Method for preparing a catalyst containing an active nickel phase distributed in a shell - Patents.com

Abstract

Disclosed is a method for preparing a catalyst comprising a nickel-based active phase and an alumina support, the method comprising the following steps: (a) impregnating said support with a butanol solution having a volume V1 representing 0.2 to 0.8 times the total pore volume VPT; (b) statically aging the impregnated support obtained at the end of step (a) for a period of 0.5 to 40 hours; (c) impregnating the impregnated and aged support obtained at the end of step (b) with a solution comprising at least one precursor of the active nickel phase to obtain a catalyst precursor; (d) drying the catalyst precursor obtained at the end of step (c) at a temperature below 250°C.

Description

[Technical Field]

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

[0002] Monounsaturated organic compounds, such as ethylene and propylene, are at the heart of the production of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or gas oils processed by steam cracking or catalytic cracking. These processes, carried out at high temperatures, produce, in addition to the desired monounsaturated compounds, polyunsaturated organic compounds, such as acetylene, propadiene, and methylacetylene (or propyne), 1,2-butadiene and 1,3-butadiene, vinylacetylene and ethylacetylene, and other polyunsaturated compounds whose boiling points correspond to the C5+ gasoline fraction (gasoline containing hydrocarbon compounds with five or more carbon atoms), particularly styrene or indene compounds. These polyunsaturated compounds are highly reactive and cause side reactions in the polymerization unit. Therefore, their removal is necessary before these fractions can be economically utilized. Selective hydrogenation is the primary process developed to specifically remove undesired polyunsaturated compounds from these hydrocarbon feedstocks. This allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatic compounds while avoiding their complete saturation and therefore the formation of the corresponding alkanes or naphthenes.

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

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

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

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

[0007] Patent document 3 describes an "eggshell" catalyst containing nickel on a porous support, which has a pore volume of at least 0.2 mL / g for pores with a size less than 11.7 nm and a pore volume of at least 0.1 mL / g for pores with a size greater than 11.7 nm. More than 50% by weight of the nickel is found in the crust, the thickness of which is equal to 0.15 times the radius of the support. This catalyst is used for the hydrogenation of fats.

[0008] The document (Patent Document 4) describes supported nickel catalysts in which more than 90% by weight of the nickel is found in a 700 μm thick crust. The catalysts are prepared using an ammoniacal solution in which nickel salts are dissolved. These catalysts are used in selective hydrogenation applications.

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

[0010] The French patent application filed by the applicant under No. 19 / 08.719 describes a method for preparing a nickel-based catalyst on an alumina support obtained by a very specific method, in which the nickel is distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst. The method for preparing such a catalyst requires, first, the use of a specific alumina support that has undergone hydrothermal treatment in the presence of an acid solution, and, second, the implementation of a step of hydrothermal treatment after adding specific organic additives to the catalyst precursor. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] French Patent Application Publication No. 2922784 (Patent Publication No. 2011-500327) [Patent Document 2] US Patent Application Publication No. 2010 / 217052 [Patent Document 3] U.S. Patent No. 4,519,951 [Patent Document 4] Chinese Patent Application Publication No. 101890351 [Patent Document 5] US Patent Application Publication No. 2012 / 0065442 Summary of the Invention [Means for solving the problem]

[0012] (Subject of the Invention) The present invention therefore relates to a new method for preparing a catalyst, which makes it possible to obtain catalysts which comprise at least equally good, and even better, performance qualities in terms of activity and selectivity within the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds, while using a lower effective amount of nickel phase (i.e. the amount of nickel ultimately located in a crust at the periphery of the support which makes it possible to carry out the selective hydrogenation or the hydrogenation of aromatic compounds) than that typically used in the prior art, in particular due to a better distribution of the active nickel phase in the support, which makes the active nickel phase more accessible to the reagents.

[0013] 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 between 1% and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst, and the size of the nickel particles in the catalyst, measured in the form of the oxide, being between 7 nm and 25 nm, said method comprising the following steps: a) impregnating the carrier with a butanol solution having a volume V1 that is 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) static aging of the impregnated support obtained at the end of step a) for a period of 0.5 to 40 hours; c) impregnating the impregnated and aged support obtained at the end of step b) with a solution containing at least one precursor of a nickel active phase to obtain a catalyst precursor; d) drying the catalyst precursor obtained at the end of step c) at a temperature below 250°C.

[0014] Preferably, in step c), the volume V2 of the solution containing at least one precursor of the nickel active phase impregnated onto the impregnated and aged support obtained at the end of step b) is such that V2=TPV-V1.

[0015] Surprisingly, the applicant has discovered that a specific step of impregnating a porous alumina support with a butanol solution, regardless of its origin, followed by an aging step and then a step of adding a precursor of the active nickel phase to the impregnated and aged support, without an intermediate drying step between the butanol impregnation and the impregnation of the precursor of the active nickel phase, makes it possible to obtain a catalyst in which at least a portion of the nickel is distributed on a crust at the periphery of the support and another portion of the nickel is distributed in the core of the catalyst. Without wishing to be bound by any theory, the presence of butanol limits the migration of the active nickel phase to the core of the support because only a portion of the porosity is occupied by butanol. The aging step allows the butanol solution to migrate to the core of the support and frees a "ring of free pores" at the periphery of the support that are accessible to nickel during the impregnation step of the precursor of the active phase. In addition, since butanol and water are poorly miscible, the butanol layer constitutes a barrier that limits the diffusion of nickel to the core of the support.

[0016] Preferably, step b) is carried out at a temperature of 60°C or less.

[0017] Preferably, in step a) a solution of n-butanol is used.

[0018] Preferably, step d) is carried out over a period of between 0.5 hours and 12 hours.

[0019] Preferably, the method further comprises a step e) in which the catalyst obtained at the end of step d) is calcined at a temperature between 250°C and 600°C.

[0020] Preferably, step e) is carried out for 0.5 hours to 24 hours.

[0021] Preferably, in step a), the volume V1 of the butanol solution is 0.25 to 0.75 times the total pore volume TPV of the support.

[0022] Preferably, the precursor of the nickel active phase is nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate.

[0023] Preferably, the catalyst has a specific surface area of ​​10 m 2 / g~350m 2 / g.

[0024] Another subject matter according to the invention relates to catalysts obtainable via the preparation process according to the invention.

[0025] Another subject of the invention relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule contained in a hydrocarbon feedstock having a final boiling point of 300°C or less, which is carried out in the presence of a catalyst according to the invention or a catalyst obtained by the preparation process according to the invention, at a temperature of 0°C to 300°C, at a pressure of 0.1 MPa to 10 MPa, and when the process is carried out in the liquid phase, at a hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio of 0.1 to 10, and at an hourly space velocity of 0.1 h -1 ~200h -1 or, if the process is carried out in the gas phase, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is 0.5 to 1000, and the hourly space velocity is 100 h -1 ~40,000h -1 is.

[0026] Another subject of the invention relates to a process for the hydrogenation of at least one aromatic or polyaromatic compound contained in a hydrocarbon feedstock having a final boiling point of less than or equal to 650°C, said process being carried out in the gas or liquid phase in the presence of a catalyst according to the invention or a catalyst obtained by the preparation process according to the invention, at a temperature between 30°C and 350°C, at a pressure between 0.1 and 20 MPa, with a hydrogen / aromatic compound to be hydrogenated molar ratio between 0.1 and 10, and with an hourly space velocity of 0.05 h -1 ~50h -1 is. DETAILED DESCRIPTION OF THE INVENTION

[0027] DESCRIPTION OF THE DRAWINGS FIG. 1 shows the distribution of nickel in the catalyst. The x-axis corresponds to the thickness of the catalyst measured from the edge of the catalyst (unit: μm). The y-axis corresponds to the nickel density (grams Ni / mm 3 ) The nickel is distributed both on a crust of thickness ep1 at the periphery of the support and in the core of the support. The nickel density on the crust d crust is the nickel density in the core of the support, d core The transition interval between the core and the crust of the catalyst has a thickness denoted as ep2-ep1.

[0028] (Detailed Description of the Invention) (1.Definition) In the remainder of this specification, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, published by CRC Press, editor in chief 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.

[0029] In this specification, in accordance with the IUPAC convention, "micropores" are understood to mean pores having a diameter of less than 2 nm, i.e. less than 0.002 μm; "mesopores" are understood to mean pores having a diameter of more than 2 nm, i.e. more than 0.002 μm and less than 50 nm, i.e. less than 0.05 μm, and "macropores" are understood to mean pores having a diameter of more than 50 nm, i.e. more than 0.05 μm.

[0030] To analyze the distribution of the metal phase on the support, the crust thickness is measured by Castaing microprobe (or electron microprobe microanalysis). The device used is a CAMECA XS100 equipped with four monochromator crystals, allowing the simultaneous analysis of four elements. The Castaing microprobe analysis technique consists of detecting the X-rays emitted by a solid after excitation of the elements by a high-energy electron beam. For this characterization application, catalyst granules are coated with blocks of epoxy resin. These blocks are polished to a cross section through the diameter of the bead or extrudate and then metallized by depositing carbon in a metal evaporator. An electron probe is scanned along the diameter of five beads or extrudates to obtain an average distribution profile of the constituent elements of the solid. This method is well known to those skilled in the art and is defined in the publication "Measurement of palladium crust thickness on catalyst by EPMA" by L. Sorbier et al., Materials Science and Engineering 32 (2012). It allows the distribution profile of a given element, in this case nickel, within the granule to be established. Furthermore, the Ni concentration is defined for each measurement, i.e., for each analytical step. Therefore, the density of Ni in the granules is determined by the volume (mm 3 ) is defined as the concentration of Ni per 1000 ppm of Ni.

[0031] The total pore volume is measured by mercury porosimetry according to standard ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore III® model device from the brand Micromeritics®.

[0032] The BET specific surface area is measured by nitrogen physical adsorption according to standard ASTM D3663-03, as described in the monograph by Rouquerol F., Rouquerol J. and Singh K. "Adsorption by Powders & Porous Solids: Principles, Methodology and Applications", Academic Press, 1999.

[0033] The median mesopore diameter is also defined as the diameter such that, among the combined pores that make up the mesopore volume, all pores having a size less than this diameter make up 50% of the total mesopore volume as determined by mercury intrusion porosimetry.

[0034] The term "nickel particle size" is understood to mean the diameter of nickel crystallites in the oxide form. The diameter of nickel crystallites in the oxide form is determined by X-ray diffraction from the width of the diffraction line located at an angle 2θ=43° (i.e., along the crystallographic direction

[0200] ) using the Scherrer relation. This method, used in X-ray diffraction on polycrystalline samples or powders, relates the full width at half maximum of the diffraction peak to the particle size and is described in detail in the literature: 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.

[0035] The nickel content is measured by X-ray fluorescence.

[0036] 2. Methods for Preparing the Catalyst 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 between 1% and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst, and the size of the nickel particles in the catalyst, measured in the form of the oxide, being between 7 nm and 25 nm, said method comprising the following steps: a) impregnating the carrier with a butanol solution having a volume V1 that is 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) static aging of the impregnated support obtained at the end of step a) for 0.5 to 40 hours; c) impregnating the impregnated and aged support obtained at the end of step b) with a solution containing at least one precursor of a nickel active phase to obtain a catalyst precursor; d) drying the catalyst precursor obtained at the end of step c) at a temperature below 250°C.

[0037] The order of steps a) to d) is not interchangeable, however, it is possible to add an additional step before using the catalyst at the end of step d).

[0038] The steps of the preparation method are described in detail below.

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

[0040] Butanol has the empirical chemical formula CH 10O. Butanol is therefore understood to mean the family of organic compounds: butan-1-ol (or n-butanol), butan-2-ol, isobutanol, and tert-butanol. Preferably, step a) is carried out in the presence of butan-1-ol.

[0041] (Step b)) After step a), the impregnated support is aged in a wet state for 0.5 to 40 hours, preferably 1 to 30 hours. The temperature at which the aging step b) is carried out is preferably below 60°C, more preferentially at ambient temperature. This step allows the butanol solution to migrate into the core of the support.

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

[0043] Preferably, the volume V2 of the solution containing at least one precursor of the nickel active phase to be impregnated onto the impregnated and aged support obtained at the end of step b) is such that V2=TPV-V1.

[0044] The pH of the solution containing at least one precursor of the impregnated nickel active phase may be modified by the appropriate addition of an acid or a base.

[0045] 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 with a polyacid or acid alcohol and its salt, in the form of a complex formed with an acetylacetonate or in the form of any other inorganic derivative soluble in aqueous solution, which is brought into contact with the support. Preferably, nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate are advantageously used as nickel precursor. Highly preferably, the nickel precursor is nickel nitrate.

[0046] The concentration of nickel in the solution is adjusted for supported catalysts depending on the pore volume of the support still available to obtain a nickel content: from 1% to 50% by weight, more preferentially from 2% to 40% by weight, even more preferentially from 3% to 35% by weight, even more preferentially from 5% to 25% by weight of elemental nickel relative to the total weight of the catalyst.

[0047] (Step d)) The drying step d) is advantageously carried out at a temperature below 250° C., preferably between 15° C. and 180° C., more preferentially between 30° C. and 160° C., even more preferentially between 50° C. and 150° C., even more preferentially between 70° C. and 140° C., typically for a period of between 0.5 and 12 hours, even more preferably between 0.5 and 5 hours. Longer periods are not excluded, but do not necessarily offer any improvement.

[0048] The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or an oxygen-containing atmosphere or a mixture of an inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

[0049] At the end of step d), the total or partial presence or absence of the butanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds.

[0050] (Step e) (optional)) Calcination step e) may be carried out at temperatures between 250°C and 600°C, preferably between 350°C and 550°C, typically for a period of between 0.5 hours and 24 hours, preferably for a period of between 0.5 hours and 12 hours, even more preferably for a period of between 0.5 hours and 10 hours, preferably in an inert or oxygen-containing atmosphere. Longer periods are not unspecified but do not necessarily offer any improvement.

[0051] At the end of step e), the total or partial presence or absence of the butanol solution in the catalyst has no effect on the activity and / or selectivity of the catalyst in the context of the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatic compounds.

[0052] (Step f) (optional)) Prior to use of the catalyst in the catalytic reactor and carrying out the hydrogenation process, and advantageously after step d) or e), at least one reduction treatment step f) is carried out in the presence of a reducing gas to obtain a catalyst comprising nickel at least partly in metallic form.

[0053] This treatment makes it possible to activate the catalyst and form metal particles, in particular nickel particles in the zero valent state. The reduction treatment can be carried out in situ or ex situ, i.e. after or before loading the catalyst into the hydrogenation reactor.

[0054] The reducing gas is preferably hydrogen. Hydrogen may be used in high purity or as a mixture (for example, a mixture of hydrogen / nitrogen, or hydrogen / argon, or hydrogen / methane). When hydrogen is used as a mixture, any ratio may be envisaged.

[0055] The temperature at which the reduction treatment is carried out is 120°C to 500°C, preferably 150°C to 450°C. If the catalyst is not passivated or is passivated after the reduction treatment, the temperature at which the reduction treatment is carried out is 180°C to 500°C, preferably 200°C to 450°C, and more preferably 350°C to 450°C. If the catalyst has previously been passivated, the temperature at which the reduction treatment is carried out is generally 120°C to 350°C, preferably 150°C to 350°C.

[0056] The duration of the reduction treatment is generally 2 to 40 hours, preferably 3 to 30 hours. The temperature is generally raised to the desired reduction temperature slowly, for example, at a rate of 0.1 to 10°C / min, preferably 0.3 to 7°C / min.

[0057] The hydrogen flow rate is expressed in L / hour / gram of catalyst and is between 0.01 and 100 L / hour / gram of catalyst, preferably between 0.05 and 10 L / hour / gram of catalyst, and even more preferably between 0.1 and 5 L / hour / gram of catalyst.

[0058] (3. Catalyst) The preparation process according to the invention makes it possible to obtain a catalyst comprising a nickel-based active phase and an alumina support, said catalyst comprising between 1% and 50% by weight of elemental nickel relative to the total weight of the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, the thickness of said crust (also called ep1) being between 2% and 15% of the diameter of the catalyst, and the size of the nickel particles in the catalyst, measured in the form of oxide, being between 7 nm and 25 nm.

[0059] Preferably, the nickel is distributed both on a crust at the periphery of the support and in the core of the support, the thickness ep1 of said crust being between 2% and 15% of the diameter of the catalyst, preferably between 2.5% and 12% of the diameter of the catalyst, even more preferably between 3% and 10% of the diameter of the catalyst, even more preferably between 3% and 7.5% of the diameter of the catalyst.

[0060] Preferably, the nickel density ratio between the crust and the core (here d crust / d core (also referred to as ) is strictly greater than 3, preferably greater than 3.5, preferably 3.8-15.

[0061] Preferably, said crust comprises more than 25% by weight, preferably more than 40% by weight, more preferentially between 45% and 90% by weight, even more preferentially between 60% and 90% by weight of elemental nickel relative to the total weight of elemental nickel contained in the catalyst.

[0062] Advantageously, the transition interval between the catalyst core and crust (also referred to herein as the core / crust transition interval, or ep2-ep1 as per the notation in FIG. 1 ) is associated with a very abrupt variation in nickel density across the catalyst thickness measured from the catalyst edge to the catalyst center. Preferably, the core / crust transition interval is between 0.05% and 3% of the catalyst diameter, preferably between 0.5% and 2.5% of the catalyst diameter.

[0063] The nickel content in said catalyst is advantageously between 1% and 50% by weight, more preferentially between 2% and 40% by weight, even more preferentially between 3% and 35% by weight, even more preferentially between 5% and 25% by weight, relative to the total weight of the catalyst. The values ​​"% by weight" are based on the elemental form of nickel.

[0064] The catalyst may be described as a "semi-eggshell" catalyst in which the concentration of nickel is higher at the periphery of the support than in the core of the support, and the concentration of nickel in the core of the support is non-zero.

[0065] The specific surface area of ​​a catalyst is generally 10 m 2 / g~350m 2 / g, preferably 25m 2 / g~300m 2 / g, more preferably 40m 2 / g~250m 2 / g.

[0066] The total pore volume of the catalyst is generally 0.1 mL / g to 1 mL / g, preferably 0.2 mL / g to 0.8 mL / g, and particularly preferably 0.3 mL / g to 0.7 mL / g.

[0067] The size of the nickel particles, measured in the form of oxide, is 7 nm to 25 nm, preferably 8 nm to 23 nm in the catalyst.

[0068] Preferably, the active phase of the catalyst does not contain any metal from group VIB, in particular it does not contain molybdenum or tungsten.

[0069] The catalyst (and the support used for preparing the catalyst) is in the form of granules, advantageously having a diameter of 0.5 mm to 10 mm. The granules may have any shape known to those skilled in the art, for example, in the form of beads (preferably having a diameter of 1 mm to 8 mm), extrudates, tablets or hollow cylinders. Preferably, the catalyst (and the support used for preparing the catalyst) is in the form of extrudates having a diameter of 0.5 mm to 10 mm, preferably 0.8 mm to 3.2 mm, and highly preferably 1.0 mm to 2.5 mm, and a length of 0.5 to 20 mm. The "diameter" of the extrudates is intended to mean the diameter of the circle circumscribed in the cross section of these extrudates. The catalyst can advantageously be provided in the form of cylindrical, multilobal, trilobal or tetralobal extrudates. Preferably, the shape is trilobal or tetralobal. The shape of the lobes can be adjusted by any method known in the prior art.

[0070] (4. Carrier) The characteristics of the alumina mentioned in this section correspond to the characteristics of the alumina before step a) of the preparation method according to the invention is carried out.

[0071] The support is an alumina, i.e., it comprises at least 95% by weight, preferably at least 98% by weight, particularly preferably at least 99% by weight, of alumina relative to the weight of the support. The alumina generally exhibits a crystallographic structure of the δ-, γ- or θ-alumina type, either alone or as a mixture.

[0072] The alumina support may contain impurities such as oxides of metals from groups IIA, IIIB, IVB, IIB, IIIA and IVA according to the CAS classification, preferably silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or else alkali metals, preferably lithium, sodium or potassium, and / or alkaline earth metals, preferably magnesium, calcium, strontium or barium, or else sulfur.

[0073] The specific surface area of ​​alumina is generally 10m 2 / g~400m 2 / g, preferably 30m 2 / g~350m 2 / g, more preferably 50m 2 / g~300m 2 / g.

[0074] The total pore volume of the alumina is generally between 0.1 mL / g and 1.2 mL / g, preferably between 0.3 mL / g and 0.9 mL / g, and highly preferably between 0.5 mL / g and 0.9 mL / g.

[0075] (5. Selective Hydrogenation Method) Another subject of the present invention is a process for the selective hydrogenation of polyunsaturated compounds containing at least two carbon atoms per molecule, for example alkenyl aromatics, also known as diolefins and / or acetylenics and / or styrenics, contained in a hydrocarbon feedstock having a final boiling point of less than or equal to 300° C., said process being carried out in the presence of a catalyst obtained by the preparation process as described hereinabove, at a temperature of 0° C. to 300° C., at a pressure of 0.1 MPa to 10 MPa, and when the process is carried out in the liquid phase, with a hydrogen / polyunsaturated compound molar ratio of 0.1 to 10 and an hourly space velocity of 0.1 h -1 ~200h -1Or, if the process is carried out in the gas phase, the molar ratio of hydrogen / (polyunsaturated compound to be hydrogenated) is 0.5 to 1000, and the hourly space velocity is 100 h -1 ~40,000h -1 is.

[0076] Monounsaturated organic compounds, such as ethylene and propylene, are at the basis for the production of polymers, plastics, and other value-added chemicals. These compounds are obtained from natural gas, naphtha, or gas oils processed by steam cracking or catalytic cracking. These processes, carried out at high temperatures, produce, in addition to the desired monounsaturated compounds, polyunsaturated organic compounds, such as acetylene, propadiene, and methylacetylene (or propyne), 1,2-butadiene and 1,3-butadiene, vinylacetylene and ethylacetylene, and other polyunsaturated compounds whose boiling points correspond to the C5+ fraction (hydrocarbon compounds having at least five carbon atoms), particularly diolefins, styrene, or indene. These polyunsaturated compounds are highly reactive and cause side reactions in the polymerization unit. Therefore, their removal is necessary before these fractions can be used economically.

[0077] Selective hydrogenation is a major process developed specifically to remove unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It allows for the conversion of polyunsaturated compounds to the corresponding alkenes or aromatic compounds while avoiding their complete saturation and therefore the formation of the corresponding alkanes or naphthenes. When steam cracked gasoline is used as the feedstock, selective hydrogenation also allows for the selective hydrogenation of alkenylaromatic compounds to give aromatic compounds while avoiding hydrogenation of the aromatic ring.

[0078] The hydrocarbon feedstock to be treated in the selective hydrogenation process has a final boiling point of 300° C. or less, contains at least two carbon atoms per molecule, and comprises at least one polyunsaturated compound. The term "polyunsaturated compound" is intended to mean a compound containing at least one acetylene group and / or at least one diene group and / or at least one alkenyl aromatic group.

[0079] More particularly, the feedstock is selected from the group consisting of steam cracked C2 fraction, steam cracked C2-C3 fraction, steam cracked C3 fraction, steam cracked C4 fraction, steam cracked C5 fraction and steam cracked gasoline, also known as pyrolysis gasoline or C5+ fraction.

[0080] The steam cracked C2 fractions advantageously used for carrying out the selective hydrogenation process according to the present invention have, for example, the following composition: 40% to 95% by weight of ethylene and about 0.1% to 5% by weight of acetylene; the remainder is essentially ethane and methane. In some steam cracked C2 fractions, 0.1% to 1% by weight of C3 compounds may be present.

[0081] The steam cracked C3 fractions advantageously used for carrying out the selective hydrogenation process according to the invention have, for example, the following average composition: about 90% by weight of propylene and about 1% to 8% by weight of propadiene and methylacetylene, the remainder being essentially propane. In some C3 fractions, 0.1% to 2% by weight of C2 and C4 compounds may be present.

[0082] The C2-C3 fraction can also be advantageously used for the implementation of the selective hydrogenation process according to the invention. It has, for example, the following composition: about 0.1% to 5% by weight of acetylene, about 0.1% to 3% by weight of propadiene and methylacetylene, about 30% by weight of ethylene, and about 5% by weight of propylene, the remainder being essentially methane, ethane, and propane. This feedstock may also contain 0.1% to 2% by weight of C4 compounds.

[0083] The steam cracked C4 fractions advantageously used for carrying out the selective hydrogenation process according to the invention have, for example, the following average weight composition: 1% butane, 46.5% butene, 51% butadiene, 1.3% vinylacetylene and 0.2% butyne. In some C4 fractions, 0.1% to 2% by weight of C3 and C5 compounds may be present.

[0084] The steam cracked C5 fraction advantageously used for carrying out the selective hydrogenation process according to the invention exhibits, for example, the following composition: 21% by weight of pentane, 45% by weight of pentenes and 34% by weight of pentadiene.

[0085] The steam cracked gasoline or pyrolysis gasoline advantageously used for carrying out the selective hydrogenation process according to the invention corresponds to a hydrocarbon fraction whose boiling point is generally between 0°C and 300°C, preferably between 10°C and 250°C. The polyunsaturated hydrocarbons present in the steam cracked gasoline to be hydrogenated are, in particular, diolefin compounds (butadiene, isoprene, cyclopentadiene, etc.), styrenic compounds (styrene, α-methylstyrene, etc.) and indenic compounds (indene, etc.). Steam cracked gasoline generally contains C5-C12 fractions together with traces of C3, C4, C13, C14 and C15 (for example, 0.1% to 3% by weight of each of these fractions). For example, a feedstock formed from pyrolysis gasoline typically has the following composition: 5% to 30% by weight of saturates (paraffins and naphthenes), 40% to 80% by weight of aromatics, 5% to 20% by weight of monoolefins, 5% to 40% by weight of diolefins, and 1% to 20% by weight of alkenyl aromatics, the combined compounds forming 100% by weight. It also contains 0 to 1000 ppm by weight of sulfur, preferably 0 to 500 ppm by weight of sulfur.

[0086] Preferably, the polyunsaturated hydrocarbon feedstock to be treated by the selective hydrogenation process according to the invention is a steam cracked C2 fraction or a steam cracked C2-C3 fraction or steam cracked gasoline.

[0087] The selective hydrogenation process according to the present invention is aimed at removing the polyunsaturated hydrocarbons present in the feedstock to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, if the feedstock is a C2 fraction, the selective hydrogenation process is aimed at selectively hydrogenating acetylene. If the feedstock is a C3 fraction, the selective hydrogenation process is aimed at selectively hydrogenating propadiene and methylacetylene. In the case of the C4 fraction, the objective is to remove butadiene, vinylacetylene (VAC), and butyne; in the case of the C5 fraction, the objective is to remove pentadiene. If the feedstock is steam cracked gasoline, the selective hydrogenation process is aimed at selectively hydrogenating the polyunsaturated hydrocarbons present in the feedstock to be treated, so that diolefin compounds are partially hydrogenated to give monoolefins, and styrene and indene compounds are partially hydrogenated to give the corresponding aromatic compounds, while avoiding hydrogenation of aromatic rings.

[0088] The technical implementation of the selective hydrogenation process is, for example, carried out by injecting the polyunsaturated hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor as an upflow or downflow. The reactor can be of isothermal or adiabatic type. Adiabatic reactors are preferred. The polyunsaturated hydrocarbon feedstock can advantageously be diluted by one or more injections of the effluent from the reactor in which the selective hydrogenation reaction takes place at various points in the reactor located between the reactor inlet and outlet, thereby limiting the temperature gradient in the reactor. The technical implementation of the selective hydrogenation process according to the invention can also advantageously be carried out by embedding the supported catalyst in a reactive distillation column, a reactor-exchanger or a slurry-type reactor. The hydrogen flow can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0089] The selective hydrogenation of the steam cracked C2, C2-C3, C3, C4, C5 and C5+ fractions can be carried out in the gas phase or liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5+ fractions and in the gas phase for the C2 and C2-C3 fractions. The liquid phase reaction makes it possible to reduce energy costs and increase the catalyst cycle time.

[0090] In general, the selective hydrogenation of a hydrocarbon feedstock containing polyunsaturated compounds containing at least two carbon atoms per molecule and having a final boiling point of 300°C or less is carried out at a temperature of 0°C to 300°C, a pressure of 0.1 MPa to 10 MPa, and, if the process is carried out in the liquid phase, a hydrogen / (polyunsaturated compounds to be hydrogenated) molar ratio of 0.1 to 10, and an hourly space velocity (defined as the ratio of the volumetric flow rate of the feedstock to the volume of the catalyst) of 0.1 h -1 ~200h -1 or, if the process is carried out in the gas phase, the hydrogen / (polyunsaturated compound to be hydrogenated) molar ratio is 0.5 to 1000, and the hourly space velocity is 100 h -1 ~40,000h -1 is.

[0091] In one embodiment of the present invention, when the feedstock for the selective hydrogenation process is steam cracked gasoline containing polyunsaturated compounds, the molar ratio of (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally 0.5-10, preferably 0.7-5.0, more preferably 1.0-2.0, the temperature is 0°C-200°C, preferably 20°C-200°C, more preferably 30°C-180°C, and the hourly space velocity (HSV) is generally 0.5 h -1 ~100h -1 , preferably 1 h -1 ~50h -1 and the pressure is generally 0.3 MPa to 8.0 MPa, preferably 1.0 MPa to 7.0 MPa, and even more preferably 1.5 MPa to 4.0 MPa.

[0092] More preferentially, when the feedstock for the selective hydrogenation process is steam cracked gasoline containing polyunsaturated compounds, the molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) is 0.7-5.0, the temperature is 20°C-200°C, and the hourly space velocity (HSV) is generally 1 h -1 ~50h -1 and the pressure is 1.0 MPa to 7.0 MPa.

[0093] Even more preferentially, when the feedstock for the selective hydrogenation process is steam cracked gasoline containing polyunsaturated compounds, the molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) is 1.0-2.0, the temperature is 30 ° C.-180 ° C., and the hourly space velocity (HSV) is generally 1 h -1 ~50h -1 and the pressure is 1.5 MPa to 4.0 MPa.

[0094] The hydrogen flow rate is adjusted to have enough available to theoretically hydrogenate all of the polyunsaturated compounds and maintain an excess of hydrogen at the reactor outlet.

[0095] In another embodiment of the present invention, when the feedstock for the selective hydrogenation process is a steam cracked C2 fraction and / or a steam cracked C2-C3 fraction containing polyunsaturated compounds, the molar ratio of (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally 0.5 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 generally 100 h -1 ~40,000h -1 , preferably 500h -1 ~30,000h -1 The pressure is generally 0.1 MPa to 6.0 MPa, preferably 0.2 MPa to 5.0 MPa.

[0096] 6. Methods for Hydrogenation of Aromatic Compounds Another subject of the present invention is a process for the hydrogenation of at least one aromatic or polyaromatic compound contained in a hydrocarbon feedstock having a final boiling point below 650° C., generally between 20° C. and 650° C., preferably between 20° C. and 450° C. The hydrocarbon feedstock containing at least one aromatic or polyaromatic compound may be chosen from the following petroleum or petrochemical fractions: reformate from catalytic reforming, kerosene, light gas oil, heavy gas oil, cracked distillates, such as FCC recycle oil, coking unit gas oil or hydrocracked distillates.

[0097] The content of aromatic or polyaromatic compounds contained in the hydrocarbon feedstock to be treated in the hydrogenation process according to the invention is generally 0.1% to 80% by weight, preferably 1% to 50% by weight, particularly preferably 2% to 35% by weight, the percentages being based on the total weight of the hydrocarbon feedstock. Aromatic compounds present in the hydrocarbon feedstock are, for example, benzene or alkylaromatics, such as toluene, ethylbenzene, o-xylene, m-xylene or p-xylene, or also aromatic compounds containing several aromatic rings (polyaromatics), such as naphthalene.

[0098] The sulfur or chlorine content of the feedstock is generally less than 5000 ppm by weight of sulfur or chlorine, preferably less than 100 ppm by weight, and particularly preferably less than 10 ppm by weight.

[0099] The technical implementation of the process for the hydrogenation of aromatic or polyaromatic compounds is carried out, for example, by injecting the hydrocarbon feedstock and hydrogen into at least one fixed-bed reactor as an upflow or downflow. The reactor can be of isothermal or adiabatic type. Adiabatic reactors are preferred. The hydrocarbon feedstock can be advantageously diluted by one or more reinjections of the effluent from the reactor in which the reaction of aromatic compound hydrogenation is carried out at various points in the reactor located between the reactor inlet and outlet, thereby limiting the temperature gradient in the reactor. The technical implementation of the process for the hydrogenation of aromatic compounds according to the invention can advantageously be carried out by embedding at least the supported catalyst in a reactive distillation column, a reactor-exchanger or a slurry-type reactor. The hydrogen flow can be introduced simultaneously with the feedstock to be hydrogenated and / or at one or more different points in the reactor.

[0100] The hydrogenation of aromatic or polyaromatic compounds can be carried out in the gas phase or liquid phase, preferably in the liquid phase. Generally, the temperature during the hydrogenation of aromatic or polyaromatic compounds is 30°C to 350°C, preferably 50°C to 325°C, the pressure is 0.1 MPa to 20 MPa, preferably 0.5 MPa to 10 MPa, the molar ratio of hydrogen / (aromatic compound to be hydrogenated) is 0.1 to 10, and the hourly space velocity is 0.05 h -1 ~50h -1 , preferably 0.1 h -1 ~10h -1 and the hydrocarbon feedstock contains aromatic or polyaromatic compounds and has a final boiling point below 650°C, typically between 20°C and 650°C, preferably between 20°C and 450°C.

[0101] The hydrogen flow rate is adjusted to have enough available to theoretically hydrogenate all of the aromatics and maintain an excess of hydrogen at the reactor outlet.

[0102] The conversion 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% of the aromatic or polyaromatic compounds contained in the hydrocarbon feedstock. The conversion is calculated by dividing the difference between the total moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock and in the product by the total moles of aromatic or polyaromatic compounds in the hydrocarbon feedstock.

[0103] According to a specific alternative embodiment of the process according to the invention, a process for hydrogenating benzene from a hydrocarbon feedstock, for example a reformate derived from a catalytic reforming unit, is carried out, wherein the benzene content in said hydrocarbon feedstock is generally between 0.1% and 40% by weight, preferably between 0.5% and 35% by weight, particularly preferably between 2% and 30% by weight, the weight percentages being based on the total weight of the hydrocarbon feedstock.

[0104] The sulfur or chlorine content of the feedstock is generally less than 10 ppm by weight, preferably less than 2 ppm by weight of sulfur or chlorine, respectively.

[0105] The hydrogenation of benzene contained in the hydrocarbon feedstock can be carried out in the gas phase or the liquid phase, preferably in the liquid phase. When it is carried out in the liquid phase, a solvent such as cyclohexane, heptane, or octane may be present. Generally, the temperature during the hydrogenation of benzene is 30°C to 250°C, preferably 50°C to 200°C, more preferably 80°C to 180°C, the pressure during the hydrogenation is 0.1 MPa to 10 MPa, preferably 0.5 MPa to 4 MPa, the hydrogen / (benzene) molar ratio is 0.1 to 10, and the hourly space velocity during the hydrogenation is 0.05 h -1 ~50h -1 , preferably 0.5 h -1 ~10h -1 is.

[0106] The benzene conversion is generally greater than 50 mol %, preferably greater than 80 mol %, more preferably greater than 90 mol %, particularly preferably greater than 98 mol %.

[0107] The present invention is illustrated, but in no way limited, by way of the following examples.

[0108] (Example) For all catalysts mentioned in the examples below, the support was alumina A with a specific surface area of ​​80 m 2 / g, total pore volume TPV 0.7 mL / g, and mesopore median diameter 12 nm.

[0109] Example 1: Preparation of aqueous solution of Ni precursor The aqueous solution of Ni precursor (solution S) used for the preparation of catalysts A to G is prepared by dissolving 43.5 grams (g) of nickel nitrate (NiNO3, supplier Strem Chemicals®) in a volume of 13 mL of distilled water. Solution S is obtained, whose Ni concentration is 350 g Ni per liter of solution volume.

[0110] Example 2: Preparation of Catalyst A in Accordance with the Invention [10 wt% Ni-25% ButOH TPV, Pre-impregnated] 10 g of alumina A is impregnated with 2.4 mL of n-butanol added dropwise. The impregnated support is then left to stand at 60°C for 30 minutes to age. 7.1 mL of solution S prepared in Example 1 is then impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

[0111] Catalyst A is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0112] The characteristics of the catalyst A thus obtained are given in Table 1 below.

[0113] Example 3: Preparation of Catalyst B according to the present invention [Ni 5 wt% - ButOH 25% TPV pre-impregnated] 10 g of alumina A is impregnated with 2.4 mL of n-butanol added dropwise. The impregnated support is then left to stand at 60°C for 30 minutes to age. Next, 3.55 mL of solution S prepared in Example 1 is diluted with water to a total volume of 7.1 mL, which is then impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

[0114] Catalyst B is obtained containing 5% by weight of elemental nickel relative to the total weight of the catalyst.

[0115] The characteristics of the catalyst B thus obtained are given in Table 1 below.

[0116] Example 4: Preparation of Catalyst C according to the present invention [Ni 10 wt% - ButOH 75% TPV pre-impregnated] 10 g of alumina A is impregnated with 7.2 mL of n-butanol added dropwise. The impregnated support is then left to stand at 60°C for 30 minutes to age. 2.4 mL of solution S prepared in Example 1 is then impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

[0117] A catalyst C is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0118] The characteristics of the catalyst C thus obtained are given in Table 1 below.

[0119] Example 5: Preparation of Catalyst D Not Conforming to the Invention [Conventional Impregnation 10% Ni] Solution S prepared in Example 1 is dry-impregnated onto 10 g of alumina by adding it dropwise, and the catalyst precursor thus obtained is subsequently dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

[0120] Catalyst D is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

[0121] The characteristics of the catalyst D thus obtained are given in Table 1 below.

[0122] Example 6: Preparation of Catalyst E Not Conforming to the Invention [Ni 10 wt% - ButOH 25% TPV Post-Impregnation] 7.1 mL of solution S prepared in Example 1 is added dropwise to dry-impregnate it onto 10 g of alumina. 10 g of the prepared catalyst precursor is impregnated with 2.4 mL of n-butanol added dropwise. The solid is then left to stand at 60°C for 30 minutes.

[0123] The solid thus obtained is subsequently dried in an oven at 120° C. for 12 hours and then calcined at 450° C. for 2 hours under a flow of dry air at 1 L / h / g of catalyst.

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

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

[0126] Example 7: Preparation of Catalyst F not in accordance with the present invention [10 wt% Ni-25% Toluene TPV Pre-impregnated] 10 g of alumina A is impregnated with 2.4 mL of toluene added dropwise. The impregnated support is then left to stand at 60°C for 30 minutes to age. 7.1 mL of solution S prepared in Example 1 is then impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

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

[0128] The characteristics of the catalyst F thus obtained are given in Table 1 below.

[0129] Example 8: Preparation of Catalyst G Not Conforming to the Invention [10 wt% Ni-25% n-Propanol TPV Pre-Impregnated] 10 g of alumina A is impregnated with 2.4 mL of n-propanol added dropwise. The impregnated support is then left to stand at 60°C for 30 minutes to age. 7.1 mL of solution S prepared in Example 1 is then impregnated dropwise onto the impregnated support. The catalyst precursor thus obtained is then dried in an oven at 120°C for 12 hours, and then calcined at 450°C for 2 hours under a dry air flow of 1 L / h / g catalyst.

[0130] A catalyst G is obtained containing 10% by weight of elemental nickel relative to the total weight of the catalyst.

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

[0132] [Table 1]

[0133] Example 9: Catalytic Test: Selective Hydrogenation of a Mixture Containing Styrene and Isoprene (A HYD1 ) performance Catalysts A to G described in the above examples are tested in the reaction of selective hydrogenation of a mixture containing styrene and isoprene.

[0134] The composition of the feedstock to be selectively hydrogenated is as follows: 8% by weight of styrene (supplier Sigma Aldrich®, purity 99%), 8% by weight of isoprene (supplier Sigma Aldrich®, purity 99%), and 84% by weight of n-heptane (solvent) (supplier VWR®, purity >99% Chromanorm HPLC). This feedstock also contains very low contents of sulfur compounds: 10 ppm by weight of sulfur introduced in the form of pentanethiol (supplier Fluka®, purity >97%) and 100 ppm by weight of sulfur introduced in the form of thiophene (supplier Merck®, purity 99%). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is typical of pyrolysis gasoline.

[0135] The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave equipped with a magnetically driven mechanical stirrer and capable of operating at a maximum pressure of 100 bar (10 MPa) and temperatures between 5°C and 200°C.

[0136] Prior to its introduction into the autoclave, a quantity of 3 mL of catalyst is reduced ex situ at 400 °C for 16 hours (heating ramp 1 °C / min) under a hydrogen flow of 1 L / h / g catalyst, then transferred to the autoclave and deaerated. After the addition of 214 mL of n-heptane (supplier VWR®, purity >99% Chromanorm HPLC), the autoclave is closed, purged, and then pressurized under 35 bar (3.5 MPa) of hydrogen to a test temperature equal to 30 °C. At time t = 0, approximately 30 g of a mixture containing styrene, isoprene, n-heptane, pentanethiol, and thiophene is introduced into the autoclave. The reaction mixture now has the above-mentioned composition, and stirring is initiated at 1600 rpm. The pressure in the autoclave is kept constant at 35 bar (3.5 MPa) using a storage cylinder placed upstream of the reactor.

[0137] The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: styrene is hydrogenated to give ethylbenzene, but there is no hydrogenation of the aromatic ring, and isoprene is hydrogenated to give methylbutene. If the reaction is prolonged longer than necessary, methylbutene is hydrogenated to give isopentane. Hydrogen consumption is also monitored over time by the pressure reduction in a storage cylinder placed upstream of the reactor. The catalytic activity is expressed in moles of H2 consumed per time (minutes) and weight (grams) of Ni.

[0138] The catalytic activities (A HYD1 ) are given in Table 2 below and are related to the catalytic activity measured for catalyst D.

[0139] Example 10: Catalytic testing: Performance in toluene hydrogenation (A HYD2 )) Catalysts A to G described in the above examples are also tested in the reaction of toluene hydrogenation.

[0140] The selective hydrogenation reaction is carried out in the same autoclave as described in Example 9.

[0141] Prior to its introduction into the autoclave, a quantity of 2 mL of catalyst was reduced ex situ at 400 °C for 16 hours (heating gradient 1 °C / min) under a hydrogen flow of 1 L / h / g catalyst, then transferred to the autoclave and dewatered. After the addition of 216 mL of n-heptane (supplier VWR®, purity >99% Chromanorm HPLC), the autoclave was closed, purged, and then pressurized under 35 bar (3.5 MPa) of hydrogen to a test temperature equal to 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 now 6% by weight toluene / 94% by weight n-heptane), and stirring was started at 1600 rpm. The pressure in the autoclave was maintained constant at 35 bar (3.5 MPa) using a storage cylinder placed upstream of the reactor.

[0142] The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: toluene is completely hydrogenated to give methylcyclohexane. Hydrogen consumption is also monitored over time by pressure reduction in a storage cylinder placed upstream of the reactor. The catalytic activity is expressed in moles of H2 consumed per minute of time and per gram of Ni weight.

[0143] The catalytic activities (A HYD2 ) are given in Table 2 below and are related to the catalytic activity measured for catalyst D.

[0144] [Table 2]

[0145] This clearly shows the improved performance of catalysts A, B and C in accordance with the invention compared to catalysts D, E, F and G which are not in accordance with the invention. This is explained by the distribution of nickel in the crust of catalysts A, B and C, which gives them significantly improved activity, especially in fast hydrogenation reactions.

[0146] Catalyst D has lower activity due to conventional impregnation without butanol pre-impregnation. Catalyst E undergoes post-impregnation with butanol, which does not allow for crust distribution of nickel. Catalyst F is prepared by a toluene pre-impregnation process. Therefore, although toluene is not highly miscible with water as in the case of butanol, the absence of -OH groups in the molecule does not allow it to have strong interactions with the -OH groups of the alumina support, which may explain the migration of toluene through the water contained in the nickel nitrate solution during the nickel impregnation process. In the case of propanol, the -OH groups appear to allow it to both move toward the core of the support and interact with the support. On the other hand, unlike the butanol / water pair, water and n-propanol are highly miscible, so diffusion of the aqueous Ni nitrate solution to the core appears to occur, taking into account both the physicochemical characteristics of the final catalyst obtained and the results of catalytic tests. Therefore, for catalysts E, F, and G, nickel is uniformly distributed throughout the catalyst granules. Therefore, catalysts E and F are HYD1 and A HYD2 Catalyst F has a much lower activity in terms of solubility than Catalyst A. Catalyst F is low due to the presence of toluene, which disrupts the impregnation of the nickel nitrate solution. [Brief explanation of the drawings]

[0147] [Figure 1] FIG. 1 shows the distribution of nickel in a catalyst.

Claims

1. 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 the catalyst, the nickel being distributed both on a crust at the periphery of the support and in the core of the support, the thickness of the crust being 2% to 15% of the catalyst grain size, and the size of the nickel particles in the catalyst, measured in oxide form, being 7 nm to 25 nm, said method comprising the following steps: a) impregnating the carrier with a butanol solution having a volume V1 of 0.2 to 0.8 times the total pore volume TPV of the carrier to obtain an impregnated carrier; b) static aging of the impregnated support obtained at the end of step a) for a period of 0.5 to 40 hours; c) impregnating the impregnated and aged support obtained at the end of step b) with a solution containing at least one precursor of the nickel active phase to obtain a catalyst precursor; d) drying the catalyst precursor obtained at the end of step c) at a temperature below 250°C. Including, in step c) the volume V2 of the solution containing at least one precursor of the nickel active phase impregnated onto the impregnated and aged support obtained at the end of step b) is such that V2=TPV-V1.

2. 2. The method of claim 1, wherein step b) is carried out at a temperature of 60° C. or less.

3. The method according to claim 1 or 2, wherein in step a) an n-butanol solution is used.

4. 4. The method according to claim 1, wherein step d) is carried out for a period of 0.5 to 12 hours.

5. 5. The method according to claim 1, further comprising a step e) in which the catalyst obtained at the end of step d) is calcined at a temperature between 250°C and 600°C.

6. 6. The method of claim 5, wherein step e) is carried out for 0.5 hours to 24 hours.

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

8. 8. The method according to claim 1, wherein the precursor of the nickel active phase is nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate.

9. The specific surface area of ​​the catalyst is 10 m ２ / g~350m ２ The method according to any one of claims 1 to 8, wherein the saturation is 0.05 to 0.15.

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