Method for preparing a catalyst by organic means in the presence of a mixture of organic solvents

Abstract

The present invention relates to a method for preparing a catalyst, comprising: • a) a step of preparing an organic solution comprising: • a metal precursor of a metal element chosen from the elements of groups 3, 4 and 5 of the periodic table such as tantalum, and • an organic solvent comprising a monoalcohol such as ethanol; • b) a step of placing the organic solution in contact with an oxide matrix having a porous volume, in the presence of a carboxylic acid such as acetic acid, the carboxylic acid being present in the organic solution and / or in the porous volume of the oxide matrix; and then • c) a thermal treatment step. The present invention also relates to the catalyst obtained and to the use thereof for converting a feedstock comprising ethanol into butadiene.

Description

[0001] METHOD FOR THE ORGANIC PREPARATION OF A CATALYST IN THE PRESENCE OF A MIXTURE OF ORGANIC SOLVENTS

[0002] Technical field

[0003] The present invention relates to a method for manufacturing a supported metal oxide catalyst of a group 3, 4 and / or 5 element having improved performance. More particularly, the present invention relates to a method for preparing a heterogeneous catalyst comprising at least one metallic element selected from the elements of groups 3, 4 and 5 of the periodic table, deposited on an oxide matrix by bringing said oxide matrix into contact with an organic solution of at least one precursor of said metallic element in a mixture of at least one mono-alcohol and at least one carboxylic acid, said organic solution possibly further comprising an additive. The present invention also relates to the catalyst obtained by said preparation method and the use of this catalyst for the conversion into butadiene of a feedstock comprising at least ethanol.The present invention also relates to a process for converting a feedstock comprising at least ethanol into butadiene, comprising in particular a step corresponding to the method for preparing a heterogeneous catalyst according to the invention.

[0004] Prior art

[0005] Supported metal oxides are a class of heterogeneous catalysts that comprise one or more metal oxide species charged and deposited on the surface of a support material, such as silica (SiCh), alumina (AI2O3), titanium (TO2), zirconia (ZrC>2), magnesium oxide (MgO), and mixtures thereof. Examples of commonly used metal oxides include Group 3–10 metal oxides because they are capable of forming numerous catalysts that are used to synthesize a wide variety of chemicals.For example, supported tantalum oxide catalysts have active sites with diverse properties (acid-base and redox) and are therefore capable of catalyzing many chemical reactions relevant to industry, including the production of 1,3-butadiene (which may also be referred to in this description as butadiene) from ethanol, the decomposition of methyl-t-butyl ether into isobutene and methanol, the Beckmann rearrangement, the epoxidation of olefins. They also have utility in photocatalysis or electrocatalysis.

[0006] Patent US2421361, for example, describes the use of niobium or tantalum-based catalysts in a process for converting a mixture of ethanol and acetaldehyde into butadiene, the catalysts being prepared in particular by contacting silica with aqueous citric acid solutions comprising a precursor of niobium or tantalum. As with any catalyst composed of a metallic element deposited on a support, a particular dispersion and a specific distribution of the metallic element, for example tantalum, can be sought to characterize the catalyst. The dispersion of the metallic element at the atomic level is known to affect the selectivity and activity of the catalyst, via modulation of the nature of the active site.Completely independently, the control of the distribution of the metallic element in a support particle is another parameter to explore to manage problems of intragranular diffusional limitations when these exist. In the absence of intergranular diffusional limitations, it is generally known to use the entire available surface and volume, particularly for catalytic performance considerations.

[0007] There is still a need to improve the catalytic performance, for example the selectivity, of a heterogeneous catalyst comprising in particular a metallic element selected from the elements of group 3, 4 and / or 5.

[0008] In the case of the preparation of catalysts comprising the element tantalum, the use of commercial tantalum precursors, soluble in organic medium such as tantalum alcoholates or halides, is widely described, as in the application

[0009] WO2017 / 009107 or in Corson's 1950 article (BB Corson, at al. Butadiene from Ethyl Alcohol. Catalysis in the One- and Two-Step Processes. Industrial and Engineering Chemistry. 1950, 42 (2), 359-373). However, alkoxide precursors or tantalum halides may have the disadvantage of being extremely sensitive to hydrolysis. The formation of a tantalum hydroxide function results in the formation of tantalum clusters and can therefore lead to a modification or even a limitation of the catalytic performances (cf. Ambreen, S. et al., Characterization and photocatalytic study of tantalum oxide nanoparticles prepared by the hydrolysis of tantalum oxo-ethoxide Ta8(p3-O)2(MO)8(M-OEt)6(OEt)i4. Beilstein J. Nanotechnol. 2014, 5, 1082-1090).

[0010] To limit the hydrolysis phenomenon, it therefore seems necessary to limit the quantity of water present in the support, for example by extensive drying of the support, in particular at temperatures above 100°C, preferably at 150°C for several hours. To further limit the hydrolysis phenomenon of tantalum or niobium precursors (which are group 5 elements), it is possible to modify said precursors by adding additives.

[0011] The literature is full of various complexing agents that have varying success. For example, there are studies on the reaction of group 5 elements, especially tantalum and niobium, with compounds such as: - diketones, such as acetylacetone (see Kapoor PN, Mehrotra RC, Organic Compounds of Niobium and Tantalum. IV. Reactions of niobium and tantalum pentaethoxides with p-diketones. J. Less-Common Metals, 8 (1965) 339-346),

[0012] - des cétoesters (cf. Mehrotra R.C., Kapoor P.N., Organic Compounds of Tantalum. Reactions of tantalum pentaethoxide with p-ketoesters. J. Less-Common Metals, 7 (1964) 453-457),

[0013] - des hydroxyesters (cf. Narula A.K., et al., Some Aliphatic and Aromatic Hydroxy Ester Derivatives of Niobium and Tantalum. Transition Met. Chem. 7 (1982) 325-330),

[0014] - des glycols (cf. Mehrotra R.C., Kapoor P.N., Organic Compounds of Tantalum. I. Reactions of tantalum pentaethoxide with glycols. J. Less-Common Metals, 10 (1965) 237-245),

[0015] - des halogénures d’acyle (cf. R Mehrotra R.C., Kapoor P.N., Organic Compounds of Niobium. I. Reactions of niobium penta-alkoxides with acyl halides. J. Less-Common Metals, 10 (1966) 348-353).

[0016] While these documents detail the reactions and properties of the complexes formed, they do not specify the effect and use of such Ta or Nb complexes in the preparation of heterogeneous catalysts. Application WO2022 / 165190 describes the use of acetylacetone in the preparation of a tantalum-based catalyst deposited on silica. Patent application CN115364844 describes the preparation of a tantalum- and silica-based catalyst by contacting a silica with a solution comprising a tantalum precursor and anhydrous citric acid in absolute ethanol.

[0017] The present invention aims to prepare, in a simple manner, a heterogeneous catalyst comprising at least one metallic element, in particular chosen from the elements of groups 3, 4 and 5, which exhibits good catalytic performance, or even an improvement in performance compared to catalysts of the state of the art, in particular in terms of selectivity and productivity, and in particular during the conversion into butadiene of a feedstock comprising ethanol.

[0018] Summary of the invention

[0019] The present invention thus relates to a method for preparing a catalyst, comprising: a) a step of preparing at least one organic solution comprising: at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, an organic solvent comprising at least one mono-alcohol; b) a step of bringing the organic solution prepared in step a) into contact with an oxide matrix having a pore volume, in the presence of at least one carboxylic acid, to obtain a solid, said at least one carboxylic acid being present in the organic solution and / or in the pore volume of the oxide matrix; c) a step of heat treatment of the solid obtained at the end of step b).

[0020] Such a process makes it possible to obtain a catalyst whose catalytic performances, in particular in terms of selectivity and productivity, during the reaction for converting a feedstock comprising ethanol into butadiene, are satisfactory or even improved compared to the catalysts of the state of the art, in particular prepared by the organic route. The present invention therefore has the advantage of allowing the simple preparation of catalysts with satisfactory or even improved performances, for reasonable production costs.

[0021] The invention also relates to the catalyst obtained by the preparation process according to the invention, and which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferentially from the element tantalum, the element niobium and / or the element zirconium, very preferentially from the element tantalum and / or the element niobium, and preferably the element tantalum, and an oxide matrix preferably based on silica.

[0022] The present invention also relates to the use of said catalyst for converting a feedstock comprising ethanol into butadiene, at a temperature of between 250 and 450°C, at a pressure of between 0.05 and 2.00 MPa.

[0023] Finally, the present invention relates, according to another aspect, to a process for converting a feedstock comprising at least ethanol into butadiene, which comprises: a step of converting the feedstock comprising ethanol into butadiene, carried out in the presence of the catalyst prepared according to the preparation method of the invention, at a temperature of between 250 and 450°C, at a pressure of between 0.05 and 2.00 MPa.

[0024] Description of the embodiments

[0025] According to the invention, the expressions "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such clarification will be provided by the present description.

[0026] In the present description, the different parameter ranges for a given step, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, in the present description, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0027] In the following, particular embodiments of the invention are described. They can be implemented separately or combined with each other, without limitation of combinations when technically feasible.

[0028] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

[0029] According to the invention, the times and durations are expressed in hours (h), minutes (min) and / or seconds (sec).

[0030] In the present description, the term "ambient temperature (Tamb)" corresponds to a temperature typically of 20°C ± 5°C (the acronym "±" meaning "more or less", "20°C ± 5°C" means between 15 and 25°C), and the term "atmospheric pressure" means a pressure of approximately 0.1 MPa, i.e. between 0.05 MPa and 0.15 MPa, preferably between 0.08 MPa and 0.12 MPa, and generally a pressure of 0.101325 MPa.

[0031] The terms "upstream" and "downstream" are to be understood in relation to the general flow of the fluid(s) or stream(s) in question in the process.

[0032] According to the invention, the term hydroxy acid means any compound having a carboxylic acid function and a hydroxyl function preferably in the alpha, beta or gamma position (very preferably in alpha or beta), or their derivatives, the term derivatives here meaning their oligomers comprising in particular between 2 and 20 repeating units, possibly in cyclic form (i.e. in lactone form). Indeed, hydroxy acids are known to have a tendency to oligomerize, i.e. to condense in the form of oligomers, linear or cyclic, in particular when they are in concentrated solution. For example, lactic acid oligomerizes to form lactic acid oligomers comprising between 2 and 20 and more particularly between 2 and 10 repeating units, when the concentration of lactic acid in aqueous solution increases (cf. Vu DT, et al., Oligomer distribution in concentrated lactic acid solutions, Fluid Phase Equilibria, 236 (2005) 125-135).Lactic acid can also dimerize and cyclize to form dilactide. Thus, the hydroxy acids as optionally envisaged as additive in the process according to the invention can be in the form of monomeric compounds of a hydroxy acid whose hydroxyl function is preferably in the alpha, beta or gamma position, or oligomeric compounds of said hydroxy acid, in cyclic (for example dillactide) or linear form. In this description, the terms "hydroxy acids" and "alpha-hydroxy acids", "beta-hydroxy acids", "gamma-hydroxy acids", respectively must be understood as "hydroxy acids and their derivatives" and "alpha-hydroxy acids and their derivatives", "beta-hydroxy acids and their derivatives", "gamma-hydroxy acids and their derivatives".Likewise, the various specific hydroxy acids cited in this description, for example lactic acid, tartaric acid, malic acid, mandelic acid, levulinic acid, correspond to said specific acids in monomeric form and their oligomeric derivatives, for example respectively to lactic acid and its derivatives, tartaric acid and its derivatives, malic acid and its derivatives, mandelic acid and its derivatives, levulinic acid and its derivatives.

[0033] The present invention relates to a method for preparing a catalyst, called a heterogeneous catalyst, which comprises at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially zirconium, niobium, tantalum, and mixtures thereof, very preferentially from the element tantalum, the element niobium, and mixtures thereof, and very preferably tantalum, and an oxide matrix, preferably based on silica.

[0034] The preparation method according to the invention comprises, very particularly consists of, the following steps: a) a step of preparing at least one organic solution which comprises at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, and an organic solvent, said organic solvent comprising at least one mono-alcohol, and optionally at least one carboxylic acid, said at least one organic solution possibly further comprising at least one additive advantageously chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, polyacids (for example diacids and triacids), and their anhydrides, hydroketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof,in quantities such that the molar ratio (additive / metal) between the number of moles of said at least one additive and the number of moles of the metallic element(s) provided by said at least one metallic precursor is greater than or equal to 1, preferably between 1 and 20, preferentially between 2 and 20, more preferably between 5 and 15; a') optionally a step of introducing at least one carboxylic acid into the pore volume of an oxide matrix, preferably based on silica, to obtain a pre-impregnated oxide matrix; b) a step of bringing the organic solution prepared in step a) into contact with an oxide matrix, preferably based on silica, and having a pore volume, or optionally said pre-impregnated oxide matrix, in the presence of at least one carboxylic acid, to obtain a solid,said at least one carboxylic acid of step b) being present: i) in the organic solution which comprises a mixture composed of said at least one mono-alcohol and said at least one carboxylic acid, and / or ii) in the pore volume of the pre-impregnated oxide matrix, said at least one carboxylic acid and said at least one mono-alcohol being present in step b) in acid / alcohol weight proportions of between 0.1 / 99.9 and 90 / 10, preferably between 1 / 99 and 90 / 10, preferably between 5 / 95 and 90 / 10, preferably between 10 / 90 and 90 / 10, preferably between 25 / 75 and 75 / 25, the weight proportions being expressed by weight of said at least one carboxylic acid relative to the weight of said at least one mono-alcohol; b') possibly a step of maturation of the solid obtained at the end of step b), c) a step of heat treatment of the solid resulting from step b) of deposition or possibly b') of maturation,preferably comprising drying or drying followed by calcination, the drying being advantageously carried out at a temperature of between 50 and 200°C and preferably between 80 and 150°C, for a period of between 1 and 24 hours, advantageously under a gas flow, preferably under an air flow; the calcination, when integrated into step c), being advantageously carried out under a gas flow, preferably under a gas flow comprising oxygen, at a temperature of between 350 and 700°C, preferably between 450 and 600°C, for a period of between 1 and 6 hours, preferably between 2 and 4 hours; and d) optionally repeating the succession of steps b) of deposition and c) of heat treatment, or optionally the succession of step b) of deposition, followed by step b') of maturation and then step c) of heat treatment.

[0035] Advantageously, step a) of the preparation method makes it possible to prepare at least one organic solution which comprises at least one metal precursor, preferably which comprises one or two metal precursor(s), and very particularly a metal precursor, comprising at least one metal element chosen from the elements of groups 3, 4 and 5 of the periodic table, i.e. at least one metal precursor of at least one metal element chosen from the elements of groups 3, 4 and 5 of the periodic table, preferably one or two, and very particularly one, metal precursor(s) of at least one element of group 3, group 4 and / or group 5. Preferably, the or each metal precursor comprises a metal element chosen from the elements of groups 3, 4 and 5 of the periodic table.The or each metallic precursor may optionally comprise another element chosen from the elements of a group of the periodic table other than those of groups 3, 4 and 5.

[0036] Said at least one metallic precursor of at least one metallic element chosen from the elements of group 3, group 4 and / or group 5 of the periodic table is advantageously a metallic precursor of at least one metallic element chosen in particular from yttrium (Y), zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), and mixtures thereof, preferably from zirconium (Zr), niobium (Nb), tantalum (Ta), and mixtures thereof, preferentially from niobium (Nb), tantalum (Ta), and mixtures thereof, and very preferably tantalum. According to a very preferred embodiment of the invention, said at least one metallic precursor is a metallic precursor of the element tantalum, optionally combined with a metallic precursor of the element niobium and / or with a metallic precursor of the element zirconium.

[0037] Advantageously, a metal precursor of at least one metal element chosen from the elements of group 3, 4 and / or 5, for example a metal precursor of the element tantalum, is any compound comprising said at least one element respectively of group 3, 4 and / or 5, for example tantalum, and capable of releasing this element in solution in reactive form. The metal precursors used are thus organic or inorganic compounds comprising said metal element of group 3, 4 and / or 5, and which are advantageously soluble at least partially, preferably entirely, in the organic solution, under the temperature and pressure conditions implemented during step a) and step b) of the preparation method.The organic or inorganic compounds are in particular chosen from the group consisting of halides, nitrates, sulfates, phosphates, hydroxides, carbonates, carboxylates, alcoholates, diketonates, amines, cyclopentadienyl, of said metal element from group 3, 4 and / or 5, and combinations of two or more thereof, more preferably chosen from the group consisting of chlorides, nitrates, carboxylates, alcoholates, diketonates, of said metal element from group 3, 4 and / or 5, and combinations of two or more thereof. The alcoholate precursors have, for example, the formula M(OR). nwhere M is a metallic element from group n of the periodic table, n being an integer equal to 3, 4 or 5, preferably M is Ta or Nb or Zr, very preferably Ta, and R is a group chosen from alkyls such as ethyl, isopropyl, n-butyl, s-butyl, t-butyl groups. For example, the preferred metallic precursors of tantalum are tantalum pentachloride (TaCls) and tantalum pentaethanoate (Ta(OC2Hs)s or Ta(OEt)s) which can be used with most organic solvents. The metallic precursor of niobium can be chosen from niobium pentachloride (NbCk) and niobium pentaethanoate (Nb(OC2H5)5 or Nb(OEt)5). The metallic precursor of zirconium can be chosen from zirconium tetrachloride (ZrCL) and zirconium tetraethanoate (Zr(OC2H5)4 or Zr(OEt)4).According to a very preferred embodiment of the invention, said at least one metallic precursor is tantalum pentachloride (TaCls) or tantalum pentaethanoate (Ta(OC2H5)s or Ta(OEt)5), optionally combined with a metallic precursor of the element niobium and / or with a metallic precursor of the element zirconium.

[0038] The organic solution prepared in step a) comprises, in addition to said at least one metallic precursor of at least one element from group 3, 4 and / or 5 of the periodic table, an organic solvent.

[0039] The organic solvent of the organic solution of step a) comprises at least one monoalcohol. The organic solvent may also comprise at least one carboxylic acid. Thus, the organic solvent of the organic solution of step a) comprises at least one monoalcohol, advantageously: i) a mixture of at least one alcohol and at least one carboxylic acid, according to a first embodiment, or ii) at least one monoalcohol without carboxylic acid, according to a second embodiment.

[0040] Step b) of bringing the organic solution into contact with an oxide matrix must be carried out in the presence of at least one carboxylic acid and at least one mono-alcohol, said at least one mono-alcohol being provided by the organic solvent of the organic solution. In the embodiment where the organic solvent does not comprise a carboxylic acid, that is to say when the organic solvent comprises at least one mono-alcohol without carboxylic acid, an intermediate step a') of introducing at least one carboxylic acid onto said oxide matrix is ​​necessary, in particular prior to step b), to provide said at least one carboxylic acid essential to step b), said mono-alcohol being provided in step b) by the organic solvent of the organic solution.In the embodiment where the organic solvent comprises a mixture of at least one alcohol and at least one carboxylic acid, such an intermediate step a') of introducing at least one carboxylic acid onto the oxide matrix is ​​not necessary, and more particularly the preparation method does not comprise an intermediate step a') of introducing at least one carboxylic acid onto the oxide matrix since the organic solvent of the organic solution prepared in step a) provides said at least one carboxylic acid and said mono-alcohol, essential for step b).

[0041] Preferably, said organic solvent comprises a mixture of at least one alcohol and at least one carboxylic acid. In this preferred embodiment, in which the organic solvent comprises a mixture of at least one alcohol and at least one carboxylic acid, the organic solvent preferably comprises at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of said mixture of at least one mono-alcohol and at least one carboxylic acid, the percentages being given relative to the total weight of organic solvent of the organic solution.Very advantageously, the organic solvent of this preferred embodiment comprises at least 0.1% by weight of carboxylic acid relative to the total weight of said organic solvent, preferably the solvent, and preferably comprises, preferably consists of, a mixture of at least one mono-alcohol and at least one carboxylic acid, in acid / alcohol weight proportions of said at least one carboxylic acid relative to said at least one mono-alcohol of between 0.1 / 99.9 and 90 / 10, preferably between 1 / 99 and 90 / 10, preferably 5 / 95 and 90 / 10, preferably between 10 / 90 and 90 / 10, very preferably between 25 / 75 and 75 / 25, the weight proportions being expressed by weight of said at least one carboxylic acid relative to the weight of said at least one mono-alcohol.

[0042] In the particular embodiment in which the organic solvent comprises at least one alcohol without carboxylic acid, the organic solvent preferably comprises at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of said at least one mono-alcohol, the percentages being given relative to the total weight of organic solvent. In this particular embodiment, the preparation method comprises an intermediate step a') of introducing at least one carboxylic acid into the pore volume of an oxide matrix, carried out prior to step b), i.e. upstream of step b), thus making it possible to obtain a pre-impregnated oxide matrix. Said step a') can be carried out according to any method known to those skilled in the art.For example, the introduction in step a') of said at least one carboxylic acid into the pore volume of the oxide matrix may be carried out by pre-impregnation, in particular by liquid impregnation, of the oxide matrix with an acid solution comprising said at least one carboxylic acid, and preferably followed by drying in particular at a temperature of between 50 and 200°C, preferably between 80 and 150°C, for a period of between 1 hour and 24 hours, preferably between 2 hours and 20 hours, said acid solution possibly also comprising a solvent, in particular a mono-alcohol of the same chemical nature as the mono-alcohol of the organic solvent of the organic solution, and optionally at least one metal precursor of at least one metal element chosen from the elements of groups 3, 4 and 5 of the periodic table.The introduction in step a') of said at least one carboxylic acid into the pore volume of the oxide matrix can also be carried out by adsorption of said at least one carboxylic acid, in particular in gaseous form, into the pore volume of the oxide matrix, for example using a saturator. The pre-impregnated oxide matrix then obtained has a residual pore volume after introduction of the carboxylic acid, which is in particular less than the pore volume of the oxide matrix before introduction, and advantageously greater than 0 (preferably greater than or equal to 5% volume of the pore volume of the oxide matrix before introduction).Said carboxylic acid then partially occupies the pore volume of the oxide matrix, preferably without reacting with said oxide matrix, the occupied pore volume of the pre-impregnated oxide matrix preferably being less than the pore volume of the oxide matrix before introduction (and advantageously greater than 0%, preferably greater than or equal to 5% volume of the pore volume of the oxide matrix before introduction), the sum of the residual pore volume and the occupied pore volume being equal to the pore volume of the oxide matrix before introduction. The organic solution prepared in step a) is then brought into contact with the pre-impregnated oxide matrix during step b) during which said organic solution comprising said at least one mono-alcohol is then mixed with said at least one carboxylic acid already present.In this particular embodiment, at least one carboxylic acid is introduced into said pore volume of the oxide matrix prior to step b), so as to have said at least one mono-alcohol and said at least one carboxylic acid present in step b) in acid / alcohol weight proportions of said at least one carboxylic acid relative to said at least one mono-alcohol of between 0.1 / 99.9 and 90 / 10, preferably between 1 / 99 and 90 / 10, preferably between 5 / 95 and 90 / 10, preferably between 10 / 90 and 90 / 10, very preferably between 25 / 75 and 75 / 25, the weight proportions being expressed by weight of said at least one carboxylic acid relative to the weight of said at least one mono-alcohol.

[0043] The mono-alcohol of the organic solvent is preferably chosen from mono-alcohols having between 1 and 6 carbon atoms (i.e. C1-C6), preferably between 1 and 4 carbon atoms (i.e. C1-C4) and in particular having 1, 2, 3 or 4 carbon atoms, in particular linear, branched or cyclic, advantageously non-aromatic. The mono-alcohol is for example chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof.

[0044] The carboxylic acid may be a mono-functionalized carboxylic acid and / or a multi-functionalized carboxylic acid, such as hydroxy acids, keto acids or polyacids (such as diacids or triacids). Preferably, the carboxylic acid is a mono- or multi-functionalized carboxylic acid, very advantageously a monofunctional (or monofunctionalized) carboxylic acid, having between 2 and 8 carbon atoms (i.e. C2-C8), preferably between 2 and 6 carbon atoms (i.e. C2-C6), preferably between 2 and 4 carbon atoms (i.e. C2-C4), in particular linear, branched or cyclic, advantageously non-aromatic.The carboxylic acid is for example chosen from acetic acid, propionic acid, butyric acid, pyruvic acid, lactic acid, tartaric acid, malic acid, acetolacetic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, phenylglyoxylic acid, α-ketoglutaric acid and β-ketoglutaric acid, succinic acid, levulinic acid, maleic acid, and mixtures thereof. More particularly, the carboxylic acid is chosen from acetic acid, propionic acid, butyric acid, pyruvic acid, lactic acid, tartaric acid, oxalic acid, glycolic acid, and mixtures thereof.Very advantageously, the carboxylic acid is chosen from monofunctional (or monofunctionalized) carboxylic acids, having between 2 and 8 carbon atoms, preferably between 2 and 6 carbon atoms, and very particularly from acetic acid, propionic acid, butyric acid, and their mixtures.

[0045] According to a very particular mode, the organic solvent can for example comprise, and in a very particular manner consist of, a mixture of ethanol and acetic acid.

[0046] The organic solvent may optionally comprise other solvents, such as water, an ether, an ester, a ketone or mixtures thereof. The ether optionally present in the organic solvent is preferably a C4-C8 ether, in particular linear, branched or cyclic, advantageously non-aromatic, for example tetrahydrofuran (THF), diethyl ether, diisopropyl ether. The ester optionally present in the organic solvent is preferably an ester of a C2-C6, preferably C2-C4, carboxylic acid and a C1-C6, preferably C1-C4, alcohol, in particular linear, branched or cyclic, advantageously non-aromatic, such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, ethyl propanoate. The ketone possibly used in the organic solvent is for example a diketone, such as acetylacetone.

[0047] In addition to said at least one metallic precursor of at least one element from group 3, 4 and / or 5 of the periodic table and said organic solvent, the organic solution prepared in step a) may optionally comprise at least one additive.

[0048] Said at least one additive is advantageously chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, polyacids (for example diacids and triacids), and their anhydrides, hydroketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof. Said additive may in fact be an organic compound comprising at least one carboxylic acid function, or one generating a carboxylic acid (i.e.an acid anhydride capable of generating an acid, particularly in an alcoholic medium), and a hydroxyl and / or carbonyl function preferably located in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the acid function), in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the acid function) or position 3 (gamma position, i.e. on the third carbon adjacent to the carbon of the acid function). Said additive may also be an organic compound comprising at least one ketone function and a hydroxyl or ketone function preferably located in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the first ketone function), in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the first ketone function) or position 3 (gamma position, i.e. on the third carbon adjacent to the carbon of the first ketone function).Said additive may also be an organic compound comprising at least one ester function and a hydroxyl or carbonyl function located in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the ester function). Said additive may also be a hydrogen halide and / or a hydrogen halide precursor.

[0049] Preferably, the hydroxy acids, keto acids and polyacids are chosen from alpha-hydroxy acids, beta-hydroxy acids, alpha-keto acids, beta-keto acids, alpha-diacids, beta-diacids, their anhydrides, and their mixtures, and more particularly from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, a-ketoglutaric acid and p-ketoglutaric acid, their anhydrides, and their mixtures. Preferably, the hydroxy acids, keto acids and polyacids are chosen from alpha-hydroxy acids, alpha-keto acids, alpha-diacids, their anhydrides, and their mixtures, such as pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, their anhydrides and their mixtures.

[0050] Preferably, the hydroxyketones and diketones are chosen from alpha-hydroxyketones, beta-hydroxyketones, beta-diketones, and mixtures thereof, for example from 3-hydroxybutanone (or acetoin), pentane-2,4-dione (or acetylacetone), and mixtures thereof.

[0051] Preferably, the beta-hydroxyesters and beta-ketoesters are preferably chosen from ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, diethyl malonate, and mixtures thereof, preferably ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, and mixtures thereof. Preferably, the hydrogen halide is chosen from hydrogen chloride, hydrogen bromide, hydrogen iodide and mixtures thereof, and preferably hydrogen chloride. It can for example be introduced into the organic solution, by bubbling gaseous hydrogen halide into the organic solution, or in particular into the organic solvent; at least a portion of the gaseous hydrogen halide is then advantageously dissolved in the organic solvent.

[0052] Very advantageously, the hydrogen halide precursors are compounds comprising at least one halide and in which said at least one halide is labile. The hydrogen halide precursors are therefore advantageously capable of releasing at least one halide ion which can react with the organic solvent to form a hydrogen halide. Preferably, the hydrogen halide precursors are chosen from acyl halides (R-COHa, with Ha a halide i.e. fluoride, chloride, bromide or iodide), alcohol hydrohalides (ROH-HHa, with Ha a halide i.e. fluoride, chloride, bromide or iodide, and ROH said alcohol preferably chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof), and mixtures thereof.Very preferably, the hydrogen halide precursors are chosen from acyl halides such as formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, and mixtures thereof, and preferably acetyl chloride.

[0053] Preferably, said at least one additive is chosen from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid and their anhydrides, 3-hydroxybutanone, pentane-2,4-dione, ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, diethyl malonate, hydrogen chloride, hydrogen bromide, hydrogen iodide, formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, and mixtures thereof.

[0054] Preferably, the organic solution prepared in step a) comprises one or two additive(s) and preferably one additive, advantageously as defined in the present description above.

[0055] When at least one additive is present in the organic solution, the metal precursor(s) of at least one element from group 3, 4 and / or 5 and the additive(s) are present in the organic solution in quantities such that the molar ratio (additive / metal) of the number of moles of additive(s) relative to the number of moles of the metal element(s), i.e. the total number of moles of the elements from groups 3, 4 and 5 (for example the element tantalum), provided by the metal precursor(s) is greater than or equal to 1, preferably between 1 and 20, preferentially between 2 and 20, more preferably between 5 and 15.

[0056] The metal precursor(s) and possibly the additive(s) may be dissolved, diluted and / or in advantageously colloidal suspension, in the organic solvent of the organic solution prepared in step a). Whatever their form, the metal precursor(s), and the additive(s) possibly present, are distributed uniformly in the organic solution at the end of step a). The organic solution may then be said to be homogeneous.

[0057] In step a), several organic solutions, for example two or three organic solutions, can be prepared. The organic solutions then prepared can each advantageously contain a metal precursor identical or different between said organic solutions, an element from group 3, group 4 and / or group 5 identical or different between the organic solutions prepared, an organic solvent identical or different between them, and possibly an additive identical or different between them. In the case where several organic solutions are prepared, the method for preparing a catalyst advantageously comprises a step d) of repeating at least steps b) of deposition and c) of heat treatment, so as to bring each of the organic solutions prepared into contact at least once with the oxide matrix (or support).

[0058] Preferably, step a) of preparing the organic solution is carried out at a temperature between room temperature and 80°C, and at a pressure between atmospheric pressure and 3.0 MPa. Step a) of preparing the organic solution very advantageously comprises mixing said at least one metal precursor with the organic solvent, and optionally introducing said at least one additive.

[0059] Step a) thus makes it possible to prepare at least one organic solution comprising at least one metallic precursor of at least one element from group 3, group 4 and / or group 5 of the periodic table, in an organic solvent comprising at least one mono-alcohol and optionally at least one carboxylic acid.

[0060] Said organic solution obtained at the end of step a) can then be brought into contact with an oxide matrix having a porous volume, to obtain a solid, said contacting being carried out in the presence of said at least one mono-alcohol provided by the organic solvent of said organic solution and in the presence of at least one carboxylic acid provided by the organic solvent of said organic solution or during said intermediate step a'). This contacting step corresponds to step b) of the preparation method according to the invention which is a step of depositing said (or said) metal precursor(s) on said oxide matrix.

[0061] Said oxide matrix may also be called a support and is typically in the form of particles. Preferably, the oxide matrix comprises silica; said oxide matrix may then be called a silica-based oxide matrix. It preferably comprises at least 90% by weight (i.e. between 90% and 100% by weight), preferably at least 95% by weight (i.e. from 95% up to 100%), more preferably at least 98% by weight (i.e. from 98% up to 100%) and even more preferably at least 99.5% by weight (i.e. from 99.5% up to 100%) of silica relative to the total mass of oxide matrix. Said oxide matrix very advantageously comprises pores, in particular mesopores.The average pore diameter (or pore size) of the oxide matrix, in particular based on silica, is preferably at least 4 nm, preferably between 4.5 and 50 nm and even more preferably between 4.5 and 20 nm. Preferably, the pore volume of the oxide matrix, in particular based on silica, is in particular between 0.4 and 1.8 ml / g, and in particular between 0.5 and 1.5 ml / g. Preferably, the oxide matrix has a specific SBET surface area of ​​at least 250 m. 2 / g, preferably between 250 m 2 / g and 700 m 2 / g and even more preferably between 400 m 2 / g and 600 m 2 / g.

[0062] The above-mentioned textural parameters are determined by the analysis technique known as "Nitrogen Volumetry" which corresponds to the physical adsorption of nitrogen molecules in the porosity of the material via a progressive increase in pressure at constant temperature. According to the invention, the specific surface area, in particular of the oxide matrix, corresponds to the BET specific surface area (SBET in m 2 / g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 based on the BRUNAUER-EMMETT-TELLER method described in the periodical "The Journal of American Society", 1938, 60, 309. The representative pore distribution of a mesopore population is determined by the Barrett-Joyner-Halenda (BJH) model. The nitrogen adsorption-desorption isotherm according to the BJH model obtained is described in the periodical "The Journal of American Society", 1951, 73, 373, written by EP Barrett, LG Joyner and PP Halenda. The pore volume V is defined as the value corresponding to the volume observed for the partial pressure P / P o ma x of the nitrogen adsorption-desorption isotherm. The nitrogen adsorption volume is the volume measured for P / P o max= 0.99, pressure at which it is assumed that nitrogen has filled all the pores. The diameter of the mesopores <|) of the tested material, in particular of the oxide matrix, is determined by the formula 4000. / SBET.

[0063] The oxide matrix may optionally comprise traces of water, for example at a content greater than or equal to 0.5% by weight, relative to the total weight of the oxide matrix. The presence of traces of water in the support does not appear to affect the quality of the heterogeneous catalyst obtained, in particular its catalytic performances, such as selectivity and productivity, in particular during the reaction of converting a feedstock comprising ethanol into butadiene.Thus, as the requirement to work with dry materials is relaxed, handling constraints can be reduced, for example: prior drying of the oxide matrix can be avoided or reduced (for example, drying of the oxide matrix at 100°C for 2 hours may be sufficient); storage of the oxide matrix can be envisaged in particular without special humidity conditions; handling of the oxide matrix in a dry atmosphere can be avoided; drying of the organic solvent is not necessary. Thus, the method according to the invention makes it possible to reduce energy consumption and the cost of the preparation process.

[0064] Optionally, the oxide matrix may be dried, prior to step b), for example in a fixed or circulating oven, at a temperature typically less than or equal to 600°C, more particularly between 100 and 350°C, or even between 150 and 300°C, for example for 10 minutes to 24 hours, in particular for 1 to 16 hours. Advantageously, the oxide matrix which is brought into contact with the organic solution in step b) has a water content preferably less than or equal to 5% by weight, preferably less than or equal to 2.5% by weight, or even between 0.5 and 2.5% by weight, relative to the total weight of the oxide matrix.

[0065] The oxide matrix, in particular silica-based, may be commercially available or custom-synthesized using methods known to those skilled in the art. The oxide matrix, in particular silica-based, may be used directly in powder form or already shaped, in particular in the form of pelletized, crushed and sieved powder, beads, pellets, granules, or extrudates (hollow or non-hollow cylinders, multi-lobed cylinders with 2, 3, 4 or 5 lobes for example, twisted cylinders), or rings, etc., these shaping operations being carried out using conventional techniques known to those skilled in the art. For example, said oxide matrix, in particular silica-based, is in the form of optionally spheronized beads or extrudates, preferably of a size between 0.5 and 10 mm, preferably between 1.0 and 5 mm.

[0066] The contacting in step b), i.e. the deposition of said at least one metal precursor on said oxide matrix, can be carried out by any methods known to those skilled in the art. For example, and in a non-exhaustive manner, the methods known as dry impregnation, excess impregnation, CVD (Chemical Vapor Deposition), CLD (Chemical Liquid Deposition), etc. can be used.For example, step b) of the method for preparing the catalyst according to the invention comprises, preferably consists of: bringing a volume of organic solution prepared in step a) into contact with the oxide matrix such that said volume of organic solution can correspond to the total or partial pore volume of said oxide matrix, and impregnating the organic solution on the surface of said oxide matrix, so as to ensure the dispersion of said at least one metal precursor over the entire surface of the oxide matrix. Very advantageously, the contacting and the impregnation are carried out at a temperature between room temperature and 80°C and at a pressure between atmospheric pressure and 3.0 MPa.

[0067] The deposition step b) may optionally be followed by a step b') of maturation of the solid obtained, so as to further promote the dispersion and distribution of said at least one metal precursor over the entire surface of the oxide matrix. For example, the maturation step may be carried out between room temperature and 80°C and at a pressure between atmospheric pressure and 3.0 MPa, for a period of between 1 and 5 hours, in particular for 2 hours.

[0068] The method for preparing the catalyst according to the invention also comprises a step c) of heat treatment of the solid obtained at the end of step b) of deposition or possibly step b') of maturation.

[0069] Preferably, step c) of heat treatment comprises, preferably consists of, drying or drying followed by calcination, preferably drying followed by calcination. The drying is very advantageously carried out at a temperature of between 50 and 200°C and preferably between 80 and 150°C, for a period of between 1 and 24 hours, advantageously under a gas flow, preferably under an air flow, for example in an oven. The calcination, when carried out in step c) of the method for preparing the catalyst, is advantageously carried out under a gas flow, preferably under a gas flow comprising oxygen, for example under an air flow, at a temperature of between 350 and 700°C, preferably between 450 and 600°C, for a period of between 1 and 6 h and preferably between 2 and 4 h.

[0070] Optionally, steps b) of deposition and c) of heat treatment, or optionally steps b), b') then c), may be repeated n times, n being an integer between 1 and 10, preferably between 1 and 5. Thus, the method for preparing the catalyst may comprise a step d) of repetition, for example in the case where the targeted catalyst comprises several metallic elements from group 3, group 4 and / or group 5, for example the element Nb and the element Ta or the element Ta and the element Zr; or so as to achieve the targeted content of the metallic element (or metallic elements) in the prepared catalyst; or in the case where several organic solutions are prepared in step a) as explained above in this description, etc.When the preparation method includes a repetition step d), the organic solution is then brought into contact with the solid heat-treated in step c) during the first repetition, or with the solid heat-treated in (i-1). ième heat treatment step during the i ième repetition, i being an integer between 2 and n. When it comprises a repetition step d), i.e. the repetition n times of steps b) and c), or possibly b), b') and c), the method of preparing the catalyst therefore comprises:

[0071] - at least one step a) of preparation of an organic solution (step a) can also be repeated if necessary);

[0072] - a deposit step b), possibly followed by a maturation step b'), then

[0073] - a heat treatment step c) advantageously comprising drying or drying then calcination; then n times the succession of: a deposit step b), optionally followed by a maturation step b'), followed by a heat treatment step c) advantageously comprising drying or drying then calcination, the last heat treatment (i.e. the n ième heat treatment) preferably comprising drying followed by calcination.

[0074] The catalyst obtained at the end of step c) or possibly step d) is a heterogeneous catalyst, comprising at least one metallic element from group 3, group 4 and / or group 5, deposited on a support (or oxide matrix) in particular based on silica.

[0075] The preparation method may optionally further comprise a step of shaping the catalyst obtained, optionally followed by a heat post-treatment, in particular in the case where the oxide matrix used in step b) is in the form of an unshaped powder. Thus, during this optional shaping step, at the end of step c) or optionally of step d), the catalyst may be shaped in the form of pelletized, crushed, sieved powder, beads, pellets, granules, or extrudates (hollow or non-hollow cylinders, multi-lobed cylinders with 2, 3, 4 or 5 lobes for example, twisted cylinders), or rings, etc., these shaping operations being carried out by conventional techniques known to those skilled in the art. Preferably, said catalyst is shaped in the form of extrudates of a size between 1 and 10 mm, optionally spheronized.During this optional shaping step, the catalyst may optionally be mixed with at least one porous oxide material acting as a binder so as to generate the appropriate physical properties of the catalyst (mechanical strength, attrition resistance, etc.). The porous oxide material, which acts as a binder, is preferably chosen from the group formed by silica, magnesia, clays (such as kaolinite, antigorite, chrysotile, montmorillonnite, beidellite, vermiculite, talc, hectorite, saponite, laponite), titanium oxide, titanates (for example zinc, nickel, cobalt titanates), lanthanum oxide, cerium oxide, boron phosphates and mixtures thereof.Very preferably, the binder used is of silicic nature, and preferably at a content of between 5 and 60% by weight, and preferably between 10 and 30% by weight of binder relative to the total mass of the final catalyst shaped and optionally post-heat-treated. The post-heat treatment when carried out is of the same nature and follows the operating conditions of the heat treatment of step c).

[0076] The catalyst obtained at the end of step c) or optionally at the end of step d), or even at the end of the optional shaping step, comprises at least one metallic element chosen from the elements of group 3, group 4 and group 5, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from the element tantalum, the element niobium, the element zirconium and mixtures thereof, very preferentially from the element tantalum, the element niobium, and mixtures thereof, and very preferably the element tantalum, and very preferably at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix.

[0077] Very advantageously, the catalyst obtained can be loaded into any type of catalytic reactor known to those skilled in the art, in particular a reactor in axial, radial mode or a tubular reactor, with or without heat exchange, with or without multiple injection.

[0078] The present invention thus also relates to the catalyst obtained by the preparation method according to the invention, which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from the element tantalum, the element niobium, the element zirconium and mixtures thereof, very preferentially from the element tantalum, the element niobium, and mixtures thereof, and very preferably the element tantalum, and an oxide matrix, preferably based on silica. Preferably, said metallic element(s) is (are) present at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix.According to a highly preferred embodiment, the catalyst comprises a silica-based oxide matrix and between 0.5 and 5% by weight of tantalum relative to the weight of the oxide matrix. According to another embodiment, the catalyst comprises a silica-based oxide matrix and between 0.3 and 10% by weight, in particular between 0.5 and 5% by weight, of zirconium relative to the weight of the oxide matrix. According to another embodiment, the catalyst comprises a silica-based oxide matrix and between 0.3 and 10% by weight, in particular between 0.5 and 5% by weight, of niobium relative to the weight of the oxide matrix.

[0079] The method for preparing a catalyst, according to the invention, advantageously makes it possible to obtain, in a simple and inexpensive manner, a heterogeneous catalyst comprising at least one metallic element from group 3, group 4 and / or group 5, in particular the element Nb and / or Ta and / or Zr, very preferably the element Ta, having catalytic performances, in particular selectivity and productivity during the reaction for converting a feedstock comprising ethanol into butadiene, which are very satisfactory or even improved compared to the catalysts of the state of the art prepared organically.

[0080] The present invention also relates to the use for the conversion of a feedstock comprising at least ethanol into butadiene, of a catalyst obtained by the preparation method according to the invention, and which comprises at least one metallic element chosen from the group of elements of groups 3, 4 and 5 of the periodic table, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from the element tantalum, the element niobium, the element zirconium, and mixtures thereof, preferentially from the element tantalum, the element niobium, and mixtures thereof, and very preferentially the element tantalum, and an oxide matrix preferably based on silica, preferably at a content between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix.According to a preferred embodiment, the catalyst used comprises a silica-based oxide matrix and between 0.5 and 5% by weight of tantalum relative to the weight of the oxide matrix. The use of the catalyst obtained, for the conversion of a feedstock comprising at least ethanol into butadiene, then results in improvements in catalytic performance, particularly in terms of selectivity and productivity. The operating conditions for the conversion reaction are preferably a temperature of between 250 and 450°C, preferably between 270°C and 380°C, preferably between 300 and 360°C, a pressure of between 0.05 and 2.00 MPa, preferably between 0.05 and 1.50 MPa, preferably between 0.08 and 1.00 MPa, and preferably a space velocity of between 0.2 and 10 h'. 1 , preferably between 0.5 and 5 h -1 and preferably between 1 and 4 hours 1. Space velocity is defined as the ratio of feed mass flow rate to catalyst mass. When the feedstock being treated also includes acetaldehyde, the ethanol / acetaldehyde molar ratio is between 1 and 5, preferably between 2 and 4.

[0081] The present invention also relates, according to another aspect, to a process for converting a feedstock comprising ethanol and optionally acetaldehyde into butadiene, which comprises at least: A) the preparation of a catalyst according to the preparation method according to the invention;

[0082] B) a step of converting the feedstock comprising ethanol, preferably ethanol and acetaldehyde, into butadiene, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5, preferably between 2 and 4, the conversion step being carried out in the presence of the catalyst prepared in step A), and at a temperature of between 250 and 450°C, preferably between 270 and 380°C, preferentially between 300 and 360°C, at a pressure of between 0.05 and 2.00 MPa, preferably between 0.05 and 1.50 MPa, preferentially between 0.08 and 1.00 MPa, and preferably at a space velocity of between 0.2 and 10 h' 1 , preferably between 0.5 and 5 h -1 , preferably between 1 and 4 hours 1 .

[0083] When the feedstock comprises ethanol and acetaldehyde, the catalyst prepared in step A) very preferably comprises the element tantalum and a silica-based oxide matrix, the tantalum element content of the catalyst prepared in A) preferably being between 0.3 and 10%, and in particular between 0.5 and 5% by weight relative to the weight of the silica-based oxide matrix.

[0084] The following examples illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0085] Examples

[0086] Catalysts are prepared according to the methods described in Example 1. The catalysts are then tested: they are used to convert a feedstock comprising ethanol and acetaldehyde as described in Example 2.

[0087] Example 1: Preparation of catalysts at 3% Ta Z SiC>2

[0088] Catalysts are prepared with 3% by weight of tantalum on silica beads (also called silica support), the percentage of tantalum being given by weight of tantalum element relative to the weight of silica beads. For each of the catalysts, the preparation method (by direct impregnation of the carboxylic acid) is as follows:

[0089] The silica support used for the impregnation step has the following characteristics: Table 1

[0090] (*: the average size of the beads corresponds to an average diameter in number of silica beads.)

[0091] Before impregnation, the support is dried in an oven at 100°C for 2 hours. After drying, the water content in the silica beads is 1.5% by weight (determined by weight loss of a 50 g sample of silica beads).

[0092] For each catalyst preparation, an organic solution is prepared.

[0093] Different solvents are used: ethanol, a mixture of lactic acid and water in weight proportions of lactic acid / water 90 / 10, mixtures of ethanol and acetic acid (ethanol / acetic acid), ethanol and oxalic acid (ethanol / oxalic acid) or ethanol and tartaric acid (ethanol / tartaric acid), in different weight proportions of acid / alcohol. A tantalum precursor, tantalum pentaethanoate (Ta(OEt)5), is introduced and diluted in a volume V so organic solvent. The volume of organic solvent V so ivant is proportional to the pore volume of the silicic support and equal to the total pore volume of the silicic support used. The solution is then homogenized under stirring.

[0094] The organic solution obtained is quickly added dropwise and mixed with the silica support until wettability of the surface of the latter is observed (dry impregnation). The solid is then placed in an atmosphere saturated with ethanol for 3 hours.

[0095] The solid is then dried at 100°C for 24 hours in an oven, then calcined in air at 550°C for 4 hours, to obtain a catalyst.

[0096] The prepared catalysts and preparation parameters according to this direct impregnation method are presented in Table 2.

[0097] Example 2: Preparation of 3% Ta Z SiO2 catalysts, with pre-introduction of the carboxylic acid

[0098] Catalysts are prepared with 3% by weight of tantalum on silica beads, the percentage of tantalum being given by weight of tantalum element relative to the weight of the silica beads, according to the following preparation method (by pre-impregnation of the carboxylic acid): The same silica beads as in Example 1 are used as support in Example 2. In Example 2, the pore volume of the silica beads is at least partially filled with an acid solution comprising a carboxylic acid, acetic acid, lactic acid or pyruvic acid (the pyruvic acid being in solution in ethanol), by liquid impregnation then drying in an oven at 100°C for 16 hours. After drying, pre-impregnated silica beads are recovered. The amount of carboxylic acid introduced into the pore volume of the pre-impregnated silica beads, as well as the residual pore volume of the pre-impregnated silica beads, are determined by mass loss.

[0099] A tantalum precursor, tantalum pentaethanoate (Ta(OEt)s), is then introduced and diluted in a volume V so ethanol, the volume of this solution corresponding to the residual pore volume of the pre-impregnated silica beads, then involving a quantity of ethanol so as to have an acid / alcohol weight proportion between the quantity of carboxylic acid introduced and the ethanol of 10 / 90 or 35 / 65.

[0100] The organic solution obtained is quickly added drop by drop and mixed with the pre-impregnated silica support until wettability of the surface of the latter is observed (dry impregnation). During this introduction, the organic solution comes into contact with the carboxylic acid already present in the silica beads, and mixes with said carboxylic acid.

[0101] The solid is then placed in an atmosphere saturated with ethanol for 3 hours, then dried at 100°C for 24 hours in an oven, and finally calcined in air at 550°C for 4 hours, to obtain a catalyst.

[0102] The catalysts prepared according to the method of Example 1 or according to the method of Example 2 and the preparation parameters are presented in Table 2. The acid / alcohol weight proportions are the weight proportions between the carboxylic acid and the ethanol, present in step b) of bringing the solution into contact with the silica beads, the ethanol being provided by the organic solvent of the organic solution, the carboxylic acid being provided either by the organic solvent (direct impregnation of Example 1) or by pre-impregnation of the oxide matrix (pre-impregnation of Example 2). Table 2 convert an ethanol charge- in butadiene

[0103] Description of the catalytic test unit

[0104] The reactor used consists of a 20 cm long, 10 mm diameter stainless steel tube. The reactor is first charged with carborundum, then with the catalyst diluted in carborundum, and finally with carborundum. Carborundum is inert to the charge and does not affect the catalytic results; it allows the catalyst to be positioned in the isothermal zone of the reactor and limits the risk of heat and mass transfer problems. The reactor temperature is controlled with a tube furnace with three heating zones.

[0105] The liquid feed (ethanol and acetaldehyde mixture) is injected via a dual-piston HPLC pump. The liquid stream is vaporized in the tracer-heated lines before entering the reactor and is homogenized by passing through a static mixer.

[0106] At the reactor outlet, the products formed during the reaction are kept in the vapor phase to be analyzed online by gas chromatography (PONA capillary column) to allow the most precise identification of the hundreds of products formed. The catalyst is activated in situ under nitrogen at the test temperature.

[0107] For each test, the Ethanol / Acetaldehyde ratio of the feed is set at 2.6 (mol / mol), the temperature at 350°C and the pressure at 0.15 MPa.

[0108] For each catalyst tested, the carbon productivity value is measured at constant charge flow rate (pph of 250g / gTa / h, i.e. a space velocity of 7.5 h -1) while the butadiene selectivity measurement is determined at iso-conversion (40% feed conversion). Carbon productivity (usually expressed in % weight / weight per hour) corresponds to the mass flow rate of butadiene (in g / h), measured at the reactor outlet, per unit mass of element Ta, for a pph of the feed 250 g / gTa / h. The butadiene selectivity (expressed in % weight / weight) measured is a carbon selectivity and corresponds to the flow rate of butadiene measured at the reactor outlet relative to the sum of the flow rates of the carbon products formed (unconverted ethanol and acetaldehyde are not taken into account in the selectivity calculation).

[0109] The results obtained in terms of butadiene selectivity and carbon productivity, with catalysts A to L prepared as described in Example 1 and Example 2, are presented in Table 3, in the form of gain in butadiene selectivity compared to the reference catalyst A (i.e. gain in selectivity = [selectivity obtained with the catalyst] - [selectivity obtained with the reference catalyst A], gain expressed in points or % weight / weight) and in the form of gain in carbon productivity expressed relative to the productivity measured for the reference catalyst A (i.e. gain in productivity = ([productivity obtained with the catalyst] - [productivity obtained with the reference catalyst A]) / [productivity obtained with the reference catalyst A], expressed in % weight / weight).

[0110] Table 3 Table 3 clearly shows that the butadiene selectivity (at least +3.1 points) and the carbon productivity (at least +29%) are significantly improved when the conversion reaction is carried out in the presence of a catalyst in accordance with the invention (catalysts B, C, D, F, G, H, I, J, K, L), i.e. prepared in the presence of a mono-alcohol (ethanol) and a carboxylic acid when the oxide matrix is ​​brought into contact with the organic solution which comprises the metal precursor, compared to a conversion in the presence of a non-compliant catalyst prepared without the alcohol-carboxylic acid association (catalysts A and E).

Claims

Claims 1. Method for preparing a catalyst, comprising: a) a step of preparing at least one organic solution comprising: at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, an organic solvent comprising at least one mono-alcohol; b) a step of bringing the organic solution prepared in step a) into contact with an oxide matrix having a pore volume, in the presence of at least one carboxylic acid, to obtain a solid, said at least one carboxylic acid being present in the organic solution and / or in the pore volume of the oxide matrix; c) a step of heat treatment of the solid obtained at the end of step b).

2. Method according to claim 1, wherein said at least one carboxylic acid is present in the organic solution, said at least one carboxylic acid being introduced in step a) to form a mixture with said at least one mono-alcohol, said mixture composing said organic solvent of the organic solution prepared in step a), the organic solvent comprising at least 0.1% by weight of carboxylic acid relative to the total weight of said organic solvent, preferably the solvent having an acid / alcohol weight proportion of said at least one carboxylic acid relative to said at least one mono-alcohol of between 1 / 99 and 90 / 10, preferably between 5 / 95 and 90 / 10, preferably between 10 / 90 and 90 / 10, preferentially between 25 / 75 and 75 / 25.

3. Method according to claim 1, wherein said at least one carboxylic acid is present in the pore volume of the oxide matrix, said at least one carboxylic acid being introduced into said pore volume of the oxide matrix prior to step b), so as to have said at least one mono-alcohol and said at least one carboxylic acid present in step b) in acid / alcohol weight proportions of said at least one carboxylic acid relative to said at least one mono-alcohol of between 0.1 / 99.9 and 90 / 10, preferably between 1 / 99 and 90 / 10, preferably between 5 / 95 and 90 / 10, preferably between 10 / 90 and 90 / 10, preferably between 25 / 75 and 75 / 25.

4. Method according to one of claims 1 to 3, in which said at least one mono-alcohol is chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof.

5. Method according to one of claims 1 to 4, in which said at least one carboxylic acid is chosen from mono-functionalized carboxylic acids, hydroxy acids, keto acids, polyacids, and mixtures thereof, preferably from acetic acid, propionic acid, butyric acid, pyruvic acid, lactic acid, tartaric acid, oxalic acid, glycolic acid, and mixtures thereof, and very preferably among acetic acid, propionic acid, butyric acid, and mixtures thereof.

6. Method according to one of claims 1 to 5, in which the metallic element is chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferably from tantalum, niobium, zirconium and their mixtures, preferentially from the element tantalum, the element niobium, and their mixtures, and very preferably the element tantalum.

7. Method according to one of claims 1 to 6, in which said at least one metallic precursor is tantalum pentachloride or tantalum pentaethanoate, optionally combined with a metallic precursor of the element niobium and / or with a metallic precursor of the element zirconium.

8. Method according to one of claims 1 to 7, in which the oxide matrix comprises silica, preferably at least 90% by weight of silica relative to the total mass of the oxide matrix.

9. Method according to one of claims 1 to 8, in which step c) of heat treatment comprises drying, the drying preferably being carried out at a temperature between 50 and 200°C for a period between 1 and 24 hours, preferably under a gas flow.

10. Method according to claim 9, in which step c) of heat treatment comprises calcination following said drying, the calcination being carried out under gas flow, at a temperature between 350 and 700°C, for a duration between 1 and 6 h.

11. Catalyst obtained by the preparation method according to one of claims 1 to 10, and which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferentially from the element tantalum, the element niobium and / or the element zirconium, very preferentially from the element tantalum and / or the element niobium, and preferably the element tantalum, and an oxide matrix preferably based on silica.

12. Catalyst according to claim 11, wherein said at least one metallic element is present at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix.

13. Use of the catalyst according to claim 11 or 12 for converting a feedstock comprising ethanol into butadiene, at a temperature between 250 and 350°C, at a pressure between 0.05 and 2.00 MPa.

14. Process for converting a feedstock comprising ethanol into butadiene, which comprises: a step of converting the feedstock comprising ethanol into butadiene, carried out in the presence of the catalyst prepared according to the preparation method according to one of claims 1 to 10, at a temperature of between 250 and 350°C, at a pressure of between 0.05 and 2.00 MPa.

15. Conversion process according to claim 14, wherein the feed comprises ethanol and acetaldehyde, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5.

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