WO2025125056A1 - Method for preparing a catalyst by aqueous means in the presence of an acid additive - Google Patents

Abstract

The present invention relates to a method for preparing a catalyst, comprising: • a) a step of preparing an aqueous impregnation 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, • at least one multifunctional acid additive, comprising a carboxylic acid or ester function and at least one second chemical function in the alpha or beta position, and • an aqueous solvent; the metal precursor and the multifunctional acid additive being present in the aqueous solution in amounts such that the additive/metal molar ratio is greater than or equal to 5; • b) a step of depositing the metal precursor on an oxide matrix, by placing the aqueous solution in contact with 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

METHOD FOR THE AQUEOUS PREPARATION OF A CATALYST IN THE PRESENCE OF AN ACID ADDITIVE

Technical field

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 aqueous solution of at least one precursor of said metallic element, said aqueous solution also containing a multifunctionalized acid additive. The present invention also relates to the catalyst obtained by said preparation method and the use of this catalyst for converting a feedstock comprising at least ethanol into butadiene. The present invention also relates to a method 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.

Prior art

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 (TiOz), zirconia (ZrCh), 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 are also useful in photocatalysis or electrocatalysis.

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 the 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 intra-granular 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.

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

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

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 Ta ₈ (p3-O)2(MO)8(M-OEt) ₆ (OEt)i4. Beilstein J. Nanotechnol. 2014, 5, 1082-1090).

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.

The literature is full of various complexing agents with varying success. For example, there are studies on the reaction of group 5 elements, particularly tantalum and niobium, with compounds such as: - diketones, such as acetylacetone (cf. 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),

- ketoesters (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),

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

- 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),

- acyl halides (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).

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 organic preparation of a tantalum-based catalyst deposited on silica.

Other teams are interested in the preparation of catalysts comprising the element tantalum, in an aqueous process. Thus, patent application EP3476479 describes the preparation of catalysts based on tantalum and mesostructured silica (for example of the MCM-41 type), by contacting an aqueous solution comprising a peroxo-metallic complex with a solution comprising a silica source, then coprecipitation. Document WO21052968 also describes the preparation of catalysts based on tantalum on silica, but by depositing tantalum on a silica support, via contacting a silica with an aqueous solution comprising a water-soluble tantalum precursor, said water-soluble tantalum precursor being prepared by reacting a tantalum-based compound, such as TaCl5, in an aqueous medium and under oxidizing conditions, i.e. preferably in the presence of hydrogen peroxide. Patent application CN 115364844 describes the preparation of a catalyst based on tantalum and silica, by contact of a silica with an organic solution comprising a tantalum precursor and anhydrous citric acid.

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

Summary of the invention

The present invention thus relates to a method for preparing a catalyst, comprising: a) a step of preparing at least one aqueous impregnation solution comprising: 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, at least one multifunctionalized acid additive, comprising a carboxylic acid or ester function, and at least one second chemical function in alpha or beta position, and an aqueous solvent, said at least one metal precursor and said at least one multifunctionalized acid additive being present in the aqueous solution in amounts such that the additive/metal molar ratio between the number of moles of said at least one multifunctionalized acid additive and the number of moles of the metal element(s) provided by said at least one metal precursor is greater than or equal to 5; b) a step of depositing said at least one metal precursor on an oxide matrix, by bringing the aqueous solution prepared in step a) into contact with said oxide matrix, to obtain a solid; c) a step of heat treatment of the solid obtained at the end of step b).

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 catalysts of the state of the art, in particular prepared by organic means. The present invention therefore has the advantage of allowing the simple preparation of catalysts with satisfactory or even improved performances, for reasonable production costs.

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, preferably the element tantalum, and an oxide matrix preferably based on silica. 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.

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) the preparation of a catalyst according to the preparation method according to the invention;

B) a step of converting the feedstock comprising ethanol into butadiene, carried out in the presence of the catalyst prepared in step A), at a temperature between 250 and 450°C, at a pressure between 0.05 and 2.00 MPa.

Description of the embodiments

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.

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.

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.

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

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

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.

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. According to the invention, the term hydroxy acid means any compound having a carboxylic acid function and a hydroxyl function preferably in the alpha or beta position, 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 envisaged as a multifunctionalized acid 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", respectively must be understood as "hydroxy acids and their derivatives" and "alpha-hydroxy acids and their derivatives", "beta-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.

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 tantalum, and an oxide matrix, preferably based on silica.

The preparation method according to the invention comprises, very particularly consists of, the following steps: a) a step of preparing at least one aqueous impregnation 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, advantageously said metallic precursor is soluble in water, at least one acid additive multifunctionalized in alpha or beta, very advantageously chosen from alpha- or beta-hydroxy acids, alpha- or beta-keto acids, alpha- or beta-polyacids (for example alpha- or beta-diacids which may comprise a third carboxylic acid function), their esters, and their mixtures, and an aqueous solvent, said at least one metal precursor and said at least one multifunctionalized acid additive being present in the aqueous impregnation solution in quantities such that the molar ratio (additive/metal) between the number of moles of said at least one multifunctionalized acid additive and the number of moles of the metallic element(s) provided by said at least one metal precursor is greater than or equal to 5, preferably between 5 and 40, preferentially between 7 and 35, between 7 and 30; b) a step of depositing said at least one metal precursor on an oxide matrix, by bringing the aqueous impregnation solution prepared in step a) into contact with said oxide matrix, to obtain a solid, b') optionally a step of maturing 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 optionally b') of maturing, preferably comprising drying or drying followed by calcination, the drying being advantageously carried out at a temperature of between 80 and 300°C and preferably between 100 and 250°C, for a period of between 1 and 24 hours, advantageously under a gas flow, preferably under a flow of air or an inert gas such as nitrogen; 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 duration of between 1 and 6 h, preferably between 2 and 4 h; d) optionally the repetition of the succession of steps b) of deposition and c) of heat treatment, or optionally of the succession of step b) of deposition, followed by step b') of maturation then by step c) of heat treatment.

Advantageously, step a) of the preparation method makes it possible to prepare at least one aqueous impregnation solution which comprises at least one metallic precursor, preferably which comprises one or two metallic precursor(s), and very particularly a metallic precursor, comprising at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, that is to say 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, preferably one or two, and very particularly one, metallic precursor(s) of at least one element of group 3, group 4 and/or group 5. Preferably, the or each metallic precursor comprises a metallic 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.

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, 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.

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 reactive form in aqueous solution. Very advantageously, the metal precursor of at least one element of group 3, 4 and/or 5 is at least partially, preferably entirely, soluble in water, in particular under the temperature and pressure conditions used during step a) and step b) of the preparation method. The metal precursors used can thus advantageously be metal salts or metal oxides. The metal or metal oxide salts are in particular salts that are at least partially soluble in water and are selected from the group consisting of halides, nitrates, sulfates, phosphates, hydroxides, carbonates, carboxylates and combinations of two or more thereof, more preferably selected from the group consisting of chlorides, nitrates, hydroxides, carboxylates, and combinations of two or more thereof. For example, preferred metal precursors are oxalates of at least one metal element selected from the elements of group 5, such as tantalum oxalate, niobium oxalate and niobium ammonium oxalate, which are at least partially soluble in water. According to a very preferred embodiment of the invention, said at least one metal precursor is tantalum oxalate. Tantalum oxalate is a commercial compound. It can also be prepared for example by dissolving tantalum hydroxide in an aqueous solution of oxalic acid. The aqueous impregnation solution prepared in step a) of the method according to the invention 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, at least one multifunctionalized acid additive and an aqueous solvent.

Said at least one multifunctionalized acid additive may also optionally be called “alpha or beta multifunctionalized acid additive”. Said multifunctionalized acid additive is an organic compound comprising a carboxylic acid or ester function, and at least one second chemical function, advantageously oxygenated, nitrogenous or sulfurous, advantageously in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the acid function) or in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the acid function). It is preferably at least partially soluble in water. Said multifunctionalized acid additive is very advantageously an organic compound comprising a carboxylic acid or ester function and at least one hydroxyl function and/or one carbonyl function, located in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the acid function), or in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the acid function). Said multifunctionalized acid additive may comprise several second chemical functions, in particular oxygenated, for example several hydroxyl functions and/or a carbonyl function, such as tartaric acid which comprises, in addition to the first carboxylic acid function, two hydroxyl functions and a carboxylic acid function.

Said at least one multifunctionalized acid additive is thus preferably chosen from alpha- or beta-hydroxy acids, alpha- or beta-keto acids, alpha- or beta-polyacids (for example alpha- or beta-diacids which may comprise a third carboxylic acid function), their esters and their mixtures, preferably chosen from alpha-hydroxy acids, beta-hydroxy acids, alpha-keto acids, beta-keto acids, alpha-diacids, beta-diacids, their esters, and their mixtures, and preferably alpha-hydroxy acids, beta-hydroxy acids, and their mixtures. For example, the multifunctionalized acid additive may be selected from pyruvic acid, lactic acid, tartaric acid, malic acid, acetoacetic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, phenylglyoxylic acid, α-ketoglutaric acid and β-ketoglutaric acid, and mixtures thereof. Preferably, said at least one multifunctionalized acid additive is selected from lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, and mixtures thereof, and preferably from lactic acid, tartaric acid, citric acid, oxalic acid and mixtures thereof. Preferably, the aqueous impregnation solution prepared in step a) comprises one or two multifunctionalized acid additive(s) and preferably one multifunctionalized acid additive, advantageously as defined in the present description above.

Advantageously, the aqueous solvent of the aqueous impregnation solution prepared in step a) comprises water, preferably at least 50% by weight of water, preferably at least 90% by weight of water, more preferably at least 95% by weight of water, and advantageously up to 100% by weight of water, the percentages being given by weight of water relative to the total weight of the aqueous solvent. The pH of the aqueous solvent may be adjusted, if necessary, so as to have a pH equal to 7 or lower, so as to limit a possible risk of precipitation of the metal precursor and/or neutralization of the multifunctionalized acid additive.

The metal precursor(s) of at least one element from group 3, 4 and/or 5 and the multifunctionalized acid additive(s) are present in the aqueous impregnation solution in amounts such that the molar ratio (additive/metal) of the number of moles of multifunctionalized acid additive(s) relative to the number of moles of the metal element(s), i.e. total number of moles of elements from groups 3, 4 and 5 (for example the element tantalum), provided by the metal precursor(s) is greater than or equal to 5, preferably between 5 and 40, preferentially between 7 and 35, more preferably between 7 and 30.

The metal precursor(s) and the multifunctionalized acid additive(s) may be dissolved, diluted and/or in advantageously colloidal suspension, in the aqueous solvent of the aqueous impregnation solution prepared in step a). Whatever their form, the metal precursor(s) and the multifunctionalized acid additive(s) are distributed uniformly in the aqueous impregnation solution at the end of step a). The aqueous impregnation solution may then be said to be homogeneous.

In step a), several aqueous impregnation solutions, for example two or three aqueous impregnation solutions, may be prepared. The aqueous impregnation solutions then prepared may each advantageously contain a metal precursor that is identical or different between said aqueous impregnation solutions, an element from group 3, group 4 and/or group 5 that is identical or different between the aqueous impregnation solutions prepared, and at least one multifunctionalized acid additive that is identical or different between them. The aqueous impregnation solutions then prepared may thus be differentiated from one another by the chemical structure of the precursor. metallic, by the nature of the metallic element from group 3, 4 and/or 5 of the metallic precursor, and/or by the chemical structure of the multifunctionalized acid additive. In the case where several aqueous impregnation 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 aqueous impregnation solutions prepared into contact at least once with the oxide matrix (or support).

Preferably, step a) of preparing the aqueous impregnation 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 aqueous impregnation solution very advantageously comprises mixing said at least one metal precursor and said at least one multifunctionalized acid additive with the aqueous solvent.

Step a) thus makes it possible to prepare at least one aqueous impregnation 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, and at least one alpha or beta multifunctionalized acid additive, very advantageously chosen from polyacids, hydroxyacids, ketoacids, and mixtures thereof, in an aqueous solvent preferably comprising at least 50% by weight of water.

Said aqueous impregnation solution obtained at the end of step a) can then be brought into contact with an oxide matrix to obtain a solid. This contacting step corresponds to step b) of the preparation method according to the invention which is a step of depositing said metallic precursor(s) on said oxide matrix.

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 silica-based, 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 matrix oxide, in particular silica-based, 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 surface area SBET of at least 250 m ² /g, preferably between 250 m7g and 700 m7g and even more preferably between 400 m ² /g and 600 m ² /g.

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 the ASTM D 3663-78 standard established from the BRUNAUER-EMMETT-TELLER method described in the periodical “The Journal of the American Chemical 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 the American Chemical 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° _ma x of the nitrogen adsorption-desorption isotherm. The nitrogen adsorption volume is the volume measured for P/P° _ma x = 0.99, pressure for 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.V/SBET.

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 beads or extrudates, optionally spheronized, preferably of a size between 0.5 and 10 mm, preferably between 1.0 and 5 mm.

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 according to the English term which corresponds to chemical vapor deposition), CLD (Chemical Liquid Deposition according to the Anglo-Saxon term which corresponds to liquid phase chemical deposition), etc. may 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 aqueous impregnation solution prepared in step a) into contact with the oxide matrix such that said volume of aqueous impregnation solution can correspond to the total or partial pore volume of said oxide matrix, and impregnating the aqueous 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.

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 duration of between 1 and 5 h, in particular for 2 hours.

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.

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 80 and 300°C and preferably between 100 and 250°C, for a period of between 1 and 24 hours, advantageously under a gas flow, preferably under a flow of air or an inert gas such as nitrogen, for example in an oven. The drying can be carried out at a constant temperature or at several temperatures of between 80 and 300°C and preferably between 100 and 250°C (for example at least two temperature stages of between 80 and 300°C and preferably between 100 and 250°C, between which a more or less rapid temperature increase is carried out). 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 duration of between 1 and 6 h and preferably between 2 and 4 h.

Optionally, steps b) of deposition and c) of heat treatment, or possibly steps b), b') then c), can 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 repetition step d), for example in the case where the targeted catalyst comprises several metal 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 metal element (or metal elements) in the prepared catalyst; or in the case where several aqueous impregnation solutions are prepared in step a) as explained above in this description, etc. When the preparation method comprises a repetition step d), the aqueous impregnation solution is then brought into contact with the heat-treated solid in step c) during the first repetition, or with the heat-treated solid in the (i-1) ^th heat treatment step during the i ^th 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:

- at least one step a) of preparing an aqueous impregnation solution (step a) can also be repeated if necessary);

- a deposit step b), possibly followed by a maturation step b’), then

- 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 ^nth heat treatment) preferably comprising drying followed by calcination.

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.

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 into extrudates of size between 1 and 10 mm, possibly 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 shaped and optionally heat-post-treated catalyst. The heat post-treatment when carried out is of the same nature and follows the operating conditions of the heat treatment of step c).

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 the element tantalum, and 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.

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.

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 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.

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 of 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.

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 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 between 250 and 450°C, preferably between 270°C and 380°C, preferentially between 300 and 360°C, a pressure 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 a space velocity between 0.2 and 10 h' ¹ , preferentially between 0.5 and 5 h ^-1 and preferably between 1 and 4 h' ¹ . The space velocity is defined as the ratio between the mass flow rate of feedstock and the mass of catalyst. When the treated feedstock also comprises acetaldehyde, the ethanol/acetaldehyde molar ratio is between 1 and 5, preferably between 2 and 4. The present invention also relates, according to another aspect, to a process for converting into butadiene a feedstock comprising ethanol and optionally acetaldehyde, which comprises at least:

A) the preparation of a catalyst according to the preparation method according to the invention;

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, preferably between 300 and 360°C, at 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 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 h ^-1 .

When the feedstock comprises ethanol and acetaldehyde, the catalyst prepared in step A) very preferably comprises the tantalum element 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.

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

Examples

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.

Example 1: Preparation of catalysts at 3% Ta / SiC>2 powder, in the presence of additives of different natures

Catalysts are prepared with 3% by weight of tantalum on silica in powder form also called silicic support (Davisil 636), the percentage of tantalum being given in weight of tantalum element relative to the weight of silica powder. For each of the catalysts, the preparation method is as follows:

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

The particle size is determined by sieving and corresponds to an average mass size.

Before impregnation, the support is dried in an oven at 100°C for 2 hours. In some cases, an additive, acidic or not, is introduced into a volume V _water of water, to form an aqueous solution. In the reference case, no additive is introduced into said volume of water V _water . The volume of water V _water is proportional to the pore volume of the silicic support and equal to the total pore volume of the silicic support used.

A tantalum precursor, tantalum oxalate (supplied by the company Taniobis), is then introduced and diluted in a volume V _of water (reference) or in the aqueous solution containing the additive at a concentration corresponding to a targeted additive/Ta molar ratio (between 15 and 28). The aqueous solution is then homogenized while stirring.

The resulting aqueous solution is added dropwise and mixed with the silica support until the surface of the latter becomes wettable (dry impregnation). The solid is then placed in a water-saturated atmosphere for 3 hours. 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.

The prepared catalysts and preparation parameters are shown in Table 2.

Table 2

Example 2: Preparation of 3% Ta catalysts / SiO2 beads

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 the silica beads. For each of the catalysts, the preparation method is as follows:

The silica support used for the impregnation step has the following characteristics:

Avant imprégnation, le support est séché en étuve à 100°C pendant 2 heures. Table 3

Before impregnation, the support is dried in an oven at 100°C for 2 hours.

The preparation of the catalysts is done in a similar way to the protocol described in the example

1. The prepared catalysts and preparation parameters are shown in Table 4. Table 4

Example 3: Preparation of catalysts at 3% Ta / SiCk powder, in the presence of different quantities of additive Catalysts are prepared at 3% by weight of tantalum on silica powder whose characteristics are detailed in Example 1, the percentage of tantalum being given in weight of tantalum element relative to the weight of silica. For each of the catalysts, the preparation is carried out in a similar manner to the protocol described in Example 1.

The prepared catalysts and preparation parameters are shown in Table 5.

Table 5

Example 4: Use of the prepared catalysts to convert an ethanol-acetaldehyde feedstock into butadiene

Description of the catalytic test unit The reactor used consists of a 20 cm long, 10 mm diameter stainless steel tube. The reactor is first loaded with carborundum and then with the diluted catalyst. in carborundum and finally with carborundum. Carborundum is inert to the feedstock 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 three-heating zone tube furnace.

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.

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.

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.

For each catalyst tested, the carbon productivity value is measured at iso-feed rate (constant 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 (feed conversion at 40%). The carbon productivity (which is generally 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 Ta element, for a pph of the feed of 250 g/gTa/h. The butadiene selectivity (which is expressed in % weight/weight) measured is a carbon selectivity and corresponds to the butadiene flow rate 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).

The results obtained in terms of butadiene selectivity and carbon productivity, with catalysts A to G, H to K and A, F, L, M, N, prepared as described in Examples 1, 2 and 3 are presented respectively in Tables 6, 7 and 8, in the form of gain in butadiene selectivity compared to the corresponding reference catalyst A or H (i.e. gain in selectivity = [selectivity obtained with the catalyst] - [selectivity obtained with the corresponding reference catalyst], gain expressed in points or % weight/weight) and in the form of gain in carbon productivity expressed relative to the productivity measured for the corresponding reference catalyst A or H (i.e. gain in productivity = ([productivity obtained with the catalyst] - [productivity obtained with the corresponding reference catalyst]) / [productivity obtained with the corresponding reference catalyst], expressed in % weight/weight). Table 6

Tableau 8

Table 7

Table 8

Tables 6, 7 and 8 show that the butadiene selectivity and the carbon productivity are improved when the conversion reaction is carried out in the presence of a catalyst in accordance with the invention, i.e. prepared in the presence of an acid additive of alpha-hydroxyacid or alpha-diacid type, compared to a conversion in the presence of a non-compliant catalyst prepared without additive (catalysts references A and H), or prepared in the presence of an additive other than the acid additive multifunctionalized in alpha or beta (see Table 6, catalysts B, C, D, E).

Tables 6 and 7 show that the catalytic performances, in particular the selectivity and possibly the productivity, of the catalysts during the conversion of a feedstock comprising ethanol into butadiene, are improved when the catalysts are compliant and whatever the form of the silica used to prepare them, in the form of beads or in the form of powder.

Finally, Table 8 shows that the butadiene selectivity and carbon productivity are improved when the catalysts are prepared according to a preparation method in accordance with the invention, even for a low quantity of additive such that the additive/tantalum ratio is 5 or more. Indeed, the butadiene selectivities and carbon productivity increase with the quantities of acid additive present in the aqueous solution during the preparation of the catalyst until a plateau is reached a priori (for Additive/Ta >= 15), a plateau which can be considered as representing the optimal activity of the catalyst considered.

Claims

Claims 1. Method for preparing a catalyst, comprising: a) a step of preparing at least one aqueous impregnation solution comprising: at least one metal precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, at least one multifunctionalized acid additive, comprising a carboxylic acid or ester function, and at least one second chemical function in alpha or beta position, and an aqueous solvent, said at least one metal precursor and said at least one multifunctionalized acid additive being present in the aqueous solution in amounts such that the additive/metal molar ratio between the number of moles of said at least one multifunctionalized acid 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 5; b) a step of depositing said at least one metallic precursor on an oxide matrix, by bringing the aqueous solution prepared in step a) into contact with said oxide matrix, to obtain a solid; c) a step of heat treatment of the solid obtained at the end of step b). 2. Method according to claim 1, 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 the element tantalum. 3. Method according to claim 1 or 2, wherein said at least one metal precursor is tantalum oxalate. 4. Method according to one of claims 1 to 3, in which said at least one multifunctionalized acid additive is chosen from alpha-hydroxy acids, beta-hydroxy acids, alpha-keto acids, beta-keto acids, alpha-diacids, beta-diacids, their esters, and their mixtures, and preferably alpha-hydroxy acids, beta-hydroxy acids, and their mixtures. 5. Method according to one of claims 1 to 3, in which the multifunctional acid additive is chosen from pyruvic acid, lactic acid, tartaric acid, malic acid, acetoacetic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, phenylglyoxylic acid, α-ketoglutaric acid and β-ketoglutaric acid, and mixtures thereof, preferably from lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, and mixtures thereof. 6. Method according to one of claims 1 to 5, in which the aqueous solvent comprises at least 50% by weight of water, preferably at least 90% by weight of water, more preferably at least 95% by weight of water, the percentages being given by weight of water relative to the total weight of the aqueous solvent. 7. Method according to one of claims 1 to 6, in which the additive/metal molar ratio in step a) is between 5 and 40, preferably between 7 and 35, between 7 and 30. 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 80 and 300°C for a duration between 1 and 24 hours, preferably under 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, preferably the element tantalum, and an oxide matrix preferably based on silica. 12. Catalyst according to claim 11, in which 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 450°C, at a pressure between 0.05 and 2.00 MPa. 14. A process for converting a feedstock comprising ethanol into butadiene, which comprises: A) the preparation of a catalyst according to the preparation method according to one of claims 1 to 10; B) a step of converting the feedstock comprising ethanol into butadiene, carried out in the presence of the catalyst prepared in step A), at a temperature between 250 and 450°C, at a pressure between 0.05 and 2.00 MPa. 15. Conversion process according to claim 14, in which the feedstock comprises ethanol and acetaldehyde, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5.