FR3156345A1 - Method for activating a heterogeneous catalyst in the presence of a multifunctionalized acid compound - Google Patents

Abstract

The present invention relates to a method for activating a catalyst comprising at least one metallic element selected from the elements of groups 3, 4 and 5 of the periodic table, and an oxide matrix, said method comprising: a) a step of preparing an activation composition comprising at least one multifunctionalized acid compound, such that the activation composition has an acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound and the number of moles of said at least one metallic element of the catalyst greater than or equal to 2; b) a step of bringing the activation composition into contact with said catalyst, to obtain an impregnated intermediate solid, c) a step of heat treatment of the impregnated intermediate solid, implementing an activation phase at a temperature greater than 100°C and less than 300°C.

Description

Method for activating a heterogeneous catalyst in the presence of a multifunctionalized acid compound

The present invention relates to a method for treating a supported metal oxide catalyst of a group 3, 4 and/or 5 element to improve the catalytic performance thereof. More particularly, the present invention relates to a method for activating a heterogeneous catalyst comprising at least one metal element selected from the elements of groups 3, 4 and 5 of the periodic table, deposited on an oxide matrix, by contacting said heterogeneous catalyst with a solution containing a multifunctionalized acid compound.

Supported metal oxides are a class of heterogeneous catalysts that comprise one or more metal oxide species deposited and dispersed on the surface of a support material, such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titanium (TiO ₂ ), zirconia (ZrO 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.

As with any catalyst composed of a metallic element deposited on a porous 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 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, in particular for catalytic performance considerations.

There is still a need to improve the catalytic performance, for example the selectivity and/or productivity, of a heterogeneous catalyst comprising in particular a metallic element selected 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 application WO2017/009107 or in the 1950 article by Corson (BB Corson, at al. Butadiene form Ethyl Alcohol. Catalysis in the One- and Two-Step Processes. Industrial And Engineering Chemistry. 1950, 42 (2), 359-373). However, tantalum alcoholate precursors or 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 (i.e., tantalum atomic aggregates) 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 (μ ₃ -O) ₂ (μ-O) ₈ (μ-OEt) ₆ (OEt) ₁₄ . Beilstein J. Nanotechnol. 2014, 5, 1082–1090).

To limit the hydrolysis phenomenon of organic tantalum precursors, 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 or complexing agents.

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 β-diketones. J. Less-Common Metals , 8 (1965) 339-346),

- ketoesters (cf. Mehrotra RC, Kapoor PN, Organic Compounds of Tantalum. Reactions of tantalum pentaethoxide with β-ketoesters. J. Less-Common Metals , 7 (1964) 453-457),

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

- glycols (see Mehrotra RC, Kapoor PN, Organic Compounds of Tantalum. I. Reactions of tantalum pentaethoxide with glycols. J. Less-Common Metals , 10 (1965) 237-245),

- acyl halides (cf. R Mehrotra RC, Kapoor PN, 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 either in the preparation of heterogeneous catalysts, or in the activation or reactivation (or rejuvenation) of fresh or used heterogeneous catalysts.

Application WO2022/165190 describes the use of acetylacetone in the preparation of a tantalum-based catalyst deposited on silica, but is silent on a method of activation or reactivation (i.e. rejuvenation) of this type of tantalum-based catalyst.

The objective of the present invention is to activate or reactivate a heterogeneous catalyst comprising at least one metallic element, in particular chosen from the elements of groups 3, 4 and 5, to enable the catalytic performance of said catalyst to be significantly improved, in particular in terms of selectivity and productivity, and in particular during the conversion into butadiene of a feedstock comprising ethanol.

The present invention thus relates to a method for activating a catalyst comprising at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, and an oxide matrix, said method comprising:

a) a step of preparing an activation composition comprising:

at least one multifunctionalized acid compound, in an amount such that the activation composition has an acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound and the number of moles of said at least one metallic element of the catalyst greater than or equal to 2;

b) a step of bringing the activation composition prepared in step a) into contact with said catalyst, to obtain an impregnated intermediate solid,

c) a step of heat treatment of the impregnated intermediate solid obtained in step b) implementing an activation phase carried out at a temperature above 100°C and below 300°C.

Such a process makes it possible to obtain an activated catalyst whose catalytic performances, in particular in terms of selectivity and productivity, in particular during the reaction for converting a feedstock comprising ethanol into butadiene, are improved compared to those of the initial catalyst to be treated. The present invention therefore has the advantage of allowing the activation or reactivation (i.e. rejuvenation) of heterogeneous catalysts in a simple and economical manner, to obtain catalysts with very satisfactory performances, in particular in terms of selectivity and productivity, and superior to those of the initial catalyst.

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).

It is well known that the boiling point of a compound varies with the operating pressure. However, without further indication, i.e. without indication of the pressure, the boiling point of the compound under consideration, in particular of the multifunctionalized acid compound used, is understood to be the boiling point of said compound at atmospheric pressure (in particular at a pressure approximately equal to 0.1 MPa).

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 terms of the general flow of the fluid(s) or flow(s) in question in the process, with upstream designating a section (or stage or phase) before and downstream designating a section (or stage or phase) after.

In the following, the terms “dry”, “wet” or “intermediate humidity” may describe a gas flow, for example an air flow. In the present description, the term dry which may describe the gas flow means that said gas flow comprises at most 1% by volume of water, preferably at most 0.5% by volume of water, relative to the total volume of said gas flow. The term wet which may describe the gas flow means that said gas flow comprises at least 15% by volume of water, preferably at least 20% by volume of water, or even at least 25% by volume of water, relative to the total volume of said gas flow. Thus, the term “intermediate humidity” which may describe the gas flow means that the gas flow is neither dry nor wet, and that its water content is between 0.5% by volume and 25% by volume of water and in particular between 1% by volume and 15% by volume of water, relative to the total volume of said gas flow.

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, gamma or delta 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, 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 compound in the method 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 term "hydroxy acids" should therefore be understood as "hydroxy acids and their derivatives. Similarly, 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 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.

According to the present description, the terms "heterogeneous catalyst" and "supported catalyst" are used interchangeably and designate any type of 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, deposited on a support and in particular an oxide matrix, preferably based on silica. The catalyst to be treated by the activation method according to the invention and the activated or reactivated catalyst, obtained at the end of the activation method according to the invention are both heterogeneous catalysts as described above.

The present invention relates to a method for activating a catalyst comprising at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, and an oxide matrix preferably based on silica, to obtain an activated catalyst having improved catalytic performance compared to the initial catalyst to be treated. Said activation method comprises, very particularly consists of, the following steps:

a) a step of preparing an activation composition comprising, in particular consisting of:

at least one multifunctionalized acid compound, preferably chosen from hydroxy acids, keto acids, polyacids (in particular diacids and triacids), their anhydrides, their esters (i.e. hydroxyesters, ketoesters, polyesters such as diesters or triesters), lactones, and mixtures thereof, the quantity of said at least one multifunctionalized acid compound in the activation composition being such that the acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound and the number of moles of the metallic element(s) provided by the catalyst is greater than or equal to 2,

possibly a solvent, organic or aqueous,

optionally a metal precursor of at least one metal element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably said at least one metal element is the same as that of the catalyst, preferably according to a molar ratio of added metal/metal present between the number of moles of said at least one metal element introduced into the activation composition by said metal precursor relative to said at least one metal element of the catalyst of between 0.01 and 15.0, preferably between 0.05 and 10.0, preferentially between 0.10 and 1.00;

b) a step of bringing the activation composition resulting from step a) into contact with said catalyst, to obtain an impregnated intermediate solid;

c) a step of heat treatment of the impregnated intermediate solid obtained in step b) to obtain an activated catalyst, said step c) of heat treatment implementing at least one activation phase carried out at a temperature greater than 100°C, preferably greater than or equal to 105°C, preferentially greater than or equal to 110°C, preferably greater than or equal to 120°C, very preferably greater than or equal to 130°C, and advantageously less than 300°C, preferably less than or equal to 250°C, preferably for a duration of between 0.1 and 20 hours, preferably between 0.25 and 15 hours, preferentially between 0.5 and 10 hours, preferably between 1 and 6 hours, and preferably under a gas flow, for example under a nitrogen flow or a dry or humid air flow,

said heat treatment step c) may optionally implement a drying phase of the impregnated intermediate solid upstream of the activation phase;

d) optionally a high temperature treatment step, carried out at a temperature greater than or equal to 300°C, preferably between 350 and 700°C, preferably between 450 and 600°C, for a duration of between 1 and 6 hours and preferably between 2 and 4 hours, preferably under gas flow.

The catalyst to be treated

The catalyst which is treated by the activation method according to the invention, also called catalyst to be treated or initial catalyst, is a heterogeneous catalyst comprising at least one metallic element, preferably a metallic element, deposited on an oxide matrix (which acts as a support). Preferably, the metallic element(s) is(are) chosen from the elements of groups 3, 4 and 5 of the periodic table, in particular from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from zirconium, niobium, tantalum, and mixtures thereof, very preferentially tantalum. Preferably, the catalyst to be treated comprises between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, more preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix.

Preferably, said oxide matrix comprises silica; said oxide matrix can 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.

The catalyst to be treated may have an average pore diameter (or an average pore size) preferably greater than or equal to 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 catalyst to be treated is in particular between 0.4 and 1.8 ml/g, and in particular between 0.5 and 1.5 ml/g. Preferably, the catalyst to be treated has a specific surface area S _BET of at least 250 m²/g, preferably a specific surface area S _BET of between 250 m²/g and 700 m²/g and even more preferably between 400 m²/g and 600 m²/g.

The above-mentioned textural parameters are determined by the analysis technique known as "nitrogen physisorption" 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 corresponds to the BET specific surface area (S _BET 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 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 ⁰ _max of the nitrogen adsorption-desorption isotherm. The nitrogen adsorption volume is the volume measured for P/P ⁰ _max = 0.99, pressure for which it is assumed that nitrogen has filled all the pores of the material under study. The mesopore diameter ϕ of the tested material, in particular of the catalyst to be treated, is determined by the formula ϕ = 4000xV/S _BET .

According to a very particular embodiment, the catalyst to be treated comprises a silica-based oxide matrix and between 0.3 and 10% by weight, in particular between 0.5 and 5% by weight, of tantalum relative to the weight of the oxide matrix.

The catalyst to be treated may be 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. Preferably, the catalyst to be treated is shaped into extrudates of a size between 1 and 10 mm, possibly spheronized. In addition to said at least one metallic element chosen from the elements of groups 3, 4 and 5, and the support, in particular the oxide matrix, the catalyst to be treated may contain a binder composed in particular of a porous oxide material, 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. When the catalyst to be treated comprises a binder, said binder is present at a content preferably of between 5 and 60% by weight, and preferably between 10 and 30% by weight of binder relative to the total mass of the catalyst to be treated. Preferably, the catalyst to be treated comprises said at least one metallic element, the oxide matrix (i.e. the support) and a binder, for example a silicic binder (such as silica).

The catalyst to be treated may be a fresh catalyst, i.e. a catalyst that has been prepared but has not yet been used in a catalytic unit or reactor, or a spent catalyst, i.e. a catalyst that has been used in a reaction unit (or section) to catalyze a reaction, for example in a unit for converting a feedstock comprising ethanol into butadiene, or an aged catalyst, i.e. a catalyst that has undergone a treatment aimed at reducing its performance, for example a heat treatment, in particular under a wet gas flow, and in particular at the end of which its catalytic properties are degraded. The catalyst to be treated has unsatisfactory catalytic performances, in particular in terms of selectivity and/or productivity, and must be distinguished from the activated catalyst obtained at the end of the method according to the invention, the catalytic performances of which are very satisfactory and improved compared to those of the catalyst to be treated.

a) step of preparing an activation composition

The activation method according to the invention comprises a step a) of preparing an activation composition. The activation composition comprises at least one multifunctionalized acid compound and optionally a solvent. Optionally, said activation composition may comprise a metallic precursor of at least one metallic element chosen from the group of elements of groups 3, 4 and 5 of the periodic table.

Said at least one multifunctionalized acid compound is advantageously an organic compound comprising a carboxylic acid or ester function, and at least one second chemical function, advantageously oxygenated, nitrogenous or sulfurous, preferably in the alpha position (position 1, i.e. on the carbon directly adjacent to the carbon of the acid or ester function), in the beta position (position 2, i.e. on the second carbon adjacent to the carbon of the acid or ester function), in the gamma position (position 3, i.e. on the third carbon adjacent to the carbon of the acid or ester function), or in the delta position (position 4, i.e. on the fourth carbon adjacent to the carbon of the acid or ester function). Preferably, said second chemical function or at least one of said second chemical functions is oxygenated, and preferably is a hydroxyl and/or carbonyl function. Said at least one multifunctionalized acid compound may comprise several second chemical functions, in particular oxygenated, for example several hydroxyl and/or carbonyl functions in addition to the first carboxylic acid or ester function, such as tartaric acid which comprises, in addition to the first carboxylic acid function, a carbonyl function and three hydroxyl functions (in particular two hydroxyl functions in alpha and beta and a second carboxylic acid function in gamma), or citric acid which comprises the first carboxylic acid function and a hydroxyl function in beta and two carboxylic acid functions in gamma and delta). According to a very particular embodiment, said multifunctionalized acid compound may be a cyclic compound capable of generating an organic compound comprising a carboxylic acid or ester function and a second oxygenated chemical function, advantageously hydroxyl and/or carbonyl, such as a diacid anhydride (capable of generating, by ring opening, a compound comprising two carboxylic acid functions) or a lactone (capable of generating, by ring opening, a compound comprising an ester function and a hydroxyl function), the anhydride and the lactone possibly comprising other chemical functions, in particular oxygenated ones.

Preferably, said at least one multifunctionalized acid compound is chosen from hydroxy acids, keto acids, polyacids (in particular diacids and triacids, more particularly diacids), their anhydrides, their esters (i.e. hydroxyesters, ketoesters, polyesters such as diesters or triesters), lactones, and their mixtures. Preferably, said at least one multifunctionalized acid compound is chosen from alpha-hydroxy acids, alpha-keto acids, alpha-diacids, beta-hydroxy acids, beta-keto acids, beta-diacids, gamma-hydroxy acids, gamma-keto acids, gamma-diacids, delta-hydroxy acids, delta-keto acids, delta-diacids, their esters (i.e. alpha-, beta-, gamma, delta-hydroxyesters; alpha-, beta-, gamma, delta-ketoesters; alpha-, beta-, gamma, delta-diesters), alpha-lactones, beta-lactones, gamma-lactones, delta-lactones, and mixtures thereof. For example, said at least one multifunctionalized acid compound is selected from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, phenylglyoxylic acid, glutaric acid, succinic acid, levulinic acid, maleic acid, their esters such as triethyl citrate, benzyl glycolate, ethyl lactate, ethyl pyruvate, diethyl tartrate, methyl salicylate, methyl mandelate, ethyl levulinate, diethyl malate, diethyl oxalate, diethyl succinate, diethyl malonate, ethyl acetoacetate, ethyl pyruvate, diethyl glutarate, gamma-valerolactone, delta-valerolactone, and combinations of two or more of these.

According to a preferred embodiment, said at least one multifunctionalized acid compound is chosen from hydroxy acids, keto acids, diacids, hydroesters, ketoesters, diesters, and mixtures thereof. And in particular, said at least one multifunctionalized acid compound is chosen from pyruvic acid, lactic acid, tartaric acid, citric acid, mandelic acid, glycolic acid, oxalic acid, malic acid, ethyl lactate, ethyl pyruvate, diethyl tartrate, triethyl citrate, methyl mandelate, benzyl glycolate, diethyl oxalate, diethyl malate, and combinations of at least two of them. Very preferably, said at least one multifunctionalized acid compound is chosen from alpha-hydroxy acids, alpha-keto acids, beta-hydroxy acids, beta-keto acids, their esters (i.e. alpha-hydroxyesters, alpha-ketoesters, beta-hydroxyesters, beta-ketoesters), and mixtures thereof. Very particularly, said at least one multifunctionalized acid compound is chosen from pyruvic acid, lactic acid, tartaric acid, citric acid, mandelic acid, glycolic acid, malic acid, ethyl lactate, ethyl pyruvate, diethyl tartrate, triethyl citrate, methyl mandelate, benzyl glycolate, diethyl malate, and combinations of at least two of them.

Very advantageously, the activation composition comprises an amount of said at least one multifunctionalized acid compound adjusted so as to have an acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound and the number of moles of said at least one metallic element of the catalyst greater than or equal to 2, preferably between 2 and 200, preferably between 2 and 100, preferentially between 3 and 60, preferentially between 5 and 40, preferably between 5 and 30, and very preferably between 7 and 20.

The activation composition may also comprise a solvent, organic or aqueous, advantageously in which said at least one multifunctionalized acid compound is soluble, at least partially, preferably entirely. An advantage of using a solvent in the activation composition is to dilute the multifunctionalized acid compound and therefore to allow the acid/metal molar ratio to be adjusted while allowing the activation composition to diffuse throughout the porosity of the catalyst. Another advantage is to allow the range of possible compounds to be increased; in fact, acid compounds which are, for example, solid, particularly under ambient conditions (typically a temperature of 20°C +/- 5°C and a pressure of 0.1 MPa) can thus be solubilized in the organic or aqueous solvent used and used as multifunctionalized acid compounds. Preferably, the activation composition comprises a solvent, organic or aqueous, preferably at least 5% by weight of solvent, or even at least 20% by weight of solvent, and for example up to 90% by weight or 75% by weight of solvent, the percentages being given by weight of solvent relative to the total weight of the activation composition.

Advantageously, the solvent of the activating composition may be an organic solvent or an aqueous solvent.

When present, the organic solvent comprises, preferably consists of, at least one organic compound and preferably an oxygenated or hydrocarbon organic compound, advantageously in which the multifunctionalized acid compound is at least partially soluble. Optionally, the organic solvent may contain water, preferably up to 20% by weight, more preferably up to 10% by weight of water, relative to the total weight of organic solvent. More particularly, the organic solvent is chosen from alcohols, monofunctional carboxylic acids, ethers, esters, ketones, hydrocarbon compounds, and mixtures thereof. The alcohols which can be used as solvent in the activation composition are preferably monoalcohols 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 alcohols which can be used as organic solvent are for example chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof. Preferably, the monofunctional carboxylic acids which can be used as solvent in the activation composition are preferably carboxylic acids having between 2 and 4 carbon atoms (i.e. C2-C4), in particular linear, branched or cyclic, advantageously non-aromatic. The monofunctional carboxylic acids which can be used as organic solvent are for example chosen from acetic acid, propionic acid, butyric acid. The ethers optionally used as solvent in the activation composition are preferably C4-C8 ethers, in particular linear, branched or cyclic, advantageously non-aromatic, for example tetrahydrofuran (THF), diethyl ether, diisopropyl ether. The esters which can be used as solvent in the activation composition are preferably esters of C2-C6, preferably C2-C4, carboxylic acid and 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, ethyl acetoacetate. Preferably, the ketones optionally used as solvent in the activation composition are chosen from diketones, for example acetylacetone. The hydrocarbon compounds which can be used as solvent in the activation composition are preferably aliphatic, cyclic or aromatic hydrocarbon compounds, having between 5 and 10 carbon atoms (i.e. C5-C10), preferably between 6 and 8 carbon atoms (i.e. C6-C8), and in particular having 6, 7 or 8 carbon atoms. Very preferably, the hydrocarbon compounds which can be used as solvent are chosen from hexane isomers, heptane isomers, octane isomers and mixtures thereof. For example, the organic solvent comprises, preferably consists of, at least one organic compound selected from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, acetic acid, propionic acid, butyric acid, tetrahydrofuran (THF), diethyl ether, diisopropyl ether, methyl acetate, ethyl acetate, isopropyl acetate, ethyl propanoate, acetylacetone, hexane, heptane, and mixtures thereof, in particular from methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, acetic acid, propionic acid, isopropyl acetate, acetylacetone, hexane, heptane, and mixtures thereof.

At the same time, when present, the aqueous solvent of the activating composition comprises water, preferably at least 25% by weight of 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 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 avoid any risk of neutralization and/or precipitation of said at least one multifunctionalized acid compound.

When the multifunctionalized acid compound is an anhydride, a lactone, the activation composition preferably comprises an aqueous solvent or an organic solvent comprising at least one alcohol, preferably at least 10% by weight, preferably at least 50% by weight, of alcohol. When the multifunctionalized acid compound is an ester of a hydroxy acid, keto acid or polyacid (preferably diacid or triacid), the activation composition preferably comprises an aqueous solvent and/or step c) is advantageously carried out under a wet gas flow, i.e. under a gas flow comprising at least 15% by volume of water, preferably at least 20% by volume of water, or even at least 25% by volume of water, relative to the total volume of said gas flow.

Optionally, the activation composition may comprise a metal precursor of at least one metal element chosen from the group of elements of groups 3, 4 and 5 of the periodic table, in particular when a re-impregnation (i.e. a new active phase impregnation) is necessary in particular when the content of said at least one metal element of the catalyst to be treated is not sufficient. Said metal precursor comprises a metal element preferably chosen 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. When the activation composition comprises a metal precursor, said metal precursor preferably comprises at least one metal element identical to said at least one metal element of the catalyst to be treated.

Advantageously, a metallic precursor of at least one metallic element chosen from the elements of group 3, 4 and/or 5 of the periodic table, 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 metallic precursors used are organic or inorganic compounds comprising said metallic element of group 3, 4 and/or 5, and which are advantageously soluble or diluted at least partially in the activation composition, and in particular in the solvent when it is present, under the temperature and pressure conditions implemented in particular during step a) and step b). The metal precursors used are therefore chosen in particular 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 of these. The metal precursors used are more preferably chosen from the group consisting of chlorides, nitrates, hydroxides, carboxylates, alcoholates, diketonates, of said metal element from group 3, 4 and/or 5, and combinations of two or more of these. The alcoholate type precursors have, for example, the formula M(OR) _n where 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 methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, s-butyl, t-butyl groups. The carboxylate precursors may be mono-, di- or tri-carboxylate salts, such as oxalates, of said at least one metal element selected from the elements of groups 3, 4 and 5. For example, preferred metal precursors of tantalum are tantalum pentachloride (TaCl ₅ ), tantalum pentaethanoate (Ta(OC ₂ H ₅ ) ₅ or Ta(OEt) ₅ ) and tantalum tetraethoxide 2,4 pentadionate (or tantalum tetraethoxyacetylacetonate, denoted Ta(AcAc)(OEt) ₄ ), which can be used with most organic solvents, or tantalum oxalate ((C ₂ O ₄ )Ta) which is at least partially soluble in water. The metallic precursor of niobium may be selected from niobium pentachloride (NbCl ₅ ), niobium pentaethanoate (Nb(OC ₂ H ₅ ) ₅ or Nb(OEt) ₅ ) which are at least partially soluble in organic solvents, and niobium oxalate ((C ₂ O ₄ )Nb) and niobium ammonium oxalate (C ₆ H ₄ NO ₁₂ Nb) which are at least partially soluble in water. The metallic precursor of zirconium may be selected from zirconium tetrachloride (ZrCl ₄ ) and zirconium tetraethanoate (Zr(OC ₂ H ₅ ) ₄ or Zr(OEt) ₄ ).

When the activation composition comprises a metal precursor of at least one metal element selected from the group of elements of groups 3, 4 and 5 of the periodic table, said metal precursor is present so as to have a molar ratio of added metal/metal present between the number of moles of said at least one metal element introduced into the activation composition by said metal precursor relative to said at least one metal element of the catalyst of between 0.01 and 15.0, preferably between 0.05 and 10.0, preferentially between 0.10 and 1.00.

Preferably, step a) of preparing the activation composition is carried out at a temperature between room temperature and 80°C, and advantageously at a pressure between atmospheric pressure and 10.0 MPa, preferably between atmospheric pressure and 3.0 MPa. Step a) may very advantageously comprise mixing said at least one multifunctionalized acid compound with an organic or aqueous solvent and optionally with said metal precursor.

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

The activation composition obtained at the end of step a) of the method according to the invention is advantageously in liquid form.

b) contacting step

The activation method according to the invention comprises a step b) of bringing the activation composition into contact with a catalyst comprising at least one metallic element chosen from the group of elements in groups 3, 4 and 5 of the periodic table, and an oxide matrix preferably based on silica, i.e. the catalyst to be treated, to obtain an impregnated intermediate solid.

The contacting in step b) 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.

Step b) is very advantageously carried out at a temperature between room temperature and a temperature below 300°C, and preferably at a pressure between 0.05 and 10.00 MPa.

When contacting in step b), the activation composition may be in liquid form or in gaseous (or at least partially gaseous) form.

According to a first particular embodiment of the invention, the activation composition is in liquid form when contacting. Step b) then comprises bringing the catalyst to be treated into contact with the activation composition in liquid form, advantageously at a temperature between room temperature and 80°C, and preferably at a pressure between atmospheric pressure and 10.0 MPa, preferably between atmospheric pressure and 3.0 MPa. According to this particular embodiment, the contacting of the catalyst to be treated with the activation composition can be carried out under gas flow, for example at a flow rate greater than or equal to 0.1 NL/h/g or even greater than or equal to 0.5 NL/h/g (NL/h/ for normal liters per hour and per gram of catalyst to be treated), dry or wet or even at intermediate humidity, preferably under wet gas flow. A gas stream here corresponds to a stream of a gas, inert or not, for example an air stream, a nitrogen stream, or a stream of a nitrogen-based gas comprising oxygen, in particular less than 20% by volume of oxygen relative to the total volume of said gas. The dry term which may qualify the gas stream here means that said gas stream comprises at most 1% by volume of water, preferably at most 0.5% by volume of water, relative to the total volume of said gas stream. The wet term which may qualify the gas stream here means that said gas stream comprises at least 15% by volume of water, preferably at least 20% by volume of water, or even at least 25% by volume of water, relative to the total volume of said gas stream. Thus, an intermediate humidity means that the gas flow is neither dry nor wet, and that its water content is between 0.5% volume and 25% volume of water and in particular between 1% volume and 15% volume of water, relative to the total volume of said gas flow. According to this particular embodiment, step b) comprises, for example, bringing into contact with the catalyst to be treated, a volume of activation composition such that said volume of activation composition advantageously corresponds to the total or partial pore volume of the catalyst to be treated, or to a volume slightly greater than the pore volume of the catalyst to be treated. More particularly, the volume of activation composition (V _composition ), brought into contact with the catalyst to be treated, advantageously corresponds to a volume equal to the pore volume (Vp) of said catalyst to be treated, to plus or minus 20% volume, preferably plus or minus 10% volume, that is to say: V _composition = Vp +/- 20% vol., preferably V _composition = Vp +/- 10% vol. Preferably, the volume (V _composition ) of activation composition, brought into contact with the catalyst to be treated, corresponds to the total or partial pore volume of the catalyst to be treated, that is to say to a volume equal to the pore volume (Vp) of the catalyst to be treated, or to a volume equal to at least 80% volume, preferably at least 90% volume, of the pore volume (Vp) of said catalyst to be treated. According to this first embodiment, the activation composition resulting from step a), which is in liquid form, comprises, preferably consists of, said at least one multifunctionalized acid compound, optionally at least one organic or aqueous solvent, and optionally at least one metallic precursor.

According to a second particular embodiment of the invention, the activation composition is in gaseous form when brought into contact. The advantage of this embodiment lies in the fact that the activation of the catalyst to be treated can be carried out in situ in a reaction unit whose reactor or catalytic bed which comprises said catalyst to be treated, in particular the spent catalyst to be treated, is not operating (i.e. in which no charge to be converted is sent and therefore transformed). According to this second embodiment, the activation composition resulting from step a) comprises, preferably consists of, said at least one multifunctionalized acid compound and optionally at least one organic or aqueous solvent, preferably aqueous; it does not comprise a metal precursor. According to this second embodiment, step b) of the method according to the invention comprises the vaporization, advantageously total, of the activation composition prepared in step a), then the contacting by passage (or sweeping) of the vaporized activation composition (i.e. in gaseous form) on the catalyst to be treated, for example on a catalytic bed of said catalyst, in particular located in a reaction unit and more particularly on a line not in operation of said reaction unit. Said vaporization phase of step b), according to this second embodiment, which is located upstream of the contacting phase, can be carried out at a temperature greater than or equal to 100°C, preferably greater than or equal to 120°C, preferentially greater than or equal to 130°C, and less than 300°C, preferably less than or equal to 250°C. Said vaporization phase of step b), according to this second embodiment, can advantageously be carried out at a pressure of between 0.05 and 10.00 MPa, preferably between 0.05 and 3.00 MPa, preferably between 0.05 and 1.00 MPa, more preferably between 0.08 and 0.40 MPa. The contacting phase of step b), according to this second embodiment, is advantageously carried out for a period of between 0.1 and 48 hours, preferably between 0.2 and 12 hours, preferably between 0.5 and 5 hours, at a temperature greater than or equal to 100°C, preferably greater than or equal to 120°C, preferably greater than or equal to 130°C, and less than 300°C, preferably less than or equal to 250°C. Said contacting phase of step b), according to this second embodiment, can be carried out, advantageously at a pressure of between 0.05 and 10.00 MPa, preferably between 0.05 and 3.00 MPa, preferentially between 0.05 and 1.00 MPa, preferably between 0.08 and 0.40 MPa, and preferably at a space velocity of between 0.1 and 10 h ^-1 , preferentially 0.2 and 5 h ^-1 and preferably between 0.4 and 2 h ^-1 . The space velocity here corresponds to a weight hourly space velocity (or WHSV for Weight Hourly Spaced Velocity according to English terminology) and is defined as the ratio between the mass flow rate of vaporized activation composition relative to the mass of catalyst. According to this particular embodiment, the vaporization and contacting phases can be carried out under gas flow, for example at a flow rate greater than or equal to 0.1 NL/h/g or even greater than or equal to 0.5 NL/h/g (NL/h/ for normal liters per hour and per gram of catalyst to be treated), dry or wet or even at intermediate humidity, preferably under wet gas flow. A gas flow corresponds to a flow of a gas, inert or not, for example an air flow, a nitrogen flow, or a flow of a nitrogen-based gas comprising oxygen, in particular less than 20% by volume of oxygen relative to the total volume of said gas, preferably an inert gas flow, in particular a nitrogen flow, in particular for safety reasons. The terms "dry", "wet" and "at intermediate humidity" have the same meanings as those defined above for the first embodiment according to which the activation composition is in liquid form during contacting. According to this second particular embodiment in which the activation composition is in gaseous form when brought into contact with the catalyst to be treated, the temperature and pressure conditions, during the vaporization and contacting phases, are adjusted so as to vaporize and maintain in the gaseous state, at least partially, preferably entirely, said at least one multifunctionalized acid compound and the possible solvent of the activation composition, without however degrading said at least one multifunctionalized acid compound and the possible solvent. The vaporization and contacting of step b) can be carried out in the presence or absence of a diluting gas (or gas flow). Furthermore, a person skilled in the art will know how to choose the appropriate multifunctionalized acid compound so as to put and maintain in gaseous form at least partially, preferably entirely, the activation composition, and therefore said multifunctionalized acid compound. According to this particular embodiment, the multifunctionalized acid compound of the activation composition is then advantageously chosen so that the partial pressure of the multifunctionalized acid compound, optionally in the diluent gas, is less than or equal to the saturated vapor pressure of said multifunctionalized acid compound, at the temperature of step b), in particular of the vaporization and contacting phases of step b).

According to this second embodiment, an excess of activation composition can be vaporized and can sweep the catalyst to be treated, so as to have a total quantity of multifunctionalized acid compound deposited on the catalyst to be treated advantageously such that the acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound deposited relative to the number of moles of said at least one metallic element of the catalyst to be treated is greater than or equal to 2, preferably between 2 and 200, preferably between 2 and 100, preferentially between 3 and 60, preferentially between 5 and 40, preferably between 5 and 30, and very preferably between 7 and 20. The excess of the activation composition in gaseous form, which has swept the reactor or catalytic bed containing the catalyst to be treated, can advantageously be recovered at the outlet of the reactor or catalytic bed.

c) heat treatment step

The method according to the invention comprises a step c) of heat treatment of the impregnated intermediate solid obtained in step b), to advantageously obtain an activated catalyst.

According to the invention, the heat treatment step c) implements at least one activation phase carried out at a temperature greater than 100°C, preferably greater than or equal to 105°C, preferentially greater than or equal to 110°C, preferably greater than or equal to 120°C, very preferably greater than or equal to 130°C, and advantageously less than 300°C, preferably less than or equal to 250°C. Said activation phase of step c) is preferably carried out for a duration of between 0.1 and 20 hours, preferably between 0.25 and 15 hours, preferentially between 0.5 and 10 hours, preferably between 1 and 6 hours.

The activation phase of step c) can be carried out successively (i.e. downstream) from step b), in particular when the activation composition is in liquid form when contacting in step b), or simultaneously with step b), in particular when the activation composition is in gaseous form when contacting in step b).

The activation phase may be carried out with a single temperature step or may comprise several steps, preferably two or three steps, of temperatures greater than 100°C, preferably greater than or equal to 105°C, preferably greater than or equal to 110°C, preferably greater than or equal to 120°C, very preferably greater than or equal to 130 and advantageously less than 300°C, preferably less than or equal to 250°C. For example, the activation phase may comprise a step at 150°C followed by a step at 210°C. Each temperature step may last between 0.1 and 15 hours, preferably 0.25 and 10 hours, preferably between 0.5 and 5 hours. Between each temperature level, the activation phase advantageously comprises a rise in temperature, in particular according to a ramp of between 1 and 20°C/minute, preferably between 2 and 10°C/minute. Preferably, the activation phase is carried out at a pressure of between 0.05 and 10.0 MPa, preferably between 0.05 and 3.0 MPa, preferably between 0.05 and 1.00 MPa, very preferably between 0.08 and 0.40 MPa.

When the contacting in step b) is carried out with the activation composition in the liquid state, the activation phase of step c) is preferably carried out successively in step b), preferably at a pressure lower than the saturated vapor pressure of the multifunctionalized acid compound used, under the operating conditions of the activation phase of step c), in particular at the operating temperature of the activation phase, so as to keep said multifunctionalized acid compound in the liquid state. In this case, the activation phase can be described as a liquid activation phase.

When the contacting in step b) is carried out with the activation composition in the gaseous state, the activation phase of step c) is preferably carried out simultaneously with step b) and preferably at a pressure higher than the saturated vapor pressure of the multifunctionalized acid compound used, under the operating conditions of the activation phase of step c), in particular at the operating temperature of the activation phase, so as to keep said multifunctionalized acid compound in the gaseous state. In this case, the activation phase can be described as a gaseous activation phase.

The activation phase may be carried out, in part or in full, under a gas flow, for example at a flow rate greater than or equal to 0.1 NL/h/g or even greater than or equal to 0.5 NL/h/g (NL/h/ for normal liters per hour and per gram of catalyst to be treated), dry or wet or at intermediate humidity, preferably under a wet gas flow. A gas flow corresponds here to a flow of a gas, inert or not, for example an air flow, a nitrogen flow, or a flow of a nitrogen-based gas comprising oxygen, in particular less than 20% by volume of oxygen relative to the total volume of said gas. The term dry which may qualify the gas flow means here that said gas flow comprises at most 1% by volume of water, preferably at most 0.5% by volume of water, relative to the total volume of said gas flow. The term humid which can qualify the gas flow means here that said gas flow comprises at least 15% volume of water, preferably at least 20% volume of water, or even at least 25% volume of water, relative to the total volume of said gas flow. Thus, an intermediate humidity means that the gas flow is neither dry nor humid, and that its water content is between 0.5% volume and 25% volume of water and more particularly between 1% volume and 15% volume of water, relative to the total volume of said gas flow.

Optionally, heat treatment step c) also implements a drying phase, in particular when the contacting in step b) is carried out with the activation composition in the liquid state. When step c) comprises a drying phase, said optional drying phase is located upstream of the activation phase, during which the solvent possibly introduced with the activation composition and possibly still present in the impregnated intermediate solid, in particular in the pore volume and/or on the surface of the impregnated intermediate solid, can be at least partially evaporated and advantageously removed. Preferably, the drying phase is carried out at a temperature between 50 and 115°C and preferably between 70 and 100°C, for a duration between 1 and 24 hours, advantageously under a gas flow, preferably under an air flow, for example at a flow rate greater than or equal to 0.1 NL/h/g or even greater than or equal to 0.5 NL/h/g (NL/h/ for normal liters per hour and per gram of catalyst), dry or wet or even at intermediate humidity. A gas flow corresponds in this drying phase, as in the activation phase, to a flow of a gas, inert or not, for example an air flow, a nitrogen flow, or a flow of a nitrogen-based gas comprising oxygen, in particular at most 20% by volume of oxygen relative to the total volume of said gas. The terms “dry”, “wet” and “intermediate humidity” have the same meanings here as those defined above for the activation phase.

Step c) of heat treatment which in particular implements said activation phase advantageously makes it possible to obtain an activated catalyst whose catalytic performances, in particular in terms of selectivity and productivity, are improved compared to those of the initial catalyst.

Optionally, the activation method according to the invention may comprise the repetition of steps b) of contacting and c) of heat treatment, or possibly also step a) of preparing the solution. Indeed, steps b) of contacting and c) of heat treatment, or possibly also step a), may be repeated one to five times, preferably once or twice, successively, depending on the catalytic performances targeted for the activated catalyst. In the case of a repetition of at least steps b) and c), the contacting is carried out between the activation composition and the activated catalyst obtained at the end of the previous step c).

At the same time, a catalyst can undergo the activation method according to the invention one or more times throughout its lifetime.

d) optionally a high temperature treatment step

The activation method may comprise a high-temperature treatment step of the activated catalyst obtained at the end of step c). This high-temperature treatment step may be carried out directly at the end of step c) of heat treatment (or of the optional re-impregnation step d) in the same unit as that implemented in step c) and in particular in step b) and step c), or subsequently in particular in a catalytic unit, for example in a unit for converting a feedstock comprising ethanol into butadiene.

Step d) of high temperature treatment advantageously corresponds to a phase of calcination or pyrolysis of the activated catalyst, so as to eliminate the carbon from the activated catalyst in particular introduced during step b) of the process according to the invention. Preferably, when carried out, step d) is carried out under a gas flow, preferably under a flow of a gas comprising oxygen, for example under a flow of air, or under a flow of nitrogen, and preferably under a dry gas flow, that is to say under a gas flow containing at most 1% by volume of water, preferably at most 0.5% by volume of water. Very advantageously, step d) is carried out at a temperature greater than or equal to 300°C, preferably between 350 and 700°C, preferably between 450 and 600°C, for a duration of between 1 and 6 hours and preferably between 2 and 4 hours.

d) optionally a re-impregnation step

The activation method may optionally comprise a re-impregnation step, in particular when the catalyst to be treated does not comprise a sufficient content of metallic element, for example Ta, Nb and/or Zn. The objective of such an optional step is to reintroduce at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, so as to achieve the targeted content of said metallic element in the final activated catalyst. Preferably, said at least one metallic element possibly introduced during this optional re-impregnation step is advantageously identical to said at least one metallic element of the initial catalyst.

The re-impregnation step is advantageously carried out by bringing the initial catalyst or the activated catalyst obtained at the end of heat treatment step c) into contact with an impregnation solution which comprises a metallic precursor of at least one metallic element chosen from the elements of groups 3, 4, 5 of the periodic table, preferably identical to said at least one metallic element of the initial catalyst.

When the activation method includes such an optional step, said re-impregnation step can be implemented:

- simultaneously with steps a) and b) in the case where step b) of contacting the activation method is carried out in a liquid way, i.e. when the activation composition is in liquid form during the contacting of step b). In this case, the impregnation solution corresponds to the activation composition which comprises a metallic precursor of at least one metallic element; or

- downstream of step c) of heat treatment, and preferably upstream of a possible step d) of high temperature treatment, whatever the liquid or gaseous form of the activation composition during contact in step b).

Advantageously, the impregnation solution comprises a metallic precursor of at least one metallic element chosen from the group of elements of groups 3, 4 and 5 of the periodic table, optionally an impregnation additive which may be a compound identical to said at least one multifunctionalized acid compound of the activation composition or different, and optionally an organic or aqueous solvent which may be identical to the optional solvent of the activation composition. Said metallic precursor as well as the impregnation additive are chosen so as to be at least partially, preferably entirely, solubilized/diluted in the impregnation solution and in particular in the optional organic or aqueous solvent.

Said metallic precursor advantageously comprises a metallic element preferably chosen 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. Preferably, said metallic precursor comprises at least one metallic element identical to said at least one metallic element of the catalyst to be treated.

Advantageously, a metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table is any compound comprising said at least one metallic element and capable of releasing this element in solution in reactive form. The metallic precursors used are organic or inorganic compounds comprising said at least one metallic element of group 3, 4 and/or 5, and which are advantageously soluble at least partially, preferably entirely, in the impregnation solution, and in particular in the organic or aqueous solvent when it is present, under the temperature and pressure conditions implemented during the optional re-impregnation step. The metal precursors used are therefore chosen in particular 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 of these. The metal precursors used are more preferably chosen from the group consisting of chlorides, nitrates, hydroxides, carboxylates, alcoholates, diketonates, of said metal element from group 3, 4 and/or 5, and combinations of two or more of these. The alcoholate type precursors have, for example, the formula M(OR) _n where 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 methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl groups. The carboxylate precursors may be mono-, di- or tri-carboxylate salts, such as oxalates, of said at least one metal element selected from the elements of groups 3, 4 and 5. For example, preferred metal precursors of tantalum are tantalum pentachloride (TaCl ₅ ), tantalum pentaethanoate (Ta(OC ₂ H ₅ ) ₅ or Ta(OEt) ₅ ) and tantalum tetraethoxide 2,4 pentadionate (or tantalum tetraethoxyacetylacetonate, denoted Ta(AcAc)(OEt) ₄ ), which can be used with most organic solvents, or tantalum oxalate ((C ₂ O ₄ )Ta) which is at least partially soluble in water. The metallic precursor of niobium may be selected from niobium pentachloride (NbCl ₅ ), niobium pentaethanoate (Nb(OC ₂ H ₅ ) ₅ or Nb(OEt) ₅ ) which are at least partially soluble in organic solvents, and niobium oxalate ((C ₂ O ₄ )Nb) and niobium ammonium oxalate (C ₆ H ₄ NO ₁₂ Nb) which are at least partially soluble in water. The metallic precursor of zirconium may be selected from zirconium tetrachloride (ZrCl ₄ ) and zirconium tetraethanoate (Zr(OC ₂ H ₅ ) ₄ or Zr(OEt) ₄ ).

Preferably, the metal precursor of at least one element from group 3, 4 and/or 5 is present in the impregnation solution so as to have a molar ratio of added metal/metal present between the number of moles of said at least one metal element introduced into the impregnation solution by said metal precursor relative to said at least one metal element of the catalyst to be treated or activated of between 0.01 and 15.0, preferably between 0.05 and 10.0, preferentially between 0.10 and 1.00.

The impregnation solution may further comprise an impregnation additive. The impregnation additive may be an organic compound selected from multifunctionalized ketones, such as diketones or hydroxy-ketones (such as acetylacetone, or acetoin), monofunctional carboxylic acids, multifunctionalized acids such as hydroxy acids, keto acids, polyacids (for example diacids and triacids), their anhydrides, their esters, and their mixtures. In a very particular manner, the impregnation additive is a multifunctionalized acid and more particularly identical to said at least one multifunctionalized acid compound of the activation composition.

The metal precursor of at least one element from group 3, 4 and/or 5 and the multifunctionalized acid impregnation additive(s) are present in the impregnation solution in quantities such that the molar ratio (additive/metal added) of the number of moles of multifunctionalized acid impregnation additive(s) relative to the number of moles of the metal element(s) provided by the metal precursor is greater than or equal to 1, preferably greater than or equal to 2, preferentially between 2 and 50, more preferably between 5 and 25.

The re-impregnation step, when integrated into the method according to the invention, is very advantageously carried out under temperature and pressure conditions such that the impregnation solution is in liquid form. Preferably, the re-impregnation step is carried out at a temperature between room temperature and 80°C, and at a pressure between atmospheric pressure and 10.0 MPa, preferably between atmospheric pressure and 3.0 MPa.

According to a first embodiment, the re-impregnation step comprises bringing the impregnation solution into contact with the initial catalyst, in particular during step b) of the method according to the invention. According to this embodiment, the impregnation solution corresponds to the activation composition which then comprises at least one metallic precursor of said at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, the impregnation additive being the multifunctional acid compound of said activation composition. In this first embodiment, bringing the impregnation solution into contact with the initial catalyst is carried out in step b) and in a liquid way, that is to say that the activation composition is in liquid form during the contacting in step b).

According to a second embodiment, the re-impregnation step comprises bringing the impregnation solution into contact with the activated catalyst obtained at the end of step c). According to this second embodiment, the re-impregnation step is then carried out downstream of step c). According to this embodiment, the re-impregnation step comprises bringing the impregnation solution into contact with the activated catalyst from step c), advantageously followed by drying preferably carried out at a temperature between 50 and 200°C, 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 or under a nitrogen flow, then optionally calcination which is advantageously carried out under a gas flow comprising oxygen and/or nitrogen, for example under an air flow or under a nitrogen flow, preferably dry, at a temperature above 300°C, preferably between 350 and 700°C, preferably between 450 and 600°C, for a period of between 1 and 6 hours and preferably between 2 and 4 hours.

The method according to the invention thus makes it possible to advantageously obtain an activated catalyst, i.e. a catalyst comprising at least one heterogeneous metallic element, comprising at least one metallic element from group 3, 4 and/or 5 of the periodic table, very preferably tantalum, deposited on a support (or oxide matrix) in particular based on silica, and whose catalytic performances, in particular in terms of selectivity and productivity, in particular during the reaction for converting a feedstock comprising ethanol into butadiene, are significantly improved (i.e. beyond the uncertainty of the measurements), compared to those of the initial catalyst to be treated. The method according to the invention therefore allows the activation or reactivation (i.e. rejuvenation) of heterogeneous catalysts in a simple and economical manner, to obtain catalysts with satisfactory performances, in particular in terms of selectivity and productivity and more particularly during the conversion of a feedstock comprising ethanol into butadiene.

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

Examples

Spent catalysts (from a reaction unit for converting a feedstock containing ethanol and acetaldehyde into butadiene), containing 3% by weight of tantalum on silica, are reactivated according to the methods described in Example 1. The spent and activated catalysts are tested under the same conditions in a catalytic test unit for converting a feedstock comprising ethanol and acetaldehyde into butadiene, as described in Example 2.

Example 1: Reactivation of 3% Ta/SiO catalysts ₂

For each of the (re)activated catalysts, the activation method is as follows:

A catalyst 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) is recovered at the outlet of a unit for converting a feedstock containing ethanol and acetaldehyde into butadiene. Before unloading, the catalyst underwent a controlled combustion decoking step (regeneration). It is called spent catalyst (catalyst A) and has a carbon content of less than 2% by weight (relative to the total weight of spent catalyst A).

For each catalyst, a rejuvenation solution comprising a solvent and an additive, in particular a multifunctionalized acid compound, is prepared, at room temperature and atmospheric pressure. For catalyst B, the rejuvenation solution comprises only a solvent, at room temperature and atmospheric pressure. When the rejuvenation solution comprises an additive, in particular a multifunctionalized acid compound, said additive is mixed with the chosen solvent. The rejuvenation solution is then brought into contact with the spent catalyst (catalyst A), i) in liquid form or ii) in gaseous form.

i) Liquid route, operating method used when the rejuvenation solution is in liquid form when brought into contact:

In this embodiment, the rejuvenation solution, which is in liquid form, is brought into contact with the spent catalyst (catalyst A), at room temperature and atmospheric pressure. The volume of liquid rejuvenation solution used is proportional to the pore volume of the spent catalyst and is added dropwise to the spent catalyst until wettability of the surface of the latter is observed (dry impregnation). The solid is then left to mature for 0.5 to 53 hours. The solid finally undergoes a heat treatment according to protocol A, B, C or D as described in Table 1.

temperature levels protocol A protocol B C protocol 100°C 16 hours in air at 20% relative humidity 16 hours in dry air 16 hours in dry air 150°C 4 hours in air at 20% relative humidity 4 hours in air at 25% relative humidity - 210°C 2 hours in air at 20% relative humidity 2 hours in dry air 4 hours in air at 25% relative humidity, then
2 hours in dry air

Heat treatment protocols A, B, C and D each include a drying phase, followed by an activation phase.

The different catalysts prepared, according to the liquid route, are presented in Table 2.

Catalyst According to the invention Solvent Acidic compound Thermal protocol acid/Ta (mol/mol) HAS No - - - - B No acetylacetone --- HAS --- C No acetylacetone phenol C 15 D Yes acetylacetone lactic acid B 3 E Yes acetylacetone lactic acid B 7 F Yes acetylacetone lactic acid B 15 G Yes acetylacetone lactic acid C 15 H Yes ethanol lactic acid B 15 I acetylacetone lactic acid HAS 7 I Yes acetylacetone mandelic acid HAS 7 K Yes acetylacetone salicylic acid HAS 7 L Yes acetylacetone 3-hydroxybenzoic acid HAS 7 M Yes acetylacetone diethyl tartrate HAS 7 N Yes acetylacetone dioctyl phthalate HAS 7 O Yes acetylacetone glutaric acid HAS 7 P Yes acetylacetone ethylcyclopentanone-2-carboxylate HAS 7 Q Yes acetylacetone δ-valerolactone HAS 7

ii) Gaseous route, operating method used when the rejuvenation solution is in gaseous form when brought into contact:

In this embodiment, the prepared rejuvenation solution, completely vaporized under a nitrogen flow rate equivalent to 2 NL/h/g _catalyst , is passed over the used catalyst for 2 hours. This contact is carried out at a temperature of 190°C, 210°C, 230°C or 300°C, at a pressure of 0.1 MPa and at a space velocity of 2 h ^-1 .

The solid obtained finally undergoes stripping under _N2 for 2 hours then heat treatment in air up to 470°C.

The different catalysts prepared, according to the gaseous route, are presented in Table 3.

Catalyst According to the invention Activation composition acid / Ta (mol/mol) Duration
(hour) N2 flow rate (NL/h/g _catalyst ) Activation temperature (°C) HAS No - - - - - B’ Yes ethyl lactate / water 50/50 (wt/wt) 102 2 2 210 It Yes Lactic acid / water 90/10 (wt/wt) 134 2 2 210 From Yes Lactic acid / water 50/50 (wt/wt) 134 2 2 210 E' Yes Pyruvic acid / water 90/10 (wt/wt) 137 2 2 210 F’ Yes ethyl lactate / water 50/50 (wt/wt) 102 2 2 190 G’ Yes ethyl lactate / water 50/50 (wt/wt) 102 2 2 230 H’ No ethyl lactate / water 50/50 (wt/wt) 102 2 2 300 I’ Yes ethyl lactate / water 50/50 (wt/wt) 102 2 0.5 210

Example 2: Use of 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 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 three-zone heating 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 calcined in situ in the reactor of the catalytic unit, under dry air at 550°C for 4 hours then placed under nitrogen at the test temperature for 1 hour.

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 catalytic results are presented in Table 3 and Table 4. They are expressed as the difference in butadiene selectivity of the tested catalyst compared to the butadiene selectivity of the spent catalyst A (i.e., selectivity difference = [selectivity obtained with the tested catalyst] – [selectivity obtained with catalyst A], expressed in points or % weight/weight) and as a relative gain in carbon productivity expressed relative to the productivity measured for catalyst A (i.e., productivity gain = 100 x ([productivity obtained with the tested catalyst] – [productivity obtained with catalyst A]) / [productivity obtained with catalyst A], expressed in % weight/weight). The uncertainties of the results, based on the uncertainty of the measurements, are respectively: 1.2% weight/weight for the selectivity difference and 10% for the relative gain in carbon productivity.

Catalyst tested According to the invention solvent Acidic compound Acid/Ta (mol/mol) Activation protocol Selectivity difference (% wt/wt) Productivity gain (%) HAS No 0 0 B No acetylacetone --- - HAS +0.4 +9 C No acetylacetone phenol 15 C +0.5 +9 D Yes acetylacetone lactic acid 3 B +1.8 +40 E Yes acetylacetone lactic acid 7 B +3.4 +40 F Yes acetylacetone lactic acid 15 B +2.9 +31 G Yes acetylacetone lactic acid 15 C +4.1 +53 H Yes ethanol lactic acid 15 B +2.7 +28 I Yes acetylacetone lactic acid 7 HAS +3.4 +41 I Yes acetylacetone mandelic acid 7 HAS +3.2 +38 K Yes acetylacetone salicylic acid 7 HAS +3.7 +35 L Yes acetylacetone 3-hydroxybenzoic acid 7 HAS +3.8 +31 M Yes acetylacetone diethyl tartrate 7 HAS +2.7 +39 N Yes acetylacetone dioctyl phthalate 7 HAS +2.1 +35 O Yes acetylacetone glutaric acid 7 HAS +2.4 +27 P Yes acetylacetone ethylcyclo-pentanone-2-carboxylate 7 HAS +1.7 +26 Q Yes acetylacetone δ-valerolactone 7 HAS +1.0 +17

Catalyst tested According to invention Activation composition acid/Ta (mole / mole) N2 flow rate (NL/h/g) Activation temperature (°C) Selectivity gap
(% wt/wt) Productivity gain
(%) HAS No - - - 0 0 B’ Yes ethyl lactate / water 50/50 wt/wt 102 2 210 +1.7 +36% It Yes Lactic acid / water 90/10 wt/wt 134 2 210 +2.2 +44% From Yes Lactic acid / water 50/50 wt/wt 134 2 210 +2.7 +49% E' Yes Pyruvic acid / water 90/10 wt/wt 137 2 210 +2.2 +35% F’ Yes ethyl lactate / water 50/50 wt/wt 102 2 190 +2.2 +33% G’ Yes ethyl lactate / water 50/50 wt/wt 102 2 230 +1.7 +30% H’ No ethyl lactate / water 50/50 wt/wt 102 2 300 +0.4 +16% I’ Yes ethyl lactate / water 50/50 wt/wt 102 0.5 210 +3.2 +57%

Table 3 and Table 4 show that the butadiene selectivity and the carbon productivity are significantly improved when the conversion reaction of an ethanol-acetaldehyde feedstock is carried out in the presence of a rejuvenated catalyst, in accordance with the invention, i.e. reactivated in the presence of a multifunctionalized acid compound and at an activation phase temperature greater than 100°C and less than 300°C, compared to a conversion in the presence of the initial spent catalyst A (catalyst A) or a catalyst not in accordance with the invention (catalysts B, C).

Claims (15)

Method for activating a catalyst comprising at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, and an oxide matrix, said method comprising:
a) a step of preparing an activation composition comprising:
at least one multifunctionalized acid compound, in an amount such that the activation composition has an acid/metal molar ratio between the number of moles of said at least one multifunctionalized acid compound and the number of moles of said at least one metallic element of the catalyst greater than or equal to 2;
b) a step of bringing the activation composition prepared in step a) into contact with said catalyst, to obtain an impregnated intermediate solid,
c) a step of heat treatment of the impregnated intermediate solid obtained in step b) implementing an activation phase carried out at a temperature above 100°C and below 300°C. Method according to claim 1, wherein the catalyst comprises at least one metallic element chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferably from tantalum, niobium, zirconium and their mixtures, preferentially the element tantalum, and a silica-based oxide matrix. Method according to claim 1 or 2, wherein said at least one multifunctionalized acid compound is selected from hydroxy acids, keto acids, polyacids, their anhydrides, their esters, lactones, and mixtures thereof, preferably from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, phenylglyoxylic acid, glutaric acid, succinic acid, levulinic acid, maleic acid, their esters such as triethyl citrate, benzyl glycolate, ethyl lactate, ethyl pyruvate, diethyl tartrate, methyl salicylate, methyl mandelate, ethyl levulinate, diethyl malate, diethyl oxalate, diethyl succinate, diethyl malonate, ethyl acetoacetate, ethyl pyruvate, diethyl glutarate, gamma-valerolactone, delta-valerolactone, and combinations of two or more of these. Method according to one of claims 1 to 3, wherein said at least one multifunctionalized acid compound is chosen from hydroxy acids, keto acids, diacids, hydroesters, ketoesters, diesters, and mixtures thereof, in particular from pyruvic acid, lactic acid, tartaric acid, citric acid, mandelic acid, glycolic acid, oxalic acid, malic acid, ethyl lactate, ethyl pyruvate, diethyl tartrate, triethyl citrate, methyl mandelate, benzyl glucolate, diethyl oxalate, diethyl malate, and combinations of at least two of them. Method according to one of claims 1 to 4, in which the acid/metal molar ratio in step b) is between 2 and 200, preferably between 2 and 100, preferably between 3 and 60, preferentially between 5 and 40, preferably between 5 and 30, and very preferably between 7 and 20. A method according to any one of claims 1 to 5, wherein the activating composition comprises an organic or aqueous solvent. Method according to claim 6, wherein the organic solvent comprises at least one organic compound chosen from alcohols, monofunctionalized carboxylic acids, ethers, esters, ketones, hydrocarbon compounds, and mixtures thereof, and in particular from methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, acetic acid, propionic acid, isopropyl acetate, acetylacetone, hexane, heptane, and mixtures thereof. Method according to claim 6, wherein 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, and up to 100% by weight of water, the percentages being given by weight of water relative to the total weight of the aqueous solvent. Method according to one of claims 1 to 8, in which the activation phase of step c) is carried out at a temperature greater than or equal to 105°C, preferably greater than or equal to 110°C, preferably greater than or equal to 120°C, very preferably greater than or equal to 130°C and preferably less than 250°C. Method according to one of claims 1 to 9, in which step c) comprises a drying phase upstream of the activation phase, the drying phase preferably being carried out at a temperature between 50 and 115°C, preferably between 70 and 100°C, for a duration between 1 and 24 hours, preferably under gas flow. Method according to one of claims 1 to 10, comprising a step d) of high temperature treatment, downstream of step c), carried out under gas flow, at a temperature greater than or equal to 300°C, preferably between 350 and 700°C, preferably between 450 and 600°C, for a duration of between 1 and 6 hours. Method according to one of claims 1 to 11, in which the activation composition is in liquid form or at least partially in gaseous form during contact in step b). Method according to one of claims 1 to 12, in which the catalyst brought into contact with the activating composition is a spent catalyst previously used to convert a feedstock comprising ethanol into butadiene. Method according to one of claims 1 to 13, comprising a re-impregnation step, by bringing the initial catalyst or the activated catalyst obtained at the end of step c) of heat treatment into contact with an impregnation solution comprising at least one metallic precursor of at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table. Method according to claim 14, comprising a re-impregnation step by bringing an impregnation solution into contact with the initial catalyst and in which the impregnation solution corresponds to the activation composition, the activation composition then further comprising at least one metallic precursor of said at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table.