WO2025125059A1 - Tantalum- and silica-based catalyst for the conversion of a feedstock comprising ethanol into butadiene - Google Patents

Abstract

The present invention relates to a catalyst comprising tantalum and a silica-based matrix, wherein the catalyst has a tantalum content of between 0.1 wt% and 30 wt% relative to the weight of the silica-based matrix, and a Lewis acidity content greater than or equal to 1000 au/g_Ta, wherein the Lewis acidity content is determined by infrared spectroscopy (FTIR) following the adsorption and subsequent thermodesorption of pyridine. The present invention also relates to the use of the catalyst to convert a feedstock comprising ethanol into butadiene.

Description

TANTALUM AND SILICA BASED CATALYST FOR THE CONVERSION OF A FEED COMPRISING ETHANOL INTO BUTADIENE

Technical field

The present invention relates to a heterogeneous catalyst for optimally converting a feedstock comprising ethanol into 1,3-butadiene (which may also be referred to in this specification as butadiene). More particularly, the present invention relates to a catalyst comprising the element tantalum and a silica-based support (or matrix), exhibiting optimal catalytic performance when converting a feedstock comprising ethanol, and preferably a mixture of ethanol and acetaldehyde, into butadiene, and in particular optimized butadiene selectivity and butadiene productivity.

Prior art

Butadiene is widely used in the chemical industry, particularly as a reagent for the production of polymers. Currently, butadiene is almost entirely produced from steam cracking units, of which it is a valuable by-product. The fluctuation of the oil price and the ever-increasing demand for this chemical intermediate have made its price very volatile, which encourages a diversification of supply methods. It is thus well known to those skilled in the art that 1,3-butadiene can be produced from ethanol. Two processes were industrialized on a large scale, particularly in the 1940s and 1950s: the "S. K. Process" and the "Carbide Process". In the "S. K. Process", 1,3-butadiene is produced from ethanol in one step, whereas in the "Carbide Process", 1,3-butadiene is produced in two steps: first ethanol is converted to acetaldehyde, then an ethanol-acetaldehyde mixture is converted to 1,3-butadiene. The main distinction between the catalysts used in these processes is that one (SK Process) is capable of dehydrogenating ethanol to acetaldehyde while producing butadiene from the resulting mixture, while the other is not, hence the need for a first dehydrogenation step on a specific catalyst. The most effective chemical elements constituting the catalyst for this method of butadiene production are magnesium, tantalum, zirconium, hafnium, with butadiene selectivities between 50 and 69%, niobium being considered an unattractive element with selectivities lower than 40% (cf. B. B. Corson, at al.

Butadiene from Ethyl Alcohol. Catalysis in the One- and Two-Step Processes. Industrial And Engineering Chemistry. 1950, 42 (2), 359-373).

Whatever the process (one or two steps), the overall balance of the main reaction is written as follows: 2 CH3CH2OH CH2CHCHCH2 + H ₂ + 2 H ₂ O

Behind this overall balance are hidden numerous chemical reactions including a dehydrogenation reaction to generate acetaldehyde (I), an aldolization/crotonization reaction of acetaldehyde to crotonaldehyde (II), a Merwein-Pondorff-Verley (MPV) reaction between ethanol and crotonaldehyde (III) and finally a dehydration step of crotyl alcohol to butadiene (IV).

I: CH3CH2OH CH3CHO + _H2

II: 2 CH3CHO CH3CHCH-CHO + H ₂ O

III: CH3CHCH-CHO + CH3CH2OH CH3CHCH-CH2OH + CH3CHO

IV: CH3CHCH-CH2OH CH2CHCHCH2 + H ₂ O

This multiplicity of chemical reactions is the origin of numerous by-products if the sequence of steps is not carried out in the order specified above, notably with the presence of secondary dehydration and condensation reactions. In addition, other reactions can occur (such as isomerization, cyclization, the Diels and Aider reaction) further increasing the number of by-products. Thus, depending on the nature of the catalyst used for the transformation of ethanol (or the ethanol-acetaldehyde mixture) into 1,3-butadiene, the distribution of said by-products can change significantly. For example, the addition of an acidic element and in particular a Bronsted acid element will increase the production of dehydration products (for example ethylene or diethyl ether) while the addition of a basic element will promote the formation of multiple condensation products (for example hexenes or hexadienes).

Consequently, regardless of the process (one or two stages), the selectivity and productivity of the transformation of a feedstock comprising ethanol into 1,3-butadiene are moderate. However, due to the relatively high price of the raw material, the economic study of the process shows that the efficiency of the transformation of the feedstock constitutes an important lever to ensure its viability. Many efforts have therefore been made to maximize the catalytic performances and in particular the butadiene selectivity and the carbon productivity of the catalysts for the conversion of ethanol (or the ethanol-acetaldehyde mixture) into 1,3-butadiene.

In particular, during the development of the process for producing butadiene from an ethanol/acetaldehyde mixture (two-step process) in the 1940s and 1950s, the best catalyst found was a tantalum oxide deposited on amorphous silica (Ind. Eng. Chem., 1949, 41, p. 1012-1017). The selectivity to butadiene was 69% for an initial feed conversion of 34%. It has also been shown that the use of this same catalyst in an industrial unit "Carbide" led to the formation of the following major impurities (by-products): diethyl ether (23% by weight of impurities), ethylene (11% by weight of impurities), hexenes, hexadienes (11% by weight of impurities), etc. (WJ Toussaint, JT Dunn, DR Jackson, Industrial and Engineering Chemistry, 1947, 39 (2), p 120-125). Despite the presence of by-products, their formation is limited by the relatively weak acid-base properties of the element tantalum. The latter also makes it possible to catalyze reactions II, III and IV very effectively.

Various studies have then been carried out to optimize the efficiency of tantalum and/or to substitute this element. Patent US2421361 describes, for example, a process for the preparation of butadiene which comprises the transformation of an acyclic monoolefinic aldehyde (crotonaldehyde or acetaldehyde) and a monohydroxy alcohol (ethanol) on a catalyst from the group of zirconium oxide, tantalum oxide, niobium oxide and one of the combinations of these oxides with silica. However, according to the examples provided, tantalum oxide used alone remains the best catalyst for converting the specific ethanol/acetaldehyde mixture. According to Ind. Eng. Chem., 1950, 42 (2), p 359-373, the best associations for the transformation of the ethanol/acetaldehyde mixture are: Ta-Cu, Ta-Zr, Zr-Nb, Zr-Ti and Zr-Th deposited on a silicic support (patents US2374433, US2436125, US2438464, US2357855, US2447181).

Studies have also focused on improving the silica support and/or optimizing the process for preparing heterogeneous catalysts, particularly those based on tantalum and silica. For example, application WO2014/061917 describes a catalyst based on tantalum and a silica support characterized by mesopores of uniform size and morphology and distributed periodically within the material (so-called mesostructured silica). Application WO2017/009107 discloses a catalyst comprising the element tantalum and a mesoporous oxide matrix based on silica that has undergone acid washing. More recently, application WO2022/165190 describes a process for preparing a tantalum and silica catalyst, having a controlled distribution of tantalum in the silica particles, by organic deposition of a specific tantalum precursor, preferably chosen from a tantalum ethanoate, in particular tantalum tetra-ethanoate 2,4-pentanedione or tantalum pentaethanoate optionally combined with acetylacetone. Patent application CN115364844 describes the preparation of a tantalum and silica catalyst, by contacting a silica with a solution comprising a tantalum precursor and anhydrous citric acid in absolute ethanol. Finally, Ushikubo's team compares tantalum oxide on silica catalysts prepared from a solution of tantalum alkoxide in hexane to tantalum oxide on silica catalysts prepared by impregnating silica with a 1% wt. 1M aqueous hydrochloric acid solution. TaCl5, said catalysts being used in the vapor phase decomposition of methyl tert-butyl ether (Ushikubo T. et al., "Preparation, characterization, and catalytic activities of silica-supported tantalum oxide for the vapor phase decomposition of methyl tert-butyl ether", Applied Catalysis A: General, vol. 124, no. 1, March 1, 1995 (1995-03-01), pages 19-31).

There is still a need to improve the catalytic performance of a catalyst comprising the element tantalum and a silica support. Thus, the present invention aims to provide a heterogeneous catalyst based on tantalum and silica, for converting a feedstock comprising ethanol into butadiene (or 1,3 butadiene), and having optimized catalytic performance, in particular optimized selectivity and productivity in butadiene.

Summary of the invention

The present invention thus relates to a catalyst comprising tantalum and a silica-based matrix, the catalyst having a tantalum content by weight of between 0.1 and 30% by weight relative to the weight of the silica-based matrix, the catalyst having a Lewis acidity [LAS] content greater than or equal to 1000 au/gTa, the Lewis acidity [LAS] content being determined by integration of the A1612 area under an IR spectrum, over the wavenumber range between 1622 and 1593 cm ^-1 , the IR spectrum being obtained for a sample of said catalyst, reduced to powder and then formed into a pellet, by infrared spectroscopy (FTIR) after adsorption and subsequent thermodesorption of pyridine at 150°C, and using the following calculation:

[LAS] = A ₁₆₁₂ ^X Z=-Z

L ^{1 a} J where S corresponds to the surface area of the sample pellet (in cm ² ) and [Ta] to the weight content of tantalum in the catalyst per unit weight of said catalyst.

Surprisingly, a catalyst according to the invention, based on tantalum and a silicic matrix, and having such a quantity of acid sites per weight unit of tantalum element, exhibits optimized catalytic performances during the conversion of a feedstock comprising ethanol into 1,3-butadiene, and in particular in terms of selectivity and productivity in butadiene. Thus, a catalyst according to the invention, used to convert a feedstock comprising ethanol, in particular an ethanol-acetaldehyde feedstock (in particular at an ethanol/acetaldehyde molar ratio of 2.6), into 1,3-butadiene, in particular at a reaction temperature of 350°C and 0.15 MPa, makes it possible to achieve a high butadiene selectivity, in particular greater than or equal to 70%, preferably greater than or equal to 72%, for a feedstock conversion of 40% by weight, and a satisfactory butadiene productivity, in particular greater than or equal to 30 g/gTa/h (g/gTa/h meaning: gram of butadiene produced per gram of tantalum, contained in the catalyst used to convert said charge, per hour), preferably greater than or equal to 32 g/gTa/h, for an hourly weight rate of the charge of 250 g/gTa/h (the hourly weight rate or pph being expressed in weight of charge per unit of weight of tantalum, contained in the catalyst, used to convert said charge, and per hour).

The present invention also relates to the use of the catalyst according to the invention 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.

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.

According to the invention, the different parameter ranges for a given step may be used alone or in combination. For example, a range of preferred tantalum content values may be combined with a range of more preferred silica content values.

In the following description, particular embodiments of the invention are described. According to the invention, they can be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

In the following description, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

In the following description, times and durations are expressed in hours (h), minutes (min) and/or seconds (sec).

According to the invention, the terms “catalyst”, “heterogeneous catalyst” and “supported catalyst” are used interchangeably and designate any type of catalyst which comprises the element tantalum and a support and in particular a silica-based matrix.

In the present description, the terms “matrix” and “support” are used interchangeably to designate the solid support of the catalyst. In the catalyst according to the invention, the support is based on silica.

In the present description, the terms “1,3-butadiene” and “butadiene” are used interchangeably and designate one of the isomers of butadiene (hydrocarbon compound with four carbon atoms and having two double bonds), comprising a double bond between carbon 1 and carbon 2 and a second double bond between carbon 3 and carbon 4 the 1,3 isomer of butadiene.

In the present description, the term “butadiene productivity” corresponds to the carbon productivity of butadiene (which is generally expressed in % weight/weight per hour) of a unit for converting a feedstock comprising ethanol into 1,3-butadiene, and corresponds in particular to the mass flow rate of butadiene (in g/h), measured at the outlet of the unit or reactor, per unit mass of element Ta, for a pph of the feedstock of 250 g/gTa/h. At the same time, the term “butadiene selectivity” (which is expressed in % weight/weight) is a carbon selectivity and corresponds to the flow rate of butadiene measured at the outlet of the unit or reactor relative to the sum of the flow rates of the carbon products formed (the unconverted ethanol and possibly acetaldehyde are not taken into account in the calculation of the selectivity).

The present invention thus relates to a heterogeneous catalyst, comprising the element tantalum and a silica-based matrix, and having a Lewis acidity advantageously at a content ([LAS]) greater than or equal to 1000 au/gTa (arbitrary unit per gram of tantalum contained in the catalyst), preferably greater than or equal to 1100 au/gTa, and preferably at a Lewis acidity content ([LAS]) less than or equal to 1900 au/gTa, very preferably less than or equal to 1800 au/gTa. Very advantageously, the catalyst has a low Bronsted acidity content, i.e. less than the Lewis acidity content. In particular, the catalyst has a relative Lewis acidity content (%LAS) corresponding to the ratio between the Lewis acidity content relative to the total acidity content of the catalyst (i.e. the total number of acid sites, i.e. the sum of the Lewis acid and Bronsted acid sites), greater than or equal to 90%, preferably greater than or equal to 92%.

The acidity, in particular Lewis and Bronsted, of the catalysts is determined by an indirect analysis method and more particularly by infrared spectroscopy (FTIR) after adsorption and subsequent thermodesorption of pyridine. This method is conventionally used to characterize acidic solids such as zeolites as described in the article Zholobenko et al., Journal of Catalysis, 385, 52 (2020). Before analysis, the catalyst is ground into powder form and then the catalyst powder is compacted into a pellet preferably 13 mm or 16 mm in diameter, in particular 13 mm. The pellet is then activated in situ in the infrared (IR) cell furnace under secondary vacuum (in particular at a pressure below 10' ⁵ mbar) at 450°C for 10 hours and then the temperature is reduced to 150°C. An excess of pyridine in the gas phase is introduced into the IR cell so as to have a partial pressure of pyridine greater than 1 mbar, and brought into contact with the pellet for 10 minutes (adsorption phase). A thermodesorption phase is then carried out at 150°C for 2 hours. The adsorption phase allows the pyridine to react with the acid sites of the sample, while the thermodesorption step allows the elimination of the physisorbed pyridine molecules (i.e. the pyridine molecules which have not reacted with the acid sites, in other words which do not have chemical bonds with the acid sites of the analyzed catalyst) to keep only the chemisorbed pyridine molecules. After this thermodesorption phase, the sample is analyzed by infrared spectroscopy (FTIR for Fourier Transform Infra Red spectroscopy according to the English term) in transmission to obtain an IR spectrum of the sample; said IR spectrum corresponds to the 'thermodesorbed spectrum' of the sample.

avec [LAS] : la teneur en acidité de Lewis de l’échantillon analysé (c’est-à-dire du catalyseur), exprimée en unité arbitraire par gramme de tantale contenu dans le catalyseur (ua/gTa), l’unité arbitraire étant ici proportionnelle au nombre de moles de sites acide de Lewis de l’échantillon analysé (c’est-à-dire du catalyseur), The Lewis and Bronsted acidity contents, which are functions of the concentrations of the Lewis ([LAS]) and Bronsted ([BAS]) acid sites, respectively, of the sample are determined using the thermodesorbed spectrum. For the Lewis acidity ([LAS]) content, the contribution area centered at 1612 cm ^-1 +/- 4 cm ^-1 , corresponding to the u8a mode of pyridine coordinated to a Lewis acid site on the catalyst surface, is preferred to the contribution area centered at 1450 cm ^-1 +/- 4 cm ^-1 which corresponds to the u19b mode of protonated pyridine because the u19b mode of protonated pyridine can be impacted by the residual presence of hydrogen-bonded pyridine. Thus, the Lewis acidity ([LAS]) content of the sample, i.e. of the analyzed catalyst, is determined by integrating the area of the A1612 signal, i.e. the area under the IR spectrum, over the wavenumber range between 1622 and 1593 cm ^{- 1} , and then using the following calculation:

with [LAS]: the Lewis acidity content of the analyzed sample (i.e. of the catalyst), expressed in arbitrary units per gram of tantalum contained in the catalyst (au/gTa), the arbitrary unit here being proportional to the number of moles of Lewis acid sites of the analyzed sample (i.e. of the catalyst),

A1612: absorbance of the contribution centered at 1612 cm ^-1 , expressed in cm ^-1 per gram of catalyst (i.e. per gram of sample analyzed), and determined by integration of the signal area, i.e. the area under the IR spectrum, over the wavenumber range between 1622 and 1593 cm ^-1 ,

S: the surface area of the sample pellet analyzed in transmission (in cm ² ), i.e. for a pellet of 1.3 cm (i.e. 13 mm) in diameter S = TT X (1 ,3/2) ² , [Ta]: the weight content of tantalum in the catalyst per unit weight of said catalyst (for example a content of 3% by weight of tantalum in a catalyst corresponds to 0.03 g of tantalum per unit weight, i.e. per gram of catalyst).

avec [BAS] : la teneur en acidité de Bronsted de l’échantillon analysé (c’est-à-dire du catalyseur), exprimée en unité arbitraire par gramme de tantale contenu dans le catalyseur (ua/gTa), l’unité arbitraire étant ici proportionnelle au nombre de moles de sites acide de Bronsted de l’échantillon analysé (c’est-à-dire du catalyseur), Concerning the Bronsted acidity content ([BAS]), the area of the contribution centered at 1545 cm ^-1 +/- 4 cm ^{- 1} corresponding to the u 19b mode of protonated pyridine on a Bronsted acid site of the catalyst surface is used. Thus, the Bronsted acidity content ([BAS]) of the sample, i.e. of the analyzed catalyst, is determined by integrating the area of the A1545 signal centered at 1545 cm ^-1 +/- 4 cm ^-1 , i.e. the area under the IR spectrum, over the wavenumber range between 1555 and 1532 cm ^-1 , and then using the following calculation:

with [BAS]: the Bronsted acidity content of the analyzed sample (i.e. of the catalyst), expressed in arbitrary units per gram of tantalum contained in the catalyst (au/gTa), the arbitrary unit here being proportional to the number of moles of Bronsted acid sites of the analyzed sample (i.e. of the catalyst),

A1545: absorbance of the contribution centered at 1545 cm ^-1 , expressed in cm ^-1 per gram of catalyst (i.e. per gram of sample analyzed), and determined by integration of the signal area, i.e. the area under the IR spectrum, over the wavenumber range between 1555 and 1532 cm ^-1 ,

S: the surface area of the sample pellet analyzed in transmission (in cm ² ), i.e. for a pellet of 1.3 cm (i.e. 13 mm) in diameter S = TT X (1 ,3/2) ² ,

[Ta]: tantalum content by weight of the catalyst per unit of weight of said catalyst (for example, a tantalum content of 3% by weight of a catalyst corresponds to 0.03 g of tantalum per unit of weight, i.e. per gram of catalyst).

The relative Lewis acidity content of the catalyst (%LAS), i.e. the ratio of the Lewis acidity content to the total acidity of the catalyst (i.e. the total number of acid sites, i.e. the sum of the Lewis acid and Bronsted acid sites), can then be calculated as follows:

%LAS = 100 x [LAS] / ([LAS]+[BAS]) with [LAS]: the Lewis acidity content of the analyzed sample (i.e., the catalyst), expressed in arbitrary units per gram of tantalum contained in the catalyst (au/gTa), determined as detailed above, and [BAS]: the Bnansted acidity content of the analyzed sample (i.e., catalyst), expressed in arbitrary units per gram of tantalum contained in the catalyst (au/gTa), determined as detailed above.

Advantageously, the catalyst according to the invention comprises tantalum at a weight 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 the element tantalum relative to the weight of the silica-based matrix. The catalyst may optionally comprise at least one other metallic element, chosen from the elements of groups 3, 4, 5, 11 and 12 of the periodic table (other than tantalum). Preferably, the catalyst according to the invention comprises only the element tantalum as metallic element.

The silica-based matrix of the catalyst according to the invention has a silica content by weight preferably greater than or equal to 95% dry weight (i.e. between 95% dry weight and 100% dry weight), preferably greater than or equal to 98% dry weight (i.e. from 98% dry weight up to 100% dry weight), preferably greater than or equal to 99.5% dry weight (i.e. from 99.5% dry weight up to 100% dry weight) and more preferably greater than or equal to 99.9% dry weight (i.e. from 99.9% dry weight up to 100% dry weight) of silica relative to the total weight of the silica-based matrix, dry (i.e. without water, or excluding the weight of any water possibly present). The silica contents are given here as a percentage of the weight of silica (excluding water) relative to the total weight of the dry silica matrix (i.e. excluding the weight of any water present in the matrix).

Advantageously, the silica-based matrix of the catalyst according to the invention comprises pores, in particular mesopores. Preferably, the catalyst according to the invention has an average pore diameter 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 catalyst according to the invention has a pore volume greater than or equal to 0.47 ml/g, preferably between 0.47 and 1.8 ml/g, preferentially between 0.58 and 1.5 ml/g, preferably between 0.8 and 1.5 ml/g. Preferably, the catalyst according to the invention has a specific surface area SBET greater than or equal to 100 m ² /g, preferably greater than or equal to 200 m ² /g, preferentially greater than or equal to 250 m ² /g, preferably between 250 m ² /g and 700 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 of the material tested, in particular of the catalyst, corresponds to the BET specific surface area (SBET in m ² /g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 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° _max of the nitrogen adsorption-nitrogen 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 material tested, in particular of the catalyst, is determined by the formula 4000.V/SBET.

The catalyst according to the invention may be in powder form or 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. For example, the catalyst 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. Thus, in addition to the tantalum element and the silica-based matrix, the catalyst according to the invention may comprise at least one porous oxide material, advantageously inert with regard to the reaction of conversion into butadiene of a charge comprising ethanol, and having the role of binder so as to assist in the shaping and to generate the appropriate physical properties of the catalyst (mechanical resistance, resistance to attrition, etc.). The porous oxide material, which acts as a binder, may be 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, and preferably from silica and titanium oxide. 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 weight of the catalyst.

The catalyst according to the invention may preferably 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 reactivated catalyst, i.e. a spent catalyst (i.e. a catalyst which has been used in a reaction section for converting a feedstock comprising ethanol into butadiene) and which has undergone a reactivation process (regeneration by burning the coke, in particular in the presence of oxygen, and/or rejuvenation using a reactivation compound possibly accompanied by the addition of tantalum element, said reactivation compound being, for example, a hydroxy acid, a keto acid, a polyacid, one of their esters, or their mixtures, or even a monofunctional acid, a hydroxyketone or a diketone) so as to be able to recover at least part of its catalytic performance. Optionally, the catalyst may be:

- a spent catalyst, i.e. a catalyst which has been used in a reaction section for converting a feedstock comprising ethanol into butadiene,

- an aged catalyst, i.e. a catalyst which has undergone treatment, for example heat treatment, particularly under a wet gas flow.

Such a catalyst very advantageously makes it possible to optimize the catalytic performances during the conversion reaction of a feedstock comprising ethanol into 1,3-butadiene, particularly in terms of selectivity and productivity in butadiene. Thus, a catalyst according to the invention, used to convert a feedstock comprising ethanol, in particular an ethanol-acetaldehyde feedstock, into 1,3-butadiene, makes it possible to achieve a high butadiene selectivity, in particular greater than or equal to 70%, preferably greater than or equal to 72%, for a feedstock conversion of 40% by weight (the conversion being a weight conversion of the feedstock and corresponding to the difference between the weight flow rate of the feedstock at the inlet and the weight flow rate of the feedstock at the outlet, relative to the weight flow rate of the feedstock at the inlet), and a satisfactory butadiene productivity, in particular greater than or equal to 30 g/gTa/h, preferably greater than or equal to 32 g/gTa/h, for an hourly weight rate of the feedstock equal to 250 g/gTa/h (the hourly weight rate or pph being expressed as the weight of feedstock per unit of weight of tantalum contained in the catalyst used, i.e. in the quantity total weight of catalyst used, and per hour).

The present invention also relates to the use of the catalyst according to the invention, for converting into 1,3-butadiene a feedstock comprising ethanol, and according to a particular embodiment a mixture of ethanol and acetaldehyde. 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 feedstock also comprises acetaldehyde, the ethanol/acetaldehyde molar ratio is between 1 and 5, preferably between 2 and 4. The use of the catalyst according to the invention for the conversion of a feedstock comprising ethanol into butadiene then results in an optimization of the selectivity to butadiene and the carbon productivity of butadiene.

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

Examples

Example 1: Preparation of tantalum-based catalysts on a silica support

Catalysts are prepared at 2.5% or 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:

Before impregnation, the silica support is dried in an oven at a temperature of 100°C or 250°C for 2 hours.

A tantalum precursor, tantalum pentaethanoate (Ta(OEt)s) or tantalum tetraethoxyacetylacetonate (Ta(AcAc)(OEt)4), is introduced and diluted in a volume of solvent V, the solvent _being ethanol, a hydrochloric ethanolic solution (ethanol comprising 1.25 M HCl, with M for Molar, i.e. mol/l) or a 70/30 weight/weight ethanol/acetic acid mixture.

The organic solution is then homogenized while stirring.

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

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, preparation parameters and textural characteristics of the catalysts, in particular the average pore diameter Dp, the pore volume Vp and the specific surface area SBET, measured by the analysis technique called "Nitrogen Volumetry" as described above in the description) are presented in Table 1. The content, or purity, of the matrix (or support) in SiC>2 (excluding the element Tantalum) is determined by ICP (Inductively Coupled Plasma) spectroscopy via multi-element detection; it is given as a percentage by weight of silica relative to the total weight of the dry support (i.e. excluding water).

Table 1

*: Catalyst F is prepared from a silica support different from that used to prepare catalysts A to E.

A catalyst prepared as catalyst D is used to convert a feedstock containing ethanol and acetaldehyde, at an Ethanol/Acetaldehyde molar ratio of 2.6, into butadiene, at a temperature of 350°C and a pressure of 0.15 MPa. After several hours, the feedstock supply (and therefore the reaction) is stopped and the catalyst undergoes a controlled combustion decoking step (regeneration phase). The recovered catalyst is a spent catalyst: catalyst G. A portion of the spent catalyst, catalyst G, is then reactivated, by contacting with a rejuvenation solution, at room temperature and atmospheric pressure. The rejuvenation solution comprises lactic acid and tantalum pentaethanoate (Ta(OEt)s) in ethanol, such that the amount of lactic acid in the rejuvenation solution corresponds to a molar ratio between the lactic acid in the rejuvenation solution and the tantalum present on the spent catalyst equal to 15, and the amount of tantalum pentaethanoate in the rejuvenation solution corresponds to an additional tantalum content of 1% by weight relative to the weight of spent catalyst. 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, at room temperature and atmospheric pressure, until wettability of the surface of the latter is observed (dry impregnation). The solid is then left to mature for 0.5 to 2 hours. The solid is dried at 100°C and finally undergoes a heat treatment at a flow rate of gas of 2.5NL/h under a flow of humid air (20% vol) up to 250°C. The catalyst obtained is catalyst H.

Example 2: Measuring the acidity of catalysts

Sample preparation and IR measurement

The acidity of the catalysts prepared as described in Example 1 is measured by adsorption and subsequent thermodesorption of pyridine followed by infrared spectroscopy (FTIR) measurement. This method is conventionally used to characterize acidic solids such as zeolites as described in the periodical Zholobenko et al, Journal of Catalysis, 385, 52 (2020).

For each catalyst, a catalyst sample is ground to a powder which is compacted into a 13 mm diameter pellet. The pellet is then placed in the IR measuring cell and is activated in situ under secondary vacuum (<10 ^-5 mbar) at 450°C for 10 hours. The temperature is then reduced to 150°C.

When the temperature is at 150°C, an excess of pyridine in the gas phase is introduced into the IR cell so as to have a partial pressure of pyridine greater than 1 mbar, and is brought into contact with the pellet for 10 minutes (adsorption phase). A thermodesorption step is then carried out at 150°C for 2 hours. Then an FTIR measurement is carried out and an IR spectrum of the sample is recorded.

Data analysis

For each catalyst tested, the Lewis and Bronsted acidity contents, respectively [LAS] and [BAS], of the sample are determined using the IR spectrum.

avec S : la surface de la pastille de l’échantillon analysée en transmission (en cm²), la pastille ayant un diamètre de 13 mm : S est environ égale à 1 ,327 cm²,More specifically, the Lewis acidity ([LAS] in au/gTa) content of the sample is determined by integrating the A1612 area under the IR spectrum and over the wavenumber range between 1622 and 1593 cm ^-1 , and then using the following calculation:

with S: the surface area of the sample pellet analyzed in transmission (in cm ² ), the pellet having a diameter of 13 mm: S is approximately equal to 1.327 cm ² ,

[Ta]: tantalum content by weight of the catalyst per unit weight of the catalyst, i.e. 0.03 g for catalysts A to D, F and G, 0.025 g for catalyst E and 0.04 g for catalyst H.

The Bronsted acidity content ([BAS] in au/gTa) of the sample is determined by integrating the A1545 area under the IR spectrum and over the wavenumber range between 1555 and 1532 cm ^{- 1} , then using the following calculation: S

[BAS] — A ₁₅₄₅ x — —

L ^{1 a} J with S: the surface of the sample pellet analyzed in transmission (in cm ² ), the pellet having a diameter of 13 mm: S is approximately equal to 1.327 cm ² ,

[Ta]: tantalum content by weight of the catalyst per unit weight of the catalyst, i.e. 0.03 g for catalysts A to D, F and G, 0.025 g for catalyst E and 0.04 g for catalyst H.

The relative Lewis acidity content of the catalyst (%LAS) is also calculated for each of the catalysts tested, as follows:

%LAS = 100 x [LAS] / ([LAS]+[BAS]).

The results obtained for each of the catalysts tested are grouped in Table 2. Table 2 also classifies the catalysts tested according to whether they comply or do not comply with the invention.

Table 2

Example 3: Catalyst Performance Testing

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. The reactor temperature is controlled with a three-zone tube furnace.

The catalyst is calcined in situ in dry air at 550°C for 4 hours and then placed under nitrogen at the test temperature for 1 hour. The liquid feedstock, which is a mixture of ethanol and acetaldehyde, with an Ethanol/Acetaldehyde molar ratio of 2.6 mol/mol, is injected into the catalytic system using a double-piston HPLC pump. The liquid feedstock is vaporized before entering the reactor and is homogenized by passing through a static mixer. For each test, the Ethanol/Acetaldehyde ratio of the feedstock is set at 2.6 (mol/mol), the reaction temperature at 350°C and the pressure at 0.15 MPa.

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 enable the identification of the products formed.

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 in comparison with the threshold values in selectivity (greater than or equal to 70, preferably greater than or equal to 72) and in productivity (greater than or equal to 30, preferably greater than or equal to 32). Table 3 also shows the Lewis acidity content ([LAS]) (in au/gTa) and the relative Lewis acidity content (%LAS) of each catalyst determined according to Example 2.

Table 3

Catalysts B, C, D, E and H, in accordance with the invention, which are tantalum and silica-based catalysts, comprising 2.5%, 3% or 4% by weight of tantalum relative to the silica support and having a Lewis acidity content, measured by FTIR after adsorption and thermodesorption of pyridine, of at least 1000 au/gTa, have satisfactory butadiene selectivity and productivity. In particular, catalysts B, C, D, E and H, in accordance with the invention, used to convert an ethanol-acetaldehyde feedstock at 350°C into butadiene, make it possible to achieve a butadiene selectivity (at 40% conversion) greater than or equal to 72% and a butadiene productivity greater than 32 g/gTa/h (at an hourly feedstock weight rate of 250 g/gTa/h).

In contrast, non-compliant catalysts A, F and G, which have a Lewis acidity content, measured by FTIR after pyridine adsorption and thermodesorption, of less than 1000 au/gTa, exhibit poor catalytic performance. Indeed, non-compliant catalysts A and G, used to convert an ethanol-acetaldehyde feedstock at 350°C into butadiene, exhibit a butadiene selectivity (at 40% conversion) of less than 70% and a butadiene productivity of less than 30 g/gTa/h (at an hourly feedstock weight rate of 250 g/gTa/h). Concerning catalyst F, which is non-compliant, even if it allows a selectivity in butadiene (at 40% conversion) equal to 70% to be achieved when it is used under the same conditions to convert the ethanol-acetaldehyde feed into butadiene, the productivity obtained with this catalyst F remains much lower than 30 g/gTa/h (for an hourly feed weight rate of 250 g/gTa/h).

Claims

Claims 1. A catalyst comprising tantalum and a silica-based matrix, the catalyst having a tantalum content by weight of between 0.1 and 30% by weight relative to the weight of the silica-based matrix, the catalyst having a Lewis acidity [LAS] content greater than or equal to 1000 au/gTa, the Lewis acidity [LAS] content being determined by integration of the A1612 area under an IR spectrum, over the wavenumber range between 1622 and 1593 cm ^-1 , the IR spectrum being obtained for a sample of said catalyst, reduced to powder and then formed into a pellet, by infrared spectroscopy (FTIR) after adsorption and subsequent thermodesorption of pyridine at 150°C, and using the following calculation: [LAS] = A ₁₆₁₂ ^X ] =-7 L ^{1 a} J where [LAS] the Lewis acidity content of the catalyst is expressed in arbitrary units per tantalum range (au/gTa); A1612 corresponds to the absorbance of the contribution centered at 1612 cm ^-1 , expressed in cm ^-1 per gram of catalyst and determined by integration of the area under the IR spectrum over the wavenumber range between 1622 and 1593 cm ^-1 ; S corresponds to the surface area of the sample pellet (in cm ² ); and [Ta] corresponds to the weight content of tantalum in the catalyst per unit weight of said catalyst. 2. Catalyst according to claim 1, having a Lewis acidity [LAS] content less than or equal to 1900 au/gTa, very preferably less than or equal to 1800 au/gTa, 3. Catalyst according to claim 1 or 2, having a tantalum content by weight of between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of the tantalum element relative to the weight of the silica-based matrix. 4. Catalyst according to one of the preceding claims, in which the silica-based matrix has a silica content by weight greater than or equal to 95% dry weight, preferably greater than or equal to 98% dry weight, preferably greater than or equal to 99.5% dry weight and more preferably greater than or equal to 99.9% by weight of silica relative to the total weight of the dry silica-based matrix. 5. Catalyst according to one of the preceding claims, having a relative Lewis acidity content, noted %LAS, which corresponds to the ratio between the Lewis acidity content relative to the total acidity content of the catalyst, greater than or equal to 90%, preferably greater than or equal to 92%, the total acidity content being the sum of the Lewis acidity and Bronsted acidity contents, the Bronsted acidity content [BAS] being determined by integration of the A1545 area under the IR spectrum, over the range of wave numbers between 1555 and 1532 cm ^-1 , and using the following calculation:

where [BAS] the Bronsted acidity content of the catalyst is expressed in arbitrary units per tantalum range (au/gTa); A1545 corresponds to the absorbance of the contribution centered at 1545 cm ^-1 , expressed in cm ^-1 per gram of catalyst and determined by integration of the area under the IR spectrum over the wavenumber range between 1555 and 1532 cm ^-1 ; S corresponds to the surface area of the sample pellet (in cm ² ); and [Ta] corresponds to the weight content of tantalum in the catalyst per unit weight of said catalyst. 6. Catalyst according to one of the preceding claims, having an average pore diameter greater than or equal to 4 nm, preferably between 4.5 and 50 nm and even more preferably between 4.5 and 20 nm. 7. Catalyst according to one of the preceding claims, having a pore volume greater than or equal to 0.47 ml/g, preferably between 0.47 and 1.8 ml/g, preferentially between 0.58 and 1.5 ml/g, preferably between 0.8 and 1.5 ml/g. 8. Catalyst according to one of the preceding claims, having a specific surface area SBET greater than or equal to 100 m ² /g, preferably greater than or equal to 200 m ² /g, preferentially greater than or equal to 250 m ² /g, preferably between 250 m ² /g and 700 m ² /g. 9. Use of the catalyst according to one of claims 1 to 8 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.