Process for the preparation of a catalyst comprising nickel active phase distributed in the shell by heptanol impregnation

Abstract

A process for the preparation of a catalyst comprising a nickel active phase and an alumina support, said catalyst comprising from 1 to 50% by weight of elemental nickel with respect to the total weight of the catalyst, the nickel being distributed on a shell at the periphery of the support and at the core of the support, said process comprising the following steps: a) impregnation of the support with a solution of heptanol in a volume V1, said volume V1 being from 0.2 to 0.8 times the total pore volume TPV of the support, to obtain an impregnated support; b) impregnation of the impregnated support obtained at the end of step a) with a solution comprising a nickel active phase precursor, to obtain a catalyst precursor; c) drying of the catalyst precursor obtained at the end of step b) at a temperature lower than 250°C.

Description

Technical Field

[0001] This invention relates to a method for preparing a nickel-based supported metal catalyst, which is particularly suitable for the hydrogenation of unsaturated hydrocarbons, and more specifically for the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatics. Existing technology

[0002] Monounsaturated organic compounds, such as ethylene and propylene, are fundamental to the manufacture of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or gas oil processed by steam cracking or catalytic cracking processes. These processes are carried out at high temperatures and, in addition to the desired monounsaturated compounds, produce 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 C5+ gasoline fractions (gasoline containing hydrocarbons with five or more carbon atoms), particularly styrene or indene compounds. These polyunsaturated compounds are highly reactive and lead to side reactions in polymerization units. Therefore, it is necessary to remove them before economically utilizing these fractions. Selective hydrogenation is a primary processing method specifically developed for removing unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It converts polyunsaturated compounds into the corresponding olefins or aromatics while avoiding complete saturation and thus the formation of the corresponding alkanes or cycloalkanes.

[0003] Selective hydrogenation catalysts are typically based on metals 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 within the support are criteria affecting the catalyst activity and selectivity.

[0004] The macroscopic distribution of metal particles within the support constitutes an important criterion, primarily in the context of rapid and continuous reactions (e.g., selective hydrogenation). It is generally desirable for these elements to reside within a shell surrounding the support to avoid intraparticle material transfer problems that could lead to activity defects and loss of selectivity. Such catalysts are also known as "eggshell" catalysts.

[0005] Such catalysts are widely known in the case of palladium-based selective hydrogenation catalysts. In fact, a thin palladium shell can be obtained around the support particles due to the low palladium content (typically less than 1 wt% palladium relative to the catalyst) and suitable preparation methods (FR2922784, US2010 / 217052).

[0006] Nickel is often recommended as a substitute for palladium, as it is a less reactive metal and therefore requires a higher nickel content in the catalyst. Consequently, nickel-based catalysts typically have a metal content of 5% to 50% relative to the weight of nickel in the catalyst. In these catalysts, nickel is usually uniformly distributed within the support. One feasible method to improve the activity and selectivity of these catalysts is to control the distribution of nickel within the support by depositing it in a more concentrated manner on a shell surrounding the support. Such catalysts are known in the prior art.

[0007] Document US4519951 describes an "eggshell" catalyst with nickel on a porous support, exhibiting a pore volume of at least 0.2 ml / g for pores smaller than 11.7 nm and at least 0.1 ml / g for pores larger than 11.7 nm. More than 50% of the nickel is present in the shell, with a thickness equal to 0.15 times the support radius. This catalyst is used for the hydrogenation of fats.

[0008] Document CN101890351 describes a supported nickel catalyst in which over 90% of the nickel is contained within a 700 μm thick shell. The catalyst is prepared by dissolving the nickel salt in an ammonia solution. These catalysts are intended for selective hydrogenation applications.

[0009] Document US2012 / 0065442 describes a supported nickel catalyst in which nickel is distributed in a shell and a core with a thickness of 3% to 15% of the diameter, and the nickel concentration ratio between the shell and the core is 3.0:1 to 1.3:1. The nickel active phase is deposited by spraying an ammonia solution of nickel salt onto the support.

[0010] Document FR3099387 describes a method for preparing a nickel-based catalyst on an alumina support obtained according to a very specific method, wherein nickel is distributed on a shell surrounding the support and at the core of the support, the shell having a thickness of 2% to 15% of the catalyst diameter. The method for preparing this catalyst first requires the use of a specific alumina support that has undergone hydrothermal treatment in the presence of an acid solution, followed by a hydrothermal treatment step after the addition of specific organic additives to the catalyst precursor.

[0011] Invention Theme

[0012] Surprisingly, the applicant has discovered that a specific step of impregnating a heptanol solution onto a porous alumina support, regardless of its origin, and without requiring an intermediate drying step between the heptanol impregnation and the impregnation of the active nickel phase precursor, allows for the production of a catalyst in which at least a portion of the nickel is distributed on a shell surrounding the support, and another portion is distributed in the core of the catalyst. Without being bound by any theory, the presence of heptanol prevents the migration of the active nickel phase towards the support core. This is because only a portion of the porosity is occupied by heptanol. Furthermore, due to the poor miscibility of heptanol and water, the heptanol layer constitutes a barrier to the diffusion of nickel into the support core.

[0013] Therefore, the present invention relates to a novel method for preparing catalysts that enables the acquisition of catalysts with at least equally good or even better performance qualities in terms of activity and selectivity in the context of selective hydrogenation of polyunsaturated compounds or hydrogenation of aromatics, while using a lower effective amount of nickel phase (i.e., the amount of nickel in the final shell surrounding the support that allows selective hydrogenation of aromatics or hydrogenation) compared to amounts typically used in the prior art, due to better distribution of the active nickel phase in the support, which facilitates reagent ingress.

[0014] One subject of the present invention is a method for preparing a catalyst comprising a nickel-based active phase and an alumina support, said catalyst comprising 1% to 50% by weight of elemental nickel relative to the total weight of the catalyst, said nickel being distributed in a shell and a core surrounding the support, said shell having a thickness of 2% to 15% of the catalyst diameter, and said nickel particles in the catalyst having a size of less than 15 nanometers as measured in oxide form, said method comprising the following steps:

[0015] a) Impregnate the carrier with a heptanol solution of volume V1 to obtain an impregnated carrier, wherein the volume V1 is 0.2 to 0.8 times the total pore volume (TPV) of the carrier;

[0016] b) Impregnate the impregnated support obtained at the end of step a) with a solution containing at least one nickel active phase precursor to obtain a catalyst precursor;

[0017] c) Dry the catalyst precursor obtained at the end of step b) at a temperature below 250°C.

[0018] According to one or more embodiments, in step b), the volume V2 of the solution containing at least one nickel active phase precursor impregnated on the impregnation carrier obtained at the end of step a) is such that V2 = TPV - V1.

[0019] According to one or more implementation schemes, step c) takes 0.5 to 12 hours.

[0020] According to one or more embodiments, the method further includes step d), wherein the catalyst obtained at the end of step c) is calcined at a temperature of 250°C to 600°C.

[0021] According to one or more implementation schemes, step d) is carried out for 0.5 hours to 24 hours.

[0022] 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 carrier.

[0023] According to one or more embodiments, in step a), a solution of n-heptanol is used.

[0024] According to one or more embodiments, the method further includes step b1), wherein 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 functional group, or at least one alcohol functional group, or at least one ester functional group, or at least one amide functional group, or at least one amine functional group, and steps b) and b1) are performed in any order or simultaneously.

[0025] According to one or more embodiments, at the end of step a), the volume V2 of the solution containing at least one active nickel phase precursor impregnated on the impregnation carrier and the volume V3 of the solution containing at least one organic compound obtained make V2 + V3 = TPV - V1.

[0026] According to one or more implementation schemes, steps b) and b1) are performed simultaneously.

[0027] According to one or more embodiments, the volume V2' of the solution containing at least one active nickel phase precursor and at least one organic compound impregnated on the impregnation carrier obtained at the end of step a) is such that V2' = TPV - V1.

[0028] According to one or more embodiments, the molar ratio of the organic compound introduced in step b1) to the nickel element also introduced in step b) is from 0.01 to 5.0 mol / mol.

[0029] According to one or more embodiments, the organic compound in step b1) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, malonic acid, citric acid, tartaric acid, pyruvic acid, acetylpropionic acid, ethylene glycol, propane-1,3-diol, 1,4-butanediol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, γ-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylformamide, 2-pyrrolidone, γ-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, and EDTA.

[0030] According to one or more embodiments, step a1) is performed, wherein the impregnated carrier obtained at the end of step a) is left to mature for 0.5 hours to 40 hours.

[0031] According to one or more embodiments, step a1) is performed, wherein the impregnated carrier obtained at the end of step a) is left to mature for 0.5 hours to 40 hours.

[0032] According to one or more embodiments, the size of the nickel particles in the catalyst, measured in oxide form, is less than 13 nm. Attached Figure Description

[0033] Figure 1 This is a graph showing the distribution of nickel in the catalyst. The x-axis corresponds to the catalyst thickness (in μm) measured from the catalyst edge. The y-axis corresponds to the nickel density (in grams of Ni / mm²). 3 (Unit: ep1). Nickel is distributed both on the outer shell of the support, which is ep1 thick, and in the core of the support. The nickel density on the shell is d. 壳 The nickel density d in the core of the support is greater than that in the core of the support. 核 The thickness of the transition zone between the core and shell of the catalyst is denoted as ep2-ep1. Invention Details

[0035] 1. Definition

[0036] In the following text, chemical groups are given according to the CAS classification (DRLide, CRC Handbook of Chemistry and Physics, 81st edition, 2000-2001, CRC Press). For example, Group VIII according to the CAS classification corresponds to columns 8, 9, and 10 of the metals according to the new IUPAC classification.

[0037] In this specification, in accordance with the IUPAC Convention, "micropore" is understood to mean a pore with a diameter less than 2 nm, i.e., 0.002 μm; "mesopore" is understood to mean a pore with a diameter greater than 2 nm, i.e., 0.002 μm, and less than 50 nm, i.e., 0.05 μm; and "macropore" is understood to mean a pore with a diameter greater than 50 nm, i.e., 0.05 μm.

[0038] To analyze the distribution of the metallic phase on the support, the shell thickness was measured using a Castaing microprobe (or electron microprobe microanalysis). The instrument used was a CAMECAX S100 equipped with four crystal monochromators, allowing for the simultaneous analysis of four elements. The Castaing microprobe analysis technique involves detecting the X-rays emitted by the solid after its elements are excited by a high-energy electron beam. For this characterization, catalyst particles were coated in epoxy resin blocks. These blocks were polished until a cross-section was reached through the diameter of the beads or extrudate, and then metallized by depositing carbon in a metal evaporator. An electron probe was scanned along the diameter of five beads or extrudates to obtain an average distribution profile of the solid's constituent elements. This method is well known to those skilled in the art and is defined in the publication L. Sorbier et al., “Measurement of palladium crust thickness on catalyst by EPMA”, Materials Science and Engineering 32 (2012). It allows for the establishment of a distribution profile of a given element (here, nickel) within the particles. Furthermore, the Ni concentration was defined for each measurement and thus for each analytical step. Therefore, the density of Ni within the particles was thus defined as per mm. 3 Ni concentration.

[0039] Total pore volume was measured according to standard ASTM D4284-92 using the mercury porosity method at a wetting angle of 140°, for example using a sample from Micromeritics. TM Autopore III of the brand TM Model device.

[0040] BET specific surface area is measured according to standard ASTM D3663-03 by nitrogen physical adsorption method, which is described in the book "Adsorption by Powders & Porous Solids: Principles, Methodology and Applications" by Rouquerol F., Rouquerol J. and Singh K. (Academic Press, 1999).

[0041] The term “size of nickel particles” should be understood to refer to the diameter of nickel crystallites in oxide form. The diameter of nickel crystallites in oxide form is determined by X-ray diffraction using the Scherrer relation based on the width of the diffraction line at an angle of 2θ = 43° (i.e., along the crystallographic direction

[200] ). This method, used for X-ray diffraction of polycrystalline samples or powders, relates the full width at half maximum (FWHM) of the diffraction peak to the particle size, and 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.L. Langford and A.J.C. Wilson.

[0042] The nickel content was measured using X-ray fluorescence.

[0043] 2. Catalyst Preparation Method

[0044] The steps of the preparation method are described in detail below.

[0045] Step a)

[0046] According to step a) of the method, the alumina carrier is impregnated with a heptanol solution of volume V1, wherein the volume V1 is 0.2 to 0.8 times, preferably 0.25 to 0.75 times, the total pore volume (also referred to herein as TPV) of the carrier to be impregnated.

[0047] Heptanol should be understood as referring to the alcohol corresponding to the empirical chemical formula C7H. 16 O refers to organic compounds containing alcohol functional groups. Therefore, heptanol should be understood to refer to the group of organic compounds including 1-heptanol (or n-heptanol), 2-heptanol, and their isomers. Preferably, step a) is carried out in the presence of 1-heptanol.

[0048] Step a1 (optional)

[0049] Following step a), the impregnated support can be aged in a wet state for 0.5 to 40 hours, preferably 1 to 30 hours. The aging step a1) is preferably carried out at a temperature below or equal to 60°C, and more preferably at ambient temperature. This step allows the heptanol solution to migrate to the core of the support. During this process, aging step a1) enhances the migration of the heptanol solution to the support core and releases "free pore rings" at the periphery of the support, which nickel could access during the impregnation of the active phase precursor.

[0050] Step b)

[0051] In step b) of the method, 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 nickel active phase precursor to obtain a catalyst precursor. The impregnation step can be carried out by dry impregnation or over-impregnation according to methods well known to those skilled in the art.

[0052] The pH of the solution containing at least one impregnated nickel active phase precursor can be altered by optionally adding an acid or a base.

[0053] Preferably, the nickel precursor is introduced in the form of an aqueous solution, for example, as a nitrate, carbonate, acetate, chloride, or oxalate, as a complex formed from a polybasic acid or alcohol and its salt, as a complex formed with an acetylacetonate, or as any other inorganic derivative soluble in aqueous solution, and is then contacted with the support. Preferably, nickel nitrate, nickel chloride, nickel acetate, or basic nickel carbonate are advantageously used as the nickel precursor. Very preferably, the nickel precursor is nickel nitrate.

[0054] The concentration of nickel in the solution is adjusted according to the pore volume of the still available support to obtain a nickel content of 1% to 50% by weight relative to the total weight of the catalyst, more preferably 2% to 40% by weight, and even more preferably 3% to 35% by weight, and even more preferably 5% to 25% by weight of nickel for the supported catalyst.

[0055] Step b1 (optional)

[0056] When step b1) is performed, the impregnated porous alumina support obtained at the end of step a) (or the cured 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, said organic compound comprising at least one carboxylic acid functional group, or at least one alcohol functional group, or at least one ester functional group, or at least one amide functional group, or at least one amine functional group, said steps b) and b1) are performed in any order or simultaneously.

[0057] The impregnation step can be carried out by dry impregnation or over-impregnation, methods well known to those skilled in the art. This is because it has also been noted that catalysts prepared in the presence of organic compounds (described below) are more active than those prepared in the absence of such organic compounds. This effect is related to the reduction in nickel particle size.

[0058] The solution containing at least one organic compound having at least one carboxylic acid functional group is preferably aqueous. The organic compound is pre-dissolved in the solution at least partially at the desired concentration. The pH of the solution can be altered by optionally adding an acid or a base.

[0059] Advantageously, the molar ratio of the organic compound introduced in step b1) to the nickel element also introduced in step b) is 0.01 to 5.0 mol / mol, preferably 0.05 to 2.0 mol / mol, more preferably 0.1 to 1.5 mol / mol, and even more preferably 0.3 to 1.2 mol / mol.

[0060] The organic compound containing at least one carboxylic acid functional group can be a saturated or unsaturated aliphatic or aromatic organic compound. Preferably, the saturated or unsaturated aliphatic organic compound contains 1 to 9 carbon atoms, more preferably 2 to 7 carbon atoms. Preferably, the aromatic organic compound contains 7 to 10 carbon atoms, more preferably 7 to 9 carbon atoms.

[0061] The saturated or unsaturated aliphatic organic compound or the aromatic organic compound containing at least one carboxylic acid functional group may be selected from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids.

[0062] Advantageously, the organic compound containing at least one carboxylic acid functional group is selected from oxalic acid, malonic acid, glutaric acid, glycolic acid, 2-hydroxypropionic acid, 2-hydroxymalonic acid, 2-hydroxypropane-1,2,3-tricarboxylic acid, 2,3-dihydroxysuccinic acid, 2-oxopropionic acid, or 4-oxovalerate.

[0063] Implementation of steps b) and b1)

[0064] If step b1) is performed, the method for preparing the nickel catalyst may include several embodiments. They differ particularly in the order of introduction of the organic compound and the nickel precursor, which may be contacted with the support after the nickel precursor has been contacted with the impregnated support obtained at the end of step a)(or a1)), before the nickel precursor has been contacted with the impregnated support obtained at the end of step a)(or a1)), or simultaneously with the contact of the nickel precursor with the impregnated support obtained at the end of step a)(or a1)).

[0065] The first embodiment includes performing step b)(post-immersion) before step b1).

[0066] The second implementation includes performing step b1) (pre-impregnation) prior to step b).

[0067] Optionally, in the presence of the same or different nickel precursors and / or organic compounds in each step b) and / or b1), each step b) and b1) is performed at least once and can advantageously be performed multiple times, with the impregnation of the impregnated carrier with the nickel precursor and the impregnation of the impregnated, optionally aged carrier with at least one solution containing at least one organic compound comprising at least one carboxylic acid functional group. All feasible combinations of embodiments of steps b) and b1) are included within the scope of the invention.

[0068] Preferably, at the end of step a), the volume V2 of the solution containing at least one active nickel phase precursor and the volume V3 of the solution containing at least one organic compound impregnated on the impregnated, optionally cured carrier are such that V2 + V3 = TPV - V1.

[0069] The third embodiment includes performing step b) and step b1) (co-impregnation) simultaneously. This embodiment may advantageously include performing one or more steps b), optionally using the same or different nickel precursors in each step b). Specifically, one or more steps b) are performed before and / or advantageously after the co-impregnation step, optionally using the same or different nickel precursors in each step. This embodiment may also include several co-impregnation steps: steps b) and b1) are performed several times simultaneously, optionally in the presence of the same or different nickel precursors and / or organic compounds in each co-impregnation step.

[0070] Preferably, steps b) and b1) are performed simultaneously. Preferably, the volume V2' of the solution containing at least one active nickel phase precursor 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.

[0071] Step c)

[0072] The drying step c) is advantageously carried out at a temperature below 250°C, preferably 15°C to 180°C, more preferably 30°C to 160°C, even more preferably 50°C to 150°C, and even more preferably 70°C to 140°C, for a period of time typically from 0.5 hours to 12 hours, and even more preferably from 0.5 hours to 5 hours. Longer periods are not excluded, but they do not necessarily bring any improvement.

[0073] 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, an oxygen-containing atmosphere, or a mixture of an inert gas and oxygen. It is advantageously carried out at atmospheric pressure or under reduced pressure. Preferably, the step is carried out at atmospheric pressure and in the presence of air or nitrogen.

[0074] At the end of step c), the presence or absence of all or part of the heptanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the context of selective hydrogenation of polyunsaturated compounds or hydrogenation of aromatic compounds.

[0075] Step d)(optional)

[0076] The calcination step d) can be carried out at a temperature of 250°C to 600°C, preferably 350°C to 550°C, for a period of 0.5 hours to 24 hours, preferably 0.5 hours to 12 hours, and even more preferably 0.5 hours to 10 hours, preferably in an inert atmosphere or an oxygen-containing atmosphere. Longer time periods are not excluded, but they will not necessarily bring any improvement.

[0077] At the end of step d), the presence or absence of all or part of the heptanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the context of selective hydrogenation of polyunsaturated compounds or hydrogenation of aromatic compounds.

[0078] Step e) (Optional)

[0079] Before using the catalyst in the catalytic reactor and implementing the hydrogenation method, it is advantageous to carry out at least one reduction treatment step e) in the presence of a reducing gas after step c) or d) to obtain a catalyst containing at least a portion of nickel in metallic form.

[0080] This treatment allows for the activation of the catalyst and the formation of metal particles, particularly nickel particles in the zero-valence state. The reduction treatment can be carried out in situ or ex-situ, that is, after or before the catalyst is loaded into the hydrogenation reactor.

[0081] The reducing gas is preferably hydrogen. Hydrogen can be used pure or as a mixture (e.g., hydrogen / nitrogen, hydrogen / argon, or hydrogen / methane mixture). When hydrogen is used as a mixture, any proportion is conceivable.

[0082] The reduction treatment is carried out at a temperature of 120°C to 500°C, preferably 150°C to 450°C. When the catalyst does not undergo any passivation, or undergoes a reduction treatment before passivation, the reduction treatment is carried out at a temperature of 180°C to 500°C, preferably 200°C to 450°C, and even more preferably 350°C to 450°C. When the catalyst has been pre-passivated, the reduction treatment is typically carried out at a temperature of 120°C to 350°C, preferably 150°C to 350°C.

[0083] The duration of the reduction treatment is typically 2 to 40 hours, preferably 3 to 30 hours. The temperature is typically raised to the desired reduction temperature slowly, for example, set at 0.1°C / min to 10°C / min, preferably 0.3°C / min to 7°C / min.

[0084] The hydrogen flow rate, expressed in liters per hour per gram of catalyst, is from 0.01 to 100 liters per hour per gram of catalyst, preferably from 0.05 to 10 liters per hour per gram of catalyst, and even more preferably from 0.1 to 5 liters per hour per gram of catalyst.

[0085] 3. Catalyst

[0086] According to the preparation method of the present invention, a catalyst comprising a nickel-based active phase and an alumina support can be obtained, the catalyst comprising 1% to 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed on a shell surrounding the support and at the core of the support, the thickness of the shell (also referred to as ep1) being 2% to 15% of the catalyst diameter, and the nickel particle size in the catalyst, measured in oxide form, being less than 15 nanometers.

[0087] Preferably, nickel is distributed on the shell surrounding the support and in the core of the support, the thickness of which (also referred to as ep1) is 2% to 15% of the catalyst diameter, preferably 2.5% to 12% of the catalyst diameter, even more preferably 3% to 10% of the catalyst diameter, and even more preferably 3% to 7.5% of the catalyst diameter.

[0088] Preferably, the nickel density ratio between the shell and the core (also referred to herein as d) 壳 / d 核 Strictly greater than 3, preferably greater than 3.5, and more preferably 3.8 to 15.

[0089] Preferably, the shell contains more than 25% by weight of nickel relative to the total weight of nickel in the catalyst, preferably more than 40% by weight, more preferably 45% to 90% by weight, and even more preferably 60% to 90% by weight.

[0090] Advantageously, the transition region between the core and shell of the catalyst (also referred to herein as the core / shell transition region, or according to...) Figure 1 The marked ep2-ep1) is very steep, which is related to the change in nickel density measured along the catalyst thickness from the edge to the center of the catalyst. Preferably, the core / shell transition region is 0.05% to 3% of the catalyst diameter, more preferably 0.5% to 2.5% of the catalyst diameter.

[0091] The nickel content in the catalyst is advantageously from 1% to 50% by weight relative to the total weight of the catalyst, more preferably from 2% to 40% by weight relative to the total weight of the catalyst, and even more preferably from 3% to 35% by weight, and even more preferably from 5% to 25% by weight. The “% by weight” value is based on the elemental form of nickel.

[0092] The catalyst can be described as a "semi-eggshell" catalyst, meaning that the nickel concentration at the periphery of the support is higher than the nickel concentration in the core of the support, where the nickel concentration is not zero.

[0093] The specific surface area of ​​the catalyst is typically 10 m². 2 / g to 350m 2 / g, preferably 25m 2 / g to 300m 2 / g, more preferably 40m 2 / g to 250m 2 / g.

[0094] The total pore volume of the catalyst is typically from 0.1 ml / g to 1 ml / g, preferably from 0.2 ml / g to 0.8 ml / g, and particularly preferably from 0.3 ml / g to 0.7 ml / g.

[0095] The size of the nickel particles in the catalyst, measured in oxide form, is advantageously less than 15 nm, preferably less than 13 nm, and even more preferably less than 10 nm. When step b1) of the method according to the invention is performed, the size of the nickel particles in the catalyst, measured in oxide form, 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.

[0096] The active phase of the catalyst does not contain Group VIB metals. In particular, it does not contain molybdenum or tungsten.

[0097] The catalyst (and the support for preparing the catalyst) is in particulate form, advantageously having a diameter of 0.5 mm to 10 mm. The particles can have any form known to those skilled in the art, such as beads (preferably having a diameter of 1 mm to 8 mm), extrusions, tablets, or hollow cylinders. Preferably, the catalyst (and the support for preparing the catalyst) is in extrusion form, with a diameter of 0.5 mm to 10 mm, preferably 0.8 mm to 3.2 mm, and very preferably 1.0 mm to 2.5 mm, and a length of 0.5 mm to 20 mm. The “diameter” of the extrusion refers to the diameter of the circumcircle of the cross-section of these extrusions. The catalyst can advantageously be in the form of cylindrical, multi-lobed, trilobed, or tetralobed extrusions. Preferably, its shape is trilobed or tetralobed. The shape of the lobes can be adjusted according to all known methods in the art.

[0098] 4. Carrier

[0099] The properties of alumina mentioned in this section correspond to the properties of alumina prior to step a) of the preparation method according to the present invention.

[0100] The support is alumina, meaning that, relative to the weight of the support, the support contains at least 95% by weight, preferably at least 98% by weight, and particularly preferably at least 99% by weight of alumina. Alumina typically exhibits a crystal structure of the δ-, γ-, or θ-alumina type, either alone or as a mixture.

[0101] The alumina support may contain impurities, such as oxides of metals classified according to Groups IIA, IIIB, IVB, IIB, IIIA and IVA according to CAS classification, such as silicon dioxide, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alkali metals, such as lithium, sodium or potassium, and / or alkaline earth metals, such as magnesium, calcium, strontium or barium, or sulfur.

[0102] The BET specific surface area of ​​alumina is typically 10 m². 2 / g to 400m 2 / g, preferably 30m 2 / g to 350m 2 / g, more preferably 50m 2 / g to 300m 2 / g.

[0103] The total pore volume of alumina is typically from 0.1 ml / g to 1.2 ml / g, preferably from 0.3 ml / g to 0.9 ml / g, and very preferably from 0.5 ml / g to 0.9 ml / g.

[0104] 5. Selective hydrogenation method

[0105] Another subject of the present invention is a method for the selective hydrogenation of polyunsaturated compounds, such as dienes and / or alkynes and / or alkenyl aromatics, also known as styrene compounds, contained in a hydrocarbon feedstock having a final boiling point of less than or equal to 300°C and containing at least two carbon atoms per molecule, in the presence of a catalyst obtained by the preparation method described above in this specification, when the method is carried out in the liquid phase at a temperature of 0°C to 300°C, at a pressure of 0.1 MPa to 10 MPa, at a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio of 0.1 to 10, and at a time of 0.1 to 200 h. -1 The procedure is carried out at a space-time velocity of 100 h⁻¹, or when the method is carried out in the gas phase, the molar ratio of hydrogen to (the polyunsaturated compound to be hydrogenated) is 0.5 to 1000 and the space-time velocity is 100 h⁻¹. -1 Up to 40000h -1 .

[0106] Monounsaturated organic compounds, such as ethylene and propylene, are fundamental to the manufacture of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or gas oil processed by steam cracking or catalytic cracking processes. These processes are carried out at high temperatures and, in addition to the desired monounsaturated compounds, produce 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 C5+ fractions (hydrocarbon compounds with at least 5 carbon atoms), particularly dienes, styrene, or indene compounds. These polyunsaturated compounds are highly reactive and lead to side reactions in the polymerization units. Therefore, it is necessary to remove these fractions before they can be used economically.

[0107] Selective hydrogenation is a primary processing method specifically developed to remove unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It converts polyunsaturated compounds into the corresponding olefins or aromatics while avoiding complete saturation and the resulting formation of alkanes or cycloalkanes. In the case of steam-cracked gasoline as feedstock, selective hydrogenation also allows for the selective hydrogenation of alkenyl aromatics to obtain aromatics, while avoiding the hydrogenation of aromatic rings.

[0108] The hydrocarbon feedstock processed in the selective hydrogenation process has a final boiling point of 300°C or less and contains at least two carbon atoms per molecule and comprises at least one polyunsaturated compound. The term "polyunsaturated compound" means a compound containing at least one alkyne functional group and / or at least one diene functional group and / or at least one alkenyl aromatic functional group.

[0109] More specifically, the feedstock is selected from steam cracking C2 fraction, steam cracking C2-C3 fraction, steam cracking C3 fraction, steam cracking C4 fraction, steam cracking C5 fraction, and steam cracked gasoline, also known as cracked gasoline or C5+ fraction.

[0110] Steam cracking C2 fractions advantageously used for implementing the selective hydrogenation method according to the invention exhibit, for example, the following composition: 40% to 95% by weight of ethylene and about 0.1% to 5% by weight of acetylene, with the remainder being primarily ethane and methane. In some steam cracking C2 fractions, 0.1% to 1% by weight of C3 compounds may also be present.

[0111] The steam cracking C3 fraction advantageously used for implementing the selective hydrogenation method according to the invention exhibits, for example, the following average composition: about 90 wt% propylene and about 1 wt% to 8 wt% propadiene and methylacetylene, with the remainder being essentially propane. In some C3 fractions, 0.1 wt% to 2 wt% C2 and C4 compounds may also be present.

[0112] The C2-C3 fraction can also be advantageously used to implement the selective hydrogenation method according to the invention. For example, it exhibits the following composition: about 0.1 wt% to 5 wt% acetylene, about 0.1 wt% to 3 wt% propadiene and methylacetylene, about 30 wt% ethylene and about 5 wt% propylene, with the remainder being primarily methane, ethane, and propane. The feedstock may also contain 0.1 wt% to 2 wt% C4 compounds.

[0113] The steam cracking C4 fraction advantageously used for implementing the selective hydrogenation method according to the invention exhibits, for example, the following average composition by weight: 1 wt% butane, 46.5 wt% butene, 51 wt% butadiene, 1.3 wt% vinylacetylene, and 0.2 wt% butyne. In some C4 fractions, 0.1 wt% to 2 wt% of C3 and C5 compounds may also be present.

[0114] The steam cracking C5 fraction advantageously used for implementing the selective hydrogenation method according to the invention exhibits, for example, the following composition: 21% by weight of pentane, 45% by weight of pentene and 34% by weight of pentadiene.

[0115] The steam-cracked gasoline or pyrolysis gasoline advantageously used for carrying out the selective hydrogenation method according to the invention corresponds to a hydrocarbon fraction with a boiling point typically from 0°C to 300°C, preferably from 10°C to 250°C. The steam-cracked gasoline contains polyunsaturated hydrocarbons to be hydrogenated, particularly diene compounds (butadiene, isoprene, cyclopentadiene, etc.), styrene compounds (styrene, α-methylstyrene, etc.), and indene compounds (indene, etc.). The steam-cracked gasoline typically contains C5-C12 fractions and trace amounts of C3, C4, C13, C14, and C15 (e.g., 0.1% to 3% by weight of each of these fractions). For example, the feedstock formed from pyrolysis gasoline typically has the following composition: 5% to 30% by weight of saturated compounds (alkanes and cycloalkanes), 40% to 80% by weight of aromatic compounds, 5% to 20% by weight of monoolefins, 5% to 40% by weight of dienes, and 1% to 20% by weight of alkenyl aromatic compounds, 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.

[0116] Preferably, the polyunsaturated hydrocarbon feedstock processed by the selective hydrogenation method according to the present invention is a steam cracked C2 fraction, a steam cracked C2-C3 fraction, or a steam cracked gasoline.

[0117] The selective hydrogenation method according to the present invention aims 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 method aims to selectively hydrogenate acetylene. When the feedstock is a C3 fraction, the selective hydrogenation method aims to selectively hydrogenate propadiene and methylacetylene. In the case of a C4 fraction, the aim is to remove butadiene, vinylacetylene (VAC), and butyne; in the case of a C5 fraction, the aim is to remove pentadiene. When the feedstock is steam-cracked gasoline, the selective hydrogenation method aims to selectively hydrogenate the polyunsaturated hydrocarbons present in the feedstock to be treated, such that diene compounds are partially hydrogenated to obtain monoolefins, and styrene and indene compounds are partially hydrogenated to obtain the corresponding aromatic compounds, while avoiding the hydrogenation of aromatic rings.

[0118] The selective hydrogenation method is implemented, for example, by injecting a polyunsaturated hydrocarbon feedstock as an upstream or downstream stream and hydrogen into at least one fixed-bed reactor. The reactor can be isothermal or adiabatic. An adiabatic reactor is preferred. The polyunsaturated hydrocarbon feedstock can advantageously be diluted by one or more re-injections at various points within the reactor, located between the inlet and outlet, to limit the temperature gradient within the reactor. The selective hydrogenation method according to the invention can also be advantageously implemented by embedding at least the supported catalyst into a reactive distillation column, reactor-exchange unit, or slurry reactor. The hydrogen feedstock can be introduced simultaneously with the feedstock to be hydrogenated and / or introduced at one or more different points within the reactor.

[0119] Selective hydrogenation of steam cracking C2, C2-C3, C3, C4, C5, and C5+ fractions can be carried out in the gas or 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. Liquid-phase reactions allow for lower energy costs and increased catalyst cycle time.

[0120] Generally, selective hydrogenation of hydrocarbon feedstocks containing polyunsaturated compounds with at least two carbon atoms per molecule and a final boiling point below or equal to 300°C is performed in the liquid phase at a temperature of 0°C to 300°C, a pressure of 0.1 MPa to 10 MPa, a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio of 0.1 to 10, and for 0.1 h. -1 Up to 200h -1 The process is carried out at a space velocity (defined as the ratio of feed volume flow rate to catalyst volume), or for gas-phase methods at a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio of 0.5 to 1000 and a h⁻¹ of 100 to 40000. -1 It proceeds at a spacetime speed.

[0121] In one embodiment of the invention, when carrying out a selective hydrotreating method for steam-cracked gasoline containing polyunsaturated compounds as feedstock, the (hydrogen) / (polyunsaturated compound to be hydrotreated) molar ratio is typically 0.5 to 10, preferably 0.7 to 5.0, and even more preferably 1.0 to 2.0; the temperature is 0°C to 200°C, preferably 20°C to 200°C, and even more preferably 30°C to 180°C; and the space velocity (HSV) is typically 0.5 h⁻¹. -1 Up to 100h -1 Preferred time: 1 to 50 hours -1 The pressure is typically from 0.3 MPa to 8.0 MPa, preferably from 1.0 MPa to 7.0 MPa, and even more preferably from 1.5 MPa to 4.0 MPa.

[0122] More preferably, the selective hydrogenation method is carried out in which the feedstock is steam-cracked gasoline containing polyunsaturated compounds, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is 0.7 to 5.0, the temperature is 20°C to 200°C, and the hourly space velocity (HSV) is generally 1 h⁻¹. -1 Up to 50h -1 And the pressure is 1.0MPa to 7.0MPa.

[0123] More preferably, the selective hydrogenation method is carried out in which the feedstock is steam-cracked gasoline containing polyunsaturated compounds, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is 1.0 to 2.0, the temperature is 30°C to 180°C, and the hourly space velocity (HSV) is generally 1 h⁻¹. -1 Up to 50h -1 And the pressure is 1.5MPa to 4.0MPa.

[0124] Adjust the hydrogen flow rate to have a sufficient amount available to theoretically hydrogenate all polyunsaturated compounds and maintain an excess of hydrogen at the reactor outlet.

[0125] In another embodiment of the invention, when carrying out a selective hydrogenation method in which the feedstock is a steam cracking C2 fraction and / or a steam cracking C2-C3 fraction containing polyunsaturated compounds, the (hydrogen) / (polyunsaturated compound to be hydrogenated) molar ratio is typically 0.5 to 1000, preferably 0.7 to 800, the temperature is 0°C to 300°C, preferably 15°C to 280°C, and the hourly space velocity (HSV) is typically 100 h⁻¹. -1 Up to 40000h -1 500h preferred -1 Up to 30000h -1 The pressure is typically from 0.1 MPa to 6.0 MPa, preferably from 0.2 MPa to 5.0 MPa.

[0126] 6. Methods for hydrogenating aromatics

[0127] Another subject of the invention is a method for hydrogenating at least one aromatic or polyaromatic compound contained in a hydrocarbon feedstock having a final boiling point of 650°C or lower, typically between 20°C and 650°C, and preferably between 20°C and 450°C. The hydrocarbon feedstock containing at least one aromatic or polyaromatic compound may be selected from the following petroleum or petrochemical fractions: catalytic reformed reformate, kerosene, light gas oil, heavy gas oil, cracked distillate oil, such as FCC cycle oil, coking unit gas oil, or hydrocracking distillate oil.

[0128] The hydrocarbon feedstock processed in the hydrogenation method according to the invention typically contains 0.1% to 80% by weight, preferably 1% to 50% by weight, and particularly preferably 2% to 35% by weight, based on the total weight of the hydrocarbon feedstock. The aromatic compounds present in the hydrocarbon feedstock are, for example, benzene or alkyl aromatics, such as toluene, ethylbenzene, o-xylene, m-xylene, or p-xylene, or also aromatics having multiple aromatic rings (polyaromatics), such as naphthalene.

[0129] The sulfur or chlorine content of the raw material is usually less than 5000 ppm by weight, preferably less than 100 ppm by weight, and particularly preferably less than 10 ppm by weight.

[0130] Technical implementations of the method for hydrogenating aromatic or polyaromatic compounds include injecting a hydrocarbon feedstock as an upstream or downstream and hydrogen into at least one fixed-bed reactor. The reactor can be isothermal or adiabatic. Adiabatic reactors are preferred. The hydrocarbon feedstock can advantageously be diluted by one or more re-injections at various points within the reactor, between the inlet and outlet, of the effluent from the reactor in which the hydrogenation reaction of aromatics occurs, to limit the temperature gradient within the reactor. Technical implementations of the method for aromatic hydrogenation according to the invention can also advantageously be carried out by embedding at least the supported catalyst in a reactive distillation column, a reactor-exchange unit, or a slurry reactor. The hydrogen feedstock can be introduced simultaneously with the feedstock to be hydrogenated and / or introduced at one or more different points within the reactor.

[0131] Hydrogenation of aromatic or polyaromatic compounds can be carried out in the gas phase or liquid phase, preferably in the liquid phase. Typically, hydrogenation of aromatic or polyaromatic compounds from hydrocarbon feedstocks having a final boiling point of 650°C or lower, typically 20°C to 650°C, and preferably 20°C to 450°C, is performed at a temperature of 30°C to 350°C, preferably 50°C to 325°C, at a pressure of 0.1 MPa to 20 MPa, preferably 0.5 MPa to 10 MPa, at a hydrogen / (aromatic compound to be hydrogenated) molar ratio of 0.1 to 10, and over a period of 0.05 h.-1 Up to 50h -1 0.1h is preferred -1 Up to 10h -1 It proceeds at a spacetime speed.

[0132] The hydrogen flow rate is adjusted to have a sufficient amount available to theoretically hydrogenate all aromatic compounds and to maintain an excess of hydrogen at the reactor outlet.

[0133] The conversion rate of 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%. The conversion rate is calculated by dividing the difference between the total number of moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock and the product by the total number of moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock.

[0134] According to a specific alternative form of the method of the present invention, a method for hydrogenating benzene in a hydrocarbon feedstock (e.g., reformate produced by a catalytic reforming unit). The benzene content in the hydrocarbon feedstock is typically from 0.1% to 40% by weight, preferably from 0.5% to 35% by weight, and particularly preferably from 2% to 30% by weight, the weight percentage being based on the total weight of the hydrocarbon feedstock.

[0135] The sulfur or chlorine content of the raw materials is typically less than 10 ppm by weight, and preferably less than 2 ppm by weight.

[0136] The hydrogenation of benzene contained in a hydrocarbon feedstock can be carried out in the gas phase or the liquid phase, preferably in the liquid phase. When carried out in the liquid phase, a solvent, such as cyclohexane, heptane, or octane, may be present. Typically, the hydrogenation of benzene is carried out at a temperature of 30°C to 250°C, preferably 50°C to 200°C, and more preferably 80°C to 180°C, at a pressure of 0.1 MPa to 10 MPa, preferably 0.5 MPa to 4 MPa, at a hydrogen / (benzene) molar ratio of 0.1 to 10, and at a time of 0.05 h⁻¹. -1 Up to 50h -1 0.5h is preferred -1 Up to 10h -1 It proceeds at a spacetime speed.

[0137] The conversion rate of benzene is typically greater than 50 mol%, preferably greater than 80 mol%, more preferably greater than 90 mol%, and particularly preferably greater than 98 mol%.

[0138] The invention will now be illustrated by the following embodiments, which are by no means limiting. Example

[0139] For all catalysts mentioned in the following examples, the support has a specific surface area of ​​80 m². 2Alumina A with a total pore volume (TPV) of 0.7 ml / g and a median mesopore diameter of 12 nm.

[0140] WTV refers to water absorption capacity.

[0141] Example 1: Preparation of Ni precursor aqueous solution containing additives

[0142] The aqueous solution S used to prepare catalysts B to H was prepared by using 43.5 g of nickel nitrate (NiNO3, from supplier Strem). ) and 7.69g of malonic acid (CAS 141-82-2; supplier) It was prepared by dissolving in 13 ml of distilled water. The molar ratio of additive to Ni was fixed at 0.5. A solution S with a Ni concentration of 350 g Ni per liter of solution was obtained.

[0143] Example 1a: Preparation of Ni precursor aqueous solution without additives

[0144] The aqueous solution S' used to prepare catalyst A was prepared by adding 43.5 g of nickel nitrate (NiNO3, from supplier Strem) It is prepared by dissolving in 13 ml of distilled water. A solution S' with a Ni concentration of 350 g Ni per liter of solution is obtained.

[0145] Example 2: Preparation of catalyst A conforming to the present invention [pre-impregnated with 10% by weight Ni-heptanol 25% WTV]

[0146] 10 g of alumina A was impregnated by adding 2.4 ml of n-heptanol. The impregnated support was then aged at 60 °C for 30 minutes. Next, 7.1 ml of solution S' prepared in Example 1a was added dropwise to the impregnated support. The catalyst precursor thus obtained was then dried in an oven at 120 °C for 12 hours, and then calcined at 450 °C for 2 hours with a dry air feed of 1 l / h / g catalyst.

[0147] Catalyst A is obtained containing 10% by weight of nickel relative to the total weight of the catalyst.

[0148] The properties of catalyst A obtained in this way are listed in Table 1 below.

[0149] Example 3: Preparation of catalyst B conforming to the present invention [pre-impregnated with 10% by weight Ni-heptanol 25% WTV + added] [Agent]

[0150] 10g of alumina A was impregnated by adding 2.4ml of n-heptanol. The impregnated support was then aged at 60°C for 30 minutes. Next, 7.1ml of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours with a dry air feed of 1l / h / g catalyst.

[0151] Catalyst B containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0152] The properties of catalyst B obtained in this way are given in Table 1 below.

[0153] Example 4: Preparation of catalyst C conforming to the present invention [pre-impregnated with 5% by weight Ni-heptanol 25% WTV + added] [Agent]

[0154] 10g of alumina A was impregnated by adding 2.4ml of n-heptanol dropwise. The impregnated support was then aged at 60°C for 30 minutes. Next, 3.55ml of solution S prepared in Example 1 was diluted with water to a maximum of 7.1ml and impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained was then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air feed of 1l / h / g catalyst.

[0155] Catalyst C containing 5% by weight of nickel relative to the total weight of the catalyst was obtained.

[0156] The properties of the catalyst C obtained in this way are given in Table 1 below.

[0157] Example 5: Preparation of catalyst D conforming to the present invention [pre-impregnated with 10% by weight Ni-heptanol, 75% WTV + additives] Additives

[0158] 10g of alumina A was impregnated by adding 7.2ml of n-heptanol. The impregnated support was then aged at 60°C for 30 minutes. Next, 2.4ml of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours with a dry air feed of 1l / h / g catalyst.

[0159] Catalyst D containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0160] The properties of the catalyst D obtained in this way are given in Table 1 below.

[0161] Example 6: Preparation of catalyst E that does not conform to the present invention [conventional impregnation with 10% Ni+ additive]

[0162] The solution S prepared in Example 1 was dry-impregnated onto 10 g of alumina by dropwise addition. The resulting catalyst precursor was then dried in an oven at 120 °C for 12 h, and then calcined at 450 °C for 2 h at a dry air feed rate of 1 l / h / g catalyst.

[0163] Catalyst E containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0164] The properties of the catalyst E obtained in this way are given in Table 1 below.

[0165] Example 7: Preparation of catalyst F that does not conform to the present invention [10 wt% Ni-post-impregnated with heptanol 25% WTV]

[0166] The 7.1 ml solution S prepared in Example 1 was dry-impregnated onto 10 g of alumina by dropwise addition. 10 g of the prepared catalyst precursor was impregnated by dropwise addition of 2.4 ml of n-heptanol. The solid was then aged at 60°C for 30 minutes. The resulting solid was subsequently dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours with a dry air feed of 1 L / h / g catalyst.

[0167] Catalyst F containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0168] The properties of the catalyst F obtained in this way are given in Table 1 below.

[0169] Example 8: Preparation of catalyst G that does not conform to the present invention [pre-impregnated with 10% by weight Ni-toluene 25% WTV]

[0170] 10 g of alumina A was impregnated by adding 2.4 ml of toluene dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Next, 7.1 ml of solution S prepared in Example 1 was dropwise impregnated onto the impregnated support. The catalyst precursor thus obtained was then dried in an oven at 120 °C for 12 hours, and then calcined at 450 °C for 2 hours with a dry air feed of 1 L / h / g catalyst.

[0171] Catalyst G containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0172] The properties of the catalyst G obtained in this way are given in Table 1 below.

[0173] Example 9: Preparation of catalyst H that does not conform to the present invention [10 wt% Ni-n-propanol 25% WTV pre-impregnation]

[0174] 10 g of alumina A was impregnated by adding 2.4 ml of n-propanol dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Next, 7.1 ml of solution S prepared in Example 1 was dropwise impregnated onto the impregnated support. The catalyst precursor thus obtained was then dried in an oven at 120 °C for 12 hours, and then calcined at 450 °C for 2 hours under a dry air feed of 1 L / h / g catalyst.

[0175] A catalyst H containing 10% by weight of nickel relative to the total weight of the catalyst was obtained.

[0176] The properties of the catalyst H obtained in this way are given in Table 1 below.

[0177]

[0178]

[0179] Table 1: Characteristics of catalysts A to H

[0180] Example 10: Catalytic Testing: Selective Hydrogenation Performance of a Mixture Containing Styrene and Isoprene (A HYD1 )

[0181] For the selective hydrogenation reaction of a mixture containing styrene and isoprene, catalysts A to H described in the above examples were tested.

[0182] The feedstock composition for selective hydrogenation is as follows: 8% styrene by weight (supplier: Sigma) 99% purity), 8% by weight isoprene (supplier: Sigma) (99% purity) and 84% by weight n-heptane (solvent) (supplier) Purity >99% (Chromanorm HPLC). This raw material also contains very low levels of sulfur compounds: in the form of pentamethylenetetramine (supplier). The purity >97% introduces 10 ppm of sulfur by weight and in the form of thiophene (supplier). 100 ppm by weight of sulfur (99% purity) was introduced. This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of cracked gasoline.

[0183] The selective hydrogenation reaction was 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 a temperature range of 5°C to 200°C.

[0184] Before introducing it into the autoclave, 3 ml of catalyst was subjected to in-situ reduction at 400 °C for 16 hours (temperature gradient of 1 °C / min) with a hydrogen feed rate of 1 L / h / g catalyst. Then, it was transferred to the autoclave and air was removed. 214 ml of n-heptane (supplier) was then added. After achieving a purity >99% (Chromanorm HPLC), the autoclave was shut off, purged, and then pressurized under 35 bar (3.5 MPa) hydrogen gas until a test temperature equal to 30°C was reached. At time t = 0, approximately 30 g of a mixture containing styrene, isoprene, n-heptane, pentylenetetranol, and thiophene was introduced into the autoclave. The reaction mixture then had the above composition and was stirred at 1600 rpm. The pressure in the autoclave was maintained constant at 35 bar (3.5 MPa) using a gas reservoir located upstream of the reactor.

[0185] The reaction progress was monitored by periodically sampling the reaction medium: styrene was hydrogenated to ethylbenzene, while the aromatic rings remained unhydrogenated, and isoprene was hydrogenated to methylbutene. If the reaction was prolonged beyond the desired time, the methylbutene was further hydrogenated to isopentane. Hydrogen consumption could also be monitored over time by the pressure drop in a gas storage tank located upstream of the reactor. Catalytic activity was expressed as the number of moles of H2 consumed per minute and per gram of Ni.

[0186] The catalytic activities measured for catalysts A through H are given in Table 2 below. These are compared with the catalytic activities measured for catalyst E (A...). HYD1 )related.

[0187] Example 11: Catalytic Testing: Toluene Hydrogenation Performance (A) HYD2 )

[0188] Catalysts A to H described in the above examples were also tested for the toluene hydrogenation reaction.

[0189] The selective hydrogenation reaction was carried out in the same autoclave as described in Example 9.

[0190] Before introducing it into the autoclave, 2 ml of the catalyst was in vitro reduced at 400 °C for 16 hours (temperature gradient of 1 °C / min) with a hydrogen feed flow of 1 L / h / g catalyst. Then, it was transferred to the autoclave and air was removed. 216 ml of n-heptane (supplier) was then added. After achieving a purity >99% (Chromanorm HPLC), the autoclave was shut off, purged, and then pressurized under 35 bar (3.5 MPa) hydrogen gas until the test temperature of 80°C was reached. At time t = 0, approximately 26 g of toluene (from the supplier) was added. The mixture (purity > 99.8%) was introduced into the autoclave (so the initial composition of the reaction mixture was 6 wt% toluene / 94 wt% n-heptane) and stirred at 1600 rpm. The pressure in the autoclave was kept constant at 35 bar (3.5 MPa) using a gas cylinder located upstream of the reactor.

[0191] The reaction process was monitored by periodically sampling the reaction medium: toluene was completely hydrogenated to yield methylcyclohexane. Hydrogen consumption could also be monitored over time by the pressure drop in a gas storage tank located upstream of the reactor. Catalytic activity was expressed as the number of moles of H2 consumed per minute and per gram of Ni.

[0192] The catalytic activities measured for catalysts A through H are given in Table 2 below. These are compared with the catalytic activities measured for catalyst E (A...). HYD2 )related.

[0193] A (Complies) 10 105 110 B (Complies) 10 170 200 C (Complies) 5 130 160 D (Complies) 10 185 220 E (Does not comply) 10 100 100 F (Does not comply) 10 50 50 G (Does not conform) 10 70 80 H (Does not comply) 10 95 98

[0194] Table 2: Selective hydrogenation of catalysts A to H in mixtures containing styrene and isoprene (A HYD1 ) and the hydrogenation of toluene (A HYD2 Performance comparison in terms of

[0195] These examples clearly demonstrate the improved performance of catalysts A, B, C, and D according to the invention compared to catalysts E, F, G, and H, which do not conform to the invention. This is because nickel is distributed within the shell of catalysts A, B, C, and D, which significantly enhances their activity, particularly in rapid hydrogenation reactions. Although catalyst A remains quite effective due to its larger particle size (8 nm) resulting from the absence of malonic acid, the nickel is well distributed within the shell and therefore readily penetrates. Catalyst E exhibits lower activity because conventional impregnation is carried out without heptanol pre-impregnation. Catalyst F undergoes post-impregnation with heptanol, which does not allow for the shell distribution of nickel. Catalyst G is prepared via a pre-impregnation step with toluene. Therefore, although toluene is not highly miscible with water (as in the case of heptanol), the absence of -OH groups in the molecule prevents it from strongly interacting with the -OH groups of the alumina support, which can explain the migration of toluene through the water contained in the nickel nitrate solution during the nickel impregnation step. In the case of propanol, the -OH groups appear to enable it to reach the core of the support and interact with it. On the other hand, due to the high miscibility of water and n-propanol, unlike the heptanol / water pair, and considering the physicochemical properties of the final catalyst and the results of catalytic testing, the nickel nitrate aqueous solution appears to have undergone diffusion into the core. Therefore, for catalysts F, G, and H, nickel is uniformly distributed throughout the catalyst particles. Therefore, regarding A... HYD1 and A HYD2 In comparison, catalysts F and G exhibit significantly lower activity than catalyst A. Catalyst G shows lower activity due to the disruption of nickel nitrate impregnation caused by the presence of toluene.

Claims

1. A method for preparing a catalyst comprising a nickel-based active phase and an alumina support, said catalyst comprising 1% to 50% by weight of elemental nickel relative to the total weight of said catalyst, said nickel being distributed on a shell surrounding the support and at the core of said support, said shell having a thickness of 2% to 15% of the diameter of said catalyst, said catalyst having nickel particles in oxide form having a size of less than 15 nanometers, said method comprising the following steps: a) Impregnate the carrier with a heptanol solution of volume V1 to obtain an impregnated carrier, wherein the volume V1 is 0.2 to 0.8 times the total pore volume (TPV) of the carrier; b) Impregnate the impregnated support obtained at the end of step a) with a solution containing at least one nickel active phase precursor to obtain a catalyst precursor; c) Dry the catalyst precursor obtained at the end of step b) at a temperature below 250°C. The nickel density ratio between the shell and the core is greater than 3 and less than or equal to 15.

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

3. The method according to claim 1, characterized in that... Step c) lasts for 0.5 to 12 hours.

4. The method according to any one of claims 1 to 3, characterized in that, It further includes 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 performed for 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 carrier.

7. The method according to any one of claims 1 to 3, wherein in step a), a solution of n-heptanol is used.

8. The method according to any one of claims 1 to 3, wherein step b1) is performed, wherein 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 functional group, or at least one alcohol functional group, or at least one ester functional group, or at least one amide functional group, or at least one amine functional group, and steps b) and b1) are performed in any order or simultaneously.

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

10. The method according to claim 8, wherein step b) and step b1) are performed simultaneously.

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

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

13. The method according to claim 8, wherein the organic compound in step b1) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, malonic acid, citric acid, tartaric acid, pyruvic acid, acetylpropionic acid, ethylene glycol, 1,3-propanediol, 1,4-butanediol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, γ-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylformamide, γ-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, and EDTA.

14. The method of claim 13, wherein the γ-lactam comprises 2-pyrrolidone.

15. The method according to any one of claims 1 to 3, wherein step a1) is performed, wherein the impregnated carrier obtained at the end of step a) is left to mature for 0.5 hours to 40 hours.

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

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