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

Abstract

The invention relates to a process for preparing a macroporous material based on potassium and / or cesium phosphate salt, and silica in the form of cristobalite and / or tridymite crystals, comprising the following steps: a) at least one source of silica is contacted with at least one phosphate precursor and at least one potassium and / or cesium precursor to obtain a 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 between 800°C and 1200°C to obtain said material.

Description

Title of the invention: Process for preparing a material comprising silica in the crystalline form of cristobalite and / or tridymite Field of invention

[0001] The invention relates to a novel process for preparing a 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. State of the art

[0002] 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 sufficiently resistant to be implemented in catalytic processes. Indeed, from its manufacture to its implementation, the catalyst comprising such a support is confronted with numerous stages which can impact its physical integrity. In particular, it must be resistant to crushing, attrition and pressure variations linked to the operating conditions of the catalytic reactor in which it is implemented. Thus, there is a constant need for catalysts having improved mechanical and physical properties.

[0003] Patent application WO2003 / 026795 discloses a method for producing a catalyst comprising a silica support which consists in 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 consists in 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.

[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 mechanical mixing, using a planetary mill, of an amorphous fused silica (Fused silica) 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 + SiO2) mixture with a ratio mass 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 pm. The silica contained in the final material is in its amorphous form (see example 8).

[0005] However, none of the prior art documents discloses a particular preparation process for obtaining 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. Objects of the invention

[0006] The subject of the present invention is 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 phosphate precursor and at least one potassium and / or cesium precursor to obtain a material precursor;

[0008] 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;

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

[0010] According to one or more embodiments, said phosphate, potassium and / or cesium precursors in step a) are supplied in the form of at least one potassium phosphate salt and / or at least one cesium phosphate salt.

[0011] According to one or more embodiments, said potassium phosphate salt is chosen from: KH2PO4, KH2P20i2, K6P6O7, K3H2P3Oi0, K4H2P40i3, K3P3O9, K4P4O,2, K6 P60i8, K8P8O24, KioPio03o, potassium phosphate (tripotassium) (PO43,3K+), alone or as a mixture.

[0012] According to one or more embodiments, said cesium phosphate salt is chosen from: CsH2PO4, Cs2H2P3Oi0, Cs4H2P40i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, (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 qm.

[0015] According to one or more embodiments, step a) comprises the sub-steps following:

[0016] i) at least one silica 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;

[0017] ii) the mixture obtained at the end of step i) is shaped.

[0018] According to one or more embodiments, step a) comprises the following sub-steps:

[0019] i') at least one colloidal silica sol is mixed with at least one powder of at least minus a potassium and / or cesium phosphate salt to obtain a suspension;

[0020] 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;

[0021] iii') the dough obtained at the end of step ii') is shaped.

[0022] According to one or more embodiments, step a) comprises the following sub-steps:

[0023] i”) a liquid solution is supplied in aqueous phase or organic comprising at least one phosphate precursor, and at least one potassium and / or cesium precursor;

[0024] ii”) said solution obtained at the end of step i”) is impregnated onto a shaped support containing silica.

[0025] According to one or more embodiments, the preparation temperature of step i”) is between 5°C and 80°C.

[0026] 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.

[0027] According to one or more embodiments, said potassium and / or cesium precursor is chosen from the salts of carbonate M2CO3, nitrate MN03, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCI, hydroxide MOH, and oxide M2O, with M = K or Cs.

[0028] According to one or more embodiments, said phosphate precursor is chosen from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, and P2O5.

[0029] According to one or more embodiments, the support supplied in step ii”) is in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates. Detailed description 1. Definitions

[0030] 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.

[0031] 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 pressure value range can be combined with a more preferred temperature value range.

[0032] By “macropores” is meant pores with an opening greater than 50 nm.

[0033] By “mesopores” is meant pores whose opening is between 2 nm and 50 nm, inclusive.

[0034] 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.

[0035] In order to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the sample minus the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the same sample for a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0036] The volume of macropores and mesopores is measured by mercury intrusion porosimetry according to ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°. The value at which mercury fills all intergranular voids is set at 0.2 MPa, and it is considered that beyond this value, mercury penetrates into the pores of the sample.

[0037] 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.

[0038] The mesoporous volume of the material according to the invention is defined as being the cumulative volume of mercury introduced at a pressure of between 30 MPa and 400 MPa, corresponding to the volume contained in the pores with an apparent diameter of between 2 and 50 nm.

[0039] The median diameter of the macropores (Dmacro in nm) is also defined as being a diameter such that all pores smaller than this diameter constitute 50% of the macropore volume, measured by mercury porosimetry.

[0040] 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®.

[0041] In the remainder of the text, transmission electron microscopy (TEM) is the method used to characterize the materials obtained according to the invention. This technique makes it possible to obtain information on the chemical composition, the morphology and to measure the size of the grains or crystals constituting the material. For this purpose, an electron microscope (of the JEM F200 JEOL or JEOL JEM 2100F type) equipped with an energy dispersive spectrometer (EDS) is used. The EDS detector must allow the detection of light elements. The association of these two tools, TEM and EDS, makes it possible to combine imaging and local chemical analysis with good spatial resolution.

[0042] Throughout the rest of the text, the term “mechanical resistance to lateral crushing” means the mechanical resistance of the material according to the invention determined by the grain-to-grain crushing (EGG) test. This is a standardized test (ASTM D4179-01 standard) which consists of subjecting a material in the form of a millimetric object, such as a ball, a pellet or an extrudate, to a compressive force generating rupture. The analysis is repeated on a certain number of solids taken individually and typically on a number of solids between 10 and 200. The average of the measured lateral breaking forces constitutes the average EGG which is expressed in the case of granules in units of force (N), and in the case of extrudates in units of force per unit of length (daN / mm or decaNewton per millimeter of extrudate length).

[0043] In the remainder of the text, the grain size or particle size distribution of the constituents of the materials obtained according to the invention is measured by the laser scattering particle size distribution technique. This indirect measurement technique makes it possible to determine the particle size distribution (scale from micron to millimeter). This analysis method uses the principle of diffusion (Mie theory) and / or light diffraction (Fraunhoffer theory and Mie theory). The particles illuminated by the laser light deflect the light from its main axis. The quantity of deflected light and the size of the deflection angle make it possible to accurately measure the particle size. The powder is conveyed either by a solvent (water, isopropanol) or by air before passing in front of the laser beam: two routes are thus distinguished: the wet route and the dry route.

[0044] The wet method allows the characterization of dispersions (elementary particle size after dispersion) or suspended solids ("aggregated" particle size). The particles measured are in the range 0.02 microns to 2000 microns.

[0045] Dry process granulometry makes it possible to characterize powders whose initial aggregation is not destroyed. The measurement range extends from 0.2 microns to 2000 microns. In the present invention, the dry method is used to measure the grain size of the constituents of the material of the invention. 2. Detailed Description Material

[0046] The preparation process according to the invention makes it possible to obtain 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.

[0047] Indeed, the Applicant has surprisingly discovered that such a particular preparation process makes it possible to obtain a material that is stable over time while exhibiting satisfactory results in terms of conversion when the latter is used as a catalyst for the dehydration of hydroxypropanoic acid and its derivatives. The macroporous structure of the material and the particular crystallinity of the silica included in this material can be obtained by carrying out a specific preparation process 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.

[0048] 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 diagram is obtained by radiocrystallographic analysis using a diffractometer using the conventional powder method with the Kal radiation of 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.

[0049] 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.

[0050] Advantageously, said potassium phosphate and / or cesium phosphate salt is potassium metaphosphate (KPO3) and / or cesium metaphosphate (CsPO3).

[0051] Advantageously, said material has a mass ratio MPO3 / (MPO3+SiO2) between 13 and 50, preferably between 15 and 45, and even more preferably between 17 and 40, even more preferably between 20 and 40 with M being potassium and / or cesium (M = K and / or Cs). Preferably M is potassium.

[0052] Preferably, said material has a total pore volume of between 0.01 cm3 / g and 0.6 cmVg, more preferably between 0.05 cmVg and 0.5 cmVg, even more preferably between 0.06 cmVg and 0.4 cmVg, and even more preferably between 0.06 cmVg and 0.39 cmVg.

[0053] Preferably, said material has a macroporous volume of between 0.01 cmVg and 0.6 cmVg, more preferably of between 0.05 cmVg and 0.5 cmVg, even more preferably of between 0.06 cmVg and 0.4 cmVg, and even more preferably of between 0.06 cmVg and 0.39 cmVg.

[0054] 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%.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Said material is advantageously in the form of beads, extrudates, pellets, or irregular and non-spherical agglomerates. Preparation process

[0061] An object according to the 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 form crystalline cristobalite and / or tridymite, comprising at least the following steps:

[0062] a) at least one source of silica is brought into contact with at least one phosphate precursor and at least one potassium and / or cesium precursor to obtain a material precursor;

[0063] 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;

[0064] c) the matured material precursor obtained at the end of step b) is calcined at a temperature between 800°C and 1200°C to obtain said material.

[0065] All of steps a) to c) are detailed below. Step a)

[0066] Step a) can be carried out according to several embodiments. Embodiment 1

[0067] In a first embodiment according to the invention, step a) comprises the following sub-steps:

[0068] 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;

[0069] ii) the mixture obtained at the end of step i) is shaped.

[0070] 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.

[0071] 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.

[0072] Preferably, the 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, more preferably less than 1 pm.

[0073] Preferably, the colloidal silica sols are chosen, without being restrictive, 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 a mixture.

[0074] 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 the residual sodium. In order to avoid this step, the use of low-sodium colloidal silica sols is preferable. For example, Ludox AS40 stabilized with an ammonium counterion, or Nyacol 2034DI, Nalco 1034A, Ultra-Sol 7H or NexSil 20A may be mentioned.

[0075] Said source(s) of silica(s) used in the process according to the present invention are advantageously synthetic amorphous silicas or zeolites with Si / Al ratios >100.

[0076] 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.

[0077] Said potassium phosphate salt(s) are advantageously chosen from KH2 PO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, k6p6o18, k8p8o24, k10 P10O30, potassium phosphate (tripotassium) (PO43,3K+), alone or as a mixture. Preferably, the preferred potassium phosphate salt is chosen from potassium phosphate (tripotassium) (PO43,3K+) and KH2PO4, alone or as a mixture.

[0078] Said cesium phosphate salt(s) are advantageously chosen from: CsH2 PO4, Cs2H2P3Oio, Cs4H2P40i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, CsPO3, alone or as a mixture. Preferably the preferred cesium phosphate salt is CsH2PO4.

[0079] Preferably, said potassium phosphate or cesium phosphate salt(s) is (are) chosen from potassium phosphate (tripotassium) (PO43,3K+), KH2 PO4, CsH2PO4 in their hydrated or non-hydrated form.

[0080] Preferably, at least one organic adjuvant is also mixed during step i).

[0081] 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.

[0082] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0083] Said solvent is advantageously chosen from water, alcohols, in particular ethanol, and amines. Preferably, said solvent is water.

[0084] Within the scope of the invention, it is entirely possible to make mixtures of several different precipitated silica powders, silica gel, or zeolite and / or different silica sols and / or different potassium or cesium phosphate powders.

[0085] The order in which the mixing of the powders of at least the silica sources, of at least one powder of potassium and / or cesium phosphate salt and optionally of 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.

[0086] The mixing of said powders and said solvent can advantageously be carried out in a single operation.

[0087] The additions 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.

[0088] Said potassium phosphate and / or cesium phosphate salt(s) used in step i) are advantageously in the form of powders.

[0089] 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 μm.

[0090] 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.

[0091] In a particularly preferred embodiment, the use of a silica source used in step i) has a grain size of less than 60 μm, and preferably less than 25 μm, more preferably less than 5 μm, very preferably less than 2 μm, 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 μm, allows a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0092] 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.

[0093] 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 powders of potassium and / or cesium phosphate. Contact with said solvent results in a mixture which is then advantageously kneaded.

[0094] 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.

[0095] Preferably, said mixing step i) is carried out by kneading, discontinuously (“batch” according to English terminology) or continuously.

[0096] 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.

[0097] 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.

[0098] Preferably, the following quantities are introduced into mixing step i) of the process according to the invention:

[0099] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and very preferably from 15% to 65% by weight of at least one precipitated silica, silica gel or zeolite with a Si / Al ratio>100;

[0100] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and very preferably from 5% to 50% by weight of at least one colloidal silica sol;

[0101] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and very preferably from 20% to 75% by weight of at least one potassium or cesium phosphate salt powder;

[0102] - 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;

[0103] 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%.

[0104] 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.

[0105] 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 mixing step i). The presence of said organic adjuvant facilitates shaping by extrusion. Said organic adjuvant is described above and is introduced in step i) in the proportions indicated above.

[0106] In the case where said preparation method 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.

[0107] 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.

[0108] 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. Embodiment 2

[0109] In a second embodiment according to the invention, step a) comprises the following sub-steps:

[0110] i') at least one colloidal silica sol is mixed with at least one powder of at least minus a potassium and / or cesium phosphate salt to obtain a suspension;

[0111] 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 i');

[0112] iii') the dough obtained at the end of step ii') is shaped.

[0113] 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.

[0114] A solvent, preferably water, may advantageously be added in step i').

[0115] Preferably, colloidal silicas or silica sols are chosen, without being restrictive, among the following commercial sources and come in the form liquid: 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.

[0116] Said source(s) of colloidal silica sol used in the process according to the present invention are advantageously synthetic amorphous silicas.

[0117] 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.

[0118] Said potassium phosphate salt(s) are advantageously chosen from KH2 PO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, k6p6o18, k8p8o24, k10 P10O30, potassium phosphate (tripotassium) (PO43,3K+), alone or as a mixture. Preferably the preferred potassium phosphate salt is KH2PO4,

[0119] Said cesium phosphate salt(s) are advantageously chosen from CsH2PO4, Cs2H2P3Oio, Cs4H2P40i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, CsPO3, alone or as a mixture. Preferably the preferred cesium phosphate salt is CsH2PO4.

[0120] Preferably, said potassium phosphate or cesium phosphate salt(s) is (are) chosen from KH2PO4, CsH2PO4 in their hydrated or non-hydrated form.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] The additions of powders, colloidal silica sol and solvent can also advantageously be alternated.

[0126] 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').

[0127] 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.

[0128] 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.

[0129] The size of the grains of precipitated silica or silica gel or zeolite with a Si / Al ratio >100 is advantageously measured by dry laser granulometry.

[0130] Preferably, the precipitated silica or silica gel is in amorphous form.

[0131] Within the scope of the invention, it is entirely possible to make mixtures of several different precipitated silica powders, silica gel, or zeolite and / or different silica sols and / or different potassium and / or cesium phosphate salt powders.

[0132] 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.

[0133] Preferably, at least one organic adjuvant may also be added during step ii').

[0134] Said organic adjuvant can be chosen from all the additives known to those skilled in the art.

[0135] 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.

[0136] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0137] Step i') and step ii') can advantageously be carried out in the same equipment and preferably in a centrifugal planetary mixer.

[0138] 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 and 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 and at least one solvent are added to said suspension, according to step ii').

[0139] 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').

[0140] 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').

[0141] Preferably, said mixing step ii') is carried out by kneading, discontinuously or continuously.

[0142] 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-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.

[0143] 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.

[0144] 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.

[0145] 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, even 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.

[0146] Preferably, the following quantities are introduced in steps i') and ii'):

[0147] - 1% to 99% by weight, preferably from 5% to 99% by weight, preferably from 5% to 95% by weight, and very preferably from 5% to 40% by weight and even more preferred from 5 to 20% by weight of at least one colloidal silica sol;

[0148] - 1% to 99% by weight, preferably 5% to 99% by weight, preferably 10% at 95% by weight, and very preferably from 10% to 60% by weight of at least one potassium and / or cesium phosphate salt;

[0149] - 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;

[0150] - 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;

[0151] 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%.

[0152] According to the second embodiment, said method comprises a step iii') of shaping the dough obtained at the end of step ii') of mixing.

[0153] Preferably, the paste obtained at the end of step ii') is advantageously shaped by extrusion.

[0154] 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.

[0155] 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.

[0156] The extrusion of the mixture, also called "kneaded paste", can be carried out either by extruding directly at the end of a continuous mixer of the twin-screw type, for example, or by connecting one or more batch mixers to an extruder. The geometry of the die, which gives the extrudates their shape, can be chosen from dies well known to those skilled in the art. They can thus be, for example, cylindrical, multi-lobed, grooved or slotted.

[0157] 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.

[0158] 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. Embodiment 3

[0159] In a third embodiment according to the invention, step a) comprises the following sub-steps:

[0160] i”) a liquid solution is supplied in aqueous or organic phase 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;

[0161] 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.

[0162] 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) element. The impregnation solution can advantageously be prepared by mixing phosphorus and alkali metal elements introduced independently. In this case, the alkali metal precursor M chosen from K or Cs is chosen for example from one or more of the salts of carbonate M2CO3, nitrate MNO3, sulfate, formate HCOOM, acetate CH2COOM, citrate, lactate, chloride MCI, hydroxide MOH, oxide M2O.

[0163] The phosphate precursor(s) may advantageously be chosen, for example, from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, P2O5.

[0164] The phosphate concentration of the solution is preferably between 50 g / L and 2000 g / L.

[0165] 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 more preferably between 10 m2 / g and 450 m2 / g.

[0166] The pore volume of the support is advantageously between 0.05 cmVg and 1.5 cmVg, preferably between 0.2 cmVg and 1.2 cmVg, and more preferably between 0.25 cmVg and 1.1 cmVg.

[0167] 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 more preferably between 0.01 cmVg and 0.3 cmVg.

[0168] 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).

[0169] 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.

[0170] Very advantageously, said support is in the form of balls or extrudates.

[0171] 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. 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.

[0172] Preferably, the impregnation step ii”) may be preceded by a heat treatment step carried out at a temperature between 80°C and 550°C.

[0173] 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). Step b)

[0174] 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.

[0175] 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. Step c)

[0176] 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.

[0177] 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. Transformation process

[0178] The preparation process according to the invention makes it possible to obtain a macroporous material containing silica in the crystalline form of cristobalite and / or tridymite, said material being advantageously able to be used as a catalyst in a process for dehydrating hydroxypropanoic acid and its derivatives.

[0179] The process for dehydrating hydroxypropanoic acid and its derivatives operates in the presence of the material prepared according to the invention, which is advantageously used as a catalyst at a temperature of between 180°C and 450°C, preferably between 190°C and 430°C, very preferably between 250°C and 420°C and very preferably between 270°C and 420°C, at a pressure of between 0.1 MPa and 12 MPa, preferably between 0.11 MPa and 10 MPa, preferably between 0.13 MPa and 9 MPa and very preferably between 0.15 MPa and 8 MPa, and at a feedstock mass flow rate to material mass ratio of between 0.01 h 1 and 100 h *, preferably between 0.02 and 50 h 1, more preferably between 0.03 and 30 h 1 and very preferably 0.05 and 20 h 1.

[0180] Said method makes it possible to selectively obtain a mixture of products comprising acrylic acid.

[0181] 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.

[0182] Said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0183] Said process is preferably operated continuously, in a fixed bed, preferably at a pressure adjusted so that the products and reactants are in the gas phase, the feedstock being injected into the process preferentially in the liquid phase. Charge

[0184] 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 the acid 2-hydroxypropanoic acid and 3-hydroxypropanoic acid. Preferably, said filler comprises 2-hydroxypropanoic acid. Said filler 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.

[0185] Said feedstock may also comprise impurities linked, in particular, to the processes for obtaining hydroxypropanoic acid and its derivatives such as fermentation. The impurity content is preferably less than 10% of the weight of said feedstock. The hydroxypropanoic acid(s) and its derivatives included in said feedstock may be of any origin, chemical, petrochemical or biosourced.

[0186] 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.

[0187] 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.

[0188] The sum of the contents of hydroxypropanoic acid and its derivatives, water, organic solvent and possible impurities represents 100% by weight of the charge.

[0189] The main products obtained by said process are hydroxypropanoic acids and its unconverted derivatives, acrylic acid resulting from the dehydration reaction.

[0190] The examples below illustrate the invention without limiting its scope. Examples

[0191] In order to exemplify the invention, several methods of preparing materials are described. The contents are expressed in mass percentages.

[0192] Example 1: Preparation of extrudates A based on embodiment 1 in the presence of a precipitated silica powder

[0193] A precipitated silica powder (Nyasil20; Nyacol) (32.5%), a colloidal silica sol (32.5%), potassium phosphate (KPO3, Aldrich) (35%) and Méthocel™ (K15M) (3%) 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 obtained (extrudates A) are then matured for 16 hours at 120°C in a ventilated oven. Finally, the extrudates A are subjected to different calcination temperatures (650°C and 850°C) in a muffle furnace for 3 hours. Extruded products calcined at 650°C are called Al materials (not in accordance with the invention) and the extradited materials calcined at 850°C are called A2 materials (in accordance with the invention) [see Table 1 below].

[0194] Example 2: Preparation of extrudates B based on embodiment 2 in the presence of a colloidal silica sol

[0195] A colloidal silica sol (9.48%), a potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (37%) ground and sieved to 100 μm are introduced and mixed in the tank of a Thinky brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. Then, the suspension obtained, a Méthocel™ (K15M) powder (3%) and a precipitated silica powder (Nyasil20; Nyacol) (53.52%) 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 obtained (extrudates B) are matured for 16 hours at 120°C in a ventilated oven. Finally, the extrudates B are subjected to different calcination temperatures (700°C, 850°C and 1000°C) in a muffle furnace for 3 hours.The extrudates calcined at 700°C are called B1 materials (not in accordance with the invention), the extrudates calcined at 850°C are called B2 materials (in accordance with the invention) and the extrudates calcined at 1000°C are called B3 materials (in accordance with the invention) [see Table 1 below].

[0196] Example 3: Preparation of extrudates C based on embodiment 2 in the presence of a zeolite powder

[0197] A colloidal silica sol (31.5%), a potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (37%) ground and sieved to 100 μm are introduced and mixed in the tank of a Thinky brand centrifugal planetary mixer. The rotation speed is set at 1500 rpm for 30 seconds. The suspension obtained, a methocel powder (K15M) (3%), a ZSM-5 zeolite powder (CBV28014; Zeolyst) (31.5%), 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 matured for 16 hours at 120°C in a ventilated oven. Finally, the extrudates obtained (extrudates C) are subjected to different calcination temperatures (450°C and 900°C) in a muffle furnace for 3 hours.Extrudates calcined at 450°C are called Cl materials (not in accordance with the invention) and extrudates calcined at 900°C are called C2 materials (in accordance with the invention) [see Table 1 below].

[0198] For each of the materials obtained (compliant or non-compliant), the structural characteristics (total pore volume, macroporous volume, median diameter macroporous, specific surface area, EGG) and the crystalline phases observed by XRD are indicated in Table 1 below. T calcination (°C) V total (cmVg ) V macro (cmVg) Dmacro (nm) S (m2 / g) EGG (daN / mm) DRX Al (non-conform e) 650 0.36 0.15 247 20 0.62 Amorphous silica + monoclinic KPO3 A2 (conform me) 850 0.33 0.31 4388 2 1.08 KPO3 of monoclinic structure + SiO2 of cristobalite type Té-tragonal B1 (non-conform e) 700 0.21 0.13 174 7 2.55 Amorphous silica + monoclinic KPO3 B2 (conform me) 850 0.17 0.16 5635 1 3 KPO3 of monoclinic structure + SiO2 of cristobalite type Té-tragonal B3 (conform me) 1000 0.06 0.06 5742 <1 1.76 Monoclinic structure KPO3 + cristobalite-type SiO2 Té-tragonal + triclinic tridymite-type SiO2 Cl (non-conform me) 450 0.17 0.16 430 25 2.14 ZSM-5 type zeolite + monoclinic KPO3 C2 (conform me) 900 0.02 0.02 2352 <1 2.69 Monoclinic structure KPO3 + cristobalite-type SiO2 Té-tragonal + triclinic tridymite-type SiO2

[0200] Example 4: Preparation of materials D according to embodiment 3

[0201] Materials DI and D2 are prepared from an amorphous silica D0 in the form of 2 mm diameter beads, with a specific surface area measured by mercury porosimetry of 93 m2 / g and a total pore volume of 0.92 cmVg and whose structural properties are indicated in Table 2 below.

[0202] 36.3 grams of potassium hydrogen phosphate (K2HPO4, M= 174 g / mol) and 28.8 g of ammonium hydrogen phosphate ((NH4)2HPO4, M= 132 g / mol) are dissolved in 90 ml of distilled water at room temperature. After complete dissolution, the mixture is added dropwise to the SiO2 beads. The solid obtained is matured at room temperature for 40 minutes and then dried for 10 hours at 120°C in air. 30 grams of the material are calcined in air at 450°C for 4 hours to prepare the DI material. 30 grams of the material are calcined in air at 800°C for 4 hours to prepare the D2 material.

[0203] Compositional analysis by X-ray fluorescence (FX) gives for each material (DI and D2) a weight content of K of 8.8% and of P of 7.5%. The equivalent weight content of KPO3 of the materials obtained after calcination is 33% by weight relative to the total weight of each material respectively (DI and D2).

[0204] The DI material (non-compliant) exhibits in XRD diffraction peaks of the metaphosphate phase KPO3. The D2 material (compliant) exhibits in XRD diffraction peaks of the crystalline silica cristobalite and tridymite as well as diffraction peaks of the metaphosphate phase KPO3.

[0205] The specific surface area (measured by Hg porosimetry) of the DI material is 46 m2 / g and its macroporous volume is 0.05 cmVg.

[0206] The specific surface area of ​​material D2 (measured by Hg porosimetry) is 4 m2 / g and the macroporous volume is 0.44 cmVg.

[0207] For each of the materials obtained (compliant or non-compliant), the structural characteristics (total pore volume, macroporous volume, specific surface area) and the crystalline phases observed by DRX are indicated in Table 2 below.

[0208] [Tables2] % wt kpo3 T calcination (°C) V total (cmVg) V macro (cmVg) sHg (m2 / g) DRX D0 0 - 0.92 0.07 93 Amorphous SiO2 DI (non-compliant) 33 450 0.49 0.05 46 Monoclinic KPO3 D2 (compliant) 33 800 0.46 0.44 2 Monoclinic KPO3, tetragonal cristobalite-type SiO2, traces triclinic tridymite

[0209] Example 5: Use of catalysts Al. A2. CL C2 for the dehydration of lactic acid into acrylic acid in the gas phase

[0210] The catalysts Al, A2, Cl and C2 are tested with an Avantium® unit comprising 16 reactors, with an internal diameter of 2 mm and a length of 560 mm. The reaction is carried out in the gas phase, at 375°C and at a total pressure of 1000 mbar (1 MPa). The feed contains 12% by weight of lactic acid and 88% by weight of water. The gas (N2) and the liquid feed are co-injected and mixed upstream of the reactor head. The evaporation of the feed is carried out in the first part of the reactor with the help of a cord. The pph of lactic acid is 0.2 h 1 and with a mass of catalyst loaded of approximately 190 mg. At the outlet of the unit, all the products are analyzed by gas chromatography. The results are presented in Table 3 below.

[0211] [T ableaux3 ] Catalyst mpo3 / (MPO3+Si 02) Calcination T (°C) Bed height (mm) m catalyst (mg) Catalyst stability after test Al (non-compliant) 35 650 140 188 no A2 (compliant) 35 850 132 190 yes Cl (non-compliant) 33 450 96 187 no C2 (compliant) 33 900 91 188 yes

[0212] Catalysts A1, A2, C1 and C2 convert a lactic acid feedstock into acrylic acid. After 150 hours under load, unloading of catalysts A2 and C2 is easier than that of catalysts A1 and C1 which are stuck to the reactor walls. The shaped catalysts for which calcination at a temperature above 800°C is applied are more stable under operating conditions and after a time under load of 200 hours, can be easily unloaded.

[0213] Example 6: Use of catalysts BL B2. DI and D2 for the dehydration of lactic acid into acrylic acid in the gas phase

[0214] The catalysts 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 top of the reactor. The reactor is located in a furnace using several temperature maintenance zones, a mechanical pressure regulator per 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).

[0215] The gases from the unit 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.

[0216] The reaction is carried out at 365°C at a total pressure of 12 bara (1.2 MPa). The flow rate gas flow rate is 8 g / h of nitrogen and the liquid feed rate is 5 g / h. Conversion

[0217] The conversion of lactic acid (LA) is calculated according to the following formula:

[0218] LA conversion (%) = 100 x ([LA]C charge - [LA]C effluent) / [LA]C charge

[0219] with [AL]C = carbon concentration in AL in gC / L determined by HPLC.

[0220] The results are presented in Table 4 below.

[0221] [Tables4] Catalyst mpo3 / (MPO3+Si 02) Calcination temperature (°C) Test duration (h) AL conversion (%) Catalyst stability after test B1 (non-compliant) 34,700 160 99.3 no B2 (compliant) 34,850 160 98 yes Dl (non-compliant) 33,450 160 99.3 no D2 (compliant) 33,900 160 97 yes

[0222] When unloading catalysts B1 and D1, the catalyst is no longer intact and part of the KPO3 is found in the reactor. Catalysts B2 and D2 are identical in appearance to the loaded catalyst after 160 hours of testing under operating conditions.

[0223] The catalysts in accordance with the invention are therefore active and stable during the dehydration reaction of lactic acid into acrylic acid.

Claims

Claims

1. 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 phosphate precursor and at least one potassium and / or cesium precursor to obtain a 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 said material.

2. A method according to claim 1, wherein in step a) said 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. A method according to claim 2, wherein said potassium phosphate salt is selected from: KH2PO4, KH2P20i2, K6P6O7, K3H2P3Oi0, K4 H2P4On, K3P3O9, K^Ob, KgPgOig, K8P8O24, KiqPio03o, potassium phosphate (tripotassium) (PO43,3K+), alone or in mixture.

4. A method according to one of claims 2 or 3, wherein said cesium phosphate salt is selected from: CsH2PO4, Cs2H2P3Oi0, Cs4H2P4O i3, Cs3P3O9, Cs4P40i2, Cs6P60i8, Cs8P8O24, (CsPO3), alone or as 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. A method according to claim 5, wherein 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 qm.

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 precipitated silica powder, silica gel, or zeolite with a Si / Al ratio >100, at least one silica sol colloidal and at least one powder of at least one potassium and / or cesium phosphate salt 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 comprising at least one phosphate precursor, and at least one potassium and / or cesium precursor, is supplied, ii”) said solution obtained at the end of step i”) is impregnated 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. 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. A method according to any one of claims 9 to 11, wherein said potassium and / or cesium precursor is selected from the salts of carbonate M2CO3, nitrate MN03, 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 phosphate precursor is selected from H3PO4, (NH4)H2PO4, (NH4)2HPO4, (NH4)PO4, and P2O5.

14. A method according to any one of claims 9 to 13, wherein the support supplied in step ii”) is in the form of beads, extrudates, pellets, or irregular, non-spherical agglomerates.