Method for preparing a reimpregnated material based on silica in the cristobalite and / or tridymite crystalline form

Abstract

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

Description

[0001] Process for the preparation of a reimpregnated silica-based material in the crystalline form of cristobalite and / or tridymite

[0002] Field of invention

[0003] The invention relates to a novel macroporous material containing silica in the crystalline form of cristobalite and / or tridymite. The material can be advantageously used as a support or as a catalyst in catalytic processes.

[0004] State of the art

[0005] Silica is an interesting compound to use as a catalyst support, it cannot be extruded like other materials in conventional extrusion equipment to give products strong enough 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 for catalysts with improved mechanical and physical properties.

[0006] Patent application WO2003 / 026795 discloses a method for producing a catalyst comprising a silica support which comprises impregnating a silica component with a catalytic metal by means of an aqueous alkaline bath before drying in order to improve its mechanical strength. More particularly, the preparation method comprises forming and washing a silica component, of the silica gel or co-gel type, for example a silica-zirconia co-gel. Then, the washed silica component is brought into contact with an alkaline bath in order to impregnate the catalytic metal, of the cesium type, and to form an activated silica component. The activated silica component is then dried in order to form the catalyst without a calcination step.

[0007] Patent application WO17040383 discloses a plurality of catalysts comprising at least one mixture of alkali phosphates, some of which have the formula M x PO y(with M = K or Cs) and a non-porous silica binder. The catalysts are prepared by mechanically mixing, using a planetary mill, an amorphous fused silica (Fused silica according to English terminology), which is a dense material with no surface or porosity properties, and potassium phosphate precursors. The catalyst precursor is then calcined in air at 450°C to obtain a material composed of a KPO3 / (KPO3 + SiCh) mixture with a mass ratio of 13 to 26% by weight of KPO3 relative to the total weight of said material. This document also discloses a catalyst in the form of a powder of variable particle size sieved between 106 and 212 μm. The silica contained in the final material is in its amorphous form (see example 8).

[0008] However, none of the prior art documents discloses a macroporous material based on a potassium phosphate salt and / or a cesium phosphate salt and silica at least partially in the crystalline form of cristobalite and / or tridymite.

[0009] Objects of the invention

[0010] 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: a) at least one source of silica is brought into contact with at least one first phosphate precursor and at least one first potassium and / or cesium precursor to obtain a first material precursor; b) the material precursor 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 material precursor; c) the matured material precursor obtained at the end of step b) is calcined at a temperature of 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 brought into contact with at least one second phosphate precursor, and at least one 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.;

[0011] According to one or more embodiments, in step a), said first and second phosphate, potassium and / or cesium precursors are supplied in the form of at least one potassium phosphate salt and / or at least one cesium phosphate salt.

[0012] According to one or more embodiments, said potassium phosphate salt is selected from KH2PO4, KH2P2O12, KePeO?, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, KePeOis, K8P8O24, K10P10O30, potassium phosphate (tripotassium) (PO4 3 3K +), alone or as a mixture. According to one or more embodiments, said cesium phosphate salt is chosen from CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, Cs8PsO24, CSPO3, alone or as a mixture.

[0013] 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.

[0014] According to one or more embodiments, prior to their introduction into 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.

[0015] According to one or more embodiments, step a) comprises the following sub-steps: i) at least one precipitated silica, silica gel or zeolite powder 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.

[0016] According to one or more embodiments, step a) comprises the following sub-steps: 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') a powder of at least one precipitated silica, or a silica gel, or a 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.

[0017] According to one or more embodiments, step a) comprises the following sub-steps: i”) a liquid solution in aqueous or organic phase is supplied comprising at least the first phosphate precursor, and at least the first potassium and / or cesium precursor; ii”) said solution obtained at the end of step i”) is impregnated onto a shaped support containing silica.

[0018] According to one or more embodiments, the preparation temperature of step i”) is between 5°C and 80°C. 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.

[0019] According to one or more embodiments, said first potassium and / or cesium precursor is chosen from the salts of carbonate M2CO3, nitrate MNO3, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCI, hydroxide MOH, and oxide M2O, with M = K or Cs.

[0020] According to one or more embodiments, said first phosphate precursor is selected from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, and P2O5.

[0021] According to one or more embodiments, step d) comprises the following sub-steps: d1) a liquid solution in aqueous or organic phase is prepared comprising at least one second phosphate precursor, and at least one second potassium and / or cesium precursor, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C; d2) the solution prepared in step d1) 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 pore volume of the calcined material obtained at the end of step c); d3) optionally, a step of maturation of the second precursor of material obtained at the end of step d2), d4) optionally, a step of drying of the second precursor of matured material obtained at the end of step d3).

[0022] Detailed description

[0023] 1. Definitions

[0024] For the purposes of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.

[0025] For the purposes 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, for the purposes of the present invention, a preferred pressure value range can be combined with a more preferred temperature value range. By "macropores" is meant pores with an opening larger than 50 nm.

[0026] By "mesopores" we mean pores with an opening between 2 nm and 50 nm, inclusive.

[0027] 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 bars (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.

[0028] For greater accuracy, the total pore volume value is the total pore volume value measured by mercury porosimeter intrusion measured on the sample minus the total pore volume value measured by mercury porosimeter intrusion measured on the same sample at a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0029] The volume of macropores and mesopores was 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 was set at 0.2 MPa, and above this value, mercury was considered to penetrate into the pores of the sample.

[0030] The macroporous volume of the material according to the invention is defined as being the cumulative volume of mercury introduced at a pressure between 0.2 MPa and 30 MPa, corresponding to the volume contained in the pores with an apparent diameter greater than 50 nm.

[0031] The mesoporous volume of the material according to the invention is defined as being 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.

[0032] 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 macropore volume, measured by mercury porosimetry.

[0033] 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®. In the rest 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, morphology and to measure the size of the grains or crystals constituting the material. For this, an electron microscope (of the J EM F200 JEOL or JEOL J EM 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.

[0034] Throughout the rest of the text, the term “lateral crushing strength” means the mechanical strength of the material according to the invention determined by the grain-to-grain crushing test (GTC). This is a standardized test (ASTM D4179-01 standard) which consists of subjecting a material in the form of a millimeter-sized object, such as a ball, a pellet or an extrudate, to a compressive force generating rupture. 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 GTC 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).

[0035] 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 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 magnitude 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.

[0036] The wet method allows the characterization of dispersions (elementary particle size after dispersion) or suspended solids ("aggregate" particle size). The particles measured are in the range of 0.02 microns to 2000 microns.

[0037] Dry process particle size analysis is used 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

[0038] Material

[0039] 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 at least partially in the crystalline form of cristobalite and / or tridymite.

[0040] Indeed, the Applicant has surprisingly discovered that the use of such a macroporous material as a catalyst for the dehydration of hydroxypropanoic acid allows a significant increase in the conversion of hydroxypropanoic acid and an improvement in the yield of corresponding propenoic acid compared to a catalyst obtained according to conventional preparation methods, in particular in which the silica is in amorphous form. The macroporous structure of the material and the particular crystallinity of the silica included in this material could be obtained by carrying out a specific preparation method comprising a step in which a calcination step is carried out at a temperature greater than or equal to 800°C on the basis of a material precursor comprising at least one source of silica and at least one precursor of potassium and / or cesium.

[0041] X-ray diffraction makes it possible to verify that the material according to the invention does indeed contain silica 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 PDF4+ 2020 crystallographic database of the ICDD® (International Centre for Diffraction Data). The X-ray diffraction pattern is obtained by radiocrystallographic analysis using a diffractometer using the classical powder method with Ka1 radiation from copper (X = 1.54060Â). From the position of the diffraction peaks represented by the angle 20, the characteristic reticular equidistances dhkl of the sample are calculated using the Bragg relation. The measurement error A(dhkl) on dhkl is calculated using the Bragg 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.

[0042] More specifically, the 20 line of 22° is associated mainly with the crystallographic form cristobalite. The 28.4, 31.4° and 36° lines are also attributed to the formation of cristobalite. The 20 lines of 20.7°, 21.7°, 23.4° and 27.5° are associated with the crystallographic form tridymite. Advantageously, said potassium phosphate and / or cesium phosphate salt is potassium metaphosphate (KPO3) and / or cesium metaphosphate (CsPCh).

[0043] 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.

[0044] Preferably, said material has a total pore volume of between 0.01 cm 3 / g and 0.6 cm 3 / g, more preferably between 0.05 cm 3 / g and 0.5 cm 3 / g, even more preferably between 0.1 cm 3 / g and 0.4 cm 3 / g, and even more preferably between 0.15 cm 3 / g and 0.39 cm 3 / g.

[0045] Preferably, said material has a macroporous volume of between 0.01 cm 3 / g and 0.6 cm 3 / g, more preferably between 0.05 cm 3 / g and 0.5 cm 3 / g, even more preferably between 0.1 cm 3 / g and 0.4 cm 3 / g, and even more preferably between 0.15 cm 3 / g and 0.39 cm 3 / g.

[0046] Preferably, the macroporous volume of the material represents between 50% and 100% of the total pore volume of said material, preferably between 60% and 100% and even more preferably between 80% and 100%.

[0047] Advantageously, said material has a specific surface area greater than or equal to 1 m 2 / g and less than 50 m2 / g, preferably between 1 m 2 / g and 20 m 2 / g, more preferably between 1 m 2 / g and 15 m 2 / g, and even more preferably between 1 m 2 / g and 10 m 2 / g.

[0048] Advantageously, said material has a mechanical resistance value measured by grain-to-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.

[0049] 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.

[0050] 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. In one embodiment according to the invention, the silica is present only in the crystalline form cristobalite.

[0051] Said material according to the invention advantageously has a macroporous median diameter of between 80 nm and 7000 nm, preferably between 200 nm and 6500 nm, and more preferably between 500 nm and 4000 nm.

[0052] Said material is advantageously in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates.

[0053] Preparation process

[0054] An object according to the invention relates to a method 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 at least partially in the crystalline form of cristobalite and / or tridymite, comprising at least the following steps: a) at least one source of silica is brought into contact with at least one first phosphate precursor and at least one first potassium and / or cesium precursor to obtain a first material precursor; b) the material precursor 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 material precursor; c) the matured material precursor obtained at the end of step b) is calcined at a temperature of 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 brought into contact with at least one second phosphate precursor, and at least one 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 1200°C to obtain the material.;

[0055] All steps a) to e) are detailed below.

[0056] Step a)

[0057] Step a) can be carried out according to several embodiments.

[0058] Embodiment 1

[0059] In a first embodiment according to the invention, step a) comprises the following sub-steps: i) at least one precipitated silica, silica gel or zeolite powder 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.

[0060] According to this embodiment, said step i) consists of mixing at least one powder of precipitated silica, 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.

[0061] Preferably, the precipitated silica powder, silica gel or zeolite with a Si / Al ratio >100 is chosen, without being restrictive, 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 as a mixture.

[0062] Preferably, the precipitated silica, silica gel or zeolite powder with a Si / Al ratio >100 has a grain size of less than 10 pm, and preferably less than 5 pm, more preferably less than 1 pm.

[0063] 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.

[0064] 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, and examples include Ludox AS40 stabilized with an ammonium counterion, or Nyacol 2034DI, Nalco 1034A, Ultra-Sol 7H, or NexSil 20A.

[0065] Said silica source(s) used in the process according to the present invention are advantageously synthetic amorphous silicas or zeolites with Si / Al ratios. 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 as a mixture.

[0066] Said potassium phosphate salt(s) are advantageously chosen from: KH2PO4, KH2P2O12, KePeO?, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, KePeOis, KsPsO24, K10P10O30, I© potassium phosphate (tripotassium) (PO4 3 3K + ), alone or in mixture. Preferably the preferred potassium phosphate salt is chosen from potassium phosphate (tripotassium) (PCL 3- , 3K + ) and KH2PO4, alone or in mixture.

[0067] Said cesium phosphate salt(s) are advantageously chosen from CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, Cs8PsO24, CsPOs, alone or as a mixture. Preferably the preferred cesium phosphate salt is CSH2PO4.

[0068] Preferably, said potassium phosphate or cesium phosphate salt(s) is (are) chosen from potassium phosphate (tripotassium) (PO4 3 3K + ), KH2PO4, CSH2PO4 in their hydrated or non-hydrated form.

[0069] Preferably, at least one organic adjuvant is also mixed during step i).

[0070] Said organic adjuvant may 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 i), 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.

[0071] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0072] Said solvent is advantageously chosen from water, alcohols, and in particular ethanol, and amines. Preferably, said solvent is water.

[0073] In the context of the invention, it is entirely possible to carry out mixtures of several different silica, silica gel or zeolite powders and / or different silica sols and / or different potassium or cesium phosphate powders. The order in which the mixing of the powders of at least the silica sources, at least one potassium and / or cesium phosphate salt powder and optionally at least one organic adjuvant in the case where these are mixed in the form of powders, with at least one solvent is carried out is indifferent.

[0074] The mixing of said powders and said solvent can advantageously be carried out in a single operation.

[0075] The addition of powders and solvent can also advantageously be carried out in several stages, for example alternating between the addition of powder(s) and solvent.

[0076] Said potassium phosphate and / or cesium phosphate salt(s) used in step i) are advantageously in the form of powders.

[0077] Preferably, said potassium and / or cesium phosphate salt(s), in the case where these are mixed in the form of powders, can advantageously be ground and sieved to a particle size of less than 100 pm.

[0078] Preferably, the silica source used in step i) has a grain size of less than 60 pm, and preferably less than 25 pm, more preferably less than 5 pm, very preferably less than 2 pm.

[0079] In a particularly preferred embodiment, the use of a silica source used in step i) has a grain size of less than 60 pm, and preferably less than 25 pm, more preferably less than 5 pm, very 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.

[0080] Preferably, said powders of at least one source of silica, of at least one salt of potassium and / or cesium phosphate and optionally of at least one organic adjuvant, in the case where these are mixed in the form of powders, are first pre-mixed, dry, before the introduction of the solvent.

[0081] Said pre-mixed powders are then advantageously brought into contact with said solvent. In another embodiment, at least said silica sources and at least said organic adjuvant may previously be in solution or suspension in said solvent when said solvent is brought into contact with the potassium and / or cesium phosphate powders. Contacting with said solvent results in obtaining a mixture which is then advantageously kneaded. 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.

[0082] Preferably, said mixing step i) is carried out by kneading, discontinuously (“batch” according to English terminology) or continuously.

[0083] 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-shaped arms, or 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.

[0084] Preferably, said step i) is carried out at a temperature of between 13 and 25°C, for a duration of between 5 minutes and 60 minutes, and preferably between 10 minutes and 50 minutes. The rotation speed of the mixer arms is advantageously between 10 and 75 revolutions / minute, preferably between 25 and 50 revolutions / minute.

[0085] Preferably, the following quantities are introduced into mixing step i) of the process according to the invention:

[0086] - 1% to 99% by weight, preferably from 5% to 99% by weight, more preferably from 10% to 95% by weight, and very preferably from 15% to 65% by weight of at least one precipitated silica powder, silica gel or a zeolite with a Si / Al ratio>100;

[0087] - 1% to 99% by weight, preferably 5% to 99% by weight, more preferably 10% to 95% by weight, and very preferably 5% to 50% by weight of at least one colloidal silica sol;

[0088] - 1% to 99% by weight, preferably 5% to 99% by weight, more preferably 10% to 95% by weight, and very preferably 20% to 75% by weight of at least one potassium or cesium phosphate salt powder;

[0089] - 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; the weight percentages being expressed relative 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%.

[0090] 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. In the case where the shaping of the mixture resulting 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 adjuvant may optionally be added in the mixing step i). The presence of said organic adjuvant facilitates shaping by extrusion. Said organic adjuvant is described above and is introduced into step i) in the proportions indicated above.

[0091] In the case where said preparation process is carried out continuously, said mixing step i) may 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 paste" may 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, may be chosen from dies well known to those skilled in the art. They may thus be, for example, cylindrical or multi-lobed, and more preferably tri-lobed or quadri-lobed.

[0092] In the case where the shaping of the mixture resulting from step i) is carried out by extrusion, the quantity of solvent added in the mixing step i) 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.

[0093] Preferably, said step ii) of shaping by extrusion is carried out at an extrusion pressure greater than 1 MPa, and preferably between 3 MPa and 10 MPa.

[0094] Embodiment 2

[0095] In a second embodiment according to the invention, step a) comprises the following sub-steps: 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') a powder of at least one precipitated silica, a silica gel, or a zeolite with a Si / Al ratio >100 and at least one solvent is added to said suspension obtained at the end of step ü; iii') the paste obtained at the end of step ii' is shaped. 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.

[0096] A solvent, preferably water, may advantageously be added in step i').

[0097] Preferably, the colloidal silicas or silica sols are chosen, without being restrictive, from the following commercial sources and are in liquid form: 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 a mixture.

[0098] Said source(s) of colloidal silica sol used in the process according to the present invention are advantageously synthetic amorphous silicas.

[0099] 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.

[0100] Said potassium phosphate salt(s) are advantageously chosen from the following list: KH2PO4, KH2P2O12, KePeO?, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, KePeOis, K8P8O24, K10P10O30, potassium phosphate (tripotassium) (PC>4 3 ', 3K + ), alone or in mixture. Preferably the preferred potassium phosphate salt is KH2PO4.

[0101] Said cesium phosphate salt(s) are advantageously chosen from the following list: CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, CS8P8O24, CSPO3, alone or as a mixture. Preferably the preferred cesium phosphate salt is CSH2PO4.

[0102] Preferably, said potassium phosphate or cesium phosphate salt(s) is (are) chosen from KH2PO4, CSH2PO4 in their hydrated or non-hydrated form.

[0103] 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 i'). The grain size of the potassium phosphate and / or cesium phosphate salts is advantageously measured by dry laser granulometry.

[0104] Very 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 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.

[0105] Said step i') is advantageously carried out at a mixing speed applied to the centrifugal planetary mixer, between 100 and 2000 revolutions per minute, preferably between 200 and 500 revolutions per minute.

[0106] 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.

[0107] The additions of powders, colloidal silica sol and solvent can also be advantageously alternated.

[0108] According to the second embodiment, the method comprises a step ii') of adding a powder of at least one precipitated silica, a silica gel, or a zeolite with a Si / Al ratio >100 and at least one solvent in said suspension obtained at the end of step i').

[0109] Preferably, the precipitated silicas, silica gels, or zeolites with a Si / Al ratio >100 added in step ii') are chosen, without being restrictive, 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 as a mixture.

[0110] 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, more preferably less than 5 pm, very preferably less than 2 pm.

[0111] The size of precipitated silica or silica gel or zeolite grains with a Si / Al ratio >100 is advantageously measured by dry laser granulometry.

[0112] Preferably, the precipitated silica or silica gel is in amorphous form.

[0113] Within the scope of the invention, it is entirely possible to make mixtures of several different silica, silica gel or zeolite powders and / or different silica sols and / or different potassium and / or cesium phosphate salt powders.

[0114] 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. Preferably, at least one organic adjuvant may also be added during step ii').

[0115] Said organic adjuvant can be chosen from all the additives known to those skilled in the art.

[0116] In the case where at least one organic adjuvant is added in step ii'), 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.

[0117] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0118] Step i') and step ii') can advantageously be carried out in the same equipment, and preferably in a centrifugal planetary mixer.

[0119] In another embodiment, step i') and step ii') can advantageously be implemented in different equipment. In this case, step i') is preferably implemented in a centrifugal planetary mixer, then the suspension obtained at the end of step i') is transferred into a Z-arm type batch mixer in which are added to said suspension, a powder of at least one precipitated silica or silica gel or zeolite and at least one solvent, according to step ii').

[0120] In the case where step i') and step ii') are not carried out in the same equipment, preferably, the source of silica (precipitated silica, silica gel or zeolite with a Si / Al ratio>100), at least one solvent and optionally 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').

[0121] 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').

[0122] Preferably, said mixing step ii') is carried out by kneading, either discontinuously or continuously. 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-shaped 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.

[0123] 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.

[0124] In the case of implementing step ii') in a centrifugal planetary mixer, the rotation speed is advantageously between 300 and 2000 revolutions / minute, preferably between 1500 and 2000 revolutions / minute so as to obtain a paste.

[0125] 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 i') combined with the use of a source of silica (precipitated silica or silica gel, or zeolite with a Si / Al ratio>100) having a reduced size and preferably less than 10 pm, 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.

[0126] Preferably, the following quantities are introduced in steps i') and ii'):

[0127] - 1% to 99% by weight, preferably from 5% to 99% by weight, more 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;

[0128] - 1% to 99% by weight, preferably from 5% to 99% by weight, more preferably from 10% to 95% by weight, and very preferably from 10% to 60% by weight of at least one potassium and / or cesium phosphate salt;

[0129] - 1% to 99% by weight, preferably from 5% to 99% by weight, more preferably from 10% to 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;

[0130] - 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; 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%. According to the second embodiment, said method comprises a step iii') of shaping the paste obtained at the end of step ii') of mixing.

[0131] Preferably, the paste obtained at the end of step ii') is advantageously shaped by extrusion.

[0132] In the case where the shaping of the mixture resulting from step ii') is carried out by extrusion, said step ii') is advantageously carried out in a piston, single-screw or twin-screw extruder.

[0133] In this case, an organic adjuvant may optionally be added in mixing step ii'). The presence of said organic adjuvant facilitates shaping by extrusion. Said organic adjuvant is described above and is introduced in step ii') in the proportions indicated above.

[0134] The extrusion of the mixture, also called "kneaded paste", can be carried out either by extruding directly at 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. They can thus be, for example, cylindrical, multi-lobed, grooved or slotted.

[0135] In the case where the shaping of the mixture resulting from step ii') is carried out by extrusion, the quantity of solvent added in the mixing step ii') 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.

[0136] Preferably, said step iii') of shaping by extrusion is carried out at an extrusion pressure greater than 1 MPa and preferably between 3 MPa and 10 MPa.

[0137] Embodiment 3

[0138] In a third embodiment according to the invention, step a) comprises the following sub-steps: 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; 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 pore volume of the support, preferably between 0.8 and 1.05 times the pore volume of the support, and the phosphate concentration of the solution being preferably between 50 g / L and 2000 g / L.

[0139] The impregnation solution of step i”) is preferably prepared by dissolving in an aqueous or organic phase one or more precursors of phosphate and potassium (K) or cesium (Cs) elements. 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.

[0140] The phosphate precursor(s) may advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, P2O5.

[0141] The phosphate concentration of the solution is preferably between 50 g / L and 2000 g / L.

[0142] The support supplied in step ii”) advantageously comprises an amorphous SiC>2 phase, characterizable by X-ray diffraction. Said support preferably has a specific surface area greater than or equal to 5 m 2 / g, preferably between 5 m 2 / g and 500 m 2 / g, and more preferably between 10 m 2 / g and 450 m 2 / g.

[0143] The pore volume of the support is advantageously between 0.05 cm 3 / g and 1.5 cm 3 / g, preferably between 0.2 cm 3 / g and 1.2 cm 3 / g, and more preferably between 0.25 cm 3 / g and 1.1 cm 3 / g.

[0144] The macroporous volume of the support is advantageously between 0.01 cm 3 / g and 0.5 cm 3 / g, preferably between 0.01 cm 3 / g and 0.4 cm 3 / g, and more preferably between 0.01 cm 3 / g and 0.3 cm 3 / g.

[0145] The manufacture of amorphous silicon oxide type supports and their shaping is well known and taught to those skilled in the art, for example in the Handbook of Porous Solids, Wiley-VCH (Volume 3, pages 1543-1590).

[0146] 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.

[0147] Very advantageously, said support is in the form of balls or extrudates. When the support is in the form of balls, the diameter of the balls is generally between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm. When the support is in the form of an extrudate, the extrudates have a diameter generally 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.

[0148] Preferably, the impregnation step ii”) may be preceded by a heat treatment step carried out at a temperature between 80°C and 550°C.

[0149] Preferably, the impregnation step ii”) may be followed, optionally, by other impregnation steps. The impregnation steps following the first may advantageously be carried out after the maturation step b).

[0150] Step b)

[0151] The preparation process according to the invention comprises a step b) of maturation of 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.

[0152] 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 necessary to limit the appearance of cracks which are detrimental to mechanical strength. At the end of step b), a matured material precursor is obtained.

[0153] Step c)

[0154] According to an essential step of 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 very preferably between 800°C and 900°C. Step c) is carried out for a period advantageously between 1 hour and 12 hours, preferably between 1 hour and 4 hours. This step is essential for the formation of the cristobalite and / or tridymite crystallographic phases. This step also makes it possible to eliminate the organic additives used in order to facilitate the shaping of the material.

[0155] Said calcination step c) is advantageously carried out under a gas flow comprising oxygen, for example preferably the matured material precursor 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.

[0156] Step d)

[0157] According to step d) of the preparation process, the calcined material obtained at the end of step c) is brought into contact with at least one second phosphate precursor, and at least one second potassium and / or cesium precursor to obtain a second material precursor.

[0158] Advantageously, step d) comprises the following sub-steps: d1) a liquid solution in aqueous or organic phase is prepared comprising at least one second phosphate precursor, and at least one second potassium and / or cesium precursor, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C; d2) the solution prepared in step d1) 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 pore volume of the calcined material obtained at the end of step c); d3) optionally, a step of maturing the second material precursor obtained at the end of step d2), d4) optionally, a step of drying the second matured material precursor obtained at the end of step d3).

[0159] Preferably, the phosphate concentration of the solution supplied in step d1) is between either 50 g / L and 2000 g / L.

[0160] The impregnation solution of step d1) is preferably prepared by dissolving in an aqueous or organic phase one or more precursors of phosphate and potassium (K) or cesium (Cs) elements. 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. The phosphate precursor(s) can advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, P2O5.

[0161] The phosphate concentration of the solution is preferably between 50 g / L and 2000 g / L.

[0162] 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 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.

[0163] 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 necessary to limit the appearance of cracks which are detrimental to mechanical resistance.

[0164] 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 for a duration between 0.5 hours and 5 hours. Longer durations are not excluded, but do not necessarily provide an improvement.

[0165] Preferably, the impregnation step d) may be followed, optionally, by other impregnation steps.

[0166] Step e)

[0167] According to the method for preparing the material, 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 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.

[0168] 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

[0169] % volume of oxygen.

[0170] At the end of step e), the material according to the invention is obtained.

[0171] Transformation process

[0172] The material according to the invention can advantageously be used as a catalyst in a process for dehydrating hydroxypropanoic acid and its derivatives.

[0173] 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 -1, preferably between 0.02 and 50 h -1 , more preferably between 0.03 and 30 h -1 and very preferably between 0.05 and 20 h -1 .

[0174] Said method makes it possible to selectively obtain a mixture of products comprising acrylic acid.

[0175] When dehydrating hydroxypropanoic acid and its derivatives to acrylic acid, a mixture of different products, called by-products, is obtained, including propanoic acid, carbon monoxide, carbon dioxide, acetaldehyde, heavy compounds containing more than 3 carbon atoms.

[0176] Said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0177] Said process is preferably operated continuously, in a fixed bed, preferably at a pressure adjusted so that the products and the reactants are in the gas phase, the feedstock being injected into the process preferably in the liquid phase.

[0178] Charge

[0179] 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.

[0180] Said feedstock may also include 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.

[0181] 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.

[0182] 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.

[0183] The sum of the contents of hydroxypropanoic acid and its derivatives, water, organic solvent and any impurities represents 100% by weight of the charge.

[0184] The main products obtained by the said process are hydroxypropanoic acids and its unconverted derivatives, acrylic acid resulting from the dehydration reaction.

[0185] The examples below illustrate the invention without limiting its scope.

[0186] Examples

[0187] In order to exemplify the invention, several methods of preparing materials are described. The contents are expressed in mass percentages.

[0188] The examples below illustrate the invention without limiting its scope. of materials A based on embodiment 1 in of silica

[0189] Precipitated silica powder (Siliaflash P60 40-63 pm; Silicycle) (38%), colloidal silica sol (36%), potassium phosphate (KPO3, Aldrich) (26%) and Méthocel™ (K15M) (3%) are introduced and pre-mixed in a Brabender mixer. Water is added dropwise until a paste is obtained and mixing is continued for 20 minutes. The paste obtained is then extruded on an MTS piston extruder using a cylindrical die with a diameter of 1.6 mm. The extrudates obtained (extrudates A) are then matured for 16 hours at 120°C in a ventilated oven.

[0190] Finally, the A extrudates were subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C were called A1 materials and the extrudates calcined at 800°C were called A2 material precursors.

[0191] Then, 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 of 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 (in accordance with the invention).

[0192] Compositional analysis of the A3 material by X-ray fluorescence gives a weight content of K of 12% by weight and P of 10% by weight. The average equivalent weight content of KPO3 of the A3 material after calcination is 36%.

[0193] Material A1 (not in accordance with the invention) shows in DRX diffraction peaks of the metaphosphate phase KPO3.

[0194] Material A3 (in accordance with the invention) exhibits in DRX diffraction peaks of the metaphosphate phase KPO3 and of the crystalline silica cristobalite.

[0195] Example 2: Preparation of Materials B Based on Embodiment 1 in the Presence of Precipitated Silica Powder

[0196] Precipitated silica powder (Nyasil 20 1.5 pm; Nyacol (53%), colloidal silica sol (32%), potassium phosphate (KPO3, Aldrich) (15%) and Méthocel™ (K15M) (3%) are introduced and pre-mixed in a Brabender mixer. Water is added dropwise until a paste is obtained and mixing is continued for 20 minutes. The paste obtained is then extruded on an MTS piston extruder using a cylindrical die with a diameter of 1.6 mm. The extrudates obtained (extrudates B) are then matured for 16 hours at 120°C in a ventilated oven. Finally, extrudates B are subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The calcined extrudates at 450°C are called B1 materials and the extrudates calcined at 800°C are called B2 material precursors. Tl

[0197] Then, 1.6 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 1.2 g of ammonium hydrogen phosphate (NH^HPC, 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 of 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 (in accordance with the invention).

[0198] Compositional analysis of material B3 by FX gives a weight content of K of 7.3% and of P of 6.4%. The average equivalent weight content of KPO3 of material B3 after calcination is 22%.

[0199] Material B1 (non-compliant) shows in DRX diffraction peaks of the metaphosphate phase KPO3.

[0200] Material B3 (compliant) shows in DRX diffraction peaks of crystalline silica cristobalite as well as diffraction peaks of the metaphosphate phase KPO3.

[0201] Example 3: Preparation of calcined material precursor C based on embodiment 2 in the presence of a colloidal silica sol

[0202] Colloidal silica sol (12.4%), potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (15.2%) ground and sieved to 100 μm are introduced and mixed in the bowl of a Thinky brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, Méthocel™ powder (K15M) (3%), precipitated silica powder (Nyasil20; Nyacol) (72.4%), 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 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. The extrudates obtained (extrudates C) are then matured for 16 hours at 120°C in a ventilated oven.Finally, the C extrudates were subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C were called C1 materials and the extrudates calcined at 800°C were called C2 material precursors.

[0203] Then, 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 of 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 (in accordance with the invention).

[0204] Compositional analysis of the C3 material by FX gives a weight content of 8.8% K and 7.5% P. The average equivalent weight content of KPO3 in the C3 material after calcination is 27%.

[0205] Material C1 (non-compliant) shows in DRX diffraction peaks of the metaphosphate phase KPO3.

[0206] The C3 (compliant) material shows in XRD diffraction peaks of the crystalline silica cristobalite as well as diffraction peaks of the metaphosphate phase KPO3.

[0207] For each of the materials obtained (compliant or non-compliant), the structural characteristics (total pore volume, macropore volume, macropore median diameter, specific surface area, EGG) and the crystalline phases observed by DRX are indicated in Table 1 below.

[0208] Table 1

[0209] Example 4: Preparation of materials D according to embodiment 3 Materials D1 and D3 are prepared from an amorphous silica DO in the form of beads 2 mm in diameter, with a specific surface area measured by mercury porosimetry of 90 m 2 / g and total pore volume of 0.92 cm 3 / g and whose structural properties are indicated in Table 2 below.

[0210] Table 2

[0211] For the preparation of materials D1 and D3, 100 grams of commercial amorphous silica DO are calcined in air in a thin-layer muffle furnace at 450°C for 2 hours.

[0212] 10 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 8.6 g of ammonium hydrogen phosphate (NH^HPC, M= 132 g / mol) are 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 in air.

[0213] 20 grams of the material are calcined in air at 450°C for 4 hours to prepare material D1 (not in accordance with the invention).

[0214] 20 grams of the material are calcined in air at 900°C for 4 hours to prepare the precursor of material D2.

[0215] 3.3 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 2.5 g of ammonium hydrogen phosphate ((NH4)2HPO4, M= 132 g / mol) are first dissolved in 5.3 ml of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to 20 grams of beads of precursor of material D2. The solid is matured at room temperature for 40 minutes 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 (in accordance with the invention). Compositional analysis of material D3 by FX gives a weight content of K of 14% and of P of 12%. The average equivalent weight content of KPO3 of material D3 after calcination is 44.5%.

[0216] Material D1 (non-compliant) shows in DRX diffraction peaks of the metaphosphate phase KPO3.

[0217] The D3 material (compliant) presents in DRX diffraction peaks of the crystalline silica cristobalite as well as diffraction peaks of the metaphosphate phase KPO3.

[0218] The specific surface area (Hg porosimetry) of the D1 material of 46 m 2 / g and its macroporous volume of 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 m 2 / g and the macropore volume of 0.30 ml / g.

[0219] Example 5: Use of materials A1, A3, C1 and C3 as catalyst for the dehydration of lactic acid into acrylic acid in the gas phase

[0220] Materials A1, A3, C1 and C3 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 10 barg (1 MPa). The feedstock contains 12% by weight of lactic acid and 88% by weight of water. The gas (N2) and the liquid feedstock are co-injected and mixed upstream of the reactor head. The evaporation of the feedstock is carried out in the first part of the reactor with the help of a cord. The pph of lactic acid is 0.2 h' 1 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.

[0221] Table 3

[0222] Catalysts A1, A3, C1, C3 convert a lactic acid feedstock into acrylic acid with a carbon yield greater than or equal to 70%. Catalysts A3 and C3 in accordance with the invention have a carbon yield in acrylic acid (AA) higher than those obtained respectively by non-compliant catalysts A1 and C1. After 150 hours under load, unloading of catalysts A3 and C3 is easier than that of catalysts A1 and C1 which are stuck to the walls of the reactor. Catalysts A3 and C3 in accordance with the invention and for which calcination at a temperature greater than 800°C is applied are more stable under operating conditions and after a time under load of 150 hours can be easily unloaded.

[0223] Example 6: Use of materials B1, B3, D1 and D3 as catalyst for the dehydration of lactic acid into acrylic acid in the gas phase

[0224] Materials B1, B3, D1 and D3 are tested with 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 charge, composed of 20% lactic acid and 80% by weight of water, is co-injected with nitrogen at the reactor head. The reactor is located in a furnace using several temperature maintenance zones, a mechanical pressure regulator by barrier, and two gas-liquid separation stages, the first allowing the condensation of the water contained in the reaction effluent and the second separator being located on the residual vapor of the first separator to ensure post-condensation (T=-5°C).The unit gases are analyzed (hot for the total effluent and cold for the separator overhead gases) by gas chromatography. The liquid effluent is weighed and analyzed by high-pressure liquid chromatography (HPLC) on a regular basis.

[0225] 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 flow rate is 5 g / h.

[0226] Conversion

[0227] Lactic acid (LA) conversion is calculated using the following formula: LA Conversion (%) = 100 x ([LA] C charge - [AL] C effluent) / [AL] C charge with [AL] C = carbon concentration in AL in gC / L determined by HPLC.

[0228] The carbon yield in acrylic acid (AA) is determined according to the following formula: AA yield (%) = 100 x [AA]c effluent / [AL]c load

[0229] The results are presented in Table 4 below.

[0230] Table 4

[0231] Catalysts B1, B3, D1, D3 convert a lactic acid feedstock into acrylic acid with a carbon yield greater than 50% 160 hours under load. Catalysts B3 and D3 in accordance with the invention have an acrylic acid (AA) yield higher than those obtained respectively by non-compliant catalysts B1 and D1. When catalysts B1 and D1 are unloaded, the latter are no longer intact and part of the KPO3 is found in the reactor. Catalysts B3 and D3 have an identical appearance to the loaded catalyst after 160 hours under operating conditions.

[0232] Catalysts B3 and D3 in accordance with the invention are therefore more active and stable during the dehydration reaction of lactic acid into acrylic acid than non-compliant catalysts B1 and D1.

Claims

CLAIMS 1. A method 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: a) at least one source of silica is brought into contact with at least one first phosphate precursor and at least one first potassium and / or cesium precursor to obtain a first material precursor; b) the material precursor 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 material precursor; c) the matured material precursor obtained at the end of step b) is calcined at a temperature of 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 brought into contact with at least one second phosphate precursor, and at least one 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. Method according to claim 1, wherein in step a) said first and second phosphate, potassium and / or cesium precursors are supplied in the form of at least one potassium phosphate salt and / or at least one cesium phosphate salt.

3. The method of claim 2, wherein said potassium phosphate salt is selected from KH2PO4, KH2P2O12, KePeO?, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, KePeOis, K8P8O24, K10P10O30, potassium phosphate (tripotassium) (PO4 3 3K + ), alone or in a mixture.

4. Method according to one of claims 2 or 3, in which said cesium phosphate salt is chosen from CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, CS8P8O24, CsPOs, alone or in a mixture.

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

6. Method according to claim 5, in which 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. Preparation process according to any one of claims 1 to 6, in which step a) comprises the following sub-steps: i) at least one powder of precipitated silica, 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. Preparation process according to any one of claims 1 to 6, in which step a) comprises the following sub-steps: 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') a powder of at least one precipitated silica, or a silica gel, or a 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. Preparation process according to claim 1, in which step a) comprises the following sub-steps: i”) a liquid solution in aqueous or organic phase is supplied comprising at least the first phosphate precursor, and at least the first potassium and / or cesium precursor; ii”) said solution obtained at the end of step i”) is impregnated onto a shaped support containing silica.

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

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

12. Method according to any one of claims 9 to 11, wherein said first potassium and / or cesium precursor is chosen from the salts of carbonate M2CO3, nitrate MNO3, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCI, hydroxide MOH, and oxide M2O, with M = K or Cs.

13. A method according to any one of claims 9 to 12, wherein said first phosphate precursor is selected from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PC>4, and P2O5.

14. Method according to any one of claims 9 to 13, in which step d) comprises the following sub-steps: d1) a liquid solution in aqueous or organic phase is prepared comprising at least one second phosphate precursor, and at least one second potassium and / or cesium precursor, at a temperature preferably between 5°C and 80°C, more preferably between 10°C and 70°C; d2) the solution prepared in step d1) 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 pore volume of the calcined material obtained at the end of step c); d3) optionally, a step of maturation of the second precursor of material obtained at the end of step d2), d4) optionally, a step of drying of the second precursor of matured material obtained at the end of step d3).

Images