Process for preparing catalyst comprising active nickel phase distributed in shell layer via decanol impregnation

Abstract

The invention relates to a method for preparing a catalyst comprising an active nickel phase and an alumina support, said catalyst comprising 1 to 50 wt%, relative to the total weight of the catalyst, of elemental nickel, said nickel being distributed in the shell layer of the periphery of the support and in the core of the support, the process comprises the steps of: a) impregnating the support with a decanol solution having a volume V1 of 0.2 to 0.8 times the total pore volume TPV of the support to obtain an impregnated support; b) impregnating the impregnated support obtained at the end of step a) with a solution comprising a precursor of an active nickel phase to obtain a catalyst precursor; and c) drying the catalyst precursor obtained at the end of step b) at a temperature of less than 250 DEG C.

Description

Technical Field

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

[0002] Monounsaturated organic compounds, such as ethylene and propylene, are sources for the production of polymers, plastics, and other value-added chemicals. These compounds are derived from natural gas, naphtha, or gas oil processed by steam cracking or catalytic cracking. 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, particularly styrene or indene, whose boiling points correspond to C5+ gasoline fractions (gasoline containing hydrocarbons with five or more carbon atoms). These polyunsaturated compounds are highly reactive and cause side reactions in polymerization units. Therefore, they must be removed before upgrading these fractions. Selective hydrogenation is a major process developed specifically to remove undesirable polyunsaturated compounds from these hydrocarbon feedstocks. It enables the conversion of polyunsaturated compounds into the corresponding olefins or aromatics while avoiding their 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 important criteria for the activity and selectivity of the catalyst.

[0004] In rapid and continuous reactions, such as selective hydrogenation, the macroscopic distribution of metal particles within the support constitutes an important criterion. Ideally, these elements should be located in a shell on the outer periphery of the support to avoid intraparticle material transfer problems that could lead to activity defects and selectivity loss. Such catalysts are also known as "eggshell" catalysts.

[0005] Such catalysts are known in the case of palladium-based selective hydrogenation catalysts. This is because, due to the low palladium content (typically less than 1 wt% palladium relative to the catalyst) and suitable preparation methods, a thin palladium shell layer on the periphery of the support particles can be obtained (FR 2 922 784, US2010 / 217052).

[0006] It is frequently proposed to replace palladium with nickel, a metal with lower reactivity than palladium, and therefore it must be provided in a larger quantity in the catalyst. Consequently, nickel-based catalysts typically have a nickel content of 5 to 50% by weight relative to the catalyst. In these catalysts, nickel is usually uniformly distributed within the support. One possible way to improve the activity and selectivity of these catalysts is to control the distribution of nickel within the support by depositing it more concentratedly on a shell on the outer periphery of the support. Such catalysts are known in the prior art.

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

[0008] Document CN101890351 describes a supported nickel catalyst in which more than 90% of the nickel is contained in a shell with a thickness of 700 μm. The catalyst is prepared by dissolving the nickel salt using an ammonia solution. These catalysts are used for selective hydrogenation applications.

[0009] Document US 2012 / 0065442 describes a supported catalyst in which nickel is distributed both in a shell layer with a thickness of 3% to 15% of the diameter and in the core, with a nickel concentration ratio between the shell and the core ranging from 3.0:1 to 1.3:1. The nickel active phase is deposited by spraying an ammonia solution of nickel salt onto a support.

[0010] Reference FR 3099387 describes a method for preparing a nickel-based catalyst on an alumina support obtained according to a very specific method, wherein nickel is distributed both in a shell on the outer periphery of the support and in the core of the support, the thickness of which is 2% to 15% of the catalyst diameter. The method for preparing this catalyst requires, on the one hand, the use of a specific alumina support that has already undergone hydrothermal treatment in the presence of an acidic solution, and on the other hand, a hydrothermal treatment stage following the addition of specific organic additives to the catalyst precursor.

[0011] Applications WO2021239497, WO2023001641, and WO2023001642 disclose nickel-based catalysts on an alumina support, with nickel distributed as a shell on the periphery of the support and in the core of the support, obtained by a very specific preparation method comprising an impregnation stage upstream of a stage of impregnation with a nickel-based active phase precursor with solutions based on butanol, hexanol, and heptanol, respectively. However, these organic compounds are difficult to use on an industrial scale due to their high volatility and flammability; butanol has a flash point of 29°C, hexanol 63°C, and heptanol 70°C, all significantly lower than the Category 4 ATEX limit of 93°C according to the Globally Harmonized System (GHS).

[0012] Invention Theme Surprisingly, the applicant company has discovered that a specific stage of impregnation with decanol solution on a porous alumina support enables the production of catalysts in which at least a portion of the nickel is distributed in a shell on the outer periphery of the support, and another portion in the core of the catalyst, regardless of the source of the support, and without an intermediate drying stage between impregnation with decanol and impregnation with the nickel active phase precursor. While not wishing to be bound by any single theory, the presence of decanol prevents the migration of the nickel active phase into the core of the support. In fact, only a portion of the pores are occupied by decanol. Furthermore, since decanol and water are not very miscible, the decanol layer constitutes a barrier to the diffusion of nickel into the core of the support.

[0013] This invention therefore relates to a novel method for preparing catalysts that enables the acquisition of catalysts with at least as good, or even better, performance qualities in terms of activity and selectivity as those of the prior art in the selective hydrogenation of polyunsaturated compounds or aromatics, while using a lower effective amount of nickel phase than typically used in the prior art (i.e., the amount of nickel ultimately located in the shell surrounding the support to enable the selective hydrogenation of polyunsaturated compounds or aromatics). This is due to a better distribution of the nickel active phase in the support, making it easier for reactants to access the nickel active phase. Furthermore, the use of decanol as an organic compound in the catalyst preparation process limits flammability and volatility issues, as its flash point is 108°C according to standard ASTM D93, which is significantly higher than the Category 4 ATEX limit of 93°C according to the Globally Harmonized System (GHS), thus limiting safety concerns during catalyst synthesis.

[0014] One subject of this 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 on a shell layer on the outer periphery of the support and at the core of the support, said shell layer having a thickness between 2% and 15% of the diameter of said catalyst, and said nickel particles in said catalyst having a size less than 15 nm as measured in oxide form, said method comprising the following stages: a) Impregnate the carrier with a solution of decanol in a volume V1 of 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) Impregnate the impregnated support obtained at the end of stage a) with a solution containing at least one precursor of nickel active phase to obtain a catalyst precursor; c) Dry the catalyst precursor obtained at the end of stage b) at a temperature below 250°C.

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

[0016] According to one or more implementation schemes, phase c) lasts for 0.5 to 12 hours.

[0017] According to one or more embodiments, the method further includes stage d), wherein the catalyst obtained at the end of stage c) is calcined at a temperature between 250°C and 600°C.

[0018] According to one or more implementation schemes, phase d) lasts for 0.5 to 24 hours.

[0019] According to one or more embodiments, in stage a), the volume V1 of the decanol solution is between 0.25 and 0.75 times the total pore volume TPV of the carrier.

[0020] According to one or more implementation schemes, in stage a), a solution of n-decyl alcohol is used.

[0021] According to one or more embodiments, the method further includes stage b1), wherein the impregnated support obtained at the end of stage a) or the catalyst precursor obtained at the end of stage 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 stages b) and b1) are performed in any order or simultaneously.

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

[0023] According to one or more implementation schemes, phases b) and b1) are carried out simultaneously.

[0024] According to one or more embodiments, the volume V2' of the solution containing at least one precursor of nickel active phase and at least one organic compound impregnated on the impregnation carrier at the end of stage a) is such that V2' = TPV - V1.

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

[0026] According to one or more embodiments, the organic compound in stage b1) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, malonic acid, citric acid, tartaric acid, pyruvic acid, acetylpropionic acid, ethylene glycol, propylene-1,3-diol, butane-1,4-diol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, γ-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylformamide, 2-pyrrolidone, γ-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, or EDTA.

[0027] According to one or more embodiments, stage a1) is performed, wherein the impregnated carrier obtained at the end of stage a) is aged 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] Attached Figure Description Figure 1 This is a graph showing the distribution of nickel in the catalyst. The x-axis corresponds to the thickness of the catalyst (in µm) measured from the edge. The y-axis corresponds to the nickel density (in grams of Ni / mm²). 3 (Calculated). Nickel is distributed both in the outer shell of the support with a thickness of th1 and in the core of the support. The nickel density d in the shell is... 壳层 The nickel density d at the core of the support is greater than that at the core. 核 The transition space between the core and shell of the catalyst has a thickness denoted as th2 - th1. Invention Details 1. Definition In the following text, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, CRC Press, ed. DR. Lide, 81st edition, 2000-2001). For example, Group VIII according to the CAS classification corresponds to the metals in columns 8, 9, and 10 according to the new IUPAC classification.

[0031] In this specification, in accordance with 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 or equal to 2 nm, i.e., 0.002 µm and less than or equal to 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.

[0032] 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 apparatus used was a CAMECA XS100 equipped with four crystal monochromators to enable simultaneous analysis of four elements. Castaing microprobe analysis involves detecting the X-rays emitted by the solid after the elements are excited by a high-energy electron beam. For this characterization requirement, catalyst particles were encapsulated in epoxy resin blocks. These blocks were polished to a cross-section reaching the diameter of the beads or extrusions, and then metallized by depositing carbon in a metal evaporator. An electron probe was scanned along the diameter of five beads or extrusions to obtain an average distribution profile of the constituent elements of the solid. In the publication by L. Sorbier et al., “ Measurement of palladium crust thickness on catalyst by EPMA This method, well-known to those skilled in the art, is defined in Materials Science and Engineering, 32 (2012). It enables the establishment of a distribution curve of a given element (in this case, nickel) within the grain. Furthermore, the Ni concentration is defined for each measurement and therefore also for each analytical step. Thus, the Ni density within the grain is defined as per mm². 3 Ni concentration.

[0033] Total pore volume is measured according to standard ASTM D4284-92 with a wetting angle of 140°, for example using a Micromeritics™ Autopore III™ device via mercury porosimetry.

[0034] BET specific surface area was measured by nitrogen physical adsorption according to standard ASTM D3663-03, in a work by Rouquerol F., Rouquerol J., and Singh K. Adsorption by Powders and Porous Solids:Principles, Methodology and Applications The method described in Academic Press, 1999.

[0035] The term “nickel particle size” is understood to refer to the diameter of nickel crystallites in the form of nickel oxide. The diameter of nickel crystallites in the form of nickel oxide is determined by X-ray diffraction using the Scherrer relation from the width of the diffraction line located at an angle of 2θ = 43° (i.e., along the crystallographic direction

[200] ). This method used in X-ray diffraction for polycrystalline samples or powders (which correlates the full width at half maximum (FWHM) of the diffraction peaks with the particle size) is described in detail in the following references: Appl. Cryst. (1978), 11, 102-113, “Scherrer after sixty years: A survey and some new results in the determination of crystallite size”, JI Langford and AJC Wilson.

[0036] Nickel content was measured using X-ray fluorescence.

[0037] 2. Methods for preparing catalysts The stages of the preparation method are described in detail below.

[0038] Phase a) According to stage a) of the method, the alumina carrier is impregnated with a decanol solution of 0.2 to 0.8 times, preferably 0.25 to 0.75 times, the total pore volume (also referred to as TPV) of the carrier to be impregnated.

[0039] Decanol is understood to refer to substances containing the C10 ... 10 H 22 Organic compounds with an alcohol functional group of O, such as dec-1-ol (or n-decyl alcohol), dec-2-ol and their isomers. Preferably, stage a) is carried out in the presence of dec-1-ol.

[0040] Phase a1) (Optional) Following stage a), the impregnated support can be aged in a wet state for 0.5 to 40 hours, preferably 1 to 30 hours. The aging stage a1) is preferably carried out at a temperature of 60°C or less, more preferably at ambient temperature. This stage allows the decanol solution to migrate into the core of the support. During this stage, aging stage a1) enhances the migration of the decanol solution into the core of the support and releases a ring of free pores at the periphery of the support, which was accessible to nickel during the active phase precursor impregnation stage.

[0041] Phase b) During stage b) of the method, the impregnated porous alumina support obtained at the end of stage a) (or the matured impregnated porous alumina support obtained at the end of stage a1) is impregnated with a solution containing at least one precursor of nickel active phase to obtain a catalyst precursor. This impregnation stage can be carried out by dry impregnation or over-impregnation according to methods known to those skilled in the art.

[0042] The pH of the solution containing at least one precursor of the impregnated nickel active phase can be altered by optionally adding an acid or a base.

[0043] Preferably, the nickel precursor is introduced into an aqueous solution, for example, in the form of a nitrate, carbonate, acetate, chloride, or oxalate, in the form of a complex formed from a polybasic acid or alcohol and its salt, in the form of a complex formed with an acetylacetonate, or in the form of any other inorganic derivative soluble in aqueous solution, thereby contacting it 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.

[0044] The nickel concentration in the solution is adjusted according to the pore volume of the still available support to obtain an elemental nickel content of between 1% and 50% by weight relative to the total weight of the catalyst for the supported catalyst, more preferably between 2% and 40% by weight, and even more preferably between 3% and 35% by weight, and even more preferably between 5% and 25% by weight.

[0045] Phase b1) (Optional) When stage b1) is performed, the impregnated porous alumina support obtained at the end of stage a) (or the aged impregnated porous alumina support obtained at the end of stage a1) or the catalyst precursor obtained at the end of stage b) is impregnated with a solution containing at least one organic compound, wherein the organic compound comprises 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, wherein stages b) and b1) are performed in any order or simultaneously.

[0046] This impregnation stage can be carried out by dry impregnation or over-impregnation, methods known to those skilled in the art. This is because it has also been noted that catalysts prepared in the presence of organic compounds (mentioned below) are more active than those prepared in the absence of such organic compounds. This effect is related to the reduction in the size of the nickel particles.

[0047] 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.

[0048] Advantageously, the molar ratio of the organic compound introduced in stage b1) to the element nickel also introduced in stage 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.

[0049] 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.

[0050] 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.

[0051] Advantageously, the organic compound containing at least one carboxylic acid functional group is selected from oxalic acid, malonic acid, pentanedioic acid, glycolic acid, 2-hydroxypropionic acid, 2-hydroxymalonic acid, 2-hydroxypropionic acid, 2-hydroxypropionic acid, citric acid, 2,3-dihydroxysuccinic acid, tartaric acid, 2-oxopropionic acid, and 4-oxovalerate.

[0052] Implementation of phases b) and b1) The preparation methods of nickel catalysts can include several implementation schemes. The difference between them lies in the order of introducing the organic compound and the nickel precursor. The operation of contacting the organic compound with the support can be carried out after the nickel precursor is contacted with the impregnated support obtained at the end of stage a) (or a1)), or before the nickel precursor is contacted with the impregnated support obtained at the end of stage a) (or a1)), or simultaneously with the contact of the nickel precursor with the impregnated support obtained at the end of stage a) (or a1)).

[0053] The first implementation involves performing stage b) (post-impregnation) prior to stage b1).

[0054] The second implementation involves performing stage b1) (pre-impregnation) prior to stage b).

[0055] Each stage b) and b1) of impregnating the impregnating carrier with a nickel precursor and impregnating (optionally aging) the impregnating carrier with at least one solution containing at least one organic compound comprising at least one carboxylic acid functional group is performed at least once, and may advantageously be performed several times, optionally in the presence of the same or different nickel precursors and / or organic compounds in each stage b) and / or b1), and all possible combinations of the implementation of stages b) and b1) are included within the scope of the invention.

[0056] Preferably, at the end of stage a), the volume V2 of the solution containing at least one precursor of nickel active phase and the volume V3 of the solution containing at least one organic compound impregnated on the optionally cured impregnation carrier are such that V2 + V3 = TPV - V1.

[0057] A third embodiment involves simultaneously performing stage b) and stage b1) (co-impregnation). This embodiment may advantageously include performing one or more stages b), optionally using the same or different nickel precursors in each stage b). In particular, it is advantageous to perform one or more stages b) before and / or after the co-impregnation stages, optionally using the same or different nickel precursors in each stage. This embodiment may also include multiple co-impregnation stages: stages b) and b1) are performed multiple times simultaneously, optionally in the presence of the same or different nickel precursors and / or organic compounds in each co-impregnation stage.

[0058] Preferably, stages b) and b1) are performed simultaneously. Preferably, the volume V2' of the solution containing at least one precursor and at least one organic compound impregnated on the support at the end of stage a) (or a1) is such that V2' = TPV - V1.

[0059] Phase c) The drying stage 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, typically for 0.5 hours to 12 hours, and even more preferably for 0.5 hours to 5 hours. Longer times are not excluded, but do not necessarily lead to improvements.

[0060] The drying stage 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, this stage is carried out at atmospheric pressure and in the presence of air or nitrogen.

[0061] At the end of stage c), the complete or partial presence or absence of the decanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the selective hydrogenation of polyunsaturated compounds or aromatic compounds.

[0062] Phase d) (Optional) The calcination stage d) can be carried out at a temperature between 250°C and 600°C, preferably between 350°C and 550°C, for a time typically between 0.5 hours and 24 hours, preferably between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 10 hours, preferably under an inert atmosphere or an oxygen-containing atmosphere. Longer times are not excluded, but do not necessarily lead to improvements.

[0063] At the end of stage d), the complete or partial presence or absence of the decanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the selective hydrogenation of polyunsaturated compounds or aromatic compounds.

[0064] Phase e) (Optional) Before using the catalyst in the catalytic reactor and implementing the hydrogenation process, it is advantageous to carry out at least one reduction treatment stage e) in the presence of a reducing gas after stage c) or d) to obtain a catalyst containing nickel in at least part of its metallic form.

[0065] This treatment makes it possible to activate the catalyst and form metal particles, particularly nickel particles in the zero-valence state. The reduction treatment can be carried out in situ or ex-situ, i.e., after or before the catalyst is loaded into the hydrogenation reactor.

[0066] 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, all proportions can be considered.

[0067] The reduction treatment is carried out at a temperature between 120°C and 500°C, preferably between 150°C and 450°C. When the catalyst has not undergone passivation or has undergone reduction treatment prior to passivation, the reduction treatment is carried out at a temperature between 180°C and 500°C, preferably between 200°C and 450°C, and even more preferably between 350°C and 450°C. When the catalyst has been pre-passivated, the reduction treatment is typically carried out at a temperature between 120°C and 350°C, preferably between 150°C and 350°C.

[0068] The duration of the reduction treatment is typically between 2 and 40 hours, preferably between 3 and 30 hours. The temperature is typically increased slowly to the desired reduction temperature, for example, set between 0.1°C / min and 10°C / min, preferably between 0.3°C / min and 7°C / min.

[0069] The hydrogen flow rate, expressed in liters per hour per gram of catalyst, is between 0.01 and 100 liters per hour per gram of catalyst, preferably between 0.05 and 10 liters per hour per gram of catalyst, and even more preferably between 0.1 and 5 liters per hour per gram of catalyst.

[0070] 3. Catalyst The preparation method according to the present invention enables the preparation of a catalyst comprising a nickel-based active phase and an alumina support, 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 on the outer periphery of the support and at the core of the support, the thickness of the shell (also referred to as th1) being between 2% and 15% of the catalyst diameter, and the size of the nickel particles in the catalyst, measured in oxide form, being less than 15 nm.

[0071] Preferably, nickel is distributed on the outer shell of the support and in the core of the support, and the thickness of the shell (also known as th1) is between 2% and 15% of the catalyst diameter, preferably between 2.5% and 12% of the catalyst diameter, more preferably between 3% and 10% of the catalyst diameter, and even more preferably between 3% and 7.5% of the catalyst diameter.

[0072] Preferably, the nickel density ratio between the shell and the core (also referred to as d in this case) 壳层 / d 核 It is strictly greater than 3, preferably greater than 3.5, and more preferably between 3.8 and 15.

[0073] Preferably, the shell contains more than 25% by weight of elemental nickel relative to the total weight of elemental nickel contained in the catalyst, more preferably more than 40% by weight, more preferably between 45% and 90% by weight, and even more preferably between 60% and 90% by weight.

[0074] Advantageously, the transition interval between the core and shell of the catalyst (also referred to in this case as the core / shell transition interval, or according to the change in nickel density measured along the catalyst thickness from the catalyst edge to the catalyst center) is related to the change in nickel density along the catalyst thickness. Figure 1 The transition from th2 to th1 is very steep. Preferably, the core / shell transition interval is between 0.05% and 3% of the catalyst diameter, more preferably between 0.5% and 2.5% of the catalyst diameter.

[0075] The nickel content in the catalyst is advantageously between 1% by weight and 50% by weight relative to the total weight of the catalyst, more preferably between 2% by weight and 40% by weight, and even more preferably between 3% by weight and 35% by weight, and even more preferably between 5% by weight and 25% by weight relative to the total weight of the catalyst. The "% by weight" value is based on the elemental form of nickel.

[0076] 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, and the nickel concentration in the core of the support is not zero.

[0077] The specific surface area of ​​this catalyst is typically in the range of 10 m². 2 / g to 350 m 2 Between / g, preferably between 25 m 2 / g to 300 m 2 Between / g, and more preferably between 40 m 2 / g to 250 m 2 Between / g.

[0078] The total pore volume of the catalyst is typically 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.

[0079] 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 more preferably less than 10 nm. When performing stage b1) of the method according to the invention, 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.

[0080] The active phase of this catalyst does not contain Group VIB metals. In particular, it does not contain molybdenum or tungsten.

[0081] The catalyst (and the support for preparing the catalyst) is advantageously in particulate form having a diameter between 0.5 mm and 10 mm. The particles can have any form known to those skilled in the art, such as beads (preferably having a diameter between 1 mm and 8 mm), extrusions, flakes, or hollow cylinders. Preferably, the catalyst (and the support for preparing the catalyst) is in extrusion form having a diameter 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 between 0.5 mm and 20 mm. The term "diameter" for extrusions is understood to refer to the diameter of the circle circumscribed in the cross-section of these extrusions. The catalyst can advantageously be in the form of cylindrical, multi-lobed, trilobed, or tetralobed extrusions. Preferably, it is trilobed or tetralobed. The shape of the lobes can be adjusted according to any method known in the art.

[0082] 4. Carrier The characteristics of alumina mentioned in this section correspond to the characteristics of alumina prior to stage a) of the preparation method according to the invention.

[0083] The support is alumina, meaning that the support contains at least 95% by weight, preferably at least 98% by weight, and particularly preferably at least 99% by weight of alumina relative to the weight of the support. Alumina typically exhibits a crystal structure of the δ-, γ-, or θ-alumina type, either alone or as a mixture.

[0084] The alumina support may contain impurities such as oxides of metals classified according to CAS Groups IIA, IIIB, IVB, IIB, IIIA and IVA, 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.

[0085] The BET specific surface area of ​​alumina is typically around 10 m². 2 / g to 400 m 2 Between / g, preferably 30 m 2 / g to 350 m 2 Between / g, and more preferably between 50 m 2 / g to 300 m 2 Between / g.

[0086] The total pore volume of alumina is typically 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.

[0087] 5. Selective hydrogenation method 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-based compounds), containing at least two carbon atoms per molecule in a hydrocarbon feedstock having a final boiling point less than or equal to 300°C. The method is carried out at a temperature between 0°C and 300°C, at a pressure between 0.1 MPa and 10 MPa, and when the method is carried out in the liquid phase, at a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio between 0.1 and 10, and for 0.1 h. -1 Up to 200 h -1 At space-time velocities between 0.5 and 1000, or when the method is carried out in the gas phase, at hydrogen / (polyunsaturated compound to be hydrogenated) molar ratios between 0.5 and 1000 and 100 h⁻¹ -1 Up to 40,000 h -1 The process is carried out at spacetime velocities between these values ​​in the presence of a catalyst obtained by the preparation method described above.

[0088] Monounsaturated organic compounds, such as ethylene and propylene, are sources for the manufacture of polymers, plastics, and other value-added chemicals. These compounds are derived from natural gas, naphtha, or gas oil processed by steam cracking or catalytic cracking. 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 the C5+ fraction (hydrocarbon compounds with at least 5 carbon atoms), particularly dienes, styrene, or indene compounds. These polyunsaturated compounds are highly reactive and cause side reactions in the polymerization unit. Therefore, they must be removed before these fractions are upgraded.

[0089] Selective hydrogenation is a primary process developed to specifically remove undesirable polyunsaturated compounds from these hydrocarbon feedstocks. It enables the conversion of polyunsaturated compounds into the corresponding olefins or aromatics while avoiding their complete saturation and the resulting formation of alkanes or cycloalkanes. In the case of steam-cracked gasoline used as feedstock, selective hydrogenation can also selectively hydrogenate alkenyl aromatics into aromatics while avoiding the hydrogenation of aromatic rings.

[0090] The hydrocarbon feedstock processed in selective hydrogenation has a final boiling point of less than or equal to 300°C, contains at least two carbon atoms per molecule, and comprises at least one polyunsaturated compound. The term "polyunsaturated compound" is understood to refer to 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.

[0091] More specifically, the feedstock is selected from C2 steam cracking fraction, C2-C3 steam cracking fraction, C3 steam cracking fraction, C4 steam cracking fraction, C5 steam cracking fraction, and steam cracking gasoline, also known as pyrolytic gasoline or C5+ fraction.

[0092] C2 steam cracking fractions advantageously used for carrying out the selective hydrogenation process 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 C2 steam cracking fractions, 0.1% to 1% by weight of C3 compounds may also be present.

[0093] The C3 steam cracking fractions advantageously used for implementing the selective hydrogenation process according to the invention exhibit, for example, the following average composition: approximately 90 wt% propylene and approximately 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.

[0094] The C2-C3 fraction can also be advantageously used to implement the selective hydrogenation process according to the invention. It exhibits, for example, the following composition: approximately 0.1% to 5% by weight of acetylene, approximately 0.1% to 3% by weight of propadiene and methylacetylene, approximately 30% by weight of ethylene and approximately 5% by weight of propylene, with the remainder being primarily methane, ethane, and propane. This feedstock may also contain 0.1% to 2% by weight of C4 compounds.

[0095] The C4 steam cracking fraction advantageously used for carrying out the selective hydrogenation process 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.

[0096] The C5 steam cracking 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.

[0097] The vapor-cracked gasoline or pyrolysis gasoline advantageously used for carrying out the selective hydrogenation process according to the invention corresponds to hydrocarbon fractions with boiling points generally between 0°C and 300°C, preferably between 10°C and 250°C. The vapor-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 vapor-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, totaling 100% compounds. It also contains 0 to 1000 ppm by weight of sulfur, preferably 0 to 500 ppm by weight of sulfur.

[0098] Preferably, the polyunsaturated hydrocarbon feedstock processed by the selective hydrogenation method according to the present invention is a C2 steam cracking fraction, a C2-C3 steam cracking fraction, or a steam cracking gasoline.

[0099] The selective hydrogenation method according to the 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 objective is to remove butadiene, vinylacetylene (VAC), and butyne; in the case of a C5 fraction, the objective is to remove pentadiene. When the feedstock is vapor-cracked gasoline, the selective hydrogenation method aims to selectively hydrogenate the polyunsaturated hydrocarbons present in the feedstock to be treated to partially hydrogenate diene compounds to monoolefins and partially hydrogenate styrene and indene compounds to the corresponding aromatic compounds, while avoiding the hydrogenation of aromatic rings.

[0100] The selective hydrogenation process is implemented, for example, by injecting a polyunsaturated hydrocarbon feedstock and hydrogen as an upward or downward feedstream 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 re-injecting the effluent from the reactor where the selective hydrogenation reaction occurs at various points in the reactor located between the reactor inlet and outlet, thereby limiting the temperature gradient in the reactor. The selective hydrogenation process according to the invention can also advantageously be carried out by implanting at least the supported catalyst in a reactive distillation column, an exchanger reactor, or a slurry reactor. The hydrogen feedstream can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0101] Selective hydrogenation of C2, C2-C3, C3, C4, C5, and C5+ steam cracking fractions can be carried out in the gas phase or the liquid phase. For C3, C4, C5, and C5+ fractions, the liquid phase is preferred, while for C2 and C2-C3 fractions, the gas phase is preferred. Liquid-phase reactions have the potential to reduce energy costs and increase catalyst cycle time.

[0102] Typically, 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 carried out at temperatures between 0°C and 300°C, pressures between 0.1 MPa and 10 MPa, and for methods carried out in the liquid phase, a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio between 0.1 and 10, and a 0.1 h⁻¹ ... -1 Up to 200 h -1 The space velocity (defined as the ratio of feed volume flow rate to catalyst volume) between 0.5 and 1000, or for methods carried out in the gas phase, at 100 h⁻¹. -1 Up to 40,000 h -1 It proceeds at the spacetime speed between them.

[0103] In one embodiment of the invention, when selective hydrogenation of gasoline containing polyunsaturated compounds as feedstock is carried out, the (hydrogen) / (polyunsaturated compound to be hydrogenated) molar ratio is typically between 0.5 and 10, preferably between 0.7 and 5.0, more preferably between 1.0 and 2.0, the temperature is between 0°C and 200°C, preferably between 20°C and 200°C, more preferably between 30°C and 180°C, and the space velocity (HSV) is typically between 0.5 h⁻¹. -1 Up to 100 h -1 Between, preferably within 1 hour -1 Up to 50 h -1The pressure is typically 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.

[0104] More preferably, selective hydrogenation is carried out, wherein the feedstock is vapor-cracked gasoline containing polyunsaturated compounds, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is between 0.7 and 5.0, the temperature is between 20°C and 200°C, and the space velocity (HSV) is typically between 1 h⁻¹. -1 Up to 50 h -1 The pressure is between 1.0 MPa and 7.0 MPa.

[0105] More preferably, selective hydrogenation is carried out, wherein the feedstock is vapor-cracked gasoline containing polyunsaturated compounds, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is between 1.0 and 2.0, the temperature is between 30°C and 180°C, and the hourly space velocity (HSV) is typically between 1 h⁻¹. -1 Up to 50 h -1 The pressure is between 1.5 MPa and 4.0 MPa.

[0106] The hydrogen flow rate is adjusted to provide a sufficient amount of hydrogen to theoretically hydrogenate all polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

[0107] In another embodiment of the invention, when selective hydrogenation is carried out where the feedstock is a steam-cracked C2 fraction and / or a steam-cracked C2-C3 fraction containing polyunsaturated compounds, the (hydrogen) / (polyunsaturated compound to be hydrogenated) molar ratio is typically 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, and the hourly space velocity (HSV) is typically between 100 h⁻¹. -1 Up to 40,000 h -1 Between, preferably within 500 h -1 Up to 30,000h -1 The pressure is typically between 0.1 MPa and 6.0 MPa, preferably between 0.2 MPa and 5.0 MPa.

[0108] 6. Hydrogenation methods for aromatics Another subject of the invention is a hydrogenation method for a hydrocarbon feedstock containing at least one aromatic or polyaromatic compound, having a final boiling point of less than or equal to 650°C, 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: reformate from catalytic reforming, kerosene, light gas oil, heavy gas oil, cracked distillate oils such as FCC cycle oil, coking unit gas oil, or hydrocracking distillate oil.

[0109] The content of aromatic or polyaromatic compounds in the hydrocarbon feedstock processed in the hydrogenation method according to the invention is typically between 0.1% by weight and 80% by weight, preferably between 1% by weight and 50% by weight, and particularly preferably between 2% by weight and 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 aromatics having several aromatic rings (polycyclic aromatics) such as naphthalene.

[0110] The sulfur or chlorine content of the raw material is typically less than 5000 ppm by weight, preferably less than 100 ppm by weight, and particularly preferably less than 10 ppm by weight.

[0111] The technical implementation of the hydrogenation method for aromatic or polyaromatic compounds is carried out, for example, by injecting a hydrocarbon feedstock and hydrogen as an upflow or downflow into at least one fixed-bed reactor. The reactor can be isothermal or adiabatic. An adiabatic reactor is preferred. The hydrocarbon feedstock can advantageously be diluted by re-injecting, once or multiple times, the effluent from the reactor where the aromatic hydrogenation reaction is taking place at various points in the reactor located between the reactor inlet and outlet, to limit the temperature gradient in the reactor. The technical implementation of the aromatic hydrogenation method according to the invention can also advantageously be carried out by implanting at least the supported catalyst in a reactive distillation column, in an exchanger reactor, or in a slurry reactor. The hydrogen feedstock can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0112] The hydrogenation of aromatic or polyaromatic compounds can be carried out in the gas phase or the liquid phase, preferably in the liquid phase. Typically, 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 compound to be hydrogenated) molar ratio between 0.1 and 10, and for 0.05 h. -1 Up to 50 h -1 Between, preferably 0.1 h -1 Up to 10 h -1The process is carried out at a space velocity of a hydrocarbon feedstock containing aromatic or polyaromatic compounds and having a temperature of 650°C or lower, typically between 20°C and 650°C, and preferably between 20°C and 450°C.

[0113] The hydrogen flow rate is adjusted to provide a sufficient amount of hydrogen to theoretically hydrogenate all aromatic compounds and to maintain an excess of hydrogen at the reactor outlet.

[0114] The conversion rate of aromatic or polyaromatic compounds is typically 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 rate is calculated by dividing the difference between the total number of moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock and the total number of moles of aromatic or polyaromatic compounds in the product by the total number of moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock.

[0115] According to a specific variant of the method of the invention, a method for hydrogenating benzene from a hydrocarbon feedstock (such as a reforming product obtained from a catalytic reforming unit) is carried out. The benzene content in the hydrocarbon feedstock is typically between 0.1% by weight and 40% by weight, preferably between 0.5% by weight and 35% by weight, and particularly preferably between 2% by weight and 30% by weight, based on the total weight of the hydrocarbon feedstock.

[0116] The sulfur or chlorine content of the raw material is typically less than 10 ppm by weight, and preferably less than 2 ppm by weight.

[0117] 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 between 30°C and 250°C, preferably between 50°C and 200°C, and more preferably between 80°C and 180°C, at a pressure between 0.1 MPa and 10 MPa, preferably between 0.5 MPa and 4 MPa, at a hydrogen / (benzene) molar ratio between 0.1 and 10, and at a time of 0.05 h⁻¹. -1 Up to 50 h -1 Between, preferably 0.5 h -1 Up to 10 h -1 It proceeds at the spacetime speed between them.

[0118] 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.

[0119] The invention is now illustrated by the following examples, which are in no way limiting. Example

[0120] For all catalysts mentioned in the following examples, the support was alumina A exhibiting a specific surface area of ​​80 m² / g, a total pore volume (TPV) of 0.7 ml / g, and a median mesopore diameter of 12 nm.

[0121] Example 1: Preparation of an aqueous solution of a Ni precursor with additives An aqueous solution S for the preparation of catalysts B to H was prepared by dissolving 43.5 g of nickel nitrate (Ni(NO3)2·6H2O, supplier Strem Chemicals®) and 7.69 g of malonic acid (CAS 141-82-2, supplier Fluka®) in 13 mL of distilled water. The additive / N molar ratio was fixed at 0.5. Solution S was obtained with a Ni concentration of 350 g Ni / L.

[0122] Example 1a: Preparation of an aqueous solution of Ni precursor without additives An aqueous solution S' for the preparation of catalyst A was prepared by dissolving 43.5 g of nickel nitrate (Ni(NO3)2·6H2O, supplier Strem Chemicals®) in 13 mL of distilled water. Solution S' was obtained with a Ni concentration of 350 g Ni / L.

[0123] Example 2: Preparation of catalyst A according to the present invention 10 g of alumina A was impregnated with 2.4 mL of decanol added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, 7.1 mL of solution S' prepared in Example 1a was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0124] Catalyst A was obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0125] The characteristics of catalyst A obtained thus are given in Table 1 below.

[0126] Example 3: Preparation of catalyst B according to the present invention 10 g of alumina A was impregnated with 2.4 mL of decanol added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, 7.1 mL of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0127] Catalyst B containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0128] The characteristics of catalyst B obtained therefrom are given in Table 1 below.

[0129] Example 4: Preparation of catalyst C according to the present invention 10 g of alumina A was impregnated with 2.4 mL of decanol added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, a solution S prepared in Example 1, diluted with water to prepare 7.1 mL, was dropwise impregnated onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0130] A catalyst C containing 5% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0131] The characteristics of the catalyst C obtained therefrom are given in Table 1 below.

[0132] Example 5: Preparation of catalyst D according to the present invention 10 g of alumina A was impregnated with 7.2 mL of decanol added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, 2.4 mL of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0133] A catalyst D containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0134] The characteristics of the catalyst D obtained therefrom are given in Table 1 below.

[0135] Example 6: Preparation of catalyst E not according to the invention [conventional impregnation of 10% Ni + additives] The solution S prepared in Example 1 was dry-impregnated onto 10 g of alumina A by dropwise addition. The resulting catalyst precursor was then dried in a furnace 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.

[0136] A catalyst E containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0137] The characteristics of the catalyst E thus obtained are given in Table 1 below.

[0138] Example 7: Preparation of catalyst F not according to the present invention 7.1 mL of solution S prepared in Example 1 was dry-impregnated onto 10 g of alumina A by dropwise addition. 10 g of the prepared catalyst precursor was impregnated with 2.4 mL of n-decyl alcohol added dropwise. The solid was then allowed to mature at 60 °C for 30 minutes.

[0139] The resulting solid was then dried in a furnace 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.

[0140] A catalyst F containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0141] The characteristics of the catalyst F obtained therefrom are given in Table 1 below.

[0142] Example 8: Preparation of catalyst G not according to the invention 10 g of alumina A was impregnated with 2.4 mL of toluene added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, 7.1 mL of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0143] A catalyst G containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0144] The characteristics of the catalyst G thus obtained are given in Table 1 below.

[0145] Example 9: Preparation of catalyst H not according to the present invention 10 g of alumina A was impregnated with 2.4 mL of n-octanol added dropwise. The impregnated support was then aged at 60 °C for 30 minutes. Subsequently, 7.1 mL of solution S prepared in Example 1 was impregnated dropwise onto the impregnated support. The resulting catalyst precursor was then dried in a furnace 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.

[0146] A catalyst H containing 10% by weight of elemental nickel relative to the total weight of the catalyst was obtained.

[0147] The characteristics of the catalyst H obtained therefrom are given in Table 1 below.

[0148] Table 1: Characteristics of catalysts A to H.

[0149] Example 10: Catalytic Testing: Performance in the Selective Hydrogenation of a Mixture Containing Styrene and Isoprene Quality (A) HYD1 ) The selective hydrogenation reaction of a mixture containing styrene and isoprene was tested using catalysts A to H described in the above examples.

[0150] The feedstock for selective hydrogenation consists of the following components: 8 wt% styrene (supplier Sigma Aldrich®, 99% purity), 8 wt% isoprene (supplier Sigma Aldrich®, 99% purity), and 84 wt% n-heptane (solvent) (supplier VWR®, >99% purity, Chromanorm HPLC). This feedstock also contains very low levels of sulfur compounds: 110 wt ppm sulfur introduced in the form of pentylenetetranol (supplier Fluka®, >97% purity) and 100 wt ppm sulfur introduced in the form of thiophene (supplier Merck®, 99% purity). This composition corresponds to the initial composition of the reaction mixture. This model molecular mixture is representative of pyrolytic gasoline.

[0151] Selective hydrogenation is carried out in a 500 mL stainless steel autoclave equipped with a magnetically driven mechanical stirrer and capable of operating at a maximum pressure of 100 bar (10 MPa) and a temperature between 5°C and 200°C.

[0152] Before introducing it into the autoclave, 3 mL of the catalyst was descaled at 400 °C for 16 h at a hydrogen feed rate of 1 L / h / g catalyst (temperature gradient 1 °C / min), and then transferred to the autoclave under air-free conditions. After adding 214 mL of n-heptane (supplier VWR®, purity >99%, Chromanorm HPLC), the autoclave was shut off, purged, and then pressurized at 35 bar (3.5 MPa) hydrogen to reach the test temperature of 30 °C. 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 was then stirred at 1600 rev / min with the above composition. The pressure in the autoclave was maintained constant at 35 bar (3.5 MPa) using a gas reservoir located upstream of the reactor.

[0153] The reaction process was monitored by extracting samples from the reaction medium at regular time intervals: styrene was hydrogenated to ethylbenzene without the hydrogenation of the aromatic ring, and isoprene was hydrogenated to methylbutene. If the reaction was prolonged beyond the necessary time, methylbutene was then hydrogenated to isopentane. Hydrogen consumption was also 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 gram of Ni per minute.

[0154] Table 2 below shows the catalytic activities measured for catalysts A through H. These are relative to the catalytic activities measured for catalyst E (A...). HYD1 )express.

[0155] Example 11: Catalytic Testing: Performance Quality in Toluene Hydrogenation (A) HYD2 ) The toluene hydrogenation reaction was also tested using catalysts A to H described in the above examples.

[0156] The selective hydrogenation reaction was carried out in the same autoclave as described in Example 9.

[0157] Before introducing it into the autoclave, 2 mL of the catalyst was descaled at 400 °C for 16 h with a hydrogen feed of 1 L / h / g catalyst (temperature gradient 1 °C / min), and then transferred to the autoclave under air-free conditions. After adding 216 mL of n-heptane (supplier VWR®, purity >99%, Chromanorm HPLC), the autoclave was shut off, purged, and then pressurized at 35 bar (3.5 MPa) with hydrogen until it reached the test temperature of 80 °C. At time t = 0, approximately 26 g of toluene (supplier SDS®, purity >99.8%) was introduced into the autoclave (the initial composition of the reaction mixture was subsequently 6 wt% toluene / 94 wt% n-heptane) and stirring was started at 1600 rev / min. The pressure in the autoclave was kept constant at 35 bar (3.5 MPa) using a gas reservoir located upstream of the reactor.

[0158] The reaction process was monitored by extracting samples from the reaction medium at regular time intervals: toluene was completely hydrogenated to methylcyclohexane. Hydrogen consumption was also 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 gram of Ni per minute.

[0159] Table 2 below shows the catalytic activities measured for catalysts A through H. These are relative to the catalytic activities measured for catalyst E (A...). HYD2 )express. Table 2: Performance characteristics of catalysts A to H in the selective hydrogenation of mixtures containing styrene and isoprene (A HYD1 ) and performance quality in toluene hydrogenation (A HYD2 A comparison of ).

[0160] These examples clearly demonstrate the improved performance qualities of catalysts A, B, C, and D according to the invention compared to catalysts E, F, G, and H not according to the invention. This is explained by the nickel distribution in the shells of catalysts A, B, C, and D, which imparts significantly improved activity, particularly in rapid hydrogenation reactions. Although the particle size (8 nm) is relatively large due to the absence of malonic acid, catalyst A remains quite efficient because the nickel is well distributed in the shells and is therefore very easily accessible. Catalyst E exhibits lower activity due to conventional impregnation without pre-impregnation with decanol. Catalyst F undergoes post-impregnation with decanol, which fails to achieve the desired nickel distribution in the shells. Catalyst G is prepared using a toluene pre-impregnation stage. Thus, although toluene is not very miscible with water, as in the case of decanol, the absence of -OH groups in the molecule prevents it from strongly interacting with the -OH units of the alumina support, which can explain the toluene migration caused by water contained in the nickel nitrate solution during the nickel impregnation stage. In the case of n-octanol, the -OH groups appear to indeed enable it to both enter the core of the support and interact with it. On the other hand, unlike with the decanol / water pair, since water and n-octanol are highly miscible, considering the physicochemical properties of the final catalyst obtained and the results of catalytic testing, it appears that diffusion of nickel nitrate aqueous solution into the core occurred. Therefore, for catalysts F, G, and H, nickel is uniformly distributed throughout the catalyst particles. Thus, catalysts F and G in A... HYD1 and A HYD2 The activity of catalyst G is much lower than that of catalyst A. Catalyst G has even lower activity due to the presence of toluene interfering with the impregnation of nickel nitrate solution.

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 layer on the outer periphery of the support and at the core of the support, said shell layer having a thickness between 2% and 15% of the diameter of said catalyst, and said nickel particles in said catalyst having a size less than 15 nm as measured in oxide form, said method comprising the following stages: a) Impregnate the carrier with a solution of decanol in a volume V1 of 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) Impregnate the impregnated support obtained at the end of stage a) with a solution containing at least one precursor of nickel active phase to obtain a catalyst precursor; c) Dry the catalyst precursor obtained at the end of stage b) at a temperature below 250°C.

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

3. The method according to claim 1 or 2, characterized in that... Phase c) lasts for 0.5 to 12 hours.

4. The method according to any one of claims 1 to 3, characterized in that... It additionally includes stage d), in which the catalyst obtained at the end of stage c) is calcined at a temperature between 250°C and 600°C.

5. The method of claim 4, wherein stage d) is performed for a period of 0.5 hours to 24 hours.

6. The method according to any one of claims 1 to 5, wherein in stage a), the volume V1 of the decanol solution is between 0.25 and 0.75 times the total pore volume TPV of the carrier.

7. The method according to any one of claims 1 to 6, wherein in stage a), a solution of n-decyl alcohol is used.

8. The method according to any one of claims 1 to 7, wherein stage b1) is performed, wherein the impregnated support obtained at the end of stage a) or the catalyst precursor obtained at the end of stage 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 stages b) and b1) are performed in any order or simultaneously.

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

10. The method according to any one of claims 8 and 9, wherein stages b) and b1) are performed simultaneously.

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

12. The method according to any one of claims 8 to 11, wherein the molar ratio of the organic compound introduced in stage b1) to element nickel also introduced in stage b) is between 0.01 and 5.0 mol / mol.

13. The method according to any one of claims 8 to 12, wherein the organic compound in stage b1) is selected from oxalic acid, malonic acid, glycolic acid, lactic acid, malonic acid, citric acid, tartaric acid, pyruvic acid, acetylpropionic acid, ethylene glycol, propylene-1,3-diol, butane-1,4-diol, glycerol, xylitol, mannitol, sorbitol, diethylene glycol, glucose, γ-valerolactone, dimethyl carbonate, diethyl carbonate, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylformamide, 2-pyrrolidone, γ-lactam, lactamide, urea, alanine, arginine, lysine, proline, serine, or EDTA.

14. The method according to any one of claims 1 to 13, wherein stage a1) is performed, wherein the impregnated carrier obtained at the end of stage a) is aged for 0.5 hours to 40 hours.

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

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