A process for preparing a material comprising silicon carbide, silica and a potassium or cesium phosphate salt

Abstract

A process for preparing a macroporous material comprising an active phase comprising a potassium phosphate salt and / or a cesium phosphate salt and a support comprising α-SiC silicon carbide and silica comprising the following steps: a) contacting a colloidal silica sol with a powder of a potassium and / or cesium phosphate salt to obtain a suspension; b) adding a powder of precipitated silica, a powder of α-SiC silicon carbide and a solvent to obtain a paste; c) shaping the paste to obtain a material precursor; d) drying the material precursor at a temperature between 15°C and 250°C; e) calcining the dried material precursor obtained at the end of step d) at a temperature above 250°C and below or equal to 1200°C.

Description

Title of the invention: Process for preparing a material comprising silicon carbide, silica and a potassium or cesium phosphate salt Scope of the invention

[0001] The invention relates to a process for preparing a material based on potassium phosphate salt(s) or cesium phosphate salt(s), silicon carbide in its alpha crystallographic form (also referred to herein as alpha-SiC or a-SiC), and silica. The material obtained by the process according to the invention can advantageously be used as a support or as a catalyst in catalytic processes. Prior art

[0002] Silica is an interesting compound for use as a catalyst support; however, it cannot be extruded like other materials in conventional extrusion equipment to produce products sufficiently robust for use in catalytic processes. Indeed, from its manufacture to its implementation, the catalyst incorporating such a support is subjected to numerous steps that can impact its physical integrity. In particular, it must be resistant to crushing, attrition, and pressure variations related to the operating conditions of the catalytic reactor in which it is used. Thus, there is a continuous need to supply catalysts with improved mechanical and physical properties.

[0003] Silicon carbide (also referred to here as SiC) is an inorganic material possessing particular properties in terms of stability, conductivity, mechanical and chemical resistance which make it interesting for applications in catalysis.

[0004] Silicon carbide (SiC), non-porous (a-SiC) or preferably porous (|3-SiC), can be used as a support for metal catalysts, as illustrated, for example, in the publication by Ledoux et al. (Journal of Catalysis, Volume 114, Issue 1, November 1988, Pages 176-185) and more recently in the review by Kulkami et al. (Catalysis Reviews, Science and Engineering, Volume 65, 2023 - Issue 1). Also noteworthy is patent application WO14140973, which discloses the preparation of a catalyst comprising a cobalt-based active phase and a silicon carbide-containing support for the synthesis of hydrocarbons via the Fisher-Tropsch synthesis.

[0005] To date, there is no catalyst in the literature comprising an active phase based on potassium or cesium phosphate salt(s) supported on a support comprising silicon carbide (SiC) in its alpha crystallographic form and silica.

[0006] The Applicant has surprisingly discovered a new preparation process for obtaining a material comprising an active phase based on potassium or cesium phosphate salt(s) and a silicon carbide (SiC)-based support and at least one silica source exhibiting good mechanical resistance and therefore being usable as a catalyst, particularly in the dehydration of hydroxypropanoic acid. Object of the invention

[0007] The present invention relates to a process for preparing a macroporous material comprising an active phase comprising at least one potassium phosphate salt and / or at least one cesium phosphate salt and a support comprising silicon carbide in its alpha crystallographic form (a-SiC) and silica, said process comprising the following steps:

[0008] a) at least one colloidal silica sol is brought into contact with at least one powder of at least one potassium and / or cesium phosphate salt to obtain a suspension;

[0009] b) a powder of at least one precipitated silica, a powder of silicon carbide in its alpha crystallographic form (a-SiC) and at least one solvent are added to said suspension obtained at the end of step a) to obtain a paste;

[0010] c) the paste obtained at the end of step b) is shaped to obtain a precursor of material;

[0011] d) the precursor material obtained at the end of step c) is dried at a temperature between 15°C and 250°C to obtain a dried precursor material;

[0012] e) the dried material precursor obtained at the end of step d) is calcined at a temperature greater than 250°C and less than or equal to 1200°C.

[0013] An advantage of the preparation process according to the invention is to provide a material exhibiting improved mechanical resistance compared to prior art materials through the implementation of a premixing step of a colloidal silica sol with a powder of potassium and / or cesium phosphate salt(s) to obtain a suspension, followed by a step of adding a powder of another silica precursor, i.e. precipitated silica, with a source of alpha-SiC and then shaping the mixture, drying, or even calcining the material.

[0014] According to one or more embodiments of the invention, step e) is carried out at a temperature above 250°C and below 800°C.

[0015] According to one or more embodiments of the invention, step e) is carried out at a temperature between 800°C and 1200°C.

[0016] According to one or more embodiments of the invention, step a) is carried out in a centrifugal planetary mixer operating at a speed between 100 and 2000 revolutions per minute.

[0017] According to one or more embodiments of the invention, step a) is carried out for a duration of between 5 seconds and 60 seconds.

[0018] According to one or more embodiments of the invention, in step a) said at least one powder of at least one potassium and / or cesium phosphate salt is previously ground and sieved to a particle size of less than 100 pm.

[0019] According to one or more embodiments of the invention, in step b) the powder of at least one silicon carbide source has a grain size of less than 20 pm.

[0020] According to one or more embodiments of the invention, in step b) the powder of at least one precipitated silica has a grain size of less than 20 pm.

[0021] According to one or more embodiments of the invention, step b) is carried out in the same equipment used in step a).

[0022] According to one or more embodiments of the invention, step b) is carried out in a centrifugal planetary mixer at a rotation speed of between 300 and 2000 revolutions per minute.

[0023] According to one or more embodiments of the invention, steps a) and b) are carried out in different equipment: step a) is carried out in a centrifugal planetary mixer to obtain said suspension, then step b) is carried out in a mixer equipped with Z-arms to obtain a paste.

[0024] According to one or more embodiments of the invention, the precipitated silica powder, the alpha type silicon carbide powder, the solvent and optionally an organic adjuvant are added to the mixer equipped with Z-arms before the introduction of the suspension obtained in step a).

[0025] According to one or more embodiments of the invention, the rotation speed of the mixer arms is between 10 revolutions / minute and 75 revolutions / minute.

[0026] According to one or more embodiments of the invention, in step a) a powder of at least one salt of potassium and / or cesium phosphate ground and sieved to a particle size of less than 100 pm is used and in step b) a silica powder precipitated to a size of less than 10 pm.

[0027] According to one or more embodiments of the invention, in step b) a silicon carbide powder with a particle size of less than 5 pm and a precipitated silica powder with a size of less than 10 pm are used. Detailed description 1. Definitions

[0028] In the sense of the present invention, the different embodiments presented can be used alone or in combination with each other, without limitation of combination.

[0029] In the sense of the present invention, the different parameter ranges for a Given the step, pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0030] By "macropores", we mean pores whose opening is greater than 50 nm.

[0031] By "mesopores" we mean pores whose opening is between 2 nm and 50 nm, inclusive.

[0032] The total pore volume (TPV) of the material according to the invention is defined as the volume measured by intrusion with a mercury porosimeter according to ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°. The wetting angle was taken to be 140° following the recommendations of the book "Techniques de l'ingénieur, traité analyse et caractérisation", pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

[0033] In order to obtain better accuracy, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with the mercury porosimeter measured on the sample less the value of the total pore volume measured by intrusion with the mercury porosimeter measured on the same sample for a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0034] The volume of macropores and mesopores is measured by mercury intrusion porosimetry according to ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°. The value at which mercury fills all intergranular voids is set at 0.2 MPa, and beyond this value, mercury is considered to penetrate the pores of the sample.

[0035] The macroporous volume of the material according to the invention is defined as the cumulative volume of mercury introduced at a pressure between 0.2 MPa and 30 MPa, corresponding to the volume contained in pores with an apparent diameter greater than 50 nm.

[0036] The mesoporous volume of the material according to the invention is defined as the cumulative volume of mercury introduced at a pressure between 30 MPa and 400 MPa, corresponding to the volume contained in the pores with an apparent diameter between 2 nm and 50 nm.

[0037] The median diameter of macropores (Dmacro in nm) is also defined as a diameter such that all pores smaller than this diameter constitute 50% of the macroporous volume, measured by mercury porosimetry.

[0038] The specific surface area of ​​the material is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140° using a Microméritics® Autopore® IV model apparatus.

[0039] In the following text, transmission electron microscopy (TEM) is the method used to characterize the materials obtained according to the invention. This technique provides information on the chemical composition and morphology, and allows for the measurement of the size of the grains or crystals constituting the material. For this purpose, an electron microscope (of the JEOL JEM F200 or JEOL JEM 2100F type) equipped with an energy-dispersive X-ray spectrometer (EDS) is used. The EDS detector must allow for the detection of light elements. The combination of these two tools, TEM and EDS, makes it possible to combine imaging and local chemical analysis with good spatial resolution.

[0040] Throughout this text, lateral crush resistance refers to the mechanical resistance of the material according to the invention as determined by the grain-by-grain crush (GBC) test. This is a standardized test (ASTM D4179-01) which consists of subjecting a material in the form of a millimeter-sized object, such as a ball, pellet, or extrudate, to a compressive force that causes it to break. This test is therefore a measure of the tensile strength of the material. The analysis is repeated on a number of individual solids, typically between 10 and 200. The average of the measured lateral breaking forces constitutes the average GBC, which is expressed in units of force (N) for granules and in units of force per unit length (daN / mm or decaNewton per millimeter of extrudate length) for extrudates.

[0041] In the following text, the grain size or particle size distribution of the constituents of the materials obtained according to the invention is measured by laser scattering particle size analysis. This indirect measurement technique makes it possible to determine the particle size distribution (on the micron to millimeter scale). This analytical method uses the principle of light scattering (Mie theory) and / or diffraction (Fraunhofer theory and Mie theory). Particles illuminated by the laser light deflect the light from its principal axis. The amount of light deflected and the magnitude of the deflection angle allow for the precise measurement of the particle size. The powder is conveyed either by a solvent (water, isopropanol) or by air before passing in front of the laser beam: two paths are thus distinguished: the wet path and the dry path.

[0042] The wet method allows for the characterization of dispersions (elementary particle size distribution after dispersion) or suspended solids (aggregate particle size distribution). The measured particles are in the range of 0.02 microns to 2000 microns.

[0043] Dry particle size analysis allows for the characterization of powders without disrupting their initial aggregation. The measurement range extends from 0.2 microns to 2000 microns. In the present invention, dry particle size analysis is used to measure the grain size of the constituents of the material of the invention. 2. Detailed Description Material

[0044] An object according to the invention relates to a macroporous material comprising an active phase comprising at least one potassium phosphate salt and / or at least one cesium phosphate salt, and a support comprising silicon carbide in its alpha crystallographic form (a-SiC) and silica exhibiting good crush resistance (EGG) compared to a silica-based support not exhibiting silicon carbide.

[0045] Indeed, the Applicant has surprisingly discovered that the use of such a macroporous material as a dehydration catalyst for hydroxypropanoic acid makes it possible to obtain a conversion at least as good, or even better, of hydroxypropanoic acid and a yield at least as good, or even better, of corresponding propenoic acid compared to a catalyst obtained according to conventional preparation processes, i.e. in the absence of a support comprising silicon carbide in its alpha crystallographic form and silica.

[0046] Advantageously, said potassium phosphate and / or cesium phosphate salt is potassium metaphosphate (KPO3) and / or cesium metaphosphate (CsPO3).

[0047] Advantageously, said material has a mass ratio MPO3 / (SiC+MPO3 +SiO2) of between 13 and 50, preferably between 15 and 45, and even more preferably between 17 and 40, with M being chosen from potassium and / or cesium (M = K and / or Cs). Preferably, M is potassium.

[0048] Advantageously, said material has a SiC / (MPO3+SiC+SiO2) mass ratio of between 10 and 40, preferably between 12 and 35, and even more preferably between 14 and 30, with M being chosen from potassium and / or cesium (M = K and / or Cs). Preferably, M is potassium.

[0049] Preferably said material has a total porous volume between 0.01 and 0.6 cmVg, more preferably between 0.01 and 0.5 cmVg, even more preferably between 0.05 and 0.4 cmVg, and even more preferably between 0.05 and 0.35 cmVg.

[0050] Preferably, said material has a macroporous volume between 0.01 and 0.5 cmVg, more preferably between 0.05 and 0.4 cmVg, even more preferably between 0.05 and 0.4 cmVg, and even more preferably between 0.05 and 0.35 cmVg.

[0051] Advantageously, said material has a specific surface area greater than 1 m2 / g and less than 50 m2 / g, preferably between 1 and 45 m2 / g, more preferably between 1 and 40 m2 / g, and even more preferably between 1 and 35 m2 / g.

[0052] Advantageously, said material has a mechanical resistance value measured by grain-by-grain crushing greater than 1.2 daN / mm, preferably greater than 1.5 daN / mm, more preferably greater than 1.7 daN / mm and preferably greater than 2 daN / mm.

[0053] The material advantageously has between 1% and 99% by weight, preferably between 5% and 99% by weight, preferably from 10% to 95% by weight, and most preferably from 20% to 75% by weight of at least one potassium and / or cesium phosphate salt relative to the total weight of said material.

[0054] The material advantageously has between 50% and 90% by weight, preferably between 55% and 90% by weight, preferably from 60% to 85% by weight, and most preferably from 60% to 80% by weight of silica, relative to the total weight of said material.

[0055] The material advantageously has between 1% and 99% by weight, preferably between 5% and 99% by weight, preferably from 7% to 95% by weight, and most preferably from 10% to 75% by weight silicon carbide in its alpha crystallographic form (a-SiC) relative to the total weight of said material.

[0056] Said material according to the invention advantageously has a macroporous median diameter between 10 nm and 7000 nm, preferably between 20 nm and 6500 nm, and more preferably between 50 nm and 5000 nm.

[0057] Said material is advantageously in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates. Preparation process

[0058] According to the invention, the present invention relates to a process for preparing a macroporous material comprising an active phase comprising at least one potassium phosphate salt and / or at least one cesium phosphate salt and a support comprising silicon carbide in its alpha crystallographic form (a-SiC) and silica, said process comprising the following steps:

[0059] a) at least one colloidal silica sol is brought into contact with at least one powder of at least one potassium and / or cesium phosphate salt to obtain a suspension;

[0060] b) a powder of at least one precipitated silica, a powder of silicon carbide in its alpha crystallographic form (a-SiC) and at least one solvent are added to said suspension obtained at the end of step a) to obtain a paste;

[0061] c) the paste obtained at the end of step b) is shaped to obtain a precursor of material;

[0062] d) the precursor material obtained at the end of step c) is dried at a temperature between 15°C and 250°C to obtain a dried precursor material;

[0063] e) the material obtained at the end of step d) is calcined at a temperature greater than 250°C and less than or equal to 1200°C.

[0064] All steps a) to e) are detailed below. Step a)

[0065] According to the invention, said step a) consists of premixing at least one colloidal silica sol with at least one powder of at least one potassium and / or cesium phosphate salt to obtain a suspension.

[0066] A solvent, preferably water, can advantageously be added in step a).

[0067] Preferably, colloidal silica soils are chosen, without being restrictive, among the following commercial sources: Ludox (WR Grâce Davison®), Nyacol (Nyacol Nano Technologies®, Inc. or PQ Corp®), Nalco (Nalco Chemical Company®), Ultra-Sol (RESI Inc®), NexSil (NNTI®), taken alone or in mixtures.

[0068] The source or sources of colloidal silica soil used in the process according to the present invention are advantageously synthetic amorphous silicas.

[0069] Said potassium phosphate and / or cesium phosphate salts used in step a) are advantageously chosen from potassium or cesium phosphate salts in amorphous or crystalline oxide form taken alone or in mixture.

[0070] Said potassium phosphate salt(s) are advantageously selected from: KH2PO4, K2HPO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, K6P6O18, K8P8O24, KioPioO3O, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixtures. Preferably, the potassium phosphate salt is selected from potassium phosphate (tripotassium) (PO43,3K+) and KH2PO4, alone or in mixtures.

[0071] Said cesium phosphate salt(s) are advantageously chosen from CsH2PO4, Cs2H2P3O10, Cs4H2P4O13, Cs3P3O9, Cs4P4O12, Cs6P6O18, Cs8P8O24, CsPO3, alone or in mixtures. Preferably the cesium phosphate salt is CsH2PO4.

[0072] Preferably, said potassium phosphate salt(s) or cesium phosphate salt(s) is / are chosen from potassium phosphate (tripotassium) (PO43,3K+), KH2 PO4, CsH2PO4 in their hydrated or non-hydrated form.

[0073] Preferably, said powders of at least one potassium and / or cesium phosphate salt can advantageously be ground and sieved to a grain size of less than 100 µm prior to their introduction in step a). The grain size of the potassium and / or cesium phosphate salts is advantageously measured by dry laser granulometry.

[0074] Most preferably, said step a) is advantageously carried out in a centrifugal planetary mixer. Said powders of at least one potassium and / or cesium phosphate salt, preferably ground and sieved to a particle size of less than 100 µm, are pre-dispersed by means of a centrifugal planetary mixer in the presence of the colloidal silica soil source so as to obtain said suspension.

[0075] Said step a) is advantageously carried out at a mixing speed applied to the centrifugal planetary mixer, between 100 and 2000 revolutions per minute, preferably between 200 and 1600 revolutions per minute.

[0076] Preferably, said step a) is carried out for a duration of between 5 seconds and 60 seconds and preferably between 20 seconds and 60 seconds.

[0077] The addition of powders, colloidal silica sol and optionally solvent (e.g. water) can also advantageously be alternated. Step b)

[0078] According to the invention, the process includes a step b) of adding a powder of at least one precipitated silica, a silicon carbide powder in its alpha crystallographic form (a-SiC) and at least one solvent into said suspension obtained at the end of step a).

[0079] Preferably, the silica powder or powders precipitated according to step b) are chosen without restriction from the following commercial sources: Nyasil20 (Nyacol ®), Siliaflash P60 (Silicycle ®), Siliaflash C60 (Silicycle ®), Ultrasil VN3 GR (Evonik ®), taken alone or in mixture.

[0080] Preferably, the powder of at least one precipitated silica added in step b) has a grain size of less than 20 pm, and preferably less than 10 pm, even more preferably less than 5 pm, and even more preferably less than 1 pm. The grain size of the precipitated silica is advantageously measured by dry laser granulometry.

[0081] Preferably, the precipitated silica is in amorphous form.

[0082] Preferably, the powder of at least one silicon carbide source in its form The alpha crystallographic material added in step b) exhibits a grain size less than 20 pm, preferably less than 15 pm, even more preferably 10 pm, and even more preferably less than 5 pm. The silicon carbide grain size is advantageously measured by dry laser granulometry.

[0083] Preferably, the powder of at least one source of silicon carbide in its alpha crystallographic form according to step b) may be selected without restriction from the following commercial sources: superfine silicon carbide powder, 600, granular from Thermo Scientific Chemicals®; alpha-phase silicon carbide, 99.8% from Thermo Scientific Chemicals®, taken alone or in mixture.

[0084] Preferably, the powder of at least one silicon carbide source in its alpha crystallographic form according to step b) has a low impurity content, preferably a low metallic impurity content, in particular an iron content of less than 1000 ppm, preferably less than 500 ppm, most preferably less than 100 ppm and an aluminum content of less than 1000 ppm, preferably less than 500 ppm, most preferably less than 100 ppm.

[0085] In a particularly preferred manner, silicon carbide in its alpha crystallographic form has a hexagonal crystal structure. Within the scope of the invention, it is entirely feasible to carry out mixtures of several different precipitated silica powders and / or different silica sols and / or different potassium and / or cesium phosphate salt powders and / or different silicon carbide powders.

[0086] According to the invention, at least one solvent is added in step b). Said solvent is advantageously chosen from water, ethanol, alcohols and amines. Preferably, said solvent is water.

[0087] Preferably, at least one organic adjuvant can also be added during step b).

[0088] Said organic adjuvant may also be chosen from all additives known to those skilled in the art. In the case where at least one organic adjuvant is added in step b), said organic adjuvant is advantageously chosen from cellulose derivatives, polyethylene glycols, monocarboxylic aliphatic acids, alkylated aromatic compounds, sulfonic acid salts, fatty acids, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, polyacrylates, polymethacrylates, polyisobutene, polytetrahydrofuran, starch, polysaccharide-type polymers (such as xanthan gum), scleroglucan, hydroxyethylated cellulose-type derivatives, carboxymethylcellulose, lignosulfonates and galactomannan derivatives, taken alone or in mixture.

[0089] Preferably, said organic adjuvant may be mixed in powder form or in solution in said solvent.

[0090] In an embodiment according to the invention, steps a) and b) are advantageously implemented in the same equipment, and preferably in a centrifugal planetary mixer.

[0091] In another embodiment of the invention, steps a) and b) are advantageously carried out in different equipment. In this case, step a) is preferably carried out in a centrifugal planetary mixer and then the suspension obtained at the end of step a) is then sent to a mixer equipped with Z-arms in step b).

[0092] In the case where step a) and step b) are not carried out in the same equipment, preferably, said source of precipitated silica, alpha type silicon carbide, solvent and optionally organic adjuvant are added to the equipment, preferably to the mixer equipped with Z-arms, before the introduction of the suspension obtained in step a).

[0093] In the case where a cesium phosphate salt powder is used, ammonia may be added to obtain an extrudable mixture in step b).

[0094] Preferably, said mixing step b) is carried out by kneading, either batchwise or continuously. If said step b) is carried out batchwise, said step b) is advantageously carried out in a mixer preferably equipped with Z-arms, or cams, or in any other type of mixer such as, for example, a planetary mixer. Said mixing step b) makes it possible to obtain a paste or a homogeneous mixture of the constituents.

[0095] In the case of the implementation of a "Z-arm" type mixer in step b), the rotation speed of the mixer arms is advantageously between 10 and 75 revolutions / minute, preferably between 25 and 50 revolutions / minute.

[0096] In the case of implementing step b) in a centrifugal planetary mixer, the rotation speed is advantageously between 300 and 2000 rpm, preferably between 1500 and 2000 rpm.

[0097] In a particularly preferred embodiment, the use of a powder of at least one salt of potassium and / or cesium phosphate ground and sieved to a particle size of less than 100 pm in step a) associated with the use of a precipitated silica source having a size of less than 10 pm, preferably less than 5 pm, even more preferably less than 2 pm in step b) allows a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0098] In another particularly preferred embodiment, the use of a silicon carbide powder with a particle size of less than 5 pm associated with the use of a precipitated silica source with a size of less than 10 pm, preferably less than 5 pm, even more preferably less than 2 pm in step b) allows a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0099] Preferably, the following quantities are introduced in steps a) and b) of the process according to the invention:

[0100] - 1% to 99% by weight, preferably from 5% to 99% by weight, preferably from 5% to 95% by weight, and most preferably 5% to 40% by weight and even more preferably 5% to 20% by weight of at least one colloidal silica sol;

[0101] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and most preferably from 10% to 60% by weight of at least one potassium and / or cesium phosphate salt;

[0102] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and very preferably from 30 to 80% by weight of at least one precipitated silica;

[0103] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and most preferably from 30 to 80% by weight of at least one silicon carbide powder in its alpha crystallographic form;

[0104] - 0% to 20% by weight, preferably from 1% to 15% by weight, preferably from 1% to 10% by weight, and preferably from 1% to 7% by weight of at least one organic adjuvant;

[0105] the weight percentages being expressed in relation to the total weight of said material and the sum of the contents of each of the compounds of said material being equal to 100%. Step c)

[0106] According to the invention, said process includes a step c) of shaping the dough obtained at the end of step b).

[0107] Preferably, the paste obtained at the end of step b) is advantageously shaped by extrusion.

[0108] In the case where the shaping of the mixture from step b) is carried out by extrusion, said step b) is advantageously carried out in a piston extruder, single screw or twin screw.

[0109] In this case, an organic additive may optionally be added in mixing step b). The presence of said organic additive facilitates shaping by extrusion. Said organic additive is described above and is introduced in step b) in the proportions indicated above.

[0110] The extrusion of the mixture, also called "kneaded paste," can be carried out either by extruding directly from the end of a continuous mixer, such as a twin-screw mixer, or by connecting one or more batch mixers to an extruder. The geometry of the die, which gives the extrudates their shape, can be chosen from among the dies well known to those skilled in the art. These can be, for example, cylindrical, multilobed, grooved, or slotted.

[0111] In the case where the shaping of the mixture from step b) is carried out by extrusion, the quantity of solvent added in step b) of mixing is adjusted so as to obtain, at the end of this step and whatever the variant implemented, a mixture or paste which does not flow but which is not too dry either in order to allow its extrusion under suitable pressure conditions well known to the person skilled in the art and dependent on the extrusion equipment used.

[0112] Preferably, said step c) of shaping by extrusion is carried out at an extrusion pressure greater than 1 MPa and preferably between 3 MPa and 10 MPa. Step d)

[0113] The preparation process according to the invention comprises a step d) of drying the precursor of shaped material obtained at the end of step c). Said step of Drying is advantageously carried out at a temperature between 15°C and 250°C, preferably between 20°C and 200°C and preferably between 20°C and 150°C, preferably for a period of between 1 minute and 72 hours, more preferably between 30 minutes and 72 hours, preferably between 1 hour and 48 hours and more preferably between 1 hour and 24 hours.

[0114] Preferably, said drying step is carried out in air, and preferably in humid air, with a relative humidity between 20% and 100%, preferably between 70% and 100%. This step allows for good hydration of the material, limiting the appearance of cracks that are detrimental to mechanical strength. Step e)

[0115] The dried material precursor obtained at the end of step d) then undergoes a calcination step e) at a temperature above 250°C and below or equal to 1200°C, and for a duration advantageously between 1 and 12 hours, preferably between 1 and 4 hours. This calcination step is particularly useful for removing the organic additives used to facilitate shaping the material.

[0116] In an embodiment according to the invention, the calcination temperature is carried out at a temperature between 800°C and 1200°C, preferably between 800°C and 1100°C, and most preferably between 800°C and 900°C. This step is essential for the formation of the cristobalite and / or tridymite crystallographic phases. This embodiment allows for a significant improvement in the mechanical strength of the final materials obtained.

[0117] In another embodiment according to the invention, the calcination temperature is carried out at a temperature above 250°C and below 800°C, preferably between 300°C and 600°C.

[0118] Said calcination step e) is advantageously carried out under a gas stream comprising oxygen; for example, preferably the extrudates are calcined under dry air or with different humidity levels, or treated at temperature in the presence of a gas mixture comprising an inert gas, preferably nitrogen, and oxygen. The gas mixture used preferably comprises at least 5% by volume, or even preferably at least 10% by volume, of oxygen. Step f) optional

[0119] In a preferred embodiment the process includes a step f) of impregnating the material from step e) with a potassium or cesium phosphate precursor.

[0120] According to step f) of the preparation process, the material obtained at the end of step e) is contacted with at least one phosphate precursor, and at least one potassium and / or cesium precursor to obtain a second material precursor.

[0121] Advantageously, step f) comprises the following substeps:

[0122] fl) a liquid solution in aqueous or organic phase is prepared comprising at least one phosphate precursor, and at least one potassium and / or cesium precursor, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C;

[0123] f2) the solution prepared in step fl) is impregnated onto the material obtained at the end of step e), the volume of the solution being advantageously between 0.9 and 1.1, preferably between 0.8 and 1.05 times the porous volume of the material obtained at the end of step e);

[0124] f3) optionally, a maturation step of the second material precursor obtained at the end of step f2).

[0125] Preferably, the phosphate concentration of the solution supplied in step fl) is between 50 g / L and 2000 g / L.

[0126] The impregnation solution of step 1f) is preferably prepared by dissolving one or more phosphate precursors and potassium (K) or cesium (Cs) in an aqueous or organic phase. The impregnation solution can advantageously be prepared by mixing phosphorus and alkali metals introduced independently. In this case, the alkali metal precursor M, chosen from K or Cs, is selected, for example, from one or more of the following salts: carbonate (M2CO3), nitrate (MNO3), sulfate, formate (HCOOM), acetate (CH2COOM), citrate, lactate, chloride (MCi), hydroxide (MOH), or oxide (M2O).

[0127] The phosphate precursor(s) may advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, P2O5.

[0128] Preferably, a maturation step f3) is carried out, advantageously carried out at a temperature between 0°C and 300°C, preferably between 20°C and 200°C and preferably between 20°C and 150°C, preferably for a duration between 1 minute and 72 hours, preferably between 30 minutes and 72 hours, preferably between 1 hour and 48 hours, and more preferably between 1 hour and 24 hours.

[0129] Preferably, said maturation step is carried out in air and preferably in humid air with a relative humidity between 20 and 100% and preferably between 70 and 100%. This step allows for good hydration of the material, limiting the appearance of cracks that are detrimental to mechanical strength.

[0130] Preferably, the impregnation step f) can optionally be followed by other impregnation steps.

[0131] The material obtained at the end of step f) of impregnation can undergo a calcination step at a temperature between 300°C and 600°C, preferably between 300°C and 550°C, and most preferably between 300°C and 525°C for a duration advantageously between 1 hour and 12 hours, preferably between 1 hour and 4 hours.

[0132] This calcination step is advantageously carried out under a gas stream comprising oxygen; for example, preferably the extrudates are calcined under dry air or with varying humidity levels, or treated at temperature in the presence of a gas mixture comprising an inert gas, preferably nitrogen, and oxygen. The gas mixture used preferably comprises at least 5% by volume, or even more preferably at least 10% by volume, of oxygen.

[0133] At the end of the material preparation process according to the invention, the material obtained is in the form of extrudates or pellets.

[0134] However, it is not excluded that the said materials obtained may then be, for example, introduced into equipment allowing their surface to be rounded, such as a drageoir or any other equipment allowing their spheronization. Transformation process

[0135] The material according to the invention can advantageously be used as a catalyst in a process for the dehydration of hydroxypropanoic acid and its derivatives.

[0136] The process for dehydrating hydroxypropanoic acid and its derivatives operates in the presence of the material prepared according to the invention, which is advantageously used as a catalyst at a temperature between 180°C and 450°C, preferably between 190°C and 430°C, most preferably between 250°C and 420°C and most preferably between 270°C and 420°C, at a pressure between 0.1 MPa and 12 MPa, preferably between 0.11 MPa and 10 MPa, most preferably between 0.13 MPa and 9 MPa and most preferably between 0.15 MPa and 8 MPa, and at a mass flow rate ratio of charge to mass of material between 0.01 h₁ and 100 h₂*, preferably between 0.02 and 50 h₂*, more preferably between 0.03 and 30 h 1 and very preferably between 0.05 and 20 h1.

[0137] Said process makes it possible to selectively obtain a mixture of products comprising acrylic acid.

[0138] During the dehydration of hydroxypropanoic acid and its derivatives into acrylic acid, a mixture of different products, called by-products, is obtained, including in particular propanoic acid, carbon monoxide, carbon dioxide, acetaldehyde, heavy compounds containing more than 3 carbon atoms.

[0139] Said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0140] Said process is preferably operated continuously, in a fixed bed, preferably at a pressure adjusted so that the products and reactants are in gas phase, the feed being injected into the process preferentially in liquid phase. Charge

[0141] The feedstock for the process of transforming hydroxypropanoic acid and its derivatives into acrylic acid advantageously comprises at least one compound included in the list of hydroxypropanoic acid and its derivatives. This feedstock advantageously comprises a hydroxypropanoic acid selected from 2-hydroxypropanoic acid and 3-hydroxypropanoic acid. Preferably, this feedstock comprises 2-hydroxypropanoic acid. This feedstock comprises between 1% and 99.9% by weight, preferably between 5% and 99.5% by weight, most preferably between 7% and 99% by weight, and even more preferably between 8% and 98% by weight of hydroxypropanoic acid and its derivatives.

[0142] Said feedstock may also include impurities related, in particular, to the processes for obtaining hydroxypropanoic acid and its derivatives, such as fermentation. The impurity content is preferably less than 10% of the weight of said feedstock. The hydroxypropanoic acid(s) and its derivatives included in said feedstock may be of any origin, chemical, petrochemical, or bio-based.

[0143] Said charge comprises between 0.1% and 99% by weight, preferably between 0.5% and 90% by weight, most preferably between 1% and 80% by weight and even more preferably between 2% and 70% by weight of water.

[0144] Said charge comprises between 0.1% and 99% by weight, preferably between 0.5% and 90% by weight, most preferably between 1% and 80% by weight and even more preferably between 2% and 70% by weight of organic solvent, such as an alcohol.

[0145] The sum of the contents of hydroxypropanoic acid and its derivatives, water, organic solvent and any impurities represents 100% by weight of the charge.

[0146] The main products obtained by said process are hydroxypropanoic acids and its unconverted derivatives, acrylic acid from the dehydration reaction.

[0147] The examples below illustrate the invention without limiting its scope. Examples

[0148] To exemplify the invention, several preparation methods are described, based on the shaping of a precipitated silica and a colloidal silica (Ludox AS40 (Grace)). The contents are expressed as mass percentages.

[0149] Example 1 (compliant'): premixing in a planetary mixer then mixing in a Z-arm type mixer and shaping by extrusion (calcination at 450°C)

[0150] A soil source of colloidal silica (14.9 wt.), of potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (38 wt.) ground and sieved to 100 pm The ingredients are introduced and mixed in the bowl of a Thinky® centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The resulting suspension, consisting of methocel powder (K15M) (3 wt% relative to the total mass of SiO2), precipitated silica powder (Nyasil20 1.5 wt%, Nyacol) (28.1 wt%), and alpha silicon carbide powder (SiC 9 wt%, Alfa AESAR) (19 wt%), is introduced and premixed in a Brabender mixer. Water is added dropwise until a paste is formed, and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 rpm. The resulting paste is then extruded on an MTS piston extruder using a 1.6 mm diameter cylindrical die. The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 450°C.

[0151] The El material exhibits: an EGG value of 2.5 daN / mm² and an SBet of 15 m² / g, a total pore volume (TPV) of 0.21 cm³ / g with a macroporous volume of 0.13 cm³ / g and a mesoporous volume of 0.08 cm³ / g, and a Dmacro of 150 nm. The El material obtained has a KPO₃ / (SiC+KPO₃+SiO₂) ratio of 35%. XRD characterization shows the presence of the following phases: amorphous silica, monoclinic KPO₃, and hexagonal SiC.

[0152] Example 2 (compliant): premixing in a planetary mixer then kneading in a Z-arm type mixer and shaping by extrusion [calcination at 800°C]

[0153] A source of colloidal silica soil (14.9 wt.), ground and sieved potassium dihydrogen phosphate (KH2PO4; Aldrich) powder (38 wt.) with a 100 µm sieve are introduced and mixed in the bowl of a Thinky® centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The resulting suspension, methocel (K15M) powder (3 wt. relative to the total wt. of SiO2), precipitated silica powder (Nyasil20 l.5 wt.; Nyacol) (28.1%), and alpha silicon carbide (SiC 9 wt., Alfa AESAR) powder (19 wt.) are introduced and premixed in a Brabender mixer. Water is added dropwise until a paste is obtained, and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 revolutions per minute. The resulting paste is then extruded on an MTS brand piston extruder using a cylindrical die with a diameter of 1.6 mm.The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 800°C.

[0154] The material E2 obtained has an EGG value of 4.4 daN / mm² and an SBet of 1 m² / g, a total pore volume (TPV) of 0.06 cm³ / g with a macroporous volume of 0.06 cm³ / g and a mesoporous volume of 0 cm³ / g and a Dmacro of 346 nm. The material E2 obtained has a KPO3 / (SiC+KPO3+SiO2) ratio of 35%. XRD characterization shows the presence of the following phases: Cristobalite, mono-structured KPO3 clinical and hexagonal structure SiC.

[0155] Example 3 (compliant): premixing in a planetary mixer then kneading in a Z-arm type mixer and shaping by extrusion (calcination 800°C)

[0156] A source of colloidal silica soil (14 wt.), ground and sieved potassium dihydrogen phosphate (KH2PO4; Aldrich) powder (29 wt.) to 100 µm are introduced and mixed in the bowl of a Thinky® centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The resulting suspension, methocel (K15M) powder (3 wt. relative to the total weight of SiO2), precipitated silica powder (Nyasil20 1.5 µm; Nyacol) (43 wt.), and alpha silicon carbide (SiC 9 µm, Alfa AESAR) powder (14 wt.) are introduced and premixed in a Brabender mixer. Water is added dropwise until a paste is obtained, and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 revolutions per minute. The resulting paste is then extruded on an MTS brand piston extruder using a cylindrical die with a diameter of 1.6 mm.The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 800°C.

[0157] The E3 material exhibits an EGG value of 2.8 daN / mm² and an SBet of 1 m² / g, a VPT of 0.14 cm³ / g with a macroporous volume of 0.1 cm³ / g and a mesoporous volume of 0.04 cm³ / g, and a Dmacro of 349 nm. The E3 material obtained has a KPO3 / (SiC+KPO3+SiO2) ratio of 26%. XRD characterization shows the presence of the following phases: cristobalite, monoclinic KPO3, and hexagonal SiC.

[0158] Example 4 (compliant): mixing in a planetary mixer and shaping by extrusion (calcination 800°C)

[0159] A source of colloidal silica soil (14 wt.), ground and sieved potassium dihydrogen phosphate (KH2PO4; Aldrich) powder (29 wt.) with a 100 µm sieve are introduced and mixed in the bowl of a Thinky® centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. To the resulting suspension, methocel (K15M) powder (3 wt. relative to the total weight of SiO2), precipitated silica powder (Nyasil20 l.5 wt.; Nyacol) (43 wt.), and alpha silicon carbide (SiC9 wt., Alfa AESAR) powder (14 wt.) are added to the bowl of the centrifugal planetary mixer. The rotation speed is set at 2000 rpm for 30 seconds. The resulting paste is then extruded using an MTS piston extruder with a 1.6 mm diameter cylindrical die. The extruded pieces are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 800°C.

[0160] The material E4 has an EGG value of 2.5 daN / mm² and an SBet of 1 m² / g, a VPT of 0.14 cm³ / g with a macroporous volume of 0.12 cm³ / g and a me The material E4 has a soporosity of 0.02 cm³ / g and a Dmacro of 460 nm. It exhibits a KPO3 / (SiC+KPO3+SiO2) ratio of 26%. XRD characterization reveals the presence of the following phases: cristobalite, monoclinic KPO3, and hexagonal SiC.

[0161] Example 5 (non-conforming): Formulation with precipitated silica 40-63 µm. Premixed in a planetary mixer then kneaded in a Z-arm type mixer and shaped by extrusion (absence of silicon carbide)

[0162] A source of colloidal silica soil (14 wt.), ground and sieved potassium dihydrogen phosphate (KH2PO4; Aldrich) powder (29 wt.) to 100 µm are introduced and mixed in the bowl of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The resulting suspension, methocel powder (K15M) (3 wt. relative to the total weight of SiO2), precipitated silica powder (Siliaflash P60 40-63 µm; Silicycle) (43 wt.), and alpha silicon carbide powder (SiC 9 µm, Alfa AESAR) (14 wt.) are introduced and premixed in a Brabender brand mixer. Water is added drop by drop until a paste is formed, and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 revolutions per minute. The resulting paste is not very cohesive.It is then introduced into an MTS brand piston extruder using a cylindrical die with a diameter of 1.6 mm. The resulting mixture proves to be inextrudable and a filtration phenomenon is observed.

[0163] Example 6: Use of materials EL E2, E3, E4 for the dehydration of lactic acid to acrylic acid in the gas phase

[0164] Materials E1, E2, E3, and E4 are tested using an Avantium® unit comprising 16 reactors, each with an internal diameter of 2 mm and a length of 560 mm. The reaction is carried out in the gas phase at 375°C and a total pressure of 1 Obarg (1 MPa). The feed contains 12 wt% lactic acid and 88 wt% water. The gas (N2) and the liquid feed are co-injected and mixed upstream of the reactor head. Evaporation of the feed is achieved in the first part of the reactor using a pull cord. The loaded bed height is 200 mm, resulting in a charged catalyst mass of approximately 200 mg. At the unit outlet, the products are analyzed by gas chromatography.

[0165] The results are presented in Table 1 below.

[0166] [Tables 1] Material mpo3 / (MPO3+SiC +SiO2) SiC / (MPO3+SiC +SiO2) Bed height (mm) m catalyst (mg) Acrylic Acid Yield (% molC) EGG (daN / mm) El 35 19 200 250 69 2.5 E2 35 19 200 250 70 4.4 E3 26 15 200 190 78 2.8 E4 26 15 200 188 77 2.5

[0167] The catalysts El, E2, E3 and E4 convert a lactic acid feed into acrylic acid with a carbon yield greater than or equal to 65. The catalysts according to the invention are therefore active and stable during the dehydration reaction of lactic acid into acrylic acid.

Claims

Demands

1. A process for preparing a macroporous material comprising an active phase comprising at least one potassium phosphate salt and / or at least one cesium phosphate salt and a support comprising silicon carbide in its alpha crystallographic form (α-SiC) and silica, said process comprising the following steps: a) contacting at least one colloidal silica sol with at least one powder of at least one potassium and / or cesium phosphate salt to obtain a suspension; b) adding at least one precipitated silica powder, silicon carbide powder in its alpha crystallographic form (α-SiC) and at least one solvent to said suspension obtained at the end of step a) to obtain a paste; c) shaping the paste obtained at the end of step b) to obtain a material precursor;d) the precursor material obtained at the end of step c) is dried at a temperature between 15°C and 250°C to obtain a dried precursor material; e) the dried precursor material obtained at the end of step d) is calcined at a temperature above 250°C and below or equal to 1200°C.

2. A method according to claim 1, wherein step e) is carried out at a temperature above 250°C and below 800°C.

3. A method according to claim 1, wherein step e) is carried out at a temperature between 800°C and 1200°C.

4. A method according to any one of claims 1 to 3, wherein step a) is carried out in a centrifugal planetary mixer operating at a speed between 100 and 2000 rpm.

5. A method according to any one of claims 1 to 4, wherein step a) is carried out for a duration of between 5 seconds and 60 seconds.

6. A method according to any one of claims 1 to 5, wherein in step a) said at least one powder of at least one potassium and / or cesium phosphate salt is pre-ground and sieved to a particle size of less than 100 pm.

7. A method according to any one of claims 1 to 6, wherein in step b) the powder of at least one silicon carbide source presents a grain size of less than 20 pm.

8. A method according to any one of claims 1 to 7, wherein in step b) the powder of at least one precipitated silica has a grain size of less than 20 pm.

9. The method according to any one of claims 1 to 8, in step b) is carried out in the same equipment used in step a).

10. A method according to claim 9, wherein step b) is carried out in a centrifugal planetary mixer at a rotational speed between 300 and 2000 rpm.

11. A method according to any one of claims 1 to 8, wherein steps a) and b) are carried out in different equipment: step a) is carried out in a centrifugal planetary mixer to obtain said suspension, and then step b) is carried out in a mixer equipped with Z-arms to obtain a paste.

12. A method according to claim 11, wherein said precipitated silica powder, said alpha-type silicon carbide powder, the solvent and optionally an organic adjuvant are added to the mixer equipped with Z-arms before the introduction of the suspension obtained in step a).

13. A method according to any one of claims 11 or 12, wherein the rotation speed of the mixer arms is between 10 revolutions / minute and 75 revolutions / minute.

14. A process according to any one of claims 1 to 13, wherein in step a) a powder of at least one salt of potassium and / or cesium phosphate ground and sieved to a particle size of less than 100 pm is used, and in step b) a silica powder precipitated to a size of less than 10 pm.

15. A method according to any one of claims 1 to 13, wherein in step b) a silicon carbide powder of a particle size less than 5 pm and a precipitated silica powder of a size less than 10 pm are used.