Method for preparing a catalyst comprising an active nickel phase distributed in a crust via hexanoic acid or heptanoic acid impregnation

Abstract

The invention relates to a method for preparing a catalyst comprising an active nickel phase and an alumina support, the catalyst comprising between 1 and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both in a crust at the periphery of the support and in the core of the support, the method comprising the following steps: a) impregnating the support with a volume V1 of a hexanoic acid or a heptanoic acid solution between 0.2 and 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 comprising a precursor of the active nickel phase to obtain a catalyst precursor; and c) drying the catalyst precursor obtained at the end of step b) at a temperature lower than 250°C.

Description

[0001] PROCESS FOR PREPARING A CATALYST COMPRISING AN ACTIVE NICKEL PHASE DISTRIBUTED IN A CRUST VIA IMPREGNATION OF HEXANOIC ACID OR HEPTANOIC ACID

[0002] Technical field

[0003] The present invention relates to a process for preparing a supported nickel-based metal catalyst intended particularly for the hydrogenation of unsaturated hydrocarbons, and more particularly, for the selective hydrogenation of polyunsaturated compounds or for the hydrogenation of aromatics.

[0004] State of the art

[0005] Monounsaturated organic compounds, such as ethylene and propylene, are used in the manufacture of polymers, plastics and other value-added chemicals. These compounds are obtained from natural gas, naphtha or diesel oil that has been treated by steam cracking or catalytic cracking processes. These processes are operated 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 with 5 or more carbon atoms), in particular styrenic or indenic compounds.These polyunsaturated compounds are highly reactive and lead to parasitic reactions in polymerization units. It is therefore necessary to eliminate them before recovering these cuts. 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, avoiding their total saturation, and therefore the formation of the corresponding alkanes or naphthenes.

[0006] 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 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 have an impact on the activity and selectivity of the catalysts.

[0007] The macroscopic distribution of metal particles in the support is an important criterion, mainly in the context of rapid and consecutive reactions such as selective hydrogenations. It is generally desirable that these elements are located in a crust at the periphery of the support in order to avoid problems of intragranular mass transfer which can lead to activity defects and a loss of selectivity. Such catalysts are also called "eggshell" catalysts according to English terminology.

[0008] 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% by weight (1% wt) of palladium relative to the catalyst) and suitable preparation methods, a thin palladium crust at the periphery of the support grains can be obtained (FR2922784, US2010 / 217052).

[0009] It is often proposed to substitute palladium with nickel, a less active metal than palladium, which therefore needs to be placed in greater quantities in the catalyst. Thus, nickel-based catalysts generally have a metal content between 5 and 50% by weight of nickel relative to the catalyst. In these catalysts, 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 the nickel in a more concentrated manner on a crust, at the periphery of the support. Such catalysts are known from the state of the art.

[0010] US 4,519,951 discloses an eggshell catalyst with nickel on a porous support having a pore volume of pores with a size less than 11.7 nm of at least 0.2 ml / g and a pore volume of pores with a size greater than 11.7 nm of at least 0.1 ml / g. More than 50% of the nickel is in a crust with a thickness equal to 0.15 times the radius of the support. This catalyst is used for the hydrogenation of fats.

[0011] CN101890351 describes a supported nickel catalyst in which more than 90% of the nickel is contained in a 700 μm thick crust. The catalyst is prepared by using an ammonia solution to dissolve the nickel salt. These catalysts are used in a selective hydrogenation application.

[0012] Document U S2012 / 0065442 describes a nickel-supported catalyst distributed both on a crust with a thickness of 3 to 15% of the diameter and at 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 spray coating an ammoniacal solution of a nickel salt onto the support. Document FR3099387 describes a process for preparing a nickel-based catalyst on an alumina support obtained using a very specific method, the nickel being distributed both on a crust at the periphery of the support and at the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst.The process for preparing such a catalyst requires on the one hand the use of a specific alumina support which has undergone hydrothermal treatment in the presence of an acid solution, and on the other hand the carrying out of a hydrothermal treatment step after the addition of a specific organic additive to the catalyst precursor.

[0013] Applications WO2021239497, WO2023001641 and WO2023001642 disclose a nickel-based catalyst on an alumina support, the nickel being distributed in a crust at the periphery of the support, and at the core of the support, obtained by a very specific preparation process comprising a step of impregnation of a solution respectively based on butanol, hexanol and heptanol upstream of the step of impregnation of the precursor of the nickel-based active phase. However, these organic compounds are difficult to use on an industrial scale due to their high volatility and flammability, the flash point of butanol being 29°C, the flash point of hexanol being 63°C and the flash point of heptanol being 70°C, i.e. well below the ATEX limit of category 4 according to the Globally Harmonized System (GHS) which is 93°C.

[0014] Objects of the invention

[0015] Surprisingly, the Applicant has discovered that carrying out a particular step of impregnating a solution of hexanoic acid or heptanoic acid on a porous alumina support, whatever its origin, and this without carrying out an intermediate drying step between the impregnation of hexanoic acid or heptanoic acid and the impregnation of the precursor of the active nickel phase, makes it possible to obtain a catalyst in which at least part of the nickel is distributed on a crust at the periphery of the support, the other part of the nickel being distributed in the heart of the catalyst. Without wishing to be bound by any theory, the presence of hexanoic acid or heptanoic acid prevents the migration of the active nickel phase to the heart of the support. Indeed, only part of the porosity is occupied by hexanoic acid or heptanoic acid.Furthermore, since hexanoic acid or heptanoic acid and water are poorly miscible, the layer of hexanoic acid or heptanoic acid constitutes a barrier to the diffusion of nickel into the core of the support.

[0016] The present invention thus relates to a new process for preparing a catalyst which makes it possible to obtain a catalyst comprising performances at least as good, or even better, in terms of activity and selectivity in the context of the reactions of selective hydrogenation of polyunsaturated compounds or hydrogenation of aromatics, while using a lower quantity of effective nickel phase (i.e. a quantity of nickel found in-fine in a crust at the periphery of the support allowing the selective hydrogenation reactions or hydrogenation of aromatics to be carried out) than that typically used in the state of the art, which is due to a better distribution of the active nickel phase in the support, making the latter more accessible to the reagents.Furthermore, the use of hexanoic acid or heptanoic acid as an organic compound during the catalyst preparation process makes it possible to limit flammability and volatility problems due to their flash points of 102°C according to ASTM D93 for hexanoic acid and 115°C according to ASTM D93 for heptanoic acid, respectively, i.e. well above the ATEX category 4 limit according to the Globally Harmonized System (GHS) which is 93°C, and therefore to limit safety problems during catalyst synthesis.

[0017] 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 at the periphery of the support, and at 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 V1 of a solution of hexanoic acid or heptanoic acid 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;

[0018] 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 - V1. According to one or more embodiments, step c) is carried out for a time of between 0.5 hours and 12 hours.

[0019] According to one or more embodiments, said 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.

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

[0021] According to one or more embodiments, in step a) said volume V1 of said hexanoic acid or heptanoic acid solution is between 0.25 and 0.75 times the total pore volume VPT of said support.

[0022] According to one or more embodiments, said 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 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 b1) being carried out in any order, or simultaneously.

[0023] 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 - V1.

[0024] According to one or more embodiments, steps b) and b1) are carried out simultaneously.

[0025] 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 - V1.

[0026] According to one or more embodiments, the molar ratio between said organic compound introduced in step b1) and the nickel element also introduced in step b) is between 0.01 and 5.0 mol / mol. According to one or more embodiments, the organic compound of step b1) is chosen 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, y-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 left to mature for 0.5 hours to 40 hours.

[0028] According to one or more embodiments, the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm.

[0029] Description of the figure

[0030] Figure 1 is a diagram showing the distribution of nickel in the catalyst. The x-axis corresponds to the catalyst thickness, measured from the edge of the catalyst (in pm). The y-axis corresponds to the nickel density (in grams of Ni / mm 3 ). Nickel is distributed both on a crust on the periphery of the support, of thickness ep1, and in the core of the support. The nickel density on the routed crust is higher than the nickel density at the core of the support d coeThe transition interval between the core and the catalyst crust has a thickness noted ep2-ep1.

[0031] Detailed description of the invention

[0032] 1. Definitions

[0033] 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 IUPAC classification.

[0034] In the present description, according to the IUPAC convention, micropores are understood to mean pores whose diameter is less than 2 nm, i.e. 0.002 pm; mesopores are understood to mean 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 understood to mean pores whose diameter is greater than 50 nm, i.e. 0.05 pm. In order to analyze the distribution of the metallic phase on the support, a crust thickness is measured by Castaing microprobe (or microanalysis by electron microprobe). The device used is a CAMECA XS100, equipped with four monochromator crystals allowing 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 purposes of this characterization, the catalyst grains are coated in epoxy resin pads. These pads are polished to the diameter of the balls or extruded and then metallized by carbon deposition in a metal evaporator. The electronic probe is scanned along the diameter of five balls or extruded 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). It allows the distribution profile of a given element, here Nickel, within the grain to be established. Furthermore, the Ni concentration is defined for each measurement and therefore for each analysis step. The density of Ni within the grain is therefore defined as the concentration of Ni per mm. 3 .

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

[0036] The BET specific surface area 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”, Academic Press, 1999.

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

[0200] ) using the Scherrer relation. This method, used in X-ray diffraction on powders or polycrystalline samples, which relates the width at half-maximum 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. Catalyst preparation process

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

[0040] Step a)

[0041] According to step a) of the process, the alumina support is impregnated with a volume V1 of a solution of hexanoic acid or heptanoic acid of between 0.2 and 0.8 times the total pore volume (also called here VPT) of said support to be impregnated, preferably between 0.25 and 0.75.

[0042] Step a1) (optional)

[0043] After step a), the impregnated support can be matured in the wet state for 0.5 hours to 40 hours, preferably for 1 hour to 30 hours. Maturation step a1) is preferably carried out at a temperature less than or equal to 60°C, and more preferably at room temperature. This step allows the migration of the hexanoic acid or heptanoic acid solution to the core of the support. When carried out, maturation step a1) allows the hexanoic acid or heptanoic acid solution to reinforce the migration to the core of the support and to release a “crown of free pores” at the periphery of the support accessible by the nickel during the step of impregnation of the precursor of the active phase.

[0044] Step b)

[0045] In step b) of the process, the impregnated alumina porous support obtained at the end of step a) (or matured impregnated obtained at the end of step a1)) is impregnated with a solution comprising at least one precursor of the active nickel 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.

[0046] 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.

[0047] 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 precursor. Very preferably, the nickel precursor is nickel nitrate.

[0048] The nickel concentration in solution is adjusted according to the pore volume of the support still available so as to obtain for the supported catalyst, a nickel content of between 1 and 50% by weight of 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 5 and 25% by weight.

[0049] Step b1) (optional)

[0050] When step b1) is carried out, the impregnated porous alumina support obtained at the end of step a) (or matured impregnated 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 b1) being carried out in any order, or simultaneously.

[0051] The impregnation step can be carried out by dry or excess impregnation according to methods well known to those skilled in the art. Indeed, it has also been noted that catalysts prepared in the presence of an organic compound (cited 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.

[0052] Said solution containing at least one organic compound comprising at least one carboxylic acid function is preferably aqueous. Said organic compound is previously at least partially dissolved in said solution at the desired concentration. The pH of said solution can be modified by the possible addition of an acid or a base.

[0053] Advantageously, the molar ratio between said organic compound introduced in step b1) 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.

[0054] 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.

[0055] Said aliphatic organic compound, saturated or unsaturated, or said aromatic organic compound, comprising at least one carboxylic acid function, may be chosen from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids.

[0056] Advantageously, the organic compound comprising at least one carboxylic acid function 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), 4-oxopentanoic acid (levulinic acid).

[0057] Implementation of steps b) and b1)

[0058] The process for preparing the nickel catalyst may include several implementation modes. 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 able to be 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)).

[0059] A first method of implementation consists of carrying out said step b) prior to said step b1) (post-impregnation).

[0060] A second method of implementation consists of carrying out said step b1) prior to said step b) (pre-impregnation).

[0061] Each step b) and b1) of impregnation of the impregnated support with the nickel precursor, and of impregnation of the optionally matured impregnated support 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 can advantageously be carried out several times, optionally in the presence of a nickel precursor and / or an organic compound identical or different to each step b) and / or b1) respectively, all possible combinations of implementations of steps b) and b1) being included in the scope of the invention.

[0062] 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 optionally matured impregnated support obtained at the end of step a) are such that V2 + V3 = VPT - V1.

[0063] A third embodiment consists in carrying out said step b) and said step b1) simultaneously (co-impregnation). This embodiment may advantageously comprise the implementation of one or more steps b), optionally with an identical or different nickel precursor at each step b). In particular, one or more steps b) advantageously precede(s) and / or follow(s) said co-impregnation step, optionally with an identical or different nickel precursor at each step. This embodiment may also comprise several co-impregnation steps: steps b) and b1) are carried out simultaneously several times, optionally in the presence of an identical or different nickel precursor and / or organic compound at each co-impregnation step.

[0064] 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' = VPT - V1.

[0065] Step c)

[0066] Drying step c) 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 duration typically between 0.5 hours and 12 hours, and even more preferably for a duration of 0.5 hours to 5 hours. Longer durations are not excluded, but do not necessarily provide an improvement.

[0067] 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. At the end of step c), the total, partial presence, or absence of the hexanoic acid or heptanoic acid solution in the catalyst has no impact on the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds.

[0068] Step d) (optional)

[0069] Calcination step d) may be carried out at a temperature of between 250°C and 600°C, preferably between 350°C and 550°C, for a period typically of between 0.5 hours and 24 hours, preferably for a period of between 0.5 hours and 12 hours, and even more preferably for a period of between 0.5 hours and 10 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen. Longer periods are not excluded, but do not necessarily provide an improvement.

[0070] At the end of step d), the total, partial presence, or absence of the hexanoic acid or heptanoic acid solution in the catalyst has no impact on the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds.

[0071] Step e) (optional)

[0072] Prior to the use of the catalyst in the catalytic reactor and the implementation of a hydrogenation process, at least one reducing treatment step e) is advantageously carried out 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.

[0073] This treatment activates the catalyst and forms metal particles, particularly nickel in the zero-valent state. The reducing treatment can be carried out in situ or ex situ, i.e. after or before loading the catalyst into the hydrogenation reactor.

[0074] The reducing gas is preferably hydrogen. Hydrogen can be used pure or in a mixture (for example, a hydrogen / nitrogen, or hydrogen / argon, or hydrogen / methane mixture). If hydrogen is used in a mixture, any proportion is possible.

[0075] Said reducing 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 reducing treatment before passivation, the reducing 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 reducing treatment is generally carried out at a temperature between 120°C and 350°C, preferably between 150°C and 350°C.

[0076] The duration of the reducing treatment is generally between 2 hours and 40 hours, preferably between 3 hours 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.

[0077] 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.

[0078] 3. Catalyst

[0079] The preparation process according to the invention makes it possible to obtain 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 at the core of the support, the thickness of said crust (also called ep1) being between 2% and 15% of the diameter of the catalyst, the size of the nickel particles, measured in oxide form, in the catalyst is less than 15 nm.

[0080] Preferably, the nickel is distributed both on a crust at the periphery of the support, and at the core of the support, the thickness of said crust (also called ep1) being between 2% and 15% of the diameter of the catalyst, preferably between 2.5% and 12% of the diameter of the catalyst, even more preferably between 3% and 10% of the diameter of the catalyst and even more preferably between 3% and 7.5% of the diameter of the catalyst.

[0081] Preferably, the nickel density ratio between the crust and the core (also called here dcroute / dcore) is strictly greater than 3, preferably greater than 3.5 and preferably between 3.8 and 15.

[0082] 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. Advantageously, the transition interval between the core and the crust of the catalyst (also called here core / crust transition interval, or ep2-ep1 according to the notations in Figure 1), linked to the variation in the nickel density measured over 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 diameter of the catalyst, preferably between 0.5% and 2.5% of the diameter of the catalyst.

[0083] 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 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.

[0084] The catalyst can be described as a “semi egg-shell” catalyst, i.e. the nickel concentration is higher at the periphery of the support than in the core of the support, said nickel concentration in the core of the support being non-zero.

[0085] The specific surface area of ​​the catalyst is generally between 10 m 2 / g and 350 m 2 / g, preferably between 25 m 2 / g and 300 m 2 / g, more preferably between 40 m 2 / g and 250 m 2 / g.

[0086] The total pore 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.

[0087] 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 b1) 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.

[0088] The active phase of the catalyst does not contain any group VI B metal. In particular, it does not contain molybdenum or tungsten.

[0089] Said catalyst (and the support used for the preparation of the catalyst) is in the form of grains advantageously having a diameter of between 0.5 mm and 10 mm. The grains may have any shape known to those skilled in the art, for example the shape of balls (preferably having a diameter of between 1 mm and 8 mm), extrudates, tablets, hollow cylinders. Preferably, the catalyst (and the support used for the preparation of the catalyst) are 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 very preferably between 1.0 mm and 2.5 mm and a length of between 0.5 mm and 20 mm. The term "diameter" of the extrudates is understood to mean the diameter of the circle circumscribed to the cross section of these extrudates. The catalyst may advantageously be presented 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 any method known in the prior art.

[0090] 4. Support

[0091] The characteristics of the alumina, mentioned in this section, correspond to the characteristics of the alumina before carrying out step a) of the preparation process according to the invention.

[0092] The support is an alumina, that is to say that 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 a mixture.

[0093] The alumina support may include impurities such as metal oxides of groups HA, 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.

[0094] The BET specific surface area of ​​alumina is generally between 10 m 2 / g and 400m 2 / g, preferably between 30 m 2 / g and 350 m 2 / g, more preferably between 50 m 2 / g and 300m 2 / g.

[0095] 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 very preferably between 0.5 ml / g and 0.9 ml / g.

[0096] 5. Selective hydrogenation process

[0097] The present invention also relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and / or acetylenics and / or alkenylaromatics, also called styrenics, contained in a hydrocarbon feedstock having a final boiling point less than or equal to 300°C, which process is carried out at a temperature of between 0 and 300°C, at a pressure of between 0.1 MPa and 10 MPa, at a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of between 0.1 and 10 and at an hourly volumetric flow rate of between 0.1 and 200 h' 1 when the process is carried out in the liquid phase, or at a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volumetric flow rate of between 100 h' 1 and 40,000 h' 1when the process is carried out in the gas phase, in the presence of a catalyst obtained by the preparation process as described above in the description.

[0098] 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 oil that has been treated by steam cracking or catalytic cracking processes. These processes are operated 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 with at least 5 carbon atoms), in particular diolefinic or styrenic or indenic compounds. These polyunsaturated compounds are very reactive and lead to parasitic reactions in the polymerization units.It is therefore necessary to eliminate them before using these cuts.

[0099] Selective hydrogenation is the main treatment developed to specifically remove unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatics while avoiding their total saturation and therefore the formation of the corresponding alkanes or naphthenes. In the case of steam cracked gasolines used as feedstock, selective hydrogenation also allows the selective hydrogenation of alkenyl aromatics to aromatics while avoiding the hydrogenation of aromatic nuclei.

[0100] The hydrocarbon feedstock treated in the selective hydrogenation process has a final boiling point less than or equal to 300°C and contains at least 2 carbon atoms per molecule and comprises at least one polyunsaturated compound. The term "polyunsaturated compounds" means compounds comprising at least one acetylenic function and / or at least one diene function and / or at least one alkenyl aromatic function. More particularly, the feedstock is selected from the group consisting of a C2 steam cracking cut, a C2-C3 steam cracking cut, a C3 steam cracking cut, a C4 steam cracking cut, a C5 steam cracking cut and a steam cracking gasoline also called pyrolysis gasoline or C5+ cut.

[0101] The C2 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following composition: between 40 and 95% by weight of ethylene, of the order of 0.1 to 5% by weight of acetylene, the remainder being essentially ethane and methane. In certain C2 steam cracking cuts, between 0.1 and 1% by weight of C3 compounds may also be present.

[0102] The C3 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following average composition: around 90% by weight of propylene, around 1 to 8% by weight of propadiene and methylacetylene, the remainder being essentially propane. In certain C3 cuts, between 0.1 and 2% by weight of C2 compounds and O4 compounds may also be present.

[0103] A C2 - C3 cut can also be advantageously used for implementing the selective hydrogenation process according to the invention. It has, for example, the following composition: of the order of 0.1 to 5% by weight of acetylene, of the order of 0.1 to 3% by weight of propadiene and methylacetylene, of the order of 30% by weight of ethylene, of the order of 5% by weight of propylene, the remainder being essentially methane, ethane and propane. This feedstock can also contain between 0.1 and 2% by weight of C4 compounds.

[0104] 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% by weight of butane, 46.5% by weight of butene, 51% by weight of butadiene, 1.3% by weight of vinylacetylene and 0.2% by weight of butyne. In certain O4 cuts, between 0.1 and 2% by weight of O3 compounds and C5 compounds may also be present.

[0105] The C5 steam cracking cut, advantageously used for implementing the selective hydrogenation process according to the invention, has, for example, the following composition: 21% by weight of pentanes, 45% by weight of pentenes, 34% by weight of pentadienes.

[0106] 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, etc.), styrenic compounds (styrene, alpha-methylstyrene, etc.) and indene compounds (indene, etc.). The steam cracking gasoline generally comprises the C5-C12 fraction with traces of O3, C4, O13, C14, C15 (for example between 0.1 and 3% by weight for each of these fractions).For example, a charge formed from pyrolysis gasoline generally has the following composition: 5 to 30% by weight of saturated compounds (paraffins and naphthenes), 40 to 80% by weight of aromatic compounds, 5 to 20% by weight of monoolefins, 5 to 40% by weight of diolefins, 1 to 20% by weight of alkenyl aromatic compounds, all of the compounds forming 100%. It also contains from 0 to 1000 ppm by weight of sulfur, preferably from 0 to 500 ppm by weight of sulfur.

[0107] Preferably, the polyunsaturated hydrocarbon feedstock treated in accordance with the selective hydrogenation process according to the invention is a C2 steam cracking cut, or a C2-C3 steam cracking cut, or a steam cracking gasoline.

[0108] The selective hydrogenation process according to the invention aims to eliminate said polyunsaturated hydrocarbons present in said feedstock to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when said feedstock is a C2 cut, the selective hydrogenation process aims to selectively hydrogenate acetylene. When said feedstock is a C3 cut, the selective hydrogenation process aims to selectively hydrogenate propadiene and methylacetylene. In the case of a C4 cut, the aim is to eliminate butadiene, vinylacetylene (VAC) and butyne, in the case of a C5 cut, the aim is to eliminate pentadienes.When said feedstock is a steam-cracking gasoline, the selective hydrogenation process aims to selectively hydrogenate said polyunsaturated hydrocarbons present in said feedstock to be treated so that the diolefinic compounds are partially hydrogenated into mono-olefins and the styrenic and indenic compounds are partially hydrogenated into corresponding aromatic compounds while avoiding the hydrogenation of the aromatic nuclei.

[0109] The technological implementation of the selective hydrogenation process is for example carried out by injecting, in ascending or descending flow, the polyunsaturated hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor. Said reactor may be of the isothermal type or of the adiabatic type. 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 occurs, at various points of the reactor, located between the inlet and the outlet of the reactor in order to limit the temperature gradient in the reactor. The technological implementation of the selective hydrogenation process according to the invention may also be advantageously carried out by the installation of at least said supported catalyst in a reactive distillation column or in exchanger reactors or in a slurry-type reactor.The hydrogen flow can be introduced at the same time as the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0110] Selective hydrogenation of steam cracking fractions C2, C2-C3, C3, C4, C5 and C5+ can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase for C3, C4, C5 and C5+ fractions and in the gas phase for C2 and C2-C3 fractions. A liquid phase reaction lowers the energy cost and increases the catalyst cycle time.

[0111] In general, the selective hydrogenation of a hydrocarbon feedstock containing polyunsaturated compounds containing at least 2 carbon atoms per molecule and having a final boiling point less than or equal to 300°C is carried out at a temperature between 0°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 flow rate (defined as the ratio of the feedstock volumetric flow rate to the catalyst volume) between 0.1 h' 1 and 200 h' 1 for a process carried out in the liquid phase, or at a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volumetric flow rate of between 100 and 40000 h' 1 for a process carried out in the gas phase.

[0112] 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 hourly volumetric velocity (HVV) is generally between 0.5 h' 1 and 100 h' 1 , preferably between 1 and 50 h' 1 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 1.5 MPa and 4.0 MPa.

[0113] More preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio is between 0.7 and 5.0, the temperature is between 20°C and 200°C, the hourly volumetric velocity (HVV) is generally between 1 h' 1 and 50 hours 1 and the pressure is between 1.0 MPa and 7.0 MPa. Even more preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio is between 1.0 and 2.0, the temperature is between 30°C and 180°C, the hourly volumetric velocity (HVV) is generally between 1 h' 1 and 50 hours 1 and the pressure is between 1.5 MPa and 4.0 MPa.

[0114] The hydrogen flow rate is adjusted to provide sufficient quantity to theoretically hydrogenate all the polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

[0115] In another embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a C2 steam cracking cut and / or a C2-C3 steam cracking cut comprising polyunsaturated compounds, the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally between 0.5 and 1000, preferably between 0.7 and 800, the temperature is between 0°C and 300°C, preferably between 15°C and 280°C, the hourly volumetric velocity (HVV) is generally between 100 h' 1 and 40,000 h -1 , preferably between 500 h' 1 and 30,000 h' 1 and the pressure is generally between 0.1 MPa and 6.0 MPa, preferably between 0.2 MPa and 5.0 MPa.

[0116] 6. Process for hydrogenation of aromatics

[0117] The present invention also relates to a process for the hydrogenation of 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 chosen from the following petroleum or petrochemical cuts: reformate from catalytic reforming, kerosene, light diesel, heavy diesel, cracking distillates, such as FCC recycle oil, coker unit diesel, hydrocracking distillates.

[0118] 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, and particularly preferably between 2% and 35% by weight, the percentage being based on the total weight of the hydrocarbon feedstock. The aromatic compounds present in said hydrocarbon feedstock are, for example, benzene or alkylaromatics such as toluene, ethylbenzene, o-xylene, m-xylene, or p-xylene, or aromatics having several aromatic rings (polyaromatics) such as naphthalene.

[0119] 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.

[0120] The technological implementation of the process for hydrogenating aromatic or polyaromatic compounds is, for example, carried out by injecting, in an ascending or descending flow, the hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor. Said reactor may be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred. The hydrocarbon feedstock may advantageously be diluted by one or more re-injections of the effluent, from said reactor where the hydrogenation reaction of the aromatics takes place, at various points in the reactor, located between the inlet and the outlet of the reactor in order to limit the temperature gradient in the reactor. The technological implementation of the process for hydrogenating aromatics according to the invention may also be advantageously carried out by installing at least said supported catalyst in a reactive distillation column or in exchanger reactors or in a slurry-type reactor.The hydrogen flow can be introduced at the same time as the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0121] The hydrogenation of aromatic or polyaromatic compounds can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase. Generally, 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 hydrogen / (aromatic compounds to be hydrogenated) molar ratio between 0.1 and 10 and at an hourly volumetric flow rate between 0.05 h' 1 and 50 hours 1 , preferably between 0.1 h' 1 and 10 a.m. 1of a hydrocarbon feedstock 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.

[0122] The hydrogen flow rate is adjusted to provide sufficient quantity to theoretically hydrogenate all the aromatic compounds and to maintain an excess of hydrogen at the reactor outlet.

[0123] The conversion of the aromatic or polyaromatic compounds is generally greater than 20 mol%, preferably greater than 40 mol%, more preferably greater than 80 mol%, and 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 the aromatic or polyaromatic compounds in the hydrocarbon feedstock and in the product by the total moles of the aromatic or polyaromatic compounds in the hydrocarbon feedstock.

[0124] According to a particular variant of the process according to the invention, a process is carried out for hydrogenating benzene from a hydrocarbon feedstock, such as the reformate from a catalytic reforming unit. The benzene content in said hydrocarbon feedstock is generally between 0.1 and 40% by weight, preferably between 0.5 and 35% by weight, and particularly preferably between 2 and 30% by weight, the percentage by weight being based on the total weight of the hydrocarbon feedstock.

[0125] 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.

[0126] The hydrogenation of benzene contained in the hydrocarbon feedstock may be carried out in the gas 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, octane. Generally, the hydrogenation of benzene is carried out at a temperature of 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 of between 0.1 MPa and 10 MPa, preferably between 0.5 MPa and 4 MPa, at a hydrogen / (benzene) molar ratio of between 0.1 and 10 and at an hourly volumetric flow rate of between 0.05 h' 1 and 50 hours 1 , preferably between 0.5 h' 1 and 10 a.m. 1 .

[0127] The conversion of benzene is generally greater than 50 mol%, preferably greater than 80 mol%, more preferably greater than 90 mol% and particularly preferably greater than 98 mol%.

[0128] The invention will now be illustrated by the following examples which are in no way limiting.

[0129] Examples

[0130] For all the catalysts mentioned in the examples below, the support is an alumina A having a specific surface area of ​​80 m 2 / g, a total pore volume (TPV) of 0.7 ml_ / g and a median mesoporous diameter of 12 nm.

[0131] Example 1: Preparation of an aqueous solution of Ni precursor with additive

[0132] The aqueous solution S used for the preparation of catalysts A to I is prepared by dissolving 43.5 g of nickel nitrate (NiNOs, 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 molar ratio additive / Ni i is set at 0.5. Solution S is obtained with a Ni concentration of 350 g of Ni per liter of solution. Example 1bis: Preparation of an aqueous solution of Ni precursor without additive

[0133] The aqueous solution S' used for the preparation of catalyst A is prepared by dissolving 43.5 g of nickel nitrate (NiNOs, supplier Strem Chemicals®) in a volume of 13 mL of distilled water. Solution S' is obtained, the Ni concentration of which is 350 g of Ni per liter of solution. A according to the invention of Ni - acid

[0134] 10 g of alumina A are impregnated with 2.4 ml of hexanoic acid added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 7.1 ml of solution S prepared in Example 1a is impregnated dropwise onto the impregnated support. The catalyst precursor 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. Catalyst A is obtained containing 10% by weight of the nickel element relative to the total weight of the catalyst.

[0135] The characteristics of catalyst A thus obtained are shown in Table 1 below. of a catalyst B according to the invention [10% by weight of Ni - hexanoic acid 25% VRE in pre-imprenation + additive]

[0136] 10 g of alumina A are impregnated with 2.4 ml of hexanoic acid added dropwise. The impregnated support is then left to mature for 30 min 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 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. Catalyst B is obtained containing 10% by weight of the nickel element relative to the total weight of the catalyst.

[0137] The characteristics of catalyst B thus obtained are reported in Table 1 below. r C according to the invention of Ni-acid

[0138] 10 g of alumina A are impregnated with 2.4 ml of hexanoic acid added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 3.55 ml of solution S prepared in Example 1 diluted with water to make up to 7.1 ml is impregnated dropwise onto the impregnated support. The catalyst precursor 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. Catalyst C is obtained containing 5% by weight of the nickel element relative to the total weight of the catalyst.

[0139] The characteristics of the catalyst C thus obtained are reported in Table 1 below. of Ni - acid

[0140] 10 g of alumina A are impregnated with 7.2 ml of hexanoic acid added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 2.4 ml of the solution S prepared in Example 1 is impregnated dropwise onto the impregnated support. The catalyst precursor 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. Catalyst D is obtained containing 10% by weight of the nickel element relative to the total weight of the catalyst.

[0141] The characteristics of catalyst D thus obtained are reported in Table 1 below. of a catalyst E according to the invention of Ni - acid in pre-im

[0142] 10 g of alumina A are impregnated with 2.4 ml of heptanoic acid added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 7.1 ml of the solution S prepared in Example 1 is impregnated dropwise onto the impregnated support. The catalyst precursor 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. Catalyst E is obtained containing 10% by weight of the nickel element relative to the total weight of the catalyst.

[0143] The characteristics of catalyst E thus obtained are reported in Table 1 below. of a catalyst F not in accordance with the invention

[0144] The solution S prepared in Example 1 is dry impregnated, 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, then calcined under a flow of dry air of 1 L / h / g of catalyst at 450°C for 2 hours.

[0145] Catalyst F is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

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

[0147] 7.1 ml of solution S prepared in Example 1 is dry impregnated, by adding it dropwise, onto 10 g of alumina. The 10 g of the prepared catalyst precursor are impregnated with 2.4 ml of hexanoic acid added dropwise. The solid is then left to mature for 30 min at 60°C.

[0148] 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.

[0149] Catalyst G is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0150] The characteristics of the catalyst G thus obtained are reported in Table 1 below.

[0151] Example 9: Preparation of a non-compliant H catalyst [10% weight of Ni - toluene 25% VRE in pre-imprenation]

[0152] 10 g of alumina A are impregnated with 2.4 ml of toluene added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 7.1 ml of the solution S prepared in Example 1 is impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven for 12 hours at 120°C, then calcined under a dry air flow of 1 L / h / g of catalyst at 450°C for 2 hours.

[0153] Catalyst H is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0154] The characteristics of the H catalyst thus obtained are reported in Table 1 below.

[0155] I non-compliant [10% weight of Ni - acid

[0156] 10 g of alumina A are impregnated with 2.4 ml of citric acid added dropwise. The impregnated support is then left to mature for 30 min at 60°C. Then, 7.1 ml of the solution S prepared in Example 1 is impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven for 12 hours at 120°C, then calcined under a dry air flow of 1 L / h / g of catalyst at 450°C for 2 hours.

[0157] Catalyst I is obtained containing 10% by weight of the element nickel relative to the total weight of the catalyst.

[0158] The characteristics of the catalyst I thus obtained are reported in Table 1 below.

[0159] AcHexa: Hexanoic acid

[0160] AcHepta: Heptanoic acid

[0161] AcCitr: Citric acid Table 1: Characteristics of catalysts A to H

[0162] Example 11: Catalytic tests: performance in selective hydrogenation of a mixture containing styrene and isoprene (AHYDI)

[0163] Catalysts A to I described in the examples above are tested for the selective hydrogenation reaction of a mixture containing styrene and isoprene. The composition of the feedstock to be selectively hydrogenated is as follows: 8% wt styrene (supplier Sigma Aldrich®, purity 99%), 8% wt isoprene (supplier Sigma Aldrich®, purity 99%), 84% wt n-heptane (solvent) (supplier VWR®, purity > 99% chromanorm HPLC). This feedstock also contains very low levels of sulfur compounds: 10 ppm wt sulfur introduced in the form of pentanethiol (supplier Fluka®, purity > 97%) and 100 ppm wt sulfur introduced in the form of thiophene (supplier Merck®, purity 99%). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis gasoline.

[0164] 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.

[0165] Prior to its introduction into the autoclave, a quantity of 3 mL of catalyst is reduced ex situ under a hydrogen flow of 1 L / h / g of catalyst, at 400 °C for 16 hours (temperature rise ramp of 1 °C / min), then it is 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, then pressurized under 35 bar (3.5 MPa) of hydrogen, and brought to the test temperature equal to 30 °C. At time t = 0, approximately 30 g of a mixture containing styrene, isoprene, n-heptane, pentanethiol and thiophene are introduced into the autoclave. The reaction mixture then has the composition described above and stirring is started at 1600 rpm. The pressure is maintained constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle located upstream of the reactor.

[0166] 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-butenes. If the reaction is prolonged longer than necessary, the methyl-butenes are in turn hydrogenated to isopentane. Hydrogen consumption is also monitored over time by the decrease in pressure in a reservoir bottle located upstream of the reactor. The catalytic activity is expressed in moles of H2 consumed per minute and per gram of Ni.

[0167] The catalytic activities measured for catalysts A to I are reported in Table 2 below. They are related to the catalytic activity (AHYDI) measured for catalyst F. in the hydrogenation of toluene Catalysts A to I described in the examples above are also tested with respect to the toluene hydrogenation reaction.

[0168] The selective hydrogenation reaction is carried out in the same autoclave as that described in Example 11.

[0169] Prior to its introduction into the autoclave, a quantity of 2 mL of catalyst is reduced ex situ under a hydrogen flow of 1 L / h / g of catalyst, at 400°C for 16 hours (temperature rise ramp of 1°C / min), then it is 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 equal to 80°C. At time t=0, approximately 26 g of toluene (supplier SDS®, 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 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.

[0170] The progress of the reaction is monitored by taking samples of the reaction medium at regular time intervals: the toluene is completely hydrogenated into 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 and per gram of Ni.

[0171] The catalytic activities measured for catalysts A to I are reported in Table 2 below. They are related to the catalytic activity (AHYDZ) measured for catalyst F.

[0172]

[0173] Table 2: Comparison of the performances of catalysts A to H in selective hydrogenation of a mixture containing styrene and isoprene (AHYDI) and in hydrogenation of toluene (A H YD2)

[0174] These examples clearly demonstrate the improved performance of catalysts A, B, C, D and E according to the invention, compared to non-compliant catalysts F, G, H and I. This is explained by the distribution of nickel in a crust on catalysts A, B, C, D and E which gives them a significantly improved activity, particularly in rapid hydrogenation reactions. Catalyst A, despite the fact that the particles are larger in size (8 nm) due to the non-use of malonic acid, remains quite efficient because the nickel is well distributed in a crust and therefore very accessible. Catalyst F is less active due to the conventional impregnation implemented without pre-impregnation of hexanoic or heptanoic acid. Catalyst G has undergone a post-impregnation of hexanoic acid which does not allow a distribution in a crust of nickel. Catalyst H is prepared with a toluene pre-impregnation step.Thus, although toluene is poorly miscible with water, as in the case of hexanoic acid, the absence of -OH groups in the molecule does not allow it to interact strongly with the -OH of the alumina support, which can explain the migration of toluene by the water contained in the nickel nitrate solution during the nickel impregnation step. In the case of citric acid, the -OH groups seem to allow it both to go to the core of the support and to interact with the support. On the other hand, since water and citric acid are very miscible unlike the hexanoic or heptanoic acid / water couples, the diffusion to the core of the aqueous nickel nitrate solution seems to take place given both the physicochemical characteristics of the final catalyst obtained and the results of catalytic tests. Thus, for catalysts G, H and I, nickel is distributed homogeneously throughout the catalyst grain.Catalysts G and H therefore have an activity well below that of catalyst A in AHYDI and A. H YD2- Catalyst H is further removed due to the presence of toluene which disrupts the impregnation of the nickel nitrate solution.

Claims

CLAIMS 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 at 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 V1 of a solution of hexanoic acid or heptanoic acid 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. Method according to claim 1, in which 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 - V1.

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

4. 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. Method according to claim 4, in which step d) is carried out for a time of between 0.5 hours and 24 hours.

6. Method according to any one of claims 1 to 5, wherein in step a) said volume V1 of said hexanoic acid or heptanoic acid solution is between 0.25 and 0.75 times the total pore volume VPT of said support.

7. Method according to any one of claims 1 to 6, in which a step b1) is carried out 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 b1) being carried out in any order, or simultaneously.

8. Method according to claim 7, in which 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 - V1.

9. Method according to one of claims 7 or 8, in which steps b) and b1) are carried out simultaneously.

10. Method according to claim 9, in which 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 - V1.

11. Method according to any one of claims 7 to 10, in which the molar ratio between said organic compound introduced in step b1) and the nickel element also introduced in step b) is between 0.01 and 5.0 mol / mol.

12. Process according to any one of claims 7 to 11, in which the organic compound of step b1) is chosen 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, y-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, EDTA.

13. Method according to any one of claims 1 to 12, in which a step a1) is carried out in which the impregnated support obtained at the end of step a) is left to mature for 0.5 hours to 40 hours.

14. A method according to any one of claims 7 to 13, wherein the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm.

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