Tantalum- and silica-based heterogeneous catalyst for converting a feedstock comprising ethanol into butadiene

Abstract

The present invention relates to a catalyst comprising tantalum and a silica-based matrix, the catalyst having a tantalum content by weight of between 0.1% and 10% by weight relative to the weight of the silica-based matrix, the catalyst comprising aluminium at a content such that the Ta / Al molar ratio is 5 or higher, and the catalyst having: a content of Gp1 alkali metal elements such that the molar ratio (Gp1 / Al) / Ta of Gp1 alkali metal elements relative to the element aluminium Al, per molar unit of tantalum Ta, is 0.01 or lower, and a content of Gp2 alkaline earth elements such that the molar ratio Ta / Gp2 of the element tantalum Ta relative to the Gp2 alkaline earth elements is 15 or higher.

Description

[0001] HETEROGENEOUS CATALYST BASED ON TANTALUM AND SILICA FOR CONVERTING A FILLER CONTAINING ETHANOL INTO BUTADIENE

[0002] technical field

[0003] The present invention relates to a heterogeneous catalyst for optimally converting a feed comprising ethanol into 1,3-butadiene (which may also be referred to in this description as butadiene). More particularly, the present invention relates to a catalyst comprising tantalum, especially in oxide form, a silica-based support (or matrix), and impurities, and exhibiting optimal catalytic performance in the conversion to butadiene of a feed comprising ethanol and preferably a mixture of ethanol and acetaldehyde, and in particular optimized butadiene selectivity and butadiene productivity.

[0004] Previous technique

[0005] Butadiene is widely used in the chemical industry, particularly as a reagent in polymer production. Currently, butadiene is almost entirely produced from steam cracking units, where it is a valuable by-product. Fluctuations in oil prices and the ever-increasing demand for this chemical intermediate have made its price highly volatile, prompting a diversification of supply methods. It is 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 SK Process and the Carbide Process. In the SK Process,In the "Carbide Process," 1,3-butadiene is produced from ethanol in a single step, whereas in the "Carbide Process," 1,3-butadiene is produced in two steps: ethanol is first converted to acetaldehyde, and then an ethanol-acetaldehyde mixture is converted to 1,3-butadiene. The main difference between the catalysts used in these processes is that one (SK Process) is capable of dehydrogenating ethanol to acetaldehyde while simultaneously producing butadiene from the resulting mixture, while the other is not, hence the need for a first dehydrogenation step using a specific catalyst. The most effective chemical elements for this butadiene production method are magnesium, tantalum, zirconium, and hafnium, with butadiene selectivities ranging from 50% to 69%. Niobium is considered a less attractive element with low butadiene selectivity. selectivities less than 40% (cf. BB Corson, et al.Butadiene form Ethyl Alcohol. Catalysis in the One- and Two-Step Processes. Industrial And Engineering Chemistry. 1950, 42 (2), 359-373).

[0006] Regardless of the process (one or two steps), the overall equation for the main reaction is as follows: 2 CH3CH2OH → CH2CHCHCH2 + H2 + 2 H2O

[0007] Behind this overall picture lie numerous chemical reactions including a dehydrogenation reaction to generate acetaldehyde (I), an aldolisation / crotonisation 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).

[0008] I: CH3CH2OH CH3CHO + H2

[0009] II: 2 CH3CHO CH3CHCH-CHO + H2O

[0010] III: CH3CHCH-CHO + CH3CH2OH CH3CHCH-CH2OH + CH3CHO

[0011] IV: CH3CHCH-CH2OH CH2CHCHCH2 + H2O

[0012] This multitude of chemical reactions generates numerous byproducts if the steps are not carried out in the order specified above, notably through the presence of secondary dehydration and condensation reactions. Furthermore, other reactions can occur (such as isomerization, cyclization, and the Diels-Aider reaction), further increasing the number of byproducts. Thus, depending on the nature of the catalyst used to transform ethanol (or the ethanol-acetaldehyde mixture) into 1,3-butadiene, the distribution of these byproducts can vary considerably.For example, adding an acidic element, and in particular a Brønsted acid, can promote step IV but will increase the production of dehydration products (e.g., ethylene or diethyl ether), while adding a basic element will positively impact step II but will promote the formation of multiple condensation products (e.g., hexenes or hexadienes). Conversely, some elements, such as alkali metals, behave as poisons, neutralizing acidic sites, particularly Lewis sites, generated by the active species.

[0013] Consequently, regardless of the process (one or two steps), the selectivity and productivity of converting a feed containing ethanol to 1,3-butadiene are moderate. However, due to the relatively high price of the raw material, the economic analysis of the process shows that the efficiency of the feed conversion is a key factor in ensuring its viability. Therefore, considerable effort has been devoted to maximizing the catalytic performance, and in particular the butadiene selectivity and carbon productivity, of catalysts for converting ethanol (or ethanol-acetaldehyde mixtures) to 1,3-butadiene.

[0014] In particular, during the development of the process for producing butadiene from an ethanol / acetaldehyde mixture (a two-stage process) in the 1940s and 1950s, the best catalyst found was tantalum oxide deposited on amorphous silica (BB Corson, et al., Ind. Eng. Chem., 1949, 41, pp. 1012-1017). The butadiene selectivity was 69% for an initial feed conversion of 34%. It was also shown that the use of this same catalyst in an industrial "Carbide" unit 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 tantalum element.The latter also allows for very efficient catalysis of reactions II, III and IV.

[0015] Various studies were then conducted to optimize the efficiency of tantalum and / or substitute for this element. US patent 2421361, for example, describes a process for the preparation of butadiene that includes the transformation of an acyclic monoolefinic aldehyde (crotonaldehyde or acetaldehyde) and a monohydroxy alcohol (ethanol) over a catalyst from the zirconium oxide group, tantalum oxide, niobium oxide, and one of the combinations of these oxides with silica. However, based on 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).

[0016] Studies have also focused on improving silica supports and / or optimizing the preparation process for heterogeneous catalysts, particularly those based on tantalum and silica. For example, application W02014 / 061917 describes a tantalum-based catalyst with a silica support characterized by mesopores of uniform size and morphology, distributed periodically within the material (so-called mesostructured silica). Application WO2017 / 009107, meanwhile, discloses a catalyst comprising tantalum and a silica-based mesoporous oxide matrix that has undergone acid washing.More recently, application WO2022 / 165190 describes a process for preparing a tantalum-silica catalyst, exhibiting controlled distribution of tantalum within the silica particles, by organically depositing a specific tantalum precursor, preferably selected from a tantalum ethanoate, in particular tantalum 2,4-pentanedione tetraethanoate or tantalum pentaethanoate, possibly combined with acetylacetone. Patent application CN 115364844 describes the preparation of a tantalum-silica catalyst by contacting silica with a solution comprising a tantalum precursor and anhydrous citric acid in absolute ethanol.Finally, Ushikubo's team compares tantalum oxide catalysts on silica prepared from a tantalum alkoxide solution in hexane to tantalum oxide catalysts on silica prepared by impregnating silica with an aqueous solution of 1M hydrochloric acid at 1 wt% 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 Analysis A: General, vol. 124, no. 1, March 1, 1995 (1995-03-01), pages 19-31).

[0017] Finally, more recently, the influence of the aluminium and sodium content of the silica used as a support on butadiene selectivity and butadiene yield or productivity has been shown for catalysts with approximately 3 wt% Ta2O5 (cf. WO2024 / 028334, WO2024 / 028336, WO2024 / 028341).

[0018] There is always a need to improve the catalytic performance of a catalyst comprising tantalum, particularly in oxide form, and a silica support. Thus, the present invention aims to provide a heterogeneous catalyst based on tantalum and silica, for converting a feed containing ethanol into butadiene (or 1,3-butadiene), and exhibiting optimized catalytic performance, in particular optimized butadiene selectivity and productivity.

[0019] Summary of the invention

[0020] The present invention relates to a catalyst comprising tantalum and a silica-based matrix, the catalyst having a tantalum weight content of between 0.1 and 10% by weight relative to the silica-based matrix, the catalyst comprising aluminum at a level such that the catalyst has a molar ratio Ta / AI of tantalum relative to aluminum, both elements being included in the catalyst, greater than or equal to 5, the catalyst having an alkali element Gp1 content such that the catalyst has a molar ratio (Gp1 / AI) / Ta of alkali elements Gp1 included in the catalyst relative to aluminum Al included in the catalyst, per molar unit of tantalum Ta, less than or equal to 0.01, the catalyst having an alkaline earth element Gp2 content such that the catalyst has a molar ratio Ta / Gp2 of tantalum Ta relative to the alkaline earth elements Gp2 included in the catalyst.greater than or equal to 15.

[0021] Surprisingly, a catalyst according to the invention, based on tantalum and a silicic matrix, and having such quantities of metallic elements other than those of groups 4 and 5, in particular other than tantalum, and more particularly such quantities of aluminium, alkali and alkaline earth elements, exhibits optimized catalytic performance when converting a feed comprising ethanol into 1,3-butadiene, and in particular in terms of butadiene selectivity and butadiene productivity.Thus, a catalyst according to the invention makes it possible, for example, in the case of the conversion of a feed comprising ethanol, in particular an ethanol-acetaldehyde feed (notably at an ethanol / acetaldehyde molar ratio of 2.6), into 1,3-butadiene, particularly under operating conditions of 350°C and 0.15 MPa, to achieve a high butadiene selectivity, in particular greater than or equal to 70%, preferably greater than or equal to 72%, for a 40% wt. It also achieves 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 (g / gTa / h meaning: gram of butadiene produced per gram of tantalum used to convert said feed, per hour), for an hourly wt. rate of the feed of 250 g / gTa / h (the hourly wt. rate or wt. being expressed in load weight per unit weight of tantalum used to convert said load, and per hour).

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

[0023] Description of the implementation methods

[0024] According to the invention, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included within the described range of values. If this is not the case and the limit values ​​are not included within the described range, this clarification will be provided in the present description.

[0025] According to the invention, the different parameter ranges for a given step can be used alone or in combination. For example, a range of preferred tantalum content values ​​can be combined with a range of more preferred silica content values.

[0026] In the following description, specific embodiments of the invention are described. According to the invention, they can be implemented separately or in combination, without limitation as to the number of combinations, when technically feasible.

[0027] In the following description, pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

[0028] In the following description, times and durations are expressed in hours (h), minutes (min) and / or seconds (sec).

[0029] According to the invention, the terms "catalyst," "heterogeneous catalyst," and "supported catalyst" are used interchangeably and refer to any type of catalyst comprising the element tantalum and a support, and in particular a silica-based matrix. In this description, the terms "matrix" and "support" are used interchangeably to refer to the solid support of the catalyst. In the catalyst according to the invention, the support is silica-based.

[0030] In this description, the terms "1,3-butadiene" and "butadiene" are used interchangeably and refer to one of the isomers of butadiene (a hydrocarbon compound with four carbon atoms and two double bonds), comprising one 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.

[0031] In this description, the term "butadiene productivity" refers to the carbon productivity of butadiene (generally expressed as wt% / wt% per hour) of a unit conversion of a feed containing ethanol to 1,3-butadiene, and specifically corresponds 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 wt% of the feed of 250 g / gTa / h. Conversely, the term "butadiene selectivity" (expressed as wt% / wt%) is a carbon selectivity and corresponds to the butadiene flow rate measured at the outlet of the unit or reactor relative to the sum of the flow rates of the carbon products formed (unconverted ethanol and possibly acetaldehyde are not taken into account in the selectivity calculation).

[0032] The present invention thus relates to a heterogeneous catalyst containing an active phase comprising the element tantalum, and a support composed in particular of a silica-based matrix.

[0033] Advantageously, the catalyst according to the invention comprises tantalum at a weight content of between 0.1 and 10%, preferably between 0.5 and 5% by weight of the tantalum element relative to the weight of the silica-based matrix. The active phase of the catalyst may optionally comprise at least one other metallic element, selected from the elements of groups 3, 4, 5, 11, and 12 of the periodic table (other than tantalum). Preferably, the active phase of the catalyst according to the invention comprises only the tantalum element.

[0034] 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 that may be 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 silicic matrix (i.e., excluding the weight of any water present in the matrix).Preferably, the silica in the silica-based matrix is ​​amorphous silica. Preferably, the silica-based matrix comprises at least 95% dry weight, preferably at least 98% dry weight, preferably at least 99.5% dry weight, and more preferably at least 99.9% dry weight of amorphous silica relative to the total dry weight of the silica-based matrix.

[0035] 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, preferably between 0.58 and 1.5 ml / g, and 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 200 m². 2 / g, preferably greater than or equal to 250 m 2 / g, preferably between 250 m 2 / g and 700 m 2 / g and in particular between 300 and 600 m 2 / g.

[0036] The aforementioned textural parameters are determined by the analysis technique known as "Nitrogen Volumetry," which involves the physical adsorption of nitrogen molecules into the material's porosity through a gradual increase in pressure at constant temperature. According to the invention, the specific surface area of ​​the tested material, particularly the catalyst, corresponds to the specific surface area BET (SBET in m²). 2 / g) determined by nitrogen adsorption in accordance with ASTM D 3663-78, established from the Brunauer-Emmett-Teller method described in *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 obtained according to the BJH model is described in *The Journal of the American Chemical Society*, 1951, 73, 373, written by E.P. Barrett, L.G. Joyner, and P.P. Halenda. The pore volume V is defined as the value corresponding to the observed volume for the partial pressure P / P° ma x of the nitrogen adsorption - nitrogen desorption isotherm. The nitrogen adsorption volume is the volume measured for P / P° max = 0.99, the pressure at which it is assumed that nitrogen has filled all the pores. The diameter of the mesopores <|) of the tested material, in particular of the catalyst, is determined by formula 4000. / SBET.

[0037] The catalyst according to the invention comprises impurities, particularly aluminum and, more generally, alkali and alkaline earth impurities. These impurities may be related, for example, to the preparation protocol of the silica support. Some impurities, such as aluminum, can generate sites capable of accelerating the dehydration rate and can cause a decrease in catalyst selectivity, notably through an increase in the conversion of ethanol to ethylene or diethyl ether. Other impurities, such as alkaline earths, can generate sites capable of accelerating the aldol condensation rate and can cause a decrease in catalyst selectivity, notably through an increase in the conversion of acetaldehyde to compounds having six or more carbon atoms (C6+ compounds). Impurities, such as alkalis, can neutralize the active sites present on the catalyst; their presence must therefore be limited.

[0038] More particularly, the catalyst according to the invention comprises aluminium at a content such that the molar ratio (Ta / AI) between the molar quantity of the tantalum element Ta present in the catalyst and the molar quantity of the aluminium element Al included in the catalyst is greater than or equal to 5, preferably greater than or equal to 6, and advantageously less than or equal to 3000, preferably less than or equal to 1000, or even less than or equal to 500.

[0039] The catalyst according to the invention may also comprise at least one alkali-earth impurity, that is to say, at least one alkali-earth element, and in particular at least one element selected from calcium (Ca), magnesium (Mg), barium (Ba), and mixtures thereof, more particularly from calcium (Ca), magnesium (Mg), and mixtures thereof. Advantageously, the catalyst according to the invention has an alkali-earth element (Gp2) content, particularly of Ca and / or Mg, such that the catalyst has a molar ratio (Ta / Gp2) between the molar quantity of tantalum (Ta) present in the catalyst and the molar quantity of alkali-earth elements, and in particular of Ca and Mg, present in the catalyst, which is greater than or equal to 15, preferably greater than or equal to 25, and for example less than or equal to 3000.

[0040] In particular, the catalyst according to the invention further comprises impurities in the form of alkali element(s), for example sodium (Na) and / or potassium (K). Preferably, the catalyst has a weight content of alkali elements (Gp1) such that the catalyst has a molar ratio ((Gp1 / AI) / Ta) between the molar quantity of alkali elements, and in particular Na and K, present in the catalyst, relative to the molar quantity of aluminum (Al) present in the catalyst, per mole of tantalum (Ta), less than or equal to 0.01 (i.e., < 10 -2 ), preferably less than or equal to 0.010 (i.e., < 1.0 x 10 - 2 ), and for example greater than or equal to 0.00001 (i.e., > 10' 5 ).

[0041] Preferably, the levels of impurities, in particular aluminium, alkaline earth elements and alkali elements, are determined by X-ray fluorescence (FX) spectrometry and / or by inductively coupled plasma (ICP) spectrometry.

[0042] X-ray fluorescence (XRF) spectrometry is a chemical analysis technique that utilizes a physical property of matter: X-ray fluorescence. Since the X-ray spectrum emitted by matter is characteristic of the sample's composition, the elemental composition—that is, the mass concentrations of elements—of the analyzed sample can be deduced by analyzing the emitted X-ray spectrum. This technique is typically used for quantitative analysis of elemental concentrations of 200 ppm or higher.

[0043] When the concentration of the target element is less than 200 ppm, inductively coupled plasma (ICP) spectroscopy is used. This technique is a physical method of chemical analysis that involves ionizing the sample of material being analyzed by injecting it into a plasma, typically argon. ICP is generally coupled with a detection method, preferably atomic emission spectrometry, to analyze the emitted ions.

[0044] The catalyst according to the invention can be in powder form or shaped, in particular as pelletized, crushed and sieved powder, beads, pellets, granules, or extrudates (hollow or solid cylinders, multilobed 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 possibly spheronized, preferably with 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 butadiene conversion reaction of a feed comprising ethanol, and having the role of binder so as to help shape and generate the appropriate physical properties of the catalyst (mechanical strength, resistance to attrition, etc.).The porous oxide material, which acts as a binder, can be selected from the group consisting of silica, magnesia, clays (such as kaolinite, antigorite, chrysotile, montmorillonite, beidellite, vermiculite, talc, hectorite, saponite, and laponite), titanium dioxide, titanates (e.g., zinc, nickel, and cobalt titanates), lanthanum oxide, cerium oxide, boron phosphates, and mixtures thereof, and preferably from silica and titanium dioxide. Most preferably, the binder used is silicic in nature, and preferably at a content of between 5 and 60% by weight, and more preferably between 10 and 30% by weight of binder relative to the total weight of the catalyst.

[0045] The catalyst according to the invention may preferably be:

[0046] - a fresh catalyst, i.e. a catalyst which has been prepared but has not yet been used in a catalytic unit or reactor, or - a re-activated catalyst, i.e. a spent catalyst (i.e. a catalyst which has been used in a reaction section converting a feed including ethanol into butadiene) and which has undergone a re-activation process (regeneration by burning of the coke, in particular in the presence of oxygen, and / or rejuvenation using a reactivation compound possibly accompanied by the addition of tantalum, said reactivation compound being for example a hydroxy acid, a keto acid, a polyacid, one of their esters, or mixtures thereof, or a monofunctional acid, a hydroxyketone or a diketone) so as to be able to recover at least part of its catalytic performance.

[0047] The catalyst could potentially be:

[0048] - a spent catalyst, that is to say a catalyst that has been used in a reaction section converting a feedstock containing ethanol into butadiene,

[0049] - an aged catalyst, that is to say a catalyst which has undergone treatment, for example heat treatment in particular under a humid gas flow.

[0050] Such a catalyst highly optimizes catalytic performance during the conversion reaction of a feed containing ethanol to 1,3-butadiene, particularly in terms of butadiene selectivity and productivity. Thus, a catalyst according to the invention, used to convert a feed containing ethanol, in particular an ethanol-acetaldehyde feed, into 1,3-butadiene, achieves high butadiene selectivity, in particular greater than or equal to 70%, preferably greater than or equal to 72%, for a feed conversion of 40% by weight (the conversion being a weight conversion of the feed and corresponding to the difference between the weight flow rate of the feed at the inlet and the weight flow rate of the feed at the outlet, relative to the weight flow rate of the feed at the inlet), and 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 charge equal to 250 g / gTa / h (the hourly weight rate or pph being expressed as weight of charge per unit weight of tantalum contained in the catalyst used, i.e. in the total quantity by weight of catalyst used, and per hour).

[0051] The present invention also relates to the use of the catalyst according to the invention for converting a feed comprising ethanol into 1,3-butadiene, 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, preferably between 300 and 360°C, a pressure between 0.05 and 2.00 MPa, preferably between 0.05 and 1.50 MPa, preferably between 0.08 and 1.00 MPa, and preferably a space velocity between 0.2 and 10 h' 1 preferably between 0.5 and 5 a.m.-1 and preferably between 1 and 4 tr 1 The spatial velocity is defined as the ratio between the mass flow rate of the feed and the mass of the catalyst. When the feed also includes 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 feed containing ethanol to butadiene then results in an optimization of the butadiene selectivity and the butadiene carbon productivity.

[0052] The following examples illustrate the invention, in particular specific embodiments of the invention, without limiting its scope.

[0053] Examples

[0054] Example 1:

[0055] Several tantalum-based catalysts on amorphous silica were tested in a catalytic unit under the operating conditions described below. The tested catalysts are listed in Table 1, along with their compositions and structural characteristics.

[0056] Tantalum content is a weight content of element Ta relative to the weight of the silica matrix, expressed as a percentage (i.e., quantities of parts of Ta per 100 parts of silica matrix).

[0057] The ratios Ta / AI, Ta / (Ca+Mg), are molar ratios of the elements respectively of tantalum to aluminum, of tantalum to the whole of calcium and magnesium, present in the catalyst considered.

[0058] The molar ratio ((Na+K) / Al) / Ta corresponds to the ratio between the sum of the molar amounts of the alkali elements sodium and potassium and the molar amount of aluminum, per molar unit of tantalum, present in the catalyst in question. In Table 1, since the molar ratios ((Na+K) / Al) / Ta can be very low, they have been multiplied by 100 for greater clarity.

[0059] Table 1

[0060] Catalyst performance test

[0061] The reactor used consists of a 20 cm long, 10 mm diameter stainless steel tube. The reactor is first loaded with carborundum, then with the catalyst diluted in carborundum, and finally with carborundum. The carborundum is inert with respect to the charge and does not affect the catalytic results. The reactor temperature is controlled with a three-zone tubular furnace.

[0062] The catalyst is calcined in situ under dry air at 550°C for 4 hours and then placed under nitrogen at the test temperature for 1 hour.

[0063] The liquid feed, 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 feed is vaporized before entering the reactor and homogenized by passing through a static mixer. For each test, the ethanol / acetaldehyde ratio of the feed is fixed at 2.6 mol / mol, the reaction temperature at 350°C, and the pressure at 0.15 MPa.

[0064] At the reactor outlet, the products formed during the reaction are kept in vapor phase to be analyzed online by gas chromatography (PONA capillary column) to allow the identification of the products formed.

[0065] For each catalyst tested, the carbon productivity value is measured at a constant feed rate (constant pph of 250 g / gTa / h), while the butadiene selectivity is determined at a constant conversion rate (40% feed conversion). Carbon productivity (generally expressed as wt% / wt% per hour) corresponds to the mass flow rate of butadiene (in g / h), measured at the reactor outlet, per unit mass of element Ta, for a feed pph of 250 g / gTa / h. The measured butadiene selectivity (expressed as wt% / wt%) 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 carbonaceous products formed (unconverted ethanol and acetaldehyde are not included in the selectivity calculation).

[0066] The catalytic results are presented in Table 2.

[0067] Table 2

[0068] It is clear that the catalysts F, G, H, I, conforming to the invention, exhibit very satisfactory catalytic performance, and in particular a butadiene selectivity greater than 70% and at the same time a butadiene productivity greater than 30. On the contrary, the non-conforming catalysts A, B, C, D, E, which do not meet at least one of the three composition criteria, i.e. a molar ratio Ta / AI of at least 5, a molar ratio Ta / Ca of at least 15, and a molar ratio (((Na+K) / AI) / Ta) of at most 0.01, exhibit either low selectivity (i.e. less than 70%, like catalyst C), or unsatisfactory butadiene productivity (i.e. less than 30g / g / h), like catalysts B and D, or again low selectivity and unsatisfactory productivity, like catalysts A and E.

Claims

Demands 1. A catalyst comprising tantalum and a silica-based matrix, the catalyst having a tantalum weight content of between 0.1 and 10% by weight relative to the silica-based matrix, the catalyst comprising aluminium at a level such that the catalyst has a molar ratio Ta / AI of tantalum relative to aluminium, both elements being included in the catalyst, greater than or equal to 5, the catalyst having an alkali element Gp1 content such that the catalyst has a molar ratio (Gp1 / AI) / Ta of alkali elements Gp1 included in the catalyst relative to aluminium Al included in the catalyst, per molar unit of tantalum Ta, less than or equal to 0.01, the catalyst having an alkaline earth element Gp2 content such that the catalyst has a molar ratio Ta / Gp2 of tantalum Ta relative to alkaline earth elements Gp2 included in the catalyst, greater than or equal to 15.

2. Catalyst according to claim 1, having a tantalum weight content of between 0.5 and 5% tantalum by weight relative to the silica-based matrix.

3. Catalyst according to claim 1 or 2, having a weight content of alkaline earth elements such as to have a molar ratio Ta / Gg2 of the tantalum element with respect to the alkaline earth elements greater than or equal to 25.

4. Catalyst according to any one of the preceding claims, having an aluminum content such that it has a molar ratio of Ta / AI of tantalum to aluminum greater than or equal to 6.

5. Catalyst according to any one of the preceding claims, wherein the silica-based matrix has a silica weight content 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% silica weight relative to the total dry weight of the silica-based matrix.

6. A catalyst according to any 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. A catalyst according to any 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, preferably between 0.58 and 1.5 ml / g, preferably between 0.8 and 1.5 ml / g.

8. Catalyst according to any one of the preceding claims, having a specific surface area SBET greater than or equal to 200 m² 2 / g, preferably greater than or equal to 250 m 2 / g, preferably between 250 m 2 / g and 700 m 2 / g and in particular between 300 and 600 m 2 / g.

9. Use of the catalyst according to any one of claims 1 to 8 to convert a feed comprising ethanol into butadiene, at a temperature between 250 and 450°C, at a pressure between 0.05 and 2.00 MPa.

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