Process for preparing a reimpregnated silica-based material in the crystalline form of cristobalite and / or tridymite

Abstract

The invention relates to a process for preparing a macroporous material based on a potassium and / or cesium phosphate salt and silica in the form of cristobalite and / or tridymite crystals, comprising the following steps: a) a silica source is contacted with a first phosphate precursor and a first potassium and / or cesium precursor; b) the material precursor is allowed to mature for a period of between 1 minute and 72 hours; c) the material precursor is calcined at a temperature between 800°C and 1200°C; d) the calcined material precursor is contacted with a second phosphate precursor and a second potassium and / or cesium precursor to obtain a second material precursor; e) the second material precursor is calcined at a temperature between 300°C and 600°C to obtain the material.

Description

Title of the invention: Process for preparing a reimpregnated silica-based material in the crystalline form of cristobalite and / or tridymite Scope of the invention

[0001] The invention relates to a new macroporous material containing silica in the crystalline form of cristobalite and / or tridymite. The material can advantageously be used as a support or as a catalyst in catalytic processes. State of the 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, a 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 constant need for catalysts with improved mechanical and physical properties.

[0003] Patent application WO2003 / 026795 discloses a process for producing a catalyst comprising a silica support, which consists of impregnating a silica constituent with a catalytic metal using an aqueous alkaline bath before drying in order to improve its mechanical strength. More specifically, the preparation process consists of forming and washing a silica constituent, such as a silica gel or co-gel, for example, a silica-zirconia co-gel. The washed silica constituent is then contacted with an alkaline bath to impregnate the catalytic metal, such as cesium, and to form an activated silica constituent. The activated silica constituent is then dried to form the catalyst without a calcination step.

[0004] Patent application WO17040383 discloses a plurality of catalysts comprising at least one mixture of alkali phosphates, some of which have the formula Mx POy (with M = K or Cs), and a non-porous silica binder. The catalysts are prepared by mechanically mixing, using a planetary mill, amorphous fused silica, which is a dense material with no surface or porosity properties, and potassium phosphate precursors. The catalyst precursor is then calcined under air at 450°C to obtain a material composed of a KPO3 / (KPO3 + SiO2) mixture with a mass ratio of 13 to 26% by weight of KPO3 relative to the total weight of said material. This The document also discloses a catalyst in the form of a powder with variable particle size, sieved between 106 and 212 pm. The silica contained in the final material is in its amorphous form (see example 8).

[0005] However, none of the prior art documents disclose a macroporous material based on a potassium phosphate salt and / or a cesium phosphate salt and silica occurring at least partially in the crystalline form of cris-tobalite and / or tridymite. Objects of the invention

[0006] The present invention relates to a process for preparing a macroporous material based on at least one potassium phosphate salt and / or at least one cesium phosphate salt, and silica, at least partially in the crystalline form of cristobalite and / or tridymite, comprising at least the following steps:

[0007] a) at least one source of silica is brought into contact with at least one first precursor of phosphate and at least one first precursor of potassium and / or cesium to obtain a first precursor of material;

[0008] b) the precursor of material obtained at the end of step a) is allowed to mature for a period of between 1 minute and 72 hours to obtain a matured precursor of material;

[0009] c) the precursor of matured material obtained at the end of step b) is calcined at a temperature between 800°C and 1200°C to obtain a precursor of calcined material;

[0010] d) the calcined material precursor obtained at the end of step c) is contacted with at least a second phosphate precursor, and at least a second potassium and / or cesium precursor to obtain a second material precursor;

[0011] e) the second precursor of material obtained at the end of step d) is calcined at a temperature between 300°C and 600°C to obtain the material.

[0012] According to one or more embodiments, in step a), said first and second precursors of phosphate, potassium and / or cesium are supplied in the form of at least one potassium phosphate salt and / or at least one cesium phosphate salt.

[0013] According to one or more embodiments, said potassium phosphate salt is selected from: KH2PO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, K6P6O18, K8P8O24, KioPioO3O, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixture.

[0014] According to one or more embodiments, said cesium phosphate salt is selected from CsH2PO4, Cs2H2P3Oi0, Cs4H2P40i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, CsPO3, alone or in mixture.

[0015] According to one or more embodiments, said potassium phosphate salt and / or said cesium phosphate salt is supplied in step a) in the form of a powder.

[0016] According to one or more embodiments, prior to their introduction in step a), said powder of at least one potassium and / or cesium phosphate salt is ground and sieved to a grain size of less than 100 pm.

[0017] According to one or more embodiments, step a) comprises the following substeps:

[0018] i) at least one precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100, at least one colloidal silica sol and at least one powder of at least one potassium and / or cesium phosphate salt in at least one solvent to obtain a mixture;

[0019] ii) the mixture obtained at the end of step i) is shaped.

[0020] According to one or more embodiments, step a) comprises the following substeps:

[0021] i') at least one colloidal silica sol is mixed with at least one water powder minus a potassium and / or cesium phosphate salt to obtain a suspension;

[0022] ii') a powder of at least one precipitated silica, or a silica gel, or a zeolite of Si / Al ratio >100 and a solvent are added to said suspension obtained at the end of step i') to obtain a paste;

[0023] iii') the dough obtained at the end of step ii' is shaped.

[0024] According to one or more embodiments, step a) comprises the following substeps:

[0025] i”) a liquid solution in aqueous or organic phase is supplied including at least the first phosphate precursor, and at least the first potassium and / or cesium precursor;

[0026] ii”) said solution obtained at the end of step i”) is impregnated onto a shaped support containing silica.

[0027] According to one or more embodiments, the preparation temperature of step i”) is between 5°C and 80°C.

[0028] According to one or more embodiments, the phosphate concentration of the solution supplied in step i”) is between 50 g / L and 2000 g / L.

[0029] According to one or more embodiments, said first precursor of potassium and / or cesium is chosen from the salts of carbonate M2CO3, nitrate MN03, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCl, hydroxide MOH, and oxide M2O, with M = K or Cs.

[0030] According to one or more embodiments, said first phosphate precursor is chosen from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, and P2O5.

[0031] According to one or more embodiments, step d) comprises the following substeps:

[0032] dl) a liquid solution is prepared in aqueous or organic phase comprising at least one second precursor of phosphate, and at least one second precursor of potassium and / or cesium, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C;

[0033] d2) the solution prepared in step d1) is impregnated onto the calcined material obtained at at the end of step c), 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 calcined material obtained at the end of step c);

[0034] d3) optionally, a maturation step of the second material precursor obtained at the end of step d2),

[0035] d4) optionally, a drying step of the second material precursor matured obtained at the end of step d3). Detailed description 1. Definitions

[0036] 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.

[0037] In the sense of the present invention, the different parameter ranges for a given step, such as 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.

[0038] By "macropores", we mean pores whose opening is greater than 50 nm.

[0039] By "mesopores" we mean pores whose opening is between 2 nm and 50 nm, inclusive.

[0040] 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 bars (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.

[0041] 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 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 cor- responding to 30 psi (approximately 0.2 MPa).

[0042] 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.

[0043] 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.

[0044] 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 and 50 nm.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Throughout this text, lateral crushing strength refers to the mechanical strength of the material according to the invention as determined by the grain-by-grain crushing (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. 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 the case of granules in unit of force (N), and in the case of extrudates in unit of force per unit of length (daN / mm or decaNewton per millimeter of extruded length).

[0049] 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.

[0050] 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.

[0051] 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

[0052] An object according to the invention relates to a macroporous material based on at least one potassium phosphate salt and / or at least one cesium phosphate salt and silica, characterized in that the silica is present at least partially in the crystalline form of cristobalite and / or tridymite.

[0053] Indeed, the Applicant has surprisingly discovered that the use of such a macroporous material as a dehydration catalyst for hydroxypropanoic acid allows for a significant increase in the conversion of hydroxypropanoic acid and an improvement in the corresponding propenoic acid yield compared to a catalyst obtained by conventional preparation processes, particularly those in which the silica is in amorphous form. The macroporous structure of the material and the specific crystallinity of the silica contained within it were obtained by carrying out a specific preparation process comprising a calcination step at a temperature of 800°C or higher, based on a precursor material comprising at least one silica source and at least one potassium and / or cesium precursor.

[0054] X-ray diffraction makes it possible to verify that the material according to the invention does indeed contain silica that is totally or partially crystallized in its cristobalite and / or tridymite form by comparing the diffractogram obtained with those existing in a database such as the ICDD® (International Centre for Diffraction Data) PDF4+ 2020 crystallographic database. The X-ray diffraction pattern is obtained by X-ray crystallography analysis using a diffractometer with the classical powder method and copper Kα radiation (X = 1.54060 Å). From the position of the diffraction peaks represented by the angle 20°, the characteristic lattice spacings dhkl of the sample are calculated using Bragg's law. The measurement error A(dhkl) on dhkl is calculated using Bragg's relation as a function of the absolute error A (20) assigned to the measurement of 20. An absolute error A (20) equal to ± 0.02° is commonly accepted.

[0055] More specifically, the 22° line 20 is primarily associated with the cristobalite crystallographic form. The 28.4°, 31.4°, and 36° lines are also attributed to the formation of cristobalite. The 20° lines 20.7°, 21.7°, 23.4°, and 27.5° are associated with the tridymite crystallographic form.

[0056] Advantageously, said potassium phosphate and / or cesium phosphate salt is potassium metaphosphate (KPO3) and / or cesium metaphosphate (CsPO3).

[0057] Advantageously, said material has a mass ratio MPO3 / (MPO3+SiO2) of between 13 and 50, preferably between 15 and 45, and even more preferably between 17 and 40, with M being potassium and / or cesium (M = K and / or Cs). Preferably M is potassium.

[0058] Preferably said material has a total porous volume between 0.01 cm3 / g and 0.6 cmVg, more preferably between 0.05 cmVg and 0.5 cmVg, even more preferably between 0.1 cmVg and 0.4 cmVg, and even more preferably between 0.15 cmVg and 0.39 cmVg.

[0059] Preferably, said material has a macroporous volume between 0.01 cmVg and 0.6 cmVg, more preferably between 0.05 cmVg and 0.5 cmVg, even more preferably between 0.1 cmVg and 0.4 cmVg, and even more preferably between 0.15 cmVg and 0.39 cmVg.

[0060] Preferably, the macroporous volume of the material represents between 50% and 100% of the total porous volume of said material, preferably between 60% and 100% and even more preferably between 80% and 100%.

[0061] Advantageously, said material has a specific surface area greater than or equal to 1 m2 / g and less than 50 m2 / g, preferably between 1 m2 / g and 20 m2 / g, more preferably between 1 m2 / g and 15 m2 / g, and even more preferably between 1 m2 / g and 10 m2 / g.

[0062] Advantageously, said material has a mechanical resistance value measured by grain-by-grain crushing greater than 0.5 daN / mm, preferably greater than 0.7 daN / mm, more preferably greater than 0.9 daN / mm and preferably greater than 1.3 daN / mm.

[0063] 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.

[0064] 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.

[0065] In an embodiment according to the invention, the silica is present only in the crystalline form cristobalite.

[0066] Said material according to the invention advantageously has a macroporous median diameter between 80 nm and 7000 nm, preferably between 200 nm and 6500 nm, and more preferably between 500 nm and 4000 nm.

[0067] Said material is advantageously in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates. Preparation process

[0068] An object according to the invention relates to a process for preparing a macroporous material according to the invention based on at least one potassium phosphate salt and / or at least one cesium phosphate salt, and silica in at least partial crystalline form cristobalite and / or tridymite, comprising at least the following steps:

[0069] a) at least one source of silica is brought into contact with at least one first precursor of phosphate and at least one first precursor of potassium and / or cesium to obtain a first precursor of material;

[0070] b) the precursor of material obtained at the end of step a) is allowed to mature for a period of between 1 minute and 72 hours to obtain a matured precursor of material;

[0071] c) the precursor of matured material obtained at the end of step b) is calcined at a temperature between 800°C and 1200°C to obtain a precursor of calcined material;

[0072] d) the calcined material precursor obtained at the end of step c) is brought into contact with at least a second phosphate precursor, and at least a second potassium and / or cesium precursor to obtain a second material precursor;

[0073] e) the second precursor of material obtained at the end of step d) is calcined at a temperature between 300°C and 1200°C to obtain the material.

[0074] All steps a) to e) are detailed below. Step a)

[0075] Step a) can be carried out according to several embodiments. Implementation method 1

[0076] In a first embodiment according to the invention, step a) comprises the following substeps:

[0077] i) at least one precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100, at least one colloidal silica sol and at least one powder of at least one potassium and / or cesium phosphate salt in at least one solvent to obtain a mixture;

[0078] ii) the mixture obtained at the end of step i) is shaped.

[0079] According to this embodiment, said step i) consists of mixing at least one precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100 with at least one colloidal silica sol, and at least one powder of at least one potassium phosphate salt and / or at least one cesium phosphate salt in at least one solvent to obtain a mixture.

[0080] Preferably, precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100 is selected, without restriction, from the following commercial sources: Nyasil20 (Nyacol ®), Siliaflash P60 (Silicycle ®), Siliaflash C60 (Silicycle ®), Ultrasil VN3 GR (Evonik ®), ZSM-5 (CBV 28014 ; Zeolyst®), HY (CBV780 ; Zeolyst®) taken alone or in mixture.

[0081] Preferably, precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100 has a grain size of less than 10 pm, and preferably less than 5 pm, even more preferably less than 1 pm.

[0082] Preferably, colloidal silica sols are chosen, without restriction, from 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.

[0083] Most colloidal silica sols are prepared from sodium silicate and inevitably contain sodium. Since the presence of sodium can be detrimental to catalytic activity, an ion exchange step may be necessary to reduce, or even eliminate, residual sodium. To avoid this step, the use of low-sodium colloidal silica sols is preferable; examples include Ludox AS40 stabilized with an ammonium counterion, as well as Nyacol 2034DI, Nalco 1034A, Ultra-Sol 7H, and NexSil 20A.

[0084] Said silica source(s) used in the process according to the present invention are advantageously synthetic amorphous silicas or zeolites with Si / Al ratios >100.

[0085] Said potassium phosphate salt(s) used in step i) is / are advantageously chosen from potassium phosphate salts in amorphous or crystalline oxide form taken alone or in mixture.

[0086] Said potassium phosphate salt(s) are advantageously selected from: KH2PO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, K6P6O18, K8P8O24, K10P10O30, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixtures. Preferably, the preferred potassium phosphate salt is selected from potassium phosphate (tripotassium) (PO43,3K+) and KH2PO4, alone or in mixtures.

[0087] Said cesium phosphate salt(s) are advantageously chosen from CsH2PO4, Cs2H2P3O10, Cs4H2P4O13, Cs3P3O9, Cs4P4O12, Cs6P6O18, Cs8P8O24, CsPO3, alone or in mixtures. Preferably, the preferred cesium phosphate salt is CsH2PO4.

[0088] 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.

[0089] Preferably, at least one organic adjuvant is also mixed in during step i).

[0090] Said organic adjuvant may be chosen from all additives known to the person skilled in the art. In the case where at least one organic adjuvant is added in step i), 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.

[0091] Preferably, said organic adjuvant may be mixed in powder form or in solution in said solvent.

[0092] Said solvent is advantageously chosen from water, alcohols, and in particular ethanol, and amines. Preferably, said solvent is water.

[0093] Within the framework of the invention, it is entirely possible to carry out mixtures of several different silica powders, silica gel, or zeolite and / or different silica soils and / or different potassium or cesium phosphate powders.

[0094] The order in which the powders of at least the silica sources, at least one potassium and / or cesium phosphate salt powder, and possibly at least one organic adjuvant are mixed in the form of powders, with at least one solvent, are produced indifferently.

[0095] The mixing of said powders and said solvent can advantageously be carried out in a single step.

[0096] The addition of powders and solvent can also advantageously be carried out in several stages, for example with an alternation between the addition of powder(s) and solvent.

[0097] Said potassium phosphate salt(s) and / or cesium phosphate used in step i) are advantageously in powder form.

[0098] Preferably, said potassium and / or cesium phosphate salt(s), in the case where these are mixed in powder form, can advantageously be ground and sieved to a particle size of less than 100 pm.

[0099] Preferably, the silica source used in step i) has a grain size of less than 60 pm, and preferably less than 25 pm, even more preferably less than 5 pm, most preferably less than 2 pm.

[0100] In a particularly preferred embodiment, the use of a silica source used in step i) having a grain size of less than 60 pm, and preferably less than 25 pm, even more preferably less than 5 pm, most preferably less than 2 pm, combined with the use of a powder of at least one potassium and / or cesium phosphate salt ground and sieved to a grain size of less than 100 pm, allows a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0101] Preferably, said powders of at least one source of silica, of at least one salt of potassium and / or cesium phosphate and possibly of at least one organic adjuvant, in the case where these are mixed in powder form, are first premixed, dry, before the introduction of the solvent.

[0102] The pre-mixed powders are then advantageously contacted with the solvent. In another embodiment, at least the silica sources and at least the organic adjuvant may be previously in solution or suspension in the solvent when the solvent is contacted with the potassium and / or cesium phosphate powders. Contacting the solvent results in a mixture which is then advantageously kneaded.

[0103] In the case where at least one cesium phosphate salt powder is used, ammonia is advantageously added to the mixture to obtain an extrudable mixture.

[0104] Preferably, said mixing step i) is carried out by kneading, either discontinuously (“batch” according to Anglo-Saxon terminology) or continuously.

[0105] In the case where said step i) is carried out discontinuously, said step i) is advantageously carried out in a mixer preferably equipped with Z-arms, or with cams, or in any other type of mixer such as, for example, a planetary mixer. Said mixing step i) makes it possible to obtain a homogeneous mixture of the powdered constituents.

[0106] Preferably, said step i) is carried out at a temperature between 13 and 25°C, for a duration between 5 and 60 minutes, and preferably between 10 and 50 minutes. The rotation speed of the mixer arms is advantageously between 10 and 75 rpm, preferably between 25 and 50 rpm.

[0107] Preferably, the following quantities are introduced in step i) of mixing of the process according to the invention:

[0108] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and most preferably from 15% to 65% by weight of at least one precipitated silica powder, silica gel or zeolite with a Si / Al ratio>100;

[0109] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and preferably from 5% to 50% by weight of at least one soil of colloidal silica;

[0110] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and preferably from 20% to 75% by weight of at least one powder of potassium or cesium phosphate salt;

[0111] - 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;

[0112] the weight percentages being expressed in relation to the total weight of said material (i.e. the final material obtained at the end of step c) and the sum of the contents of each of the compounds of said material being equal to 100%.

[0113] According to the invention, said step ii) consists of shaping the mixture obtained at the end of step i). Preferably, the mixture obtained at the end of step i) is advantageously shaped by extrusion.

[0114] If the shaping of the mixture from step i) is carried out by extrusion, said step ii) is advantageously carried out in a piston, single-screw, or twin-screw extruder. In this case, an organic additive may optionally be added in mixing step i). The presence of said organic additive facilitates shaping by extrusion. Said organic additive is described above and is introduced in step i) in the proportions indicated above.

[0115] In the case where said preparation process is implemented continuously, said step i) of mixing can be coupled with step ii) of shaping by extrusion in the same equipment. According to this implementation, the extrusion of the mixture, also called "kneaded dough", can be carried out either by extruding directly from the end of the mixer A continuous twin-screw extruder, for example, can be used by connecting one or more batch mixers to an extruder. The die geometry, which gives the extruded products their shape, can be chosen from those well-known to those skilled in the art. These can be, for example, cylindrical or multilobed, and more preferably trilobed or quadrilobed.

[0116] In the case where the shaping of the mixture from step i) is carried out by extrusion, the quantity of solvent added in step i) 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.

[0117] Preferably, said extrusion shaping step ii) is carried out at an extrusion pressure greater than 1 MPa, and preferably between 3 MPa and 10 MPa. Implementation method 2

[0118] In a second embodiment according to the invention, step a) comprises the following substeps:

[0119] i') at least one colloidal silica sol is mixed with at least one water powder minus a potassium and / or cesium phosphate salt to obtain a suspension;

[0120] ii') a powder of at least one precipitated silica, a silica gel, or a zeolite of Si / Al ratio >100 and at least one solvent are added to said suspension obtained at the end of step i');

[0121] iii') the dough obtained at the end of step ii' is shaped.

[0122] According to the second embodiment, said step i') consists of mixing 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.

[0123] A solvent, preferably water, can advantageously be added in step i').

[0124] Preferably, colloidal silicas or silica sols are selected, without restriction, from the following commercial sources and are in liquid form: 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.

[0125] Said colloidal silica soil source(s) used in the process according to the present invention are advantageously synthetic amorphous silicas.

[0126] 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.

[0127] Said potassium phosphate salt(s) are advantageously chosen from the following list: KH2PO4, KH2P2O2, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O2, K6P6O18, K8P8O24, K10P10O3, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixtures. Preferably, the preferred potassium phosphate salt is KH2PO4.

[0128] Said cesium phosphate salt(s) are advantageously chosen from the following list: CsH2PO4, Cs2H2P3O10, Cs4H2P4O13, Cs3P3O9, Cs4P4O12, Cs6P6O18, Cs8P8O24, CsPO3, alone or in mixtures. Preferably, the preferred cesium phosphate salt is CsH2PO4.

[0129] Preferably, said potassium phosphate salt(s) or cesium phosphate salt(s) is / are chosen from KH2PO4, CsH2PO4 in their hydrated or non-hydrated form.

[0130] 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 i'). The grain size of the potassium and / or cesium phosphate salts is advantageously measured by dry laser granulometry.

[0131] Most preferably, said step i') 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.

[0132] Said step i') is advantageously implemented at a mixing speed applied to the centrifugal planetary mixer, between 100 and 2000 revolutions per minute, preferably between 200 and 500 revolutions per minute.

[0133] Preferably, said step i') is carried out for a duration of between 5 seconds and 60 seconds and preferably between 20 seconds and 60 seconds.

[0134] The additions of powders, colloidal silica sol and solvent can also advantageously be alternated.

[0135] According to the second embodiment, the process includes a step ii') of adding a powder of at least one precipitated silica, a silica gel, or a zeolite of Si / Al ratio >100 and at least one solvent into said suspension obtained at the end of step i').

[0136] Preferably, precipitated silicas, silica gels, or zeolites with a Si / Al ratio >100 added in step ii') are chosen without restriction from the following commercial sources: Nyasil20 (Nyacol ®), Siliaflash P60 (Silicycle ®), Siliaflash C60 (Silicycle ®), Ultrasil VN3 GR (Evonik ®), ZSM-5 (CBV 28014; Zeolyst®), HY (CBV780; Zeolyst®) taken alone or in mixture.

[0137] Preferably, the powder of at least one precipitated silica or silica gel or zeolite with a Si / Al ratio >100 added in step ii') has a grain size of less than 60 pm, and preferably less than 25 pm, even more preferably less than 5 pm, most preferably less than 2 pm.

[0138] The grain size of precipitated silica or silica gel or zeolite with a Si / Al ratio >100 is advantageously measured by dry laser granulometry.

[0139] Preferably, the precipitated silica or silica gel is in amorphous form.

[0140] Within the framework of the invention, it is entirely possible to carry out mixtures of several different silica powders, silica gel, or zeolite and / or different silica soils and / or different potassium and / or cesium phosphate salt powders.

[0141] According to the invention, at least one solvent is added in step ii'). Said solvent is advantageously chosen from water, alcohols, and in particular ethanol, and amines. Preferably, said solvent is water.

[0142] Preferably, at least one organic adjuvant may also be added during step ii').

[0143] Said organic adjuvant may be chosen from among all additives known to a person skilled in the art.

[0144] In the case where at least one organic adjuvant is added in step ii'), said organic adjuvant is advantageously selected 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.

[0145] Preferably, said organic adjuvant may be mixed in powder form or in solution in said solvent.

[0146] Step i') and step ii') can advantageously be carried out in the same equipment, and preferably in a centrifugal planetary mixer.

[0147] In another embodiment, steps i') and ii') can advantageously be carried out in different equipment. In this case, step i') is preferably carried out in a centrifugal planetary mixer, then the suspension obtained at the end of step i') is transferred to a Z-arm type batch mixer in which a powder of at least one precipitated silica or silica gel or zeolite and at least one solvent, according to step ii'), are added to said suspension.

[0148] In the case where step i') and step ii') are not carried out in the same equipment, preferably the silica source (precipitated silica, silica gel or zeolite with a Si / Al ratio > 100), at least one solvent and possibly at least one organic adjuvant are added first, preferably in the Z-arm type batch mixer, before the introduction of the suspension obtained in step i').

[0149] 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 ii').

[0150] Preferably, said mixing step ii') is carried out by kneading, either discontinuously or continuously.

[0151] In the case where said step ii') is carried out discontinuously, said step ii') 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 ii') makes it possible to obtain a paste or a homogeneous mixture of the constituents.

[0152] In the case of the implementation of a "Z-arm" type mixer in step ii'), the rotation speed of the mixer arms is advantageously between 10 and 75 revolutions / minute, preferably between 25 and 50 revolutions / minute.

[0153] In the case of implementing step ii') in a centrifugal planetary mixer, the rotation speed is advantageously between 300 and 2000 rpm, preferably between 1500 and 2000 rpm in order to obtain a paste.

[0154] 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 i') associated with the use of a silica source (precipitated silica or silica gel, or zeolite with a Si / Al ratio > 100) having a reduced size and preferably less than 10 pm, more preferably less than 5 pm, more preferably less than 1 pm, in step ii') allows a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0155] Preferably, the following quantities are introduced in steps i') and ii'):

[0156] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 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;

[0157] -l% to 99% weight, preferably from 5% to 99% weight, preferably from 10% at 95% by weight, and most preferably from 10% to 60% by weight of at least one potassium and / or cesium phosphate salt;

[0158] - 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, silica gel or zeolite with a Si / Al ratio > 100;

[0159] - 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;

[0160] 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%.

[0161] According to the second embodiment, said process includes a step iii') of shaping the dough obtained at the end of step ii') of mixing.

[0162] Preferably, the paste obtained at the end of step ii') is advantageously shaped by extrusion.

[0163] In the case where the shaping of the mixture from step ii') is carried out by extrusion, said step ii') is advantageously carried out in a piston, single screw or twin screw extruder.

[0164] In this case, an organic additive may optionally be added in mixing step ii'). The presence of said organic additive facilitates shaping by extrusion. Said organic additive is described above and is introduced in step ii' in the proportions indicated above.

[0165] 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.

[0166] In the case where the shaping of the mixture from step ii') is carried out by extrusion, the quantity of solvent added in step ii') 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.

[0167] Preferably, said extrusion shaping step iii') is carried out at an extrusion pressure greater than 1 MPa and preferably between 3 MPa and 10 MPa. Implementation method 3

[0168] In a third embodiment according to the invention, step a) comprises the following substeps:

[0169] i”) a liquid solution in aqueous or organic phase is supplied comprising at least one phosphate precursor, and at least one potassium and / or cesium precursor, the preparation temperature being advantageously between 5°C and 80°C, preferably between 10°C and 70°C;

[0170] ii”) said solution obtained at the end of step i”) is impregnated onto a support containing silica, the volume of the solution being advantageously between 0.9 and 1.1 times the porous volume of the support, preferably between 0.8 and 1.05 times the porous volume of the support, and the phosphate concentration of the solution being preferably between 50 g / L and 2000 g / L.

[0171] The impregnation solution of step i”) 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 may 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 MCl, hydroxide MOH, or oxide M2O.

[0172] The phosphate precursor(s) may advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, P2O5.

[0173] The phosphate concentration of the solution is preferably between 50 g / L and 2000 g / L.

[0174] The support supplied in step ii”) advantageously comprises an amorphous SiO2 phase, characterizable by X-ray diffraction. Said support preferably has a specific surface area greater than or equal to 5 m2 / g, preferably between 5 m2 / g and 500 m2 / g, and even more preferably between 10 m2 / g and 450 m2 / g.

[0175] The porous volume of the support is advantageously between 0.05 cmVg and 1.5 cmVg, preferably between 0.2 cmVg and 1.2 cmVg, and even more preferably between 0.25 cmVg and 1.1 cmVg.

[0176] The macroporous volume of the support is advantageously between 0.01 cmVg and 0.5 cmVg, preferably between 0.01 cmVg and 0.4 cmVg, and even more preferably between 0.01 cmVg and 0.3 cmVg.

[0177] The manufacture of amorphous silicon oxide type supports and their shaping is well known and taught in the art, for example in the Handbook of Porous Solids, Wiley-VCH (Volume 3, pages 1543-1590).

[0178] Preferably, the support supplied in step ii”) is in the form of beads, extrudates (preferably cylindrical, trilobed or quadrilobed), pellets, or irregular and non-spherical agglomerates.

[0179] Most advantageously, said support is in the form of beads or extrudates.

[0180] When the support is in the form of beads, the diameter of the beads is generally between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm mm. When the support is in the form of an extrudate, the extrudates generally have a diameter between 0.5 mm and 10 mm, preferably between 1.0 mm and 2.5 mm and a length between 1.0 mm and 2.0 mm.

[0181] Preferably, the impregnation step ii' ' ) can be preceded by a heat treatment step carried out at a temperature between 80°C and 550°C.

[0182] Preferably, the impregnation step ii”) can be followed, optionally, by other impregnation steps. The impregnation steps following the first can advantageously be carried out after the maturation step b). Step b)

[0183] The preparation process according to the invention includes a step b) of maturing the material obtained at the end of step a). Said maturation step is 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, for a duration advantageously 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.

[0184] Preferably, this 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 ensures good hydration of the material, which is necessary to limit the appearance of cracks that would be detrimental to mechanical strength. At the end of step b), a precursor of the matured material is obtained. Step c)

[0185] According to an essential step in the preparation process, the matured material precursor from step b) undergoes a calcination step c) 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. Step c) is carried out for a duration advantageously between 1 and 12 hours, preferably between 1 and 4 hours. This step is essential for the formation of the cristobalite and / or tridymite crystallographic phases. This step also allows for the removal of the organic additives used to facilitate shaping the material.

[0186] Said calcination step c) is advantageously carried out under a gas stream comprising oxygen, for example preferably the precursor of mature material obtained at the end of step b) is calcined under dry air or with different humidity levels or 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 relative to the total volume of said gas mixture. Step d)

[0187] According to step d) of the preparation process, the calcined material obtained at the end of step c) is contacted with at least one second phosphate precursor, and at least one second potassium and / or cesium precursor to obtain a second material precursor.

[0188] Advantageously, step d) comprises the following substeps:

[0189] dl) a liquid solution in aqueous or organic phase is prepared comprising at least one second precursor of phosphate, and at least one second precursor of potassium and / or cesium, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C;

[0190] d2) the solution prepared in step d1) is impregnated onto the calcined material obtained at at the end of step c), 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 calcined material obtained at the end of step c);

[0191] d3) optionally, a maturation step of the second material precursor obtained at the end of step d2),

[0192] d4) optionally, a drying step of the second material precursor matured obtained at the end of step d3).

[0193] Preferably, the phosphate concentration of the solution supplied at step dl) is between either 50 g / L and 2000 g / L.

[0194] The impregnation solution of step d1) 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 MCl, hydroxide MOH, or oxide M2O.

[0195] The phosphate precursor(s) may advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, P2O5.

[0196] The phosphate concentration of the solution is preferably between 50 g / L and 2000 g / L.

[0197] Preferably, a maturation step d3) is 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, 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.

[0198] Preferably, said maturation step is carried out in air and preferably under 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, necessary to limit the appearance of cracks that are detrimental to mechanical strength.

[0199] Preferably, after the maturation step d3), a drying step is carried out at a temperature below 250°C, preferably between 15°C and 180°C, more preferably between 30°C and 160°C, even more preferably between 50°C and 150°C, and even more preferably between 70°C and 140°C, for a duration typically between 0.5 hours and 12 hours, and more preferably between 0.5 hours and 5 hours. Longer durations are not excluded, but do not necessarily provide any improvement.

[0200] Preferably, the impregnation step d) can be followed, optionally, by other impregnation steps. Step e)

[0201] According to the material preparation process, the second material precursor obtained at the end of step d) of impregnation, undergoes a step e) of calcination 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.

[0202] 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 more preferably at least 10% by volume, of oxygen.

[0203] At the end of step e) the material according to the invention is obtained. Transformation process

[0204] 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.

[0205] 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 in a very preferred way between 0.05 and 20 h1.

[0206] Said process makes it possible to selectively obtain a mixture of products comprising acrylic acid.

[0207] 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.

[0208] Said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0209] 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

[0210] 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.

[0211] Said feedstock may also include impurities related, in particular, to the processes of 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.

[0212] 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.

[0213] 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.

[0214] The sum of the contents of hydroxypropanoic acid and its derivatives, water, organic solvent and any impurities represents 100% by weight of the charge.

[0215] The main products obtained by said process are hydroxypropanoic acids and its unconverted derivatives, acrylic acid from the dehydration reaction.

[0216] The examples below illustrate the invention without limiting its scope. Examples

[0217] To exemplify the invention, several methods of preparing materials are described. The contents are expressed as mass percentages.

[0218] The examples below illustrate the invention without limiting its scope.

[0219] Example 1: Preparation of material A based on embodiment 1 in presence of precipitated silica powder

[0220] Precipitated silica powder (Siliaflash P60 40-63 pm; Silicycle) (38%), colloidal silica sol (36%), potassium phosphate (KPO3, Aldrich) (26%), and Methocel™ (K15M) (3%) are introduced and premixed in a Brabender brand mixer. Water is added dropwise until a paste is obtained, and mixing is continued for 20 minutes. The resulting paste is then extruded on an MTS brand piston extruder using a 1.6 mm diameter cylindrical die. The resulting extrudates (extruded A) are then cured for 16 hours at 120°C in a ventilated oven.

[0221] Finally, the extrudates A are subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are called material Al and the extrudates calcined at 800°C are called precursors of material A2.

[0222] Next, 2.6 grams of potassium hydrogen phosphate (K₂HPO₄, M = 174 g / mol) and 2.0 g of ammonium hydrogen phosphate ((NH₄)₂HPO₄, M = 132 g / mol) are first dissolved in 5 mL of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to 20 grams of precursor material A2. The solid is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C in air. It is then calcined in air at 450°C for 4 hours to obtain material A3 (according to the invention).

[0223] Compositional analysis of material A3 by X-ray fluorescence gives a K content of 12 wt% and a P content of 10 wt%. The equivalent average KPO3 content of material A3 after calcination is 36%.

[0224] The Al material (not in accordance with the invention) exhibits in XRD diffraction peaks of the metaphosphate phase KPO3.

[0225] The A3 material (according to the invention) exhibits in XRD diffraction peaks of the metaphosphate phase KPO3 and of the crystallized silica cristobalite.

[0226] Example 2: Preparation of material B based on embodiment 1 in the presence of precipitated silica powder

[0227] Precipitated silica powder (Nyasil 20 l, 5pm; Nyacol (53%), colloidal silica sol (32%), potassium phosphate (KPO3, Aldrich) (15%) and Methocel™ (K15M) (3%) are introduced and pre-mixed in a Brabender brand mixer. Water is added dropwise until a paste is formed, and mixing is continued for 20 minutes. The resulting paste is then extruded on an MTS brand piston extruder using a 1.6 mm diameter cylindrical die. The resulting extrudates (extruded material B) are then cured for 16 hours at 120°C in a ventilated oven. Finally, the extruded material B is subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are designated B1 material, and the extrudates calcined at 800°C are designated as precursors of B2 material.

[0228] Next, 1.6 grams of potassium hydrogen phosphate (K₂HPO₄, M = 174 g / mol) and 1.2 g of ammonium hydrogen phosphate ((NH₄)₂HPO₄, M = 132 g / mol) are first dissolved in 5.6 mL of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to 20 grams of precursor material B2. The solid is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C in air. It is then calcined in air at 450°C for 4 hours to prepare material B3 (according to the invention).

[0229] Compositional analysis of material B3 by FX gives a K content of 7.3% and a P content of 6.4% by weight. The equivalent average KPO3 content of material B3 after calcination is 22%.

[0230] Material B1 (non-conforming) exhibits X-ray diffraction peaks of the metaphosphate KPO3 phase.

[0231] The B3 (conforming) material exhibits in XRD diffraction peaks of the crystallized silica cristobalite as well as diffraction peaks of the metaphosphate phase KPO3.

[0232] Example 3: Preparation of precursor of calcined material C based on embodiment 2 in the presence of a colloidal silica sol

[0233] Colloidal silica sol (12.4%) and ground and sieved potassium dihydrogen phosphate (KH2PO4; Aldrich) powder (15.2%) (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%), and precipitated silica powder (Nyasil20; Nyacol) (72.4%) 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 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. The resulting extrudates (extruded C) are then matured for 16 hours at 120°C in a ventilated oven.Finally, the C extrudates are subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are called materials. Cl and the extrades calcined at 800°C are named precursors of C2 material.

[0234] Next, 2.8 grams of potassium hydrogen phosphate (K₂HPO₄, M = 174 g / mol) and 2.1 g of ammonium hydrogen phosphate ((NH₄)₂HPO₄, M = 132 g / mol) are first dissolved in 4.2 mL of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to 20 grams of precursor material C2. The solid is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C in air. It is then calcined in air at 450°C for 4 hours to prepare material C3 (according to the invention).

[0235] Compositional analysis of material C3 by FX gives a K content of 8.8% and a P content of 7.5% by weight. The equivalent average KPO3 content of material C3 after calcination is 27%.

[0236] The Cl material (non-conforming) exhibits in XRD diffraction peaks of the metaphosphate KPO3 phase.

[0237] The C3 (conforming) material exhibits in XRD diffraction peaks of the crystallized silica cristobalite as well as diffraction peaks of the metaphosphate phase KPO3.

[0238] For each of the materials obtained (conforming or non-conforming), the structural characteristics (Total pore volume, macroporous volume, macroporous median diameter, specific surface area, EGG) and the crystalline phases observed by XRD are indicated in Table 1 below.

[0239] [Tables 1] Calcination temperature (°C) Total volume (Hg) ml / g Macrovoltaic volume (Hg) ml / g Dmac ros s m2 / g EGG (daN / mm) DRX Al (non-compliant) 450 - - - - - Amorphous silica + monoclinic KPO3 A3 (compliant) 800 0.25 0.25 3006 4 0.83 Monoclinic KPO3 + cristobalite-type SiO2 B1 (non-compliant) 450 - - - - - Amorphous silica + monoclinic KPO3 B3 (compliant) 800 0.28 0.27 1069 4 2.02 Monoclinic KPO3 + cristobalite-type SiO2 Cl (non-compliant) 450 - - - - - Amorphous silica + monoclinic KPO3 C3 (compliant) 800 0.21 0.21 1000 4 2.3 Monoclinic KPO3 + SiO2 cristobalite type + e tridymite

[0240] Example 4: Preparation of materials D according to embodiment 3

[0241] Materials DI and D3 are prepared from an amorphous silica DO in the form of 2 mm diameter beads, with a specific surface area measured by mercury porosimetry of 90 m2 / g and a total pore volume of 0.92 cmVg and whose structural properties are indicated in Table 2 below.

[0242] [Tables2] % kpo3 T calcination (°C) V total (Hg) ml / g V macro (Hg) ml / g S (Hg) m2 / g DRX D0 0 - 0.92 0.07 90 Amorphous SiO2 DI (non-compliant) 33,450 - - - Monoclinic KPO3 D3 (compliant) 45,900 0.30 0.30 3 KPO3 monoclinic + cris-tobalite type SiO2

[0243] For the preparation of materials DI and D3, 100 grams of commercial amorphous silica DO are calcined under air in a muffle furnace in a thin layer at 450°C for 2 hours.

[0244] 10 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 8.6 g Ammonium hydrogen phosphate ((NH4)2HPO4, M = 132 g / mol) is first dissolved in 30 mL of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to the SiO2 beads. The solid is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C under air.

[0245] 20 grams of the material are calcined under air at 450°C for 4 hours to prepare the DI material (not in accordance with the invention).

[0246] 20 grams of the material are calcined under air at 900°C for 4 hours to prepare the precursor of material D2.

[0247] 3.3 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 2.5 g Ammonium hydrogen phosphate ((NH4)2HPO4, M = 132 g / mol) is first dissolved in 5.3 mL of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to 20 grams of precursor beads of material D2. The solid is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C in air. It is then calcined in air at 450°C for 4 hours to obtain material D3 (according to the invention).

[0248] Compositional analysis of material D3 by FX gives a K content of 14% and a P content of 12% by weight. The equivalent average KPO3 content of material D3 after calcination is 44.5%.

[0249] The DI (non-conforming) material exhibits X-ray diffraction peaks of the metaphosphate KPO3 phase.

[0250] The D3 (conforming) material exhibits silica diffraction peaks in XRD crystallized cristobalite as well as diffraction peaks of the metaphosphate phase kpo3.

[0251] The specific surface area (Hg porosity) of the DI material is 46 m² / g and its macroporous volume is 0.07 ml / g. After calcination at a temperature greater than or equal to 800°C and impregnation, the specific surface area of ​​the D3 material is 3 m² / g and the macroporous volume is 0.30 ml / g.

[0252] Example 5: Use of AL A3, Cl and C3 materials as a catalyst for the dehydration of lactic acid to acrylic acid in the gas phase

[0253] The materials Al, A3, Cl, and C3 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 pph of lactic acid is 0.2 h₁ with a catalyst mass of approximately 190 mg. At the unit outlet, all products are analyzed by gas chromatography. The results are presented in Table 3 below.

[0254] [Tables3] Catalyst mPO3 / (MPO3+SiO2) Calcination temperature (°C) Bed height (mm) Catalyst mass (mg) Yield Acrylic Acid (% molC) Al (non-compliant) 26 450 140 180 78 A3 (compliant) 37 850 132 190 83 Cl (non-compliant) 33 450 96 187 70 C3 (compliant) 45 900 91 188 72

[0255] Al, A3, Cl, and C3 catalysts convert a lactic acid feedstock to acrylic acid with a carbon yield greater than or equal to 70%. The A3 and C3 catalysts according to the invention have higher acrylic acid (AA) carbon yields than those obtained respectively by the non-conforming Al and Cl catalysts. After 150 hours under load, unloading the A3 and C3 catalysts is easier than unloading the Al and Cl catalysts, which are stuck to the reactor walls. The conforming A3 and C3 catalysts, for which calcination at a temperature of above 800°C is applied are more stable in operating conditions and after a time under load of 150 hours can be easily unloaded.

[0256] Example 6: Use of BL B3, DI and D3 materials as a catalyst for the dehydration of lactic acid to acrylic acid in the gas phase

[0257] Materials Bl, B3, DI, and D3 are tested using a single-reactor unit with an internal diameter of 10 mm and a volume of 50 mL. The tubular reactor with an internal diameter of 10 mm is loaded with approximately 10 cubic centimeters of shaped catalyst (approximately 6 grams of catalyst), located between two beds of solids validated as reaction inerts (quartz extrudates). The feed, composed of 20% lactic acid and 80% by weight water, is co-injected with nitrogen at the reactor inlet. The reactor is located in a furnace using several temperature-holding zones, a mechanical pressure regulator by dam, and two gas-liquid separation stages. The first stage allows for the condensation of water contained in the reaction effluent, and the second separator is located on the residual steam from the first separator to ensure post-condensation (T=-5°C).

[0258] The unit gases are analyzed (hot for the total effluent and cold for the separator head gases) by gas chromatography. The liquid effluent is weighed and analyzed regularly by high-pressure liquid chromatography (HPLC).

[0259] The reaction is carried out at 365°C at a total pressure of 12 bara (1.2 MPa). The gas flow rate is 8 g / h of nitrogen and the liquid feed rate is 5 g / h. Conversion

[0260] The conversion of lactic acid (LA) is calculated according to the following formula:

[0261] LA conversion (%) = 100 x ([LA]C feed - [LA]C effluent) / [LA]C feed

[0262] with [AL]C = carbon concentration in AL in gC / L determined by HPLC.

[0263] The carbon yield of acrylic acid (AA) is determined according to the following formula:

[0264] AA yield (%) = 100 x [AA]C effluent / [AL]C load

[0265] The results are presented in Table 4 below.

[0266] [Tables4] Catalyst mPO3 / (MPO3+SiO2) Calcination temperature (°C) Test time (h) AL conversion (%) AA yield (% molC) Catalyst stability after test B1 (non-compliant) 15 450 160 81 50 no B3 (compliant) 22 850 160 99.3 84 yes D1 (non-compliant) 33 450 160 99.3 82 no D3 (compliant) 45 900 160 99.3 84 yes

[0267] Catalysts Bl, B3, Dl, and D3 convert a lactic acid feedstock into acrylic acid with a carbon yield exceeding 50% after 160 hours under load. Catalysts B3 and D3 according to the invention have higher acrylic acid (AA) yields than those obtained by non-conforming catalysts Bl and Dl, respectively. Upon discharge of catalysts Bl and Dl, they are no longer intact, and some of the KPO3 is recovered in the reactor. Catalysts B3 and D3 have the same appearance as the loaded catalyst after 160 hours under operating conditions.

[0268] The B3 and D3 catalysts according to the invention are therefore more active and stable during the dehydration reaction of lactic acid to acrylic acid than the non-conforming Bl and Dl catalysts.

Claims

Demands

1. A process for preparing a macroporous material based on at least one potassium phosphate salt and / or at least one cesium phosphate salt, and silica in at least partial crystalline form cristobalite and / or tridymite, comprising at least the following steps: a) contacting at least one silica source with at least one first phosphate precursor and at least one first potassium and / or cesium precursor to obtain a first material precursor; b) allowing the material precursor obtained at the end of step a) to mature for a period of between 1 minute and 72 hours to obtain a matured material precursor; c) calcining the matured material precursor obtained at the end of step b) at a temperature between 800°C and 1200°C to obtain a calcined material precursor;d) the calcined material precursor obtained at the end of step c) is contacted with at least a second phosphate precursor, and at least a second potassium and / or cesium precursor to obtain a second material precursor; e) the second material precursor obtained at the end of step d) is calcined at a temperature between 300°C and 600°C to obtain the material.

2. A method according to claim 1, wherein in step a) said first and second precursors of phosphate, potassium and / or cesium are supplied in the form of at least one potassium phosphate salt and / or at least one cesium phosphate salt.

3. A process according to claim 2, wherein said potassium phosphate salt is selected from: KH2PO4, KH2P2O2, K6P6O7, K3H2P3O10, K4 H2P4O13, K3P3O9, K^O^, KgPgO1g, K8P8O24, KiqPioO3o, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixture.

4. A process according to any one of claims 2 or 3, wherein said cesium phosphate salt is selected from CsH2PO4, Cs2H2P3O10, Cs4H2P4O13, Cs3P3O9, Cs4P4O2, Cs6P6O18, Cs8P8O24, CsPO3, alone or in mixture.

5. A method according to any one of claims 2 to 4, wherein said potassium phosphate salt and / or said phosphate salt of cesium is supplied at step a) in powder form.

6. A method according to claim 5, wherein prior to their introduction in step a), said powder of at least one potassium and / or cesium phosphate salt is ground and sieved to a grain size of less than 100 µm.

7. A preparation method according to any one of claims 1 to 6, wherein step a) comprises the following substeps: i) at least one precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100, at least one colloidal silica sol and at least one powder of at least one potassium and / or cesium phosphate salt are mixed in at least one solvent to obtain a mixture; ii) the mixture obtained at the end of step i) is shaped.

8. A preparation method according to any one of claims 1 to 6, wherein step a) comprises the following substeps: i') at least one colloidal silica sol is mixed with at least one powder of at least one potassium and / or cesium phosphate salt to obtain a suspension; ii') at least one precipitated silica powder, or silica gel, or zeolite with a Si / Al ratio >100 and a solvent are added to said suspension obtained at the end of step i') to obtain a paste; iii') the paste obtained at the end of step ii' is shaped.

9. A preparation method according to claim 1, wherein step a) comprises the following substeps: i”) supplying a liquid solution in aqueous or organic phase comprising at least the first phosphate precursor, and at least the first potassium and / or cesium precursor; ii”) impregnating said solution obtained at the end of step i”) onto a shaped support containing silica.

10. A method according to claim 9, wherein the preparation temperature of step i”) is between 5°C and 80°C.

11. A process according to any one of claims 9 or 10, wherein the phosphate concentration of the solution supplied in step i”) is between 50 g / L and 2000 g / L.

12. A method according to any one of claims 9 to 11, wherein said first precursor of potassium and / or cesium is selected from the salts of carbonate M2CO3, nitrate MN03, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCl, of hydroxide MOH, and oxide M2O, with M = K or Cs.

13. A process according to any one of claims 9 to 12, wherein said first phosphate precursor is selected from H3PO4, (NH4)H2 PO4, (NH4)2HPO4, (NH4)PO4, and P2O5.

14. A process according to any one of claims 9 to 13, wherein step d) comprises the following substeps: dl) a liquid solution in aqueous or organic phase is prepared comprising at least one second precursor of phosphate, and at least one second precursor of potassium and / or cesium, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C; d2) the solution prepared in step dl) is impregnated onto the calcined material obtained at the end of step c), 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 calcined material obtained at the end of step c); d3) optionally, a maturation step for the second precursor material obtained at the end of step d2), d4) optionally, a drying step of the second precursor of matured material obtained at the end of step d3).