° C., typically for a period between 0.5 and 12 hours, even more preferably between 0.5 and 5 hours. Longer periods are not excluded, but do not necessarily offer any improvement.

[0061] The drying step can be carried out by any technique known to the person skilled in the art. It is advantageously carried out under an inert atmosphere or under an oxygen-containing atmosphere or under a mixture of an 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 in the presence of air or nitrogen.

[0062] At the end of step c), the total or partial presence or absence of the heptanol 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.

[0063] (Step d) (optional) The calcination step d) may be carried out at temperatures between 250° C. and 600° C., preferably between 350° C. and 550° C., typically for a period between 0.5 h and 24 h, preferably for a period between 0.5 h and 12 h, even more preferably for a period between 0.5 h and 10 h, preferably under an inert or oxygen-containing atmosphere. Longer periods are not excluded, but do not necessarily offer any improvement.

[0064] At the end of step d), the total or partial presence or absence of the heptanol 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.

[0065] (Step e) (optional) Prior to use of the catalyst in the catalytic reactor and carrying out the hydrogenation process, advantageously after step c) or d), at least one reduction treatment step e) is carried out in the presence of a reducing gas to obtain a catalyst comprising nickel at least partly in metallic form.

[0066] This treatment makes it possible to activate the catalyst and form metal particles, in particular nickel metal particles in the 0 valence state. The reduction treatment may be carried out in situ or ex situ, i.e. after or before loading the catalyst into the hydrogenation reactor.

[0067] The reducing gas is preferably hydrogen. Hydrogen may be used in high purity or as a mixture (for example, hydrogen / nitrogen, or hydrogen / argon or hydrogen / methane mixtures). When hydrogen is used as a mixture, any ratio may be envisaged.

[0068] The reduction treatment is carried out at a temperature of 120° C. to 500° C., preferably 150° C. to 450° C. If the catalyst is not passivated at all or is passivated after the reduction treatment, the temperature at which the reduction treatment is carried out is 180° C. to 500° C., preferably 200° C. to 450° C., and even more preferentially 350° C. to 450° C. If the catalyst is passivated first, the temperature at which the reduction treatment is generally carried out is 120° C. to 350° C., preferably 150° C. to 350° C.

[0069] The duration of the reduction treatment is generally 2 to 40 hours, preferably 3 to 30 hours. The temperature is generally raised to the desired reduction temperature slowly, for example, at 0.1° C. / min to 10° C. / min, preferably 0.3° C. / min to 7° C. / min.

[0070] The hydrogen flow rate is expressed in L / hour / gram of catalyst and is between 0.01 and 100 L / hour / gram of catalyst, preferably between 0.05 and 10 L / hour / gram of catalyst, and even more preferably between 0.1 and 5 L / hour / gram of catalyst.

[0071] (3. Catalyst) 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 around the support and in the core of the support, the thickness of said crust (also called ep1) being between 2% and 15% of the diameter of the catalyst, and the size of the nickel particles, measured in the oxide form, in the catalyst is less than 15 nm.

[0072] Preferably, the nickel is distributed both on a crust around the support and in the core of the support, the thickness of said crust (also called ep1) being between 2% and 15% of the catalyst diameter, preferably between 2.5% and 12% of the catalyst diameter, even more preferably between 3% and 10% of the catalyst diameter, even more preferably between 3% and 7.5% of the catalyst diameter.

[0073] Preferably, the nickel density ratio between the crust and the core (here d crust / d core (also referred to as ) is strictly greater than 3, preferably greater than 3.5, preferably between 3.8 and 15.

[0074] Preferably, said crust comprises more than 25% by weight, preferably more than 40% by weight, more preferentially between 45% by weight and 90% by weight, even more preferentially between 60% by weight and 90% by weight, of elemental nickel relative to the total weight of elemental nickel contained in the catalyst.

[0075] Advantageously, the transition interval between the catalyst core and crust (also referred to herein as the core / crust transition interval, or ep2-ep1 according to the notation in Figure 1), which relates to the change in nickel density measured across the catalyst thickness 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.

[0076] The nickel content in said catalyst is advantageously between 1% and 50% by weight, more preferentially between 2% and 40% by weight, even more preferentially between 3% and 35% by weight and even more preferentially between 5% and 25% by weight, relative to the total weight of the catalyst. The values ​​"% by weight" are based on the elemental form of nickel.

[0077] The catalyst may be described as a "semi-eggshell" catalyst, i.e., the concentration of nickel is higher at the periphery of the support than in the core of the support, and the concentration of nickel in the core of the support is non-zero.

[0078] The specific surface area of ​​a catalyst is generally 10 m 2 / g~350m 2 / g, preferably 25m 2 / g~300m 2 / g, more preferably 40m 2 / g~250m 2 / g.

[0079] The total pore volume of the catalyst is generally 0.1 mL / g to 1 mL / g, preferably 0.2 mL / g to 0.8 mL / g, and particularly preferably 0.3 mL / g to 0.7 mL / g.

[0080] The size of the nickel particles, measured in the form of the oxide, in the catalyst is advantageously less than 15 nm, preferably less than 13 nm, preferably less than 10 nm. When step b1) of the process according to the invention is carried out, the size of the nickel particles, measured in the form of the oxide, in the catalyst is advantageously less than 7 nm, preferably less than 5 nm, more preferentially less than 4 nm, even more preferentially less than 3 nm.

[0081] The active phase of the catalyst does not contain a metal from group VIB, in particular it does not contain molybdenum or tungsten.

[0082] The catalyst (and the support used for the preparation of the catalyst) is in the form of granules, advantageously having a diameter between 0.5 mm and 10 mm. The granules may have any form known to the person skilled in the art, for example in the form of beads (preferably having a diameter between 1 mm and 8 mm), extrudates, tablets or hollow cylinders. Preferably, the catalyst (and the support used for the preparation of the catalyst) is in the form of extrudates, having a diameter between 0.5 mm and 10 mm, preferably between 0.8 mm and 3.2 mm, highly preferably between 1.0 mm and 2.5 mm, and a length between 0.5 mm and 20 mm. The "diameter" of the extrudates is intended to mean the diameter of the circle circumscribing the cross section of these extrudates. The catalyst may advantageously be presented in the form of cylindrical, multilobed, trilobed or tetralobed extrudates. Preferably, the shape is trilobed or tetralobed. The shape of the lobes may be adjusted according to all known methods of the prior art.

[0083] (4. Carrier) The characteristics of the alumina mentioned in this section correspond to the characteristics of the alumina before step a) of the preparation method according to the invention is carried out.

[0084] The support is an alumina, i.e. it comprises at least 95% by weight, preferably at least 98% by weight, particularly preferably at least 99% by weight, of alumina relative to the weight of the support. The alumina generally exhibits a crystallographic structure of the δ-, γ- or θ-alumina type, either alone or as a mixture.

[0085] The alumina support may contain impurities such as oxides of metals from groups IIA, IIIB, IVB, IIB, IIIA and IVA according to the CAS classification, such as silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or else alkali metals, such as lithium, sodium or potassium, and / or alkaline earth metals, such as magnesium, calcium, strontium or barium, or else sulfur.

[0086] The BET specific surface area of ​​alumina is generally 10m 2 / g~400m 2 / g, preferably 30m 2 / g~350m 2 / g, more preferably 50m 2 / g~300m 2 / g.

[0087] The total pore volume of the 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 highly preferably between 0.5 mL / g and 0.9 mL / g.

[0088] (5. Selective Hydrogenation Method) Another subject of the invention is a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, for example alkenyl aromatics, also known as diolefins and / or acetylenes and / or styrenes, contained in a hydrocarbon feedstock with an end point of less than or equal to 300° C., said process being carried out in the presence of a catalyst obtained by the preparation process as described above in this description, wherein the temperature is between 0° C. and 300° C., the pressure is between 0.1 MPa and 10 MPa, and, if the process is carried out in the liquid phase, the hydrogen / polyunsaturated compound to be hydrogenated molar ratio is between 0.1 and 10, and the hourly space velocity is between 0.1 and 200 h -1 or if the process is carried out in the gas phase, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is 0.5 to 1000, and the hourly space velocity is 100 h -1 ~40000h -1 It is.

[0089] Monounsaturated organic compounds, such as ethylene and propylene, are the backbone for the production of polymers, plastics and other value-added chemical products. These compounds are obtained from natural gas, naphtha or gas oils processed by steam cracking or catalytic cracking processes. These processes are carried out at high temperatures and give rise to, 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 or styrenic or indene-based compounds. These polyunsaturated compounds are highly reactive and cause side reactions in the polymerization unit. It is therefore necessary to remove them before making an economical use of these fractions.

[0090] Selective hydrogenation is the main process 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 therefore the formation of the corresponding alkanes or naphthenes. In the case of steam cracked gasoline used as feedstock, selective hydrogenation also allows the selective hydrogenation of alkenyl aromatics to give aromatics while avoiding the hydrogenation of the aromatic ring.

[0091] The hydrocarbon feedstock to be treated in the selective hydrogenation process has a final boiling point below 300° C., contains at least 2 carbon atoms per molecule and comprises at least one polyunsaturated compound. The term “polyunsaturated compound” is intended to mean a compound containing at least one acetylene group and / or at least one diene group and / or at least one alkenyl aromatic group.

[0092] More particularly, the feedstock is selected from the group consisting of steam cracked C2 fraction, steam cracked C2-C3 fraction, steam cracked C3 fraction, steam cracked C4 fraction, steam cracked C5 fraction and steam cracked gasoline (also known as thermal cracked gasoline or C5+ fraction).

[0093] The steam cracked C2 fractions advantageously used for carrying out the selective hydrogenation process according to the invention have, for example, the following composition: 40% to 95% by weight of ethylene and to the extent of 0.1% to 5% by weight of acetylene; the remainder is essentially ethane and methane. In some steam cracked C2 fractions, 0.1% to 1% by weight of C3 compounds may also be present.

[0094] The steam cracked C3 fractions advantageously used in carrying out the selective hydrogenation process according to the invention have, for example, the following average composition: about 90% by weight of propylene and about 1% to 8% by weight of propadiene and methylacetylene; the remainder is essentially propane. In some C3 fractions, 0.1% to 2% by weight of C2 and C4 compounds may also be present.

[0095] The C2-C3 fraction may also be advantageously used for the implementation of the selective hydrogenation process according to the invention. It may, for example, have the following composition: acetylene 0.1% to 5% by weight, propadiene and methylacetylene 0.1% to 3% by weight, ethylene 30% by weight and propylene 5% by weight; the remainder is essentially methane, ethane and propane. This feedstock may also contain 0.1% to 2% by weight of C4 compounds.

[0096] The steam cracked C4 fractions advantageously used for the implementation of the selective hydrogenation process according to the invention have, for example, the following average weight composition: 1% butane, 46.5% butene, 51% butadiene, 1.3% vinylacetylene and 0.2% butyne. In some C4 fractions, 0.1% to 2% by weight of C3 and C5 compounds may also be present.

[0097] The steam cracked C5 fraction advantageously used for the implementation of the selective hydrogenation process according to the invention exhibits, for example, the following composition: 21% by weight of pentane, 45% by weight of pentenes and 34% by weight of pentadiene.

[0098] The steam cracked gasoline or pyrolysis gasoline advantageously used for the implementation of the selective hydrogenation process according to the invention corresponds to a hydrocarbon fraction whose boiling point is generally between 0° C. and 300° C., preferably between 10° C. and 250° C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracked gasoline are in particular diolefin compounds (butadiene, isoprene, cyclopentadiene, etc.), styrene compounds (styrene, α-methylstyrene, etc.) and indenic compounds (indene, etc.). Steam cracked gasoline generally contains C5-C12 fractions together with traces of C3, C4, C13, C14 and C15 (for example 0.1% by weight to 3% by weight for each of these fractions). For example, a feedstock formed from pyrolysis gasoline generally has the following composition: 5% to 30% by weight of saturates (paraffins and naphthenes), 40% to 80% by weight of aromatics, 5% to 20% by weight of monoolefins, 5% to 40% by weight of diolefins and 1% to 20% by weight of alkenyl aromatics, the combined compounds forming 100%. It also contains 0 to 1000 ppm by weight of sulfur, preferably 0 to 500 ppm by weight of sulfur.

[0099] Preferably, the polyunsaturated hydrocarbon feedstock treated by the selective hydrogenation process according to the invention is a steam cracked C2 fraction or a steam cracked C2-C3 fraction or a steam cracked gasoline.

[0100] The selective hydrogenation process according to the present invention is targeted to remove the polyunsaturated hydrocarbons present in the feedstock to be hydrogenated, without hydrogenating monounsaturated hydrocarbons. For example, when the feedstock is a C2 fraction, the selective hydrogenation process is targeted to selectively hydrogenate acetylene. When the feedstock is a C3 fraction, the selective hydrogenation process is targeted to selectively hydrogenate propadiene and methylacetylene. For the C4 fraction, the goal is to remove butadiene, vinylacetylene (VAC) and butyne; for the C5 fraction, the goal is to remove pentadiene. When the feedstock is steam cracked gasoline, the selective hydrogenation process is targeted to selectively hydrogenate the polyunsaturated hydrocarbons present in the feedstock to be processed, so that diolefin compounds are partially hydrogenated to give monoolefins, and styrene and indene compounds are partially hydrogenated to give the corresponding aromatic compounds, while avoiding the hydrogenation of aromatic rings.

[0101] The technical implementation of the selective hydrogenation process is, for example, carried out by injection of the polyunsaturated hydrocarbon feedstock and hydrogen as upflow or downflow into at least one fixed-bed reactor. The reactor can be of isothermal or adiabatic type. Adiabatic reactors are preferred. The polyunsaturated hydrocarbon feedstock can advantageously be diluted by one or more reinjections of the effluent from the reactor in which the selective hydrogenation reaction is carried out at various points of the reactor located between the inlet and outlet of the reactor to limit the temperature gradient in the reactor. The technical implementation of the selective hydrogenation process according to the invention can also advantageously be carried out by embedding at least the supported catalyst in a reactive distillation column or in a reactor-exchanger or in a slurry-type reactor. The hydrogen flow can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points of the reactor.

[0102] The selective hydrogenation of the steam cracked C2, C2-C3, C3, C4, C5 and C5+ fractions can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5+ fractions and in the gas phase for the C2 and C2-C3 fractions. The liquid phase reaction allows to reduce the energy costs and to increase the cycle period of the catalyst.

[0103] In general, the selective hydrogenation of a hydrocarbon feedstock containing polyunsaturated compounds containing at least two carbon atoms per molecule and having a final boiling point of 300° C. or less is carried out at a temperature of 0° C. to 300° C., a pressure of 0.1 MPa to 10 MPa, a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of 0.1 to 10, and an hourly space velocity (defined as the ratio of the volumetric flow rate of the feedstock to the volume of the catalyst) of 0.1 h -1 ~200h -1 or a process carried out in the gas phase, in which the molar ratio of hydrogen / (polyunsaturated compound to be hydrogenated) is 0.5 to 1000 and the hourly space velocity is 100 to 40,000 h -1 It is.

[0104] In one embodiment of the present invention, when the feedstock for the selective hydrogenation process is steam cracked gasoline containing polyunsaturated compounds, the molar ratio of (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally 0.5-10, preferably 0.7-5.0, more preferably 1.0-2.0, the temperature is 0° C.-200° C., preferably 20° C.-200° C., more preferably 30° C.-180° C., the hourly space velocity (HSV) is generally 0.5 h -1 ~100h -1 , preferably 1 to 50 hours -1 and the pressure is generally 0.3 MPa to 8.0 MPa, preferably 1.0 MPa to 7.0 MPa, and even more preferably 1.5 MPa to 4.0 MPa.

[0105] More preferentially, when the selective hydrogenation process is carried out and the feedstock is steam cracked gasoline containing polyunsaturated compounds, the hydrogen / polyunsaturated compounds to be hydrogenated molar ratio is 0.7-5.0, the temperature is 20°C-200°C, and the hourly space velocity (HSV) is generally 1h -1 ~50h -1 and the pressure is 1.0 MPa to 7.0 MPa.

[0106] Even more preferentially, when the selective hydrogenation process is carried out and the feedstock is steam cracked gasoline containing polyunsaturated compounds, the hydrogen / polyunsaturated compounds to be hydrogenated molar ratio is between 1.0 and 2.0, the temperature is between 30°C and 180°C, and the hourly space velocity (HSV) is generally between 1h -1 ~50h -1 and the pressure is 1.5 MPa to 4.0 MPa.

[0107] The hydrogen flow rate is adjusted to ensure a sufficient amount to theoretically hydrogenate all of the polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

[0108] In another embodiment of the present invention, when the selective hydrogenation process is carried out and the feedstock is a steam cracked C2 fraction and / or a steam cracked C2-C3 fraction containing polyunsaturated compounds, the molar ratio of (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally 0.5-1000, preferably 0.7-800, the temperature is 0° C.-300° C., preferably 15° C.-280° C., the hourly space velocity (HSV) is generally 100 h -1 ~40000h -1 , preferably 500h -1 ~30000h -1 The pressure is generally 0.1 MPa to 6.0 MPa, and preferably 0.2 MPa to 5.0 MPa.

[0109] 6. Methods for Hydrogenation of Aromatic Compounds Another subject of the invention is a process for the hydrogenation of at least one aromatic or polyaromatic compound contained in a hydrocarbon feedstock having a final boiling point below 650° C., generally between 20° C. and 650° C., preferably between 20° C. and 450° C. Said hydrocarbon feedstock containing at least one aromatic or polyaromatic compound may be chosen from the following petroleum or petrochemical fractions: reformates from catalytic reforming, kerosene, light gas oils, heavy gas oils, cracked distillates such as FCC recycle oils, coking unit gas oils or hydrocracked distillates.

[0110] The content of aromatic or polyaromatic compounds contained in the hydrocarbon feedstock 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, particularly preferably between 2% and 35% by weight, the percentages being based on the total weight of the hydrocarbon feedstock. The aromatic compounds present in the hydrocarbon feedstock are, for example, benzene or alkylaromatics, such as toluene, ethylbenzene, o-xylene, m-xylene or p-xylene, or also aromatic compounds having several aromatic rings (polyaromatics), such as naphthalene.

[0111] The sulfur or chlorine content of the feedstock is generally less than 5000 ppm by weight of sulfur or chlorine, preferably less than 100 ppm by weight, particularly preferably less than 10 ppm by weight.

[0112] The technical implementation of the process for the hydrogenation of aromatic or polyaromatic compounds is carried out, for example, by injection of the hydrocarbon feedstock and hydrogen as upflow or downflow into at least one fixed-bed reactor. The reactor can be of isothermal or adiabatic type. Adiabatic reactors are preferred. The hydrocarbon feedstock can advantageously be diluted by one or more reinjections of the effluent from the reactor in which the reaction of the hydrogenation of aromatic compounds is carried out at various points of the reactor located between the inlet and the outlet of the reactor, limiting the temperature gradient in the reactor. The technical implementation of the process for the hydrogenation of aromatic compounds according to the invention can advantageously be carried out by embedding at least the supported catalyst in a reactive distillation column or in a reactor-exchanger or in a slurry-type reactor. The flow of hydrogen can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points of the reactor.

[0113] The hydrogenation of aromatic or polyaromatic compounds can be carried out in the gas phase or liquid phase, preferably in the liquid phase. In general, the temperature during hydrogenation of aromatic or polyaromatic compounds is 30°C to 350°C, preferably 50°C to 325°C, the pressure during hydrogenation is 0.1MPa to 20MPa, preferably 0.5MPa to 10MPa, the molar ratio of hydrogen / (aromatic compound to be hydrogenated) is 0.1 to 10, and the hourly space velocity during hydrogenation is 0.05h -1 ~50h -1 , preferably 0.1h -1 ~10h -1 The hydrocarbon feedstock to be hydrogenated contains aromatic or polyaromatic compounds and has a final boiling point below 650°C, typically between 20°C and 650°C, preferably between 20°C and 450°C.

[0114] The hydrogen flow rate is adjusted to have a sufficient amount available to theoretically hydrogenate all of the aromatics and to maintain an excess of hydrogen at the reactor outlet.

[0115] The conversion of aromatic or polyaromatic compounds is generally greater than 20 mol%, preferably greater than 40 mol%, more preferably greater than 80 mol%, particularly preferably greater than 90 mol% of the aromatic or polyaromatic compounds contained in the hydrocarbon feedstock. The conversion is calculated by dividing the difference between the total moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock and in the product by the total moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock.

[0116] According to a specific alternative embodiment of the process according to the invention, a process for hydrogenation of benzene from a hydrocarbon feedstock, for example a reformate derived from a catalytic reforming unit, is carried out, the benzene content in said hydrocarbon feedstock generally being between 0.1% and 40% by weight, preferably between 0.5% and 35% by weight, particularly preferably between 2% and 30% by weight, the weight percentages being based on the total weight of the hydrocarbon feedstock.

[0117] The sulfur or chlorine content of the feedstock is generally less than 10 ppm by weight, preferably less than 2 ppm by weight of sulfur or chlorine, respectively.

[0118] The hydrogenation of benzene contained in the hydrocarbon feedstock can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase. When it is carried out in the liquid phase, a solvent may be present, for example cyclohexane, heptane or octane. In general, the temperature at which the hydrogenation of benzene is carried out is 30°C to 250°C, preferably 50°C to 200°C, more preferably 80°C to 180°C, the pressure at which it is carried out is 0.1MPa to 10MPa, preferably 0.5MPa to 4MPa, the molar ratio of hydrogen / (benzene) at which it is 0.1 to 10, and the hourly space velocity at which it is 0.05h -1 ~50h -1 , preferably 0.5h -1 ~10h -1 It is.

[0119] The benzene conversion is generally greater than 50 mol %, preferably greater than 80 mol %, more preferably greater than 90 mol %, particularly preferably greater than 98 mol %.

[0120] The present invention will now be illustrated by way of the following examples, which are It is by no means restrictive.

[0121] (Example) For all catalysts mentioned in the examples below, the support is alumina A with a specific surface area of ​​80 m 2 / g, total pore volume (TPV) 0.7 mL / g, and median mesopore diameter 12 nm.

[0122] WTV (water take-up volume) means the amount of water withdrawn.

[0123] Example 1: Preparation of an aqueous solution of Ni precursor containing additives The aqueous solution S used for the preparation of catalysts BH 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 a volume of 13 mL of distilled water. The additive / Ni molar ratio is fixed at 0.5. A solution S is obtained, whose Ni concentration is 350 g Ni per liter of solution volume.

[0124] Example 1a: Preparation of an aqueous solution of Ni precursor without additives 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 a volume of 13 mL of distilled water. A solution S' is obtained whose Ni concentration is 350 g Ni per liter of solution volume.

[0125] Example 2: Preparation of Catalyst A in Accordance with the Invention [10 wt% Ni-heptanol 25% WTV in Pre-impregnation] 10 g of alumina A are impregnated dropwise with 2.4 mL of n-heptanol. The impregnated support is then left to stand for 30 minutes at 60° C. Then, 7.1 mL of solution S′ prepared in Example 1a are impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

[0126] Catalyst A is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0127] The characteristics of the catalyst A thus obtained are given in Table 1 below.

[0128] Example 3: Preparation of Catalyst B according to the invention [10 wt% Ni-heptanol 25% WTV + additives in pre-impregnation] 10 g of alumina A are impregnated dropwise with 2.4 mL of n-heptanol. The impregnated support is then left to stand for 30 minutes at 60° C. Then, 7.1 mL of solution S prepared in Example 1 are dropwise impregnated into the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

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

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

[0131] Example 4: Preparation of Catalyst C according to the invention [5 wt% Ni-heptanol 25% WTV + additives in pre-impregnation] 10 g of alumina A are impregnated with 2.4 mL of n-heptanol dropwise. The impregnated support is then left to stand for 30 minutes at 60° C. Then 3.55 mL of solution S prepared in Example 1 is diluted with water up to 7.1 mL and impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

[0132] Catalyst C is obtained containing 5% by weight of elemental nickel relative to the total weight of the catalyst.

[0133] The characteristics of the catalyst C thus obtained are given in Table 1 below.

[0134] Example 5: Preparation of Catalyst D according to the invention [10 wt% Ni-heptanol 75% WTV + additives in pre-impregnation] 10 g of alumina A are impregnated dropwise with 7.2 mL of n-heptanol. The impregnated support is then left to stand for 30 minutes at 60° C. Then, 2.4 mL of solution S prepared in Example 1 are dropwise impregnated into the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

[0135] A catalyst D is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0136] The characteristics of the catalyst D thus obtained are given in Table 1 below.

[0137] (Example 6: Preparation of Catalyst E not in accordance with the present invention [conventional impregnated Ni 10% + additive]) Dry impregnation of solution S prepared in example 1 is carried out on 10 g of alumina by dropping it in drops. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air of 1 L / h / g of catalyst.

[0138] A catalyst E is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0139] The characteristics of the catalyst E thus obtained are given in Table 1 below.

[0140] Example 7: Preparation of Catalyst F not in accordance with the invention [10 wt% Ni-heptanol 25% WTV post-impregnation] Dry impregnation is carried out by dropping 7.1 mL of solution S prepared in Example 1 onto 10 g of alumina. 10 g of the prepared catalyst precursor is impregnated with 2.4 mL of n-heptanol. The solid is then left to stand for 30 minutes at 60°C.

[0141] The solid thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a stream of dry air of 1 L / h / g of catalyst.

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

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

[0144] Example 8: Preparation of Catalyst G not in accordance with the invention [10 wt% Ni-Toluene 25% WTV in pre-impregnation] 10 g of alumina A is impregnated with 2.4 mL of toluene dropwise. The impregnated support is then left to stand for 30 minutes at 60° C. Then, 7.1 mL of solution S prepared in Example 1 is dropwise impregnated onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

[0145] A catalyst G is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0146] The characteristics of the catalyst G thus obtained are given in Table 1 below.

[0147] Example 9: Preparation of Catalyst H not in accordance with the invention [10 wt% Ni-n-propanol 25% WTV in pre-impregnation] 10 g of alumina A is impregnated with 2.4 mL of n-propanol. The impregnated support is then left to stand for 30 minutes at 60° C. Then, 7.1 mL of solution S prepared in Example 1 is impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

[0148] A catalyst H is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0149] The characteristics of the catalyst H thus obtained are given in Table 1 below.

[0150] [Table 1]

[0151] Example 10: Catalytic testing: Performance in the selective hydrogenation of mixtures containing styrene and isoprene (A HYD1 )) Catalysts AH described in the above examples are tested for the reaction of selective hydrogenation of a mixture containing styrene and isoprene.

[0152] The composition of the feedstock to be selectively hydrogenated is as follows: 8% by weight of styrene (supplier Sigma Aldrich®, 99% purity), 8% by weight of isoprene (supplier Sigma Aldrich®, 99% purity) and 84% by weight of n-heptane (solvent) (supplier VWR®, >99% purity Chromanorm HPLC). This feedstock also contains a very low content of sulfur compounds: 10 ppm by weight of sulfur is introduced in the form of pentanethiol (supplier Fluka®, >97% purity) and 100 ppm by weight of sulfur is introduced in the form of thiophene (supplier Merck®, 99% purity). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is typical of pyrolysis gasoline.

[0153] The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave equipped with a magnetically driven mechanical stirrer and capable of operating at a maximum pressure of 100 bar (10 MPa) and temperatures between 5°C and 200°C.

[0154] Before being introduced into the autoclave, a quantity of 3 mL of catalyst is reduced ex situ at 400° C. for 16 hours (temperature ramp 1° C. / min) under a hydrogen flow of 1 L / h / g of catalyst, then it is transferred to the autoclave and the air is excluded. After the addition of 214 mL of n-heptane (supplier VWR®, purity >99% Chromanorm HPLC), the autoclave is closed, purged and then pressurized under 35 bar (3.5 MPa) of hydrogen to a 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 now has the above composition and the stirring is started at 1600 rpm. The pressure in the autoclave is kept constant at 35 bar (3.5 MPa) by means of a storage cylinder located upstream of the reactor.

[0155] The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: styrene is hydrogenated to give ethylbenzene, but there is no hydrogenation of the aromatic ring, and isoprene is hydrogenated to give methylbutene. If the reaction is extended longer than necessary, the methylbutene is in turn hydrogenated to give isopentane. The hydrogen consumption is also monitored over time by the pressure reduction in a storage cylinder placed upstream of the reactor. The catalytic activity is expressed in moles of H2 consumed per time (min) and weight (gram) of Ni.

[0156] The catalytic activities measured for catalysts A to H are given in Table 2 below. They are the catalytic activities measured for catalyst E (A HYD1 )

[0157] Example 11: Catalytic testing: performance in hydrogenation of toluene (A HYD2 )) Catalysts AH described in the above examples are also tested for the reaction of toluene hydrogenation.

[0158] The selective hydrogenation reaction is carried out in an autoclave identical to that described in Example 9.

[0159] Before its introduction into the autoclave, a quantity of 2 mL of catalyst is reduced ex situ at 400° C. for 16 h (heating gradient 1° C. / min) under a hydrogen flow of 1 L / h / g of catalyst, then it is transferred to the autoclave and the air is excluded. After the addition of 216 mL of n-heptane (supplier VWR®, purity >99% Chromanorm HPLC), the autoclave is closed, purged and then pressurized under 35 bar (3.5 MPa) of hydrogen to a test temperature equal to 30° C. At time t=0, approximately 26 g of toluene (supplier SDS®, purity >99.8%) is introduced into the autoclave (initial composition of the reaction mixture is 6% by weight toluene / 94% by weight n-heptane) and stirring is started at 1600 rpm. The pressure in the autoclave is kept constant at 35 bar (3.5 MPa) by means of a storage cylinder located upstream of the reactor.

[0160] The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: toluene is completely hydrogenated to give methylcyclohexane. Hydrogen consumption is also monitored over time by the pressure drop in a storage cylinder placed upstream of the reactor. The catalytic activity is expressed in moles of H2 consumed per time (min) and weight (gram) of Ni.

[0161] The catalytic activities measured for catalysts A to H are given in Table 2 below. They are the catalytic activities measured for catalyst E (A HYD2 )

[0162] [Table 2]

[0163] These examples are of catalysts A, B, C and D according to the invention. HYD1 and A HYD2It clearly shows that the performance of catalysts A, B, C and D is improved compared to catalysts E, F, G and H not according to the invention. This is explained by the distribution of nickel in the crust on catalysts A, B, C and D, which gives them a significantly improved activity, especially in the fast hydrogenation reaction. Despite the fact that the particles are larger in size (8 nm) because malonic acid is not used, catalyst A is still very effective because nickel is well distributed in the crust and is therefore very accessible. Catalyst E has a lower activity due to the conventional impregnation performed without pre-impregnation with heptanol. Catalyst F undergoes a post-impregnation with heptanol, which does not allow crust distribution of nickel. Catalyst G is prepared by a step of pre-impregnation with toluene. Therefore, toluene, like heptanol, is poorly miscible with water, but the lack of -OH groups in its molecule does not allow it to have a strong interaction with the -OH groups of the alumina support, which may explain the migration of toluene through the water contained in the nickel nitrate solution during the nickel impregnation process. In the case of propanol, the -OH groups seem to allow it to both go to the core of the support and to interact with it. On the other hand, water and n-propanol, unlike the heptanol / water pair, are very miscible, so that diffusion of the aqueous nickel nitrate solution to the core seems to occur, taking into account both the physicochemical characteristics of the final catalyst obtained and the results of the catalytic tests. Therefore, for catalysts F, G and H, nickel is homogeneously distributed throughout the catalyst granules. Catalysts F and G are therefore more stable than A. HYD1 and A HYD2 is much less active than catalyst A. The low activity of catalyst G is due to the presence of toluene, which inhibits the impregnation of the nickel nitrate solution. [Brief description of the drawings]

[0164] [Figure 1] FIG. 2 shows the distribution of nickel in the catalyst.

Claims

1. A method for preparing a catalyst comprising a nickel-based active phase and an alumina support, wherein the catalyst contains nickel element in an amount of 1 wt% to 50 wt% relative to the total weight of the catalyst, the nickel is distributed both on the crust around the support and in the core of the support, the thickness of the crust is 2% to 15% of the diameter of the catalyst, and the size of nickel particles in the catalyst, measured in the form of oxide, is less than 15 nm, the method comprising the following steps: a) impregnating the support with a heptanol solution having a volume V1 which is 0.2 to 0.8 times the total pore volume TPV of the support to obtain an impregnated support; b) impregnating the impregnated support obtained at the end of step a) with a solution containing at least one precursor of the nickel active phase to obtain a catalyst precursor; c) drying the catalyst precursor obtained at the end of step b) at a temperature below 250 °C.

2. The method according to claim 1, wherein in step b), the volume V2 of the solution containing at least one precursor of the nickel active phase impregnated on the impregnated support obtained at the end of step a) is such that V2 = TPV - V1.

3. The method according to claim 1 or 2, characterized in that step c) is carried out over a period of 0.5 hours to 12 hours.

4. The method according to claim 1, further comprising step d), wherein the catalyst obtained at the end of step c) is calcined at a temperature of 250 °C to 600 °C.

5. The method according to claim 4, wherein step d) is carried out over a period of 0.5 hours to 24 hours.

6. The method according to claim 1, wherein in step a), the volume V1 of the heptanol solution is 0.25 to 0.75 times the total pore volume TPV of the support.

7. The method according to claim 1, wherein in step a), a solution of n-heptanol is used.

8. Perform step b1), and in this step, impregnate either the impregnated carrier obtained at the end of step a) or the catalyst precursor obtained at the end of step b) with at least one solution containing at least one organic compound containing at least one carboxylic acid group, or at least one alcohol group, or at least one ester group, or at least one amide group, or at least one amine group, and perform steps b) and b1) in any order or simultaneously. The method according to claim 1.

9. The volume V2 of the solution containing at least one precursor of the active nickel phase impregnated on the impregnated carrier obtained at the end of step a) and the volume V3 of the solution containing at least one organic compound satisfy V2 + V3 = TPV - V1. The method according to claim 8.

10. Perform steps b) and b1) simultaneously. The method according to claim 8 or 9.

11. The volume V2' of the solution containing at least one precursor of the active nickel phase and at least one organic compound impregnated on the impregnated carrier obtained at the end of step a) satisfies V2' = TPV - V1. The method according to claim 10.

12. The molar ratio of the organic compound introduced in step b1) to the nickel element introduced in step b) is 0.01 to 5.0 mol / mol. The method according to claim 8.

13. The organic compound in step b1) 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, γ-butyrolactone, 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. The method according to claim 8.

14. Perform step a1), and in this step, allow the impregnated carrier obtained at the end of step a) to stand and age for 0.5 hour to 40 hours. The method according to claim 1.

15. The method according to claim 8, wherein the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm.

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