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

Abstract

A method for preparing a macroporous material comprising an active phase comprising a potassium phosphate salt and / or a cesium phosphate salt and a support comprising silicon carbide α-SiC and silica comprising the following steps: a) a colloidal silica sol is brought into contact with a powder of a potassium phosphate salt and / or cesium to obtain a suspension; b) a powder of a precipitated silica, a powder of silicon carbide α-SiC and a solvent are added to obtain a paste; c) the paste is shaped to obtain a material precursor; d) the material precursor is dried at a temperature between 15°C and 250°C; e) the dried material precursor obtained at the end of step d) is calcined at a temperature above 250°C and less than 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 Field of 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 called here 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 to use as a catalyst support, however it cannot be extruded like other materials in conventional extrusion equipment to give products sufficiently resistant to be implemented in catalytic processes. Indeed, from its manufacture to its implementation, the catalyst comprising such a support is confronted with numerous stages which can impact its physical integrity. In particular, it must be resistant to crushing, attrition and pressure variations linked to the operating conditions of the catalytic reactor in which it is implemented. Thus, there is a constant need to provide catalysts having improved mechanical and physical properties.

[0003] Silicon carbide (also called SiC herein) is an inorganic material having 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). We can also cite application WO14140973 which discloses the preparation of a catalyst comprising a cobalt-based active phase and a support containing silicon carbide 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 making it possible to obtain a material comprising an active phase based on potassium or cesium phosphate salt(s) and a support based on silicon carbide (SiC) and at least one source of silica having good mechanical resistance and therefore capable of being used as a catalyst, in particular in the dehydration of hydroxypropanoic acid. Subject 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 material precursor;

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

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

[0013] An advantage of the preparation method according to the invention is to provide a material having improved mechanical resistance compared to the materials of the prior art thanks to the implementation of a step of premixing 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. a precipitated silica, with a source of alpha-SiC 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 greater than 250°C and less than 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 implemented in a centrifugal planetary mixer operating at a speed of between 100 and 2000 revolutions / minute.

[0017] According to one or more embodiments of the invention, step a) is implemented 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 μm.

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

[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 μm.

[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 / minute.

[0023] According to one or more embodiments of the invention, steps a) and b) are implemented in different equipment: step a) is implemented in a centrifugal planetary mixer to obtain said suspension, then step b) is carried out in a mixer equipped with Z-shaped 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-shaped 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 potassium and / or cesium phosphate salt ground and sieved to a particle size of less than 100 μm is used and in step b) a silica powder precipitated to a size of less than 10 μm.

[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 μm and a precipitated silica powder having a size of less than 10 μm are used. Detailed description 1. Definitions

[0028] Within the meaning of the present invention, the various 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 step such that pressure ranges and temperature ranges may be used alone or in combination. For example, within the meaning of the present invention, a preferred pressure range may be combined with a more preferred temperature range.

[0030] By “macropores” is meant pores with an opening greater than 50 nm.

[0031] By “mesopores” is meant 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 understood to mean the volume measured by intrusion with a mercury porosimeter according to standard 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 equal to 140° following the recommendations of the work “Techniques de l'ingénieur, traité analyse et caractérisation”, pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

[0033] In order to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the sample minus the value of the total pore volume measured by intrusion with a 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 it is considered that beyond this, mercury penetrates into the pores of the sample.

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

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

[0037] The median diameter of the macropores (Dmacro in nm) is also defined as being a diameter such that all pores smaller than this diameter constitute 50% of the macropore 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 an Autopore® IV model device from Microméritics®.

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

[0040] Throughout the rest of the text, the term “mechanical resistance to lateral crushing” means the mechanical resistance of the material according to the invention determined by the grain-to-grain crushing (EGG) test. This is a standardized test (ASTM D4179-01 standard) which consists of subjecting a material in the form of a millimetric object, such as a ball, a pellet or an extrudate, to a compressive force generating rupture. This test is therefore a measurement of the tensile strength of the material. The analysis is repeated on a certain number of solids taken individually and typically on a number of solids between 10 and 200. The average of the measured lateral breaking forces constitutes the average EGG which is expressed in the case of granules in units of force (N), and in the case of extrudates in units of force per unit of length (daN / mm or decaNewton per millimeter of extrudate length).

[0041] In the remainder of the text, the grain size or particle size distribution of the constituents of the materials obtained according to the invention is measured by the laser scattering particle size distribution technique. This indirect measurement technique makes it possible to determine the particle size distribution (scale from micron to millimeter). This analysis method uses the principle of diffusion (Mie theory) and / or light diffraction (Fraunhoffer theory and Mie theory). The particles illuminated by the laser light deflect the light from its main axis. The quantity of deflected light and the size of the deflection angle make it possible to accurately measure 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 routes are thus distinguished: the wet route and the dry route.

[0042] The wet method makes it possible to characterize dispersions (elementary particle size after dispersion) or suspended solids ("aggregated" particle size). The particles measured are in the range 0.02 microns to 2000 microns.

[0043] Dry process granulometry makes it possible to characterize powders whose initial aggregation is not destroyed. The measurement range extends from 0.2 microns to 2000 microns. In the present invention, the dry process 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 having good crushing strength (EGG) compared to a silica-based support not having silicon carbide.

[0045] Indeed, the Applicant has surprisingly discovered that the use of such a macroporous material as a catalyst for the dehydration of 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, in corresponding propenoic acid compared to a catalyst obtained according to conventional preparation processes, that is to say 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+SiO 2) 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 pore volume of between 0.01 and 0.6 cmVg, more preferably of between 0.01 and 0.5 cmVg, even more preferably of between 0.05 and 0.4 cmVg, and even more preferably of between 0.05 and 0.35 cmVg.

[0050] Preferably, said material has a macroporous volume of between 0.01 and 0.5 cmVg, more preferably of between 0.05 and 0.4 cmVg, even more preferably of between 0.05 and 0.4 cmVg, and even more preferably of 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-to-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 very 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 between 60% and 85% by weight, and very preferably between 60% and 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 very preferably from 10% to 75% by weight of 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 of 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 material precursor;

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

[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 of 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, may advantageously be added in step a).

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

[0068] The source(s) of colloidal silica sol used in the process according to the present invention are advantageously synthetic amorphous silicas.

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

[0070] Said potassium phosphate salt(s) are advantageously chosen from: KH2 PO4, k2hpo4, kh2p2o12, k6p6o7, k3h2p3o10, K4H2p4o13, k3p3o9, K4P4o12, k6p6o18, k8 P8O24, KioPio03o, potassium phosphate (tripotassium) (PO43,3K+), alone or as a mixture. Preferably the potassium phosphate salt is chosen from potassium phosphate (tripotassium) (PO43,3K+) and KH2PO4, alone or as a mixture.

[0071] Said cesium phosphate salt(s) are advantageously chosen from CsH2PO4, Cs2H2P3Oio, Cs4H2P40i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, CsPO3, alone or as a mixture. Preferably the cesium phosphate salt is CsH2PO4.

[0072] Preferably, said potassium phosphate 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 into step a). The grain size of the potassium phosphate and / or cesium phosphate salts is advantageously measured by dry laser granulometry.

[0074] Very 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 previously dispersed by means of a centrifugal planetary mixer in the presence of the source of colloidal silica sol 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 rpm, preferably between 200 and 1600 rpm.

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

[0078] According to the invention, the method comprises a step b) of adding 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 in said suspension obtained at the end of step a).

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

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

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

[0082] Preferably, the powder of at least one source of silicon carbide in its form alpha crystallographic added in step b) has a grain size of less than 20 pm, and preferably less than 15 pm, more preferably equal to 10 pm, and even more preferably less than 5 pm. The size of the silicon carbide grains 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) can be chosen without being restrictive from the following commercial sources: silicon carbide powder, superfine, 600, in grain from Thermo Scientific Chemicals®; silicon carbide, alpha-phase, 99.8% from Thermo Scientific Chemicals®, taken alone or as a mixture.

[0084] Preferably, the powder of at least one source of silicon carbide 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, very preferably less than 100 ppm and an aluminum content of less than 1000 ppm, preferably less than 500 ppm, very preferably less than 100 ppm.

[0085] Particularly preferably, silicon carbide in its alpha crystallographic form has a hexagonal crystalline structure. In the context of the invention, it is entirely possible to make 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 may also be added during step b).

[0088] Said organic adjuvant may also be chosen from all the 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, aliphatic monocarboxylic acids, alkylated aromatic compounds, sulfonic acid salts, fatty acids, polyvinyl pyrrolidone, 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 as a mixture.

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

[0090] In one 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 according to the invention, steps a) and b) are advantageously implemented in different equipment. In this case, step a) is preferably implemented 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, the solvent and possibly the organic adjuvant are added to the equipment, preferably in 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, an addition of ammonia can be made so as to obtain an extrudable mixture in step b).

[0094] Preferably, said mixing step b) is carried out by kneading, either discontinuously or continuously. In the case where said step b) is carried out discontinuously, said step b) is advantageously carried out in a mixer preferably equipped with Z-shaped 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 the implementation of step b) in a centrifugal planetary mixer, the rotation speed is advantageously between 300 and 2000 revolutions / minute, preferably between 1500 and 2000 revolutions / minute.

[0097] In a particularly preferred embodiment, the use of a powder of at least one potassium and / or cesium phosphate salt ground and sieved to a particle size of less than 100 pm in step a) combined with the use of a source of precipitated silica 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 μm combined with the use of a source of precipitated silica having a size of less than 10 μm, preferably less than 5 μm, more preferably less than 2 μm 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 into 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 very preferably from 5% to 40% by weight and even more preferably from 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 very 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 very 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, more preferably from 1% to 10% by weight, and very preferably from 1% to 7% by weight of at least one organic adjuvant;

[0105] the weight percentages being expressed relative 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 method comprises 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 resulting from step b) is carried out by extrusion, said step b) is advantageously carried out in a piston, single-screw or twin-screw extruder.

[0109] In this case, an organic adjuvant may optionally be added in mixing step b). The presence of said organic adjuvant facilitates shaping by extrusion. Said organic adjuvant 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 at the end of a continuous mixer of the twin-screw type for example, 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 dies well known to those skilled in the art. They can thus be, for example, cylindrical, multi-lobed, grooved or slotted.

[0111] In the case where the shaping of the mixture resulting from step b) is carried out by extrusion, the quantity of solvent added in the mixing step b) is adjusted so as to obtain, at the end of this step and whatever the variant implemented, a mixture or a paste which does not flow but which is also not too dry in order to allow its extrusion under suitable pressure conditions well known to those 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 shaped material precursor 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 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 good hydration of the material, limiting the appearance of cracks which 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 greater than 250°C and less than or equal to 1200°C, and for a duration advantageously between 1 hour and 12 hours, preferably between 1 hour and 4 hours. This calcination step is particularly useful in order to eliminate the organic adjuvants used in order to facilitate the shaping of the material.

[0116] In one 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 very 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 a significant improvement in the mechanical resistance of the final materials obtained.

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

[0118] Said calcination step e) is advantageously carried out under a gas flow comprising oxygen, for example preferably the extrudates are calcined under dry air or with different humidity levels or even 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 method comprises a step f) of impregnating the material resulting 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 brought into contact 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 sub-steps:

[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 f1) 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 pore volume of the material obtained at the end of step e);

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

[0125] Preferably, the phosphate concentration of the solution supplied in step f1) is between 50 g / L and 2000 g / L.

[0126] The impregnation solution of step f1) is preferably prepared by dissolving in an aqueous or organic phase one or more precursors of phosphate and potassium (K) or cesium (Cs) element. The impregnation solution can advantageously be prepared by mixing phosphorus and alkali metal elements introduced independently. In this case, the alkali metal precursor M chosen from K or Cs is chosen for example from one or more of the salts of carbonate M2CO3, nitrate MNO3, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCI, hydroxide MOH, 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 period 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 good hydration of the material limiting the appearance of cracks which are detrimental to mechanical resistance.

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

[0131] The material obtained at the end of impregnation step f) can undergo a calcination step at a temperature between 300°C and 600°C, preferably between 300°C and 550°C, and very 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] Said calcination step is advantageously carried out under a gas flow comprising oxygen, for example preferably the extrudates are calcined under dry air or with different humidity levels or even 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.

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

[0134] However, it is not excluded that said materials obtained are then, 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 dehydrating 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 of between 180°C and 450°C, preferably between 190°C and 430°C, very preferably between 250°C and 420°C and very preferably between 270°C and 420°C, at a pressure of between 0.1 MPa and 12 MPa, preferably between 0.11 MPa and 10 MPa, preferably between 0.13 MPa and 9 MPa and very preferably between 0.15 MPa and 8 MPa, and at a feedstock mass flow rate to material mass ratio of between 0.01 h 1 and 100 h *, preferably between 0.02 and 50 h *, more preferably between 0.03 and 30 h 1 and very preferably between 0.05 and 20 h 1.

[0137] Said method 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 the gas phase, the feed being injected into the process preferentially in the liquid phase. Charge

[0141] The feedstock feeding the process for 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. Said feedstock advantageously comprises a hydroxypropanoic acid chosen from 2-hydroxypropanoic acid and 3-hydroxypropanoic acid. Preferably, said feedstock comprises 2-hydroxypropanoic acid. Said feedstock comprises between 1% and 99.9% by weight, preferably between 5% and 99.5% by weight, very 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 comprise impurities linked, 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 biosourced.

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

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

[0145] The sum of the contents of hydroxypropanoic acid and its derivatives, water, organic solvent and possible 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 resulting from the dehydration reaction.

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

[0148] In order to exemplify the invention, several methods of preparation are described, based on the shaping of a precipitated silica and a colloidal silica (Ludox AS40 (Grâce)). The contents are expressed in 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 source of colloidal silica sol (14.9% by weight), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (38% by weight) ground and sieved to 100 pm are introduced and mixed in the tank of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, a methocel powder (K15M) (3% by weight relative to the total mass of SiO2), a precipitated silica powder (Nyasil20 1.5 pm, Nyacol) (28.1% by weight), an alpha silicon carbide powder (SiC 9 pm, Alfa AESAR) (19% by weight) are introduced and pre-mixed in a Brabender brand mixer. Water is added drop by drop until a paste is obtained and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 rpm. The paste obtained 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 then calcined for 4 hours at 450°C.

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

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

[0153] A source of colloidal silica sol (14.9% by weight), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (38% by weight) ground and sieved to 100 μm are introduced and mixed in the tank of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, a methocel powder (K15M) (3% by weight relative to the total weight of SiO2), a precipitated silica powder (Nyasil20 l,5pm; Nyacol) (28.1%), an alpha silicon carbide powder (SiC 9pm, Alfa AESAR) (19% by weight) are introduced and pre-mixed in a Brabender brand 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 rpm. The resulting paste is then extruded on an MTS 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 then calcined for 4 hours at 800°C.

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

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

[0156] A source of colloidal silica sol (14% by weight), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (29% by weight) ground and sieved to 100 pm are introduced and mixed in the tank of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, a methocel powder (K15M) (3% by weight relative to the total weight of SiO2), a precipitated silica powder (Nyasil20 1.5pm; Nyacol) (43% by weight), an alpha silicon carbide powder (SiC 9pm, Alfa AESAR) (14% by weight) are introduced and pre-mixed in a Brabender brand 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 rpm. The resulting paste is then extruded on an MTS 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 then calcined for 4 hours at 800°C.

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

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

[0159] A source of colloidal silica sol (14% by weight), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (29% by weight) ground and sieved to 100 μm are introduced and mixed in the tank of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. To the suspension obtained, a methocel powder (K15M) (3% by weight relative to the total weight of SiO2), a precipitated silica powder (Nyasil20 l,5pm; Nyacol) (43% by weight), an alpha silicon carbide powder (SiC 9pm, Alfa AESAR) (14% by weight) are added to the tank of the centrifugal planetary mixer. The rotation speed is set at 2000 rpm for 30 seconds. 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 800°C.

[0160] The E4 material has an EGG value of 2.5 daN / mm and an SBet of 1 m2 / g, a VPT of 0.14 cmVg with a macroporous volume of 0.12 cmVg and a me soporous of 0.02 cm3 / g and a Dmacro of 460 nm. The obtained E4 material has a ratio KPO3 / (SiC+KPO3+SiO2) = 26%. The characterization by DRX shows the presence of the following phases: Cristobalite, KPO3 of monoclinic structure and SiC of hexagonal structure.

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

[0162] A source of colloidal silica sol (14% by weight), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (29% by weight) ground and sieved to 100 pm are introduced and mixed in the tank of a Thinky® brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, a methocel powder (K15M) (3% by weight relative to the total weight of SiO2), a precipitated silica powder (Siliaflash P60 40-63 pm; Silicycle) (43% by weight), an alpha silicon carbide powder (SiC 9pm, Alfa AESAR) (14% by weight) are introduced and pre-mixed in a Brabender brand mixer. Water is added drop by drop until a paste is obtained and mixing is continued for 20 minutes. The rotation speed of the mixing arms is set at 50 rpm. 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 mixture obtained proves to be non-extrudable and a filtration phenomenon is observed.

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

[0164] Materials E1, E2, E3 and E4 are tested with an Avantium® unit comprising 16 reactors, 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 at a total pressure of 1000 mbar (1 MPa). The feed contains 12% by weight of lactic acid and 88% by weight of water. The gas (N2) and the liquid feed are co-injected and mixed upstream of the reactor head. The evaporation of the feed is carried out in the first part of the reactor with the help of a cord. The height of the loaded bed is 200 mm, leading to a mass of loaded catalyst of approximately 200 mg. At the outlet of the unit, 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] Catalysts E1, E2, E3 and E4 convert a lactic acid feedstock into acrylic acid with a carbon yield greater than or equal to 65. The catalysts in accordance with the invention are therefore active and stable during the dehydration reaction of lactic acid into acrylic acid.

Claims

Claims

1. A method 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 method comprising the following steps: 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; 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 is added to said suspension obtained at the end of step a) to obtain a paste; c) the paste obtained at the end of step b) is shaped to obtain a material precursor;d) the material precursor obtained at the end of step c) is dried at a temperature between 15°C and 250°C to obtain a dried material precursor; e) the dried material precursor obtained at the end of step d) is calcined at a temperature above 250°C and less than 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 of 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 period 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 previously 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 source of silicon carbide has a grain size of less than 20 pm.

8. 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. A 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 rotation speed of between 300 and 2000 rpm.

11. Method according to any one of claims 1 to 8, in which 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.

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 introducing the suspension obtained in step a).

13. Method according to one of claims 11 or 12, in which the rotation speed of the mixer arms is between 10 revolutions / minute and 75 revolutions / minute.

14. Method according to any one of claims 1 to 13, in which in step a) a powder of at least one potassium and / or cesium phosphate salt 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 with a particle size of less than 5 pm and a precipitated silica powder with a size of less than 10 pm are used.