WO2025019286A1

WO2025019286A1 - Material comprising a silica in the cristobalite and/or tridymite crystalline form

Info

Publication number: WO2025019286A1
Application number: PCT/US2024/037716
Authority: WO
Inventors: Amandine Cabiac; Romain CHENEVIER; Vincent Coupard; Sandrine LAZARE; Lucile OLIVIER; Souad RAFIK-CLEMENT
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2023-07-18
Filing date: 2024-07-12
Publication date: 2025-01-23
Anticipated expiration: 2026-01-18

Abstract

Macroporous material based on silica and on at least one potassium phosphate salt and/or on at least one caesium phosphate salt, characterized in that the silica is provided at least partially in the cristobalite and/or tridymite crystalline form. Such material being useful as a catalyst particularly in reactions relating to the dehydration of hydroxy acids such as a lactic acid.

Description

MATERIAL COMPRISING A SILICA IN THE CRISTOBALITE AND/OR

TRIDYMITE CRYSTALLINE FORM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

63/514, 168, filed July 18, 2023, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates to a novel macroporous material containing silica in the cristobalite and/or tridymite crystalline form. The material can be used advantageously as support or as catalyst in catalytic processes.

STATE OF THE ART

[0003] Silica is an advantageous compound to be used as catalyst support; it cannot be extruded like other materials in a conventional item of extrusion equipment to give products which are sufficiently resistant in order to be employed in catalytic processes. This is because, from its manufacture to its use, the catalyst comprising such a support is confronted with numerous stages which can have an impact on its physical integrity. It must in particular be resistant to crushing, to attrition and to pressure variations linked to the operating conditions of the catalytic reactor in which it is employed. Thus, there exists a continual need for catalysts having improved mechanical and physical properties.

[0004] Patent Application WO 2003/026795 discloses a process for the production of a catalyst comprising a silica support which consists in impregnating a silica constituent with a catalytic metal by means of an aqueous alkaline bath before drying, in order to improve the mechanical strength thereof. More particularly, the preparation process consists in forming and in washing a silica constituent, of silica gel or co-gel type, for example a silica-zirconia co-gel. Subsequently, the washed silica constituent is brought into contact with an alkaline bath in order to impregnate the catalytic metal, of caesium type, and to form an activated silica constituent. The activated silica constituent is subsequently dried in order to form the catalyst without a calcination stage.

[0005] Patent Application WO 17/040383 discloses a plurality of catalysts comprising at least a mixture of alkaline phosphates, including some of formula M_xPO_y (with M = K or Cs), and a non-porous silicic binder. The catalysts are prepared by mechanical mixing, by means of a planetary mill, of a molten amorphous silica (fused silica), which is a dense material without surface or porosity properties, and of potassium phosphate precursors. The catalyst precursor is subsequently calcined under air at 450°C in order to obtain a material composed of a KPCE/fKPO? + S1O2) mixture with a ratio by weight of 13% to 26% by weight of KPO3. with respect to the total weight of said material. This document furthermore discloses a catalyst provided in the form of a powder with a sieved variable particle size between 106 and 212 pm. The silica contained in the final material is in its amorphous form (cf. Example 8).

[0006] However, none of the documents of the prior art discloses a macroporous material based on a potassium phosphate salt and/or on a caesium phosphate salt and on silica provided at least partially in the cristobalite and/or tridymite crystalline form.

SUBJECT-MATTERS OF THE INVENTION

[0007] A subject-matter of the present invention is a macroporous material based on at least one potassium phosphate salt and/or on at least one caesium phosphate salt and on silica, characterized in that the silica is provided at least partially in the cristobalite and/or tridymite crystalline form.

[0008] According to one or more embodiments, said potassium phosphate salt and/or said caesium phosphate salt is chosen from potassium metaphosphate (KPO3) and/or caesium metaphosphate (CsPOs).

[0009] According to one or more embodiments, said material exhibits an MPCh/IMPCE + SiCh) ratio by weight of between 13 and 50 with M being potassium and/or caesium.

[0010] According to one or more embodiments, said material exhibits a total pore volume of between 0.01 and 0.6 cm³/g.

[0011] According to one or more embodiments, said material exhibits a macropore volume of between 0.01 and 0.6 cm³/g.

[0012] According to one or more embodiments, the macropore volume represents between 50% and 100% of the total pore volume of said material.

[0013] According to one or more embodiments, said material exhibits a specific surface of greater than 1 m²/g and less than 50 m²/g.

[0014] According to one or more embodiments, said material exhibits a mechanical strength value, measured by grain-to-grain crushing, of greater than 0.5 daN/mm. [0015] According to one or more embodiments, said material comprises between 1% and 99% by weight of at least one potassium or caesium phosphate salt, with respect to the total weight of said material.

[0016] According to one or more embodiments, said material exhibits between 50% and 90% by weight of silica, with respect to the total weight of said material.

[0017] According to one or more embodiments, the silica is provided in the cristobalite crystalline form.

[0018] According to one or more embodiments, said material comprises a median macropore diameter of between 80 nm and 7000 nm.

[0019] According to one or more embodiments, said material is provided in the form of beads, extrudates, pellets or irregular and non-spherical agglomerates.

[0020] Another subject-matter according to the invention relates to a process for the dehydration of a feedstock comprising at least one hydroxypropanoic acid and its derivatives in the presence of the material according to the invention, at a temperature of between 180°C and 450°C, at a pressure of between 0.1 MPa and 12 MPa, and at a flow rate by weight of feedstock to weight of material ratio of between 0.01 h'¹ and 100 h'¹.

[0021] Advantageously, said feedstock comprises a hydroxypropanoic acid chosen from 2-hydroxypropanoic acid and 3-hydroxypropanoic acid.

DETAILED DESCRIPTION

1, Definitions

[0022] Within the meaning of the present invention, the different embodiments presented can be used alone or in combination with one another, without any limit to the combinations.

[0023] Within the meaning of the present invention, the various ranges of parameters for a given stage, such as the pressure ranges and the temperature ranges, can be used alone or in combination. For example, within the meaning of the present invention, a preferred range of pressure values can be combined with a more preferred range of temperature values.

[0024] The term “macropores” is understood to mean pores, the opening of which is greater than 50 nm.

[0025] The term “mesopores” is understood to mean pores, the opening of which is between 2 nm and 50 nm, limits inclusive.

[0026] The term “total pore volume” (TPV) of the material according to the invention is understood to mean the volume measured by mercury intrusion porosimetry according to Standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dynes/cm and a contact angle of 140°. The wetting angle used was taken as equal to 140° following the recommendations of the publication “Techniques de 1'ingenieur, traite analyse et caracterisation"’ [Techniques of the Engineer, Analysis and Characterization Treatise], pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

[0027] In order to obtain better accuracy, the value of the total pore volume corresponds to the value of the total pore volume measured by mercury' intrusion porosimetry measured on the sample minus the value of the total pore volume measured by mercury' intrusion porosimetry' measured on the same sample for a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0028] The volume of the macropores and of the mesopores is measured by mercury intrusion porosimetry according to Standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°. The value at and above which the mercury fills all the intergranular voids is set at 0.2 MPa and it is considered that, above this value, the mercury penetrates into the pores of the sample.

[0029] The macropore volume of the material according to the invention is defined as being the cumulative volume of mercury' introduced at a pressure of between 0.2 MPa and 30 MPa, corresponding to the volume contained in the pores with an apparent diameter of greater than 50 nm.

[0030] The mesopore 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.

[0031] The median diameter of the macropores (Dmacro in nm) is also defined as being a diameter such that all the pores with a size of less than this diameter constitute 50% of the macropore volume, measured by mercury' porosimetry'.

[0032] The specific surface of the material is measured by mercury' porosimetry according to Standard ASTM D4284-92 with a wetting angle of 140° by means of a model Autopore® IV appliance of the Micromeritics® trademark.

[0033] In the continuation 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 and the morphology and to measure the size of the constituent grams or crystals of the material. For that, use is made of an electron microscope (of the JEOL JEM F200 or JEOL JEM 21 OOF type) equipped with an energy dispersive spectrometer (EDS). The EDS detector must allow the light elements to be detected. The combination of these two tools, TEM and EDS, makes it possible to combine imaging and local chemical analysis with good spatial resolution.

[0034] Throughout the continuation of the text, the term “side crush strength” is understood to mean the mechanical strength of the material according to the invention, determined by the single pellet crush (SPC) test. This is a standardized test (Standard ASTM D4179-01) which consists in subjecting a material in the form of a millimetre-sized object, such as a bead, a pellet or an extrudate, to a break-generating compressive force. The analysis is repeated on a certain number of solids taken individually and typically on a number of solids of between 10 and 200. The mean of the breaking side forces measured constitutes the mean SPC which is expressed, in the case of granules, in unit of force (N) and, in the case of extrudates, in unit of force per unit of length (daN/mm or decanewtons per millimetre of extrudate length).

[0035] In the continuation of the text, the size of the grains or particle size distribution of the constituents of the materials obtained according to the invention is measured by the laser scattering particle size analysis technique. This indirect measurement technique makes it possible to determine the size distribution of particles (scale from the micron to the millimetre). This analysis method uses the principle of light scattering (Mie theory) and/or of light diffraction (Fraunhofer theory and Mie theory). The particles illuminated by the laser light deflect the light from its main axis. The amount of light deflected and the size of the angle of deflection make it possible to accurately measure the size of the particles. The powder is conveyed either by a solvent (w ater, isopropanol) or by air before passing in front of the laser beam: two approaches are thus distinguished: wet particle size analysis and dry particle size analysis.

[0036] Wet particle size analysis makes it possible to characterize dispersions (elementary particle size analysis after dispersion) or solids in suspension (“aggregated” particle size analysis). The particles measured are in the range 0.02 microns to 2000 microns.

[0037] Dry particle size analysis makes it possible to characterize powders, the initial aggregation of which is not destroyed. The measurement range extends from 0.2 microns to 2000 microns. In the present invention, dry particle size analysis is used to measure the size of the grains of the constituents of the material of the invention.

2, Material

[0038] A subject-matter according to the invention relates to a macroporous material based on at least one potassium phosphate salt and/or on at least one caesium phosphate salt and on silica, characterized in that the silica is provided at least partially in the cristobalite and/or tridymite crystalline form.

[0039] This is because the Applicant Company has discovered, surprisingly, that the use of such a macroporous material as catalyst for the dehydration of hydroxypropanoic acid makes possible a significant increase in the conversion of hydroxypropanoic acid and an improvement in the yield of corresponding propenoic acid, in comparison with a catalyst obtained according to conventional preparation processes, in particular in which the silica is in the amorphous form. The microporous structure of the material and the specific crystallinity⁷ of the silica comprised in this material could be obtained by carrying out a specific preparation process comprising a stage in which a calcination stage is carried out at a temperature of greater than or equal to 800°C on the basis of a material precursor comprising at least one silica source and at least one potassium and/or caesium precursor.

[0040] X-ray diffraction makes it possible to confirm that the material according to the invention indeed contains silica completely 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 cry stallographic database of the ICDD® (International Centre for Diffraction Data). The X-ray diffraction diagram is obtained by radiocrystallographic analysis by means of a diffractometer using the conventional powder method with the Kai radiation of copper ( = 1.5406 A). Starting from the position of the diffraction peaks represented by the angle 20, the lattice interplanar spacings dhkl characteristic of the sample are calculated using the Bragg relationship. The measurement error A(dhkl) with regard to dhkl is calculated by virtue of the Bragg relationship 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.

[0041] More specifically, the 20 line of 22° is associated mainly with the cristobalite cry stallographic form. The 28.4, 31.4° and 36° lines are also attributed to the formation of the cristobalite. The 20 lines of 20.7°. 21.7°, 23.4° and 27.5° are associated with the tridymite crystallographic form.

[0042] Advantageously, said potassium phosphate and/or caesium phosphate salt is potassium metaphosphate (KPCh) and/or caesium metaphosphate (CsPOs).

[0043] Advantageously, said material exhibits an MPCh/'lMPOs + SiCh) ratio by weight of between 13 and 50, preferably between 15 and 45 and more preferentially still between 17 and 40, with M being potassium and/or caesium (M = K and/or Cs). Preferably, M is potassium. [0044] Preferably, said material exhibits a total pore volume of between 0.01 cm³/g and 0.6 cm’/g. more preferentially of between 0.05 cm³/g and 0.5 cm³/g, more preferentially still between 0. 1 cm³/g and 0.4 cm³/g and in an even more preferred way between 0.15 cm³/g and 0.39 cm³/g.

[0045] Preferably, said material exhibits a macropore volume of between 0.01 cm³/g and 0.6 cm³/g, more preferentially of between 0.05 cm³/g and 0.5 cm³/g, more preferentially still between 0. 1 cm³/g and 0.4 cm³/g and in an even more preferred way between 0.15 cm³/g and 0.39 cm³/g.

[0046] Preferably, the macropore volume of the material represents between 50% and 100% of the total pore volume of said material, preferentially between 60% and 100% and more preferentially still between 80% and 100%.

[0047] Advantageously, said material exhibits a specific surface of greater than or equal to 1 m²/g and of less than 50 m²/g, preferably of between 1 m²/g and 20 m²/g. more preferentially between 1 m²/g and 15 m²/g and more preferably still between 1 m²/g and 10 m²/g.

[0048] Advantageously, said material exhibits a mechanical strength value, measured by single pellet crushing, of greater than 0.5 daN/mm, preferably of greater than 0.7 daN/mm, more preferentially of greater than 0.9 daN/mm and in a preferred way of greater than 1.3 daN/mm.

[0049] The material advantageously exhibits between 1% and 99% by weight, preferably between 5% and 99% by weight, in a preferred way from 10% to 95% by weight and very preferably from 20% to 75% by weight of at least one potassium and/or caesium phosphate salt, with respect to the total weight of said material.

[0050] The material advantageously exhibits between 50% and 90% by weight, preferably between 55% and 90% by weight, in a preferred way from 60% to 85% by weight and very preferably from 60% to 80% by weight of silica, with respect to the total weight of said material. [0051] In one embodiment according to the invention, the silica is provided solely in the cristobalite crystalline form.

[0052] Said material according to the invention advantageously exhibits a median macropore diameter of betw een 80 nm and 7000 nm, preferably between 200 nm and 6500 nm and more preferentially betw een 500 nm and 4000 nm.

[0053] Said material is advantageously in the form of beads, extrudates, pellets or irregular and non-spherical agglomerates. 3, Preparation process

[0054] A subject-mater according to the invention relates to a process for the preparation of a macroporous material according to the invention based on at least one potassium phosphate salt and/or on at least one caesium phosphate salt and on silica provided at least partially in the cristobalite and/or tridymite crystalline form, comprising at least the following stages: a) at least one silica source is brought into contact with at least one first phosphate precursor and at least one first potassium and/or caesium precursor in order to obtain a first material precursor; b) the material precursor obtained on conclusion of stage a) is allowed to mature for a period of time of between 1 minute and 72 hours in order to obtain a matured material precursor; c) the matured material precursor obtained on conclusion of stage b) is calcined at a temperature of between 800°C and 1200°C in order to obtain a calcined material precursor; d) the calcined material precursor obtained on conclusion of stage c) is brought into contact with at least one second phosphate precursor and at least one second potassium and/or caesium precursor in order to obtain a second material precursor; e) the second material precursor obtained on conclusion of stage d) is calcined at a temperature of between 300°C and 1200°C in order to obtain the material.

[0055] The combined stages a) to e) are described in detail below.

Stage a)

[0056] Stage a) can be carried out according to several embodiments.

Embodiment 1:

[0057] In a first embodiment according to the invention, stage a) comprises the following substages: i) at least one powder of precipitated silica, of silica gel or of zeolite with an Si/ Al ratio > 100, at least one colloidal silica sol and at least one powder of at least one potassium and/or caesium phosphate salt are mixed in at least one solvent in order to obtain a mixture; ii) the mixture obtained on conclusion of stage i) is shaped.

[0058] In accordance with this embodiment, said stage i) consists in mixing at least one powder of precipitated silica, of silica gel or of zeolite with an 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 of at least one caesium phosphate salt in at least one solvent in order to obtain a mixture. [0059] Preferably, the powder of precipitated silica, of silica gel or of zeolite with an Si/ Al ratio > 100 is chosen, without being restricted, from the following commercial sources: Nyasil 20 (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.

[0060] Preferably, the powder of precipitated silica, of silica gel or of zeolite with an Si/ Al ratio > 100 exhibits a grain size of less than 10 pm and preferably of less than 5 pm, more preferably of less than 1 pm.

[0061] Preferably, the colloidal silica sols are chosen, without being restricted, from the following commercial sources: Ludox (W.R. Grace Davison®), Nyacol (Nyacol Nano Technologies Inc.® or PQ Corp®), Nalco (Nalco Chemical Company®), Ultra-Sol (RESI Inc.®), NexSil (NNTI®), taken alone or as a mixture.

[0062] The majority⁷ of the colloidal silica sols are prepared from sodium silicate and inevitably contain sodium. Since the presence of sodium may prove to be detrimental to the catalytic activity, an ion-exchange stage may be necessary in order to reduce, indeed even eliminate, the residual sodium. In order to be freed from this stage, the use of low-sodium colloidal silica sols is preferable and, by way of example, mention may be made of Ludox AS40 stabilized with an ammonium counterion or also of Nyacol 2034DI, Nalco 1034A, Ultra-Sol 7H or NexSil 20A.

[0063] Said silica source(s) used in the process according to the present invention are advantageously amorphous synthetic silicas or zeolites with Si/ Al ratios > 100.

[0064] Said potassium phosphate salt(s) employed in stage i) is (are) advantageously chosen from potassium phosphate salts in amorphous or crystalline oxide form, taken alone or as a mixture.

[0065] Said potassium phosphate salt(s) are advantageously⁷ chosen from: KH2PO4, KH2P2O12, K6P6O7, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, K₆P60i8, K₈PSO₂4, K10P10O30, potassium (tripotassium) phosphate (K3PO4), alone or as a mixture. Preferably, the preferred potassium phosphate salt is chosen from potassium (tripotassium) phosphate (K3PO4) and KH2PO4, alone or as a mixture.

[0066] Said caesium phosphate salt(s) are advantageously chosen from CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, CS8P8O24, CsPCh, alone or as a mixture. Preferably, the preferred caesium phosphate salt is CSH2PO4. [0067] Preferably, said potassium phosphate or caesium phosphate salt(s) is (are) chosen from potassium (tripotassium) phosphate (K3PO4), KH2PO4, CSH2PO4, in or not in their hydrated form.

[0068] Preferably, at least one organic adjuvant is also mixed in during stage i).

[0069] Said organic adjuvant can be chosen from all the additives known to a person skilled in the art. In the case where at least one organic adjuvant is added in stage i), said organic adjuvant is advantageously chosen from cellulose derivatives, polyethylene glycols, aliphatic monocarboxylic acids, alkylaromatic compounds, sulfonic acid salts, fatty acids, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, poly acrylates, poly methacrylates, polyisobutene, polytetrahydrofuran, starch, polymers of polysaccharide type (such as xanthan gum), scleroglucan, derivatives of hydroxyethylcellulose type, carboxymethylcellulose, lignosulfonates and galactomannan derivatives, taken alone or as a mixture.

[0070] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0071] Said solvent is advantageously chosen from water, alcohols, and more particularly ethanol, and amines. Preferably, said solvent is water.

[0072] In the context of the invention, it is entirely possible to envisage mixing together several different powders of silica, of silica gel or of zeolite and/or different silica sols and/or different powders of potassium or caesium phosphate.

[0073] The order in which the mixing of the powders of at least the silica sources, of at least one powder of potassium and/or caesium phosphate salt and optionally of at least one organic adjuvant, in the case where they are mixed in powder form, with at least one solvent is carried out is unimportant.

[0074] The mixing of said powders and of said solvent can advantageously be carried out all at once.

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

[0076] Said potassium phosphate and/or caesium phosphate salt(s) employed in stage i) are advantageously provided in the form of powders.

[0077] Preferably, said potassium and/or caesium phosphate salt(s), in the case where they 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 stage i) exhibits a grain size of less than 60 pm, preferably of less than 25 pm, more preferably of less than 5 pm, very preferably of less than 2 pm.

[0079] In a particularly preferred embodiment, the use of a silica source used in stage i) exhibiting a grain size of less than 60 pm. preferably of less than 25 pm. more preferably of less than 5 pm, very preferably of less than 2 pm, combined with the use of a powder of at least one potassium and/or caesium phosphate salt which are ground and sieved to a grain size of less than 100 pm, makes possible a significant improvement in the mechanical strength of the materials obtained according to the invention.

[0080] Preferably, said powders of at least one silica source, of at least one potassium and/or caesium phosphate salt and optionally of at least one organic adjuvant, in the case where they are mixed in the form of powders, are first premixed, under dr ' conditions, before the introduction of the solvent.

[0081 ] Said premixed powders are subsequently advantageously brought into contact with said solvent. In another embodiment, at least said silica sources and at least said organic adjuvant can be in solution or suspension in said solvent beforehand when said solvent is brought into contact with the potassium and/or caesium phosphate powders. The operation of bringing into contact with said solvent results in a mixture being obtained which is subsequently advantageously- kneaded.

[0082] In the case where at least one pow der of caesium phosphate salt is used, aqueous ammonia is advantageously added to the mixture in order to obtain an extrudable mixture.

[0083] Preferably, said mixing stage i) is carried out by batchwise or continuous kneading. [0084] In the case where said stage i) is carried out batchwise, said stage i) is advantageously carried out in a kneader preferably equipped with Z-shaped arms, or a cam mixer, or in any other ty pe of mixer, such as, for example, a planetary mixer. Said mixing stage i) makes it possible to obtain a homogeneous mixture of the pulverulent constituents.

[0085] Preferably, said stage i) is carried out at a temperature of between 13°C and 25°C, for a period of time of between 5 minutes and 60 minutes and preferably between 10 minutes and 50 minutes. The rotational speed of the arms of the kneader is advantageously of between 10 and 75 revolutions/minute, preferably betw een 25 and 50 revolutions/minute.

[0086] Preferably, the following amounts are introduced in the mixing stage i) of the process according to the invention: 1% to 99% by weight, preferably from 5% to 99% by weight, in a preferred way from 10% to 95% by weight and very preferably from 15% to 65% by weight of at least one powder of precipitated silica, silica gel or a zeolite with an Si/ Al ratio > 100;

1% to 99% by weight, preferably from 5% to 99% by weight, in a preferred way from 10% to 95% by weight and very preferably from 5% to 50% by weight of at least one colloidal silica sol;

1% to 99% by weight, preferably from 5% to 99% by weight, in a preferred way from 10% to 95% by weight and very preferably from 20% to 75% by weight of at least one powder of potassium or caesium phosphate salt;

- 0% to 20% by weight, preferably from 1% to 15% by weight, in a preferred way from 1% to 10% by weight and very preferably from 1% to 7% by weight of at least one organic adjuvant; the percentages by weight being expressed with respect to the total weight of said material (that is to say, the final material obtained on conclusion of stage c)) and the sum of the contents of each of the compounds of said material being equal to 100%.

[0087] In accordance with the invention, said stage ii) consists of the shaping of the mixture obtained on conclusion of stage i). Preferably, the mixture obtained on conclusion of stage i) is advantageously shaped by extrusion.

[0088] In the case where the shaping of the mixture resulting from stage i) is carried out by extrusion, said stage ii) is advantageously earned out in a single-screw or twin-screw piston extruder. In this case, an organic adjuvant can optionally be added in the mixing stage i). The presence of said organic adjuvant facilitates the shaping by extrusion. Said organic adjuvant is described above and is introduced in stage i) in the proportions indicated above.

[0089] In the case where said preparation process is carried out continuously, said mixing stage i) can be coupled with stage ii) of shaping by extrusion in one and the same item of equipment. According to this embodiment, the extrusion of the mixture, also called “kneaded paste”, can be carried out either by directly extruding at the end of a continuous kneader of twin- screw type, for example, or by connecting one or more batch kneaders to an extruder. The geometry of the die, which gives the extrudates their shape, can be chosen from dies well known to a person skilled in the art. They can thus, for example, be of cylindrical or multilobe shape and more preferentially of trilobe or quadrilobe shape.

[0090] In the case where the shaping of the mixture resulting from stage i) is carried out by extrusion, the amount of solvent added in the mixing stage i) is adjusted so as to obtain, on conclusion of this stage and whatever the alternative form employed, a mixture or a paste which does not run but which is not too dry either, so as to make possible its extrusion under suitable pressure conditions well known to a person skilled in the art and dependent on the item of extrusion equipment used.

[0091] Preferably, said stage ii) of shaping by extrusion is carried out at an extrusion pressure of greater than 1 MPa and preferably of between 3 MPa and 10 MPa.

Embodiment 2:

[0092] In a second embodiment according to the invention, stage a) comprises the following substages: i') at least one colloidal silica sol is mixed with at least one powder of at least one potassium and/or caesium phosphate salt in order to obtain a suspension; ii') a powder of at least one precipitated silica, of a silica gel or of a zeolite with an Si/Al ratio > 100 and at least one solvent are added to said suspension obtained on conclusion of stage i'); iii') the paste obtained on conclusion of stage ii') is shaped.

[0093] In accordance with the second embodiment, said stage i') consists in mixing at least one colloidal silica sol with at least one powder of at least one potassium and/or caesium phosphate salt in order to obtain a suspension.

[0094] A solvent, preferably water, can advantageously be added in stage i').

[0095] Preferably, the colloidal silicas or silica sols are chosen, without being restricted, from the following commercial sources and are provided in liquid form: Ludox (W.R. Grace Davison®), Nyacol (Nyacol Nano Technologies Inc.® ou PQ Corp®), Nalco (Nalco Chemical Company®). Ultra-Sol (RESI Inc.®), NexSil (NNTI®), taken alone or as a mixture.

[0096] Said source(s) of colloidal silica sol used in the process according to the present invention are advantageously amorphous synthetic silicas.

[0097] Said potassium phosphate and/or caesium phosphate salt(s) employed in stage a) is (are) advantageously chosen from potassium or caesium phosphate salts in amorphous or crystalline oxide form, taken alone or as a mixture.

[0098] Said potassium phosphate salt(s) are advantageously chosen from the following list: KH2PO4, KH2P2O12, K₆P6O₇, K3H2P3O10, K4H2P4O13, K3P3O9, K4P4O12, KePeOis, K₈P₈O₂4, K10P10O30, potassium (tripotassium) phosphate (K3PO4), alone or as a mixture. Preferably, the preferred potassium phosphate salt is KH2PO4, [0099] Said caesium phosphate salt(s) are advantageously chosen from the following list: CSH2PO4, CS2H2P3O10, CS4H2P4O13, CS3P3O9, CS4P4O12, CsePeOis, Cs8PsO24, CsPOs, alone or as a mixture. Preferably, the preferred caesium phosphate salt is CS2HPO4.

[0100] Preferably, said potassium phosphate or caesium phosphate salt(s) is (are) chosen from KH2PO4, CSH2PO4, in or not in their hydrated form.

[0101] Preferably, said powders of at least one potassium and/or caesium phosphate salt can advantageously be ground and sieved to a grain size of less than 100 pm prior to their introduction in stage i'). The size of the grains of the potassium phosphate and/or caesium phosphate salts is advantageously measured by dry laser particle size analysis.

[0102] Very preferably, said stage i') is advantageously carried out in a planetary centrifugal mixer. Said powders of at least one potassium and/or caesium phosphate salt, preferably ground and sieved to a particle size of less than 100 pm, are dispersed beforehand by means of a planetary centrifugal mixer in the presence of the source of colloidal silica sol so as to obtain said suspension.

[0103] Said stage i') is advantageously carried out at a mixing speed applied to the planetary' centrifugal mixer of between 100 and 2000 revolutions per minute, preferably between 200 and 500 revolutions per minute.

[0104] Preferably, said stage i') is carried out for a period of time of between 5 seconds and 60 seconds and preferably between 20 seconds and 60 seconds.

[0105] The additions of powders, of colloidal silica sol and of solvent can also advantageously be alternated.

[0106] In accordance with the second embodiment, the process comprises a stage ii') of addition of a powder of at least one precipitated silica, of a silica gel or of a zeolite with an Si/Al ratio > 100 and at least one solvent to said suspension obtained on conclusion of stage i').

[0107] Preferably, the precipitated silicas, the silica gels or the zeolites with an Si/Al ratio > 100 added in stage ii') are chosen, without being restricted, from the following commercial sources: Nyasil 20 (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.

[0108] Preferably, the powder of at least one precipitated silica or silica gel or zeolite with an Si/Al ratio > 100 used in stage ii') exhibits a grain size of less than 60 pm, preferably of less than 25 pm, more preferably of less than 5 pm, very' preferably of less than 2 pm. [0109] The size of the grains of precipitated silica or of silica gel or of zeolite with an Si/ Al ratio > 100 is advantageously measured by dry laser particle size analysis.

[0110] Preferably, the precipitated silica or silica gel is in the amorphous form.

[0111] In the context of the invention, it is entirely possible to envisage mixing together several different powders of silica, of silica gel or of zeolite and/or different silica sols and/or different powders of potassium and/or caesium phosphate salt.

[0112] According to the invention, at least one solvent is added in stage ii'). Said solvent is advantageously chosen from water, alcohols, and more particularly ethanol, and amines. Preferably, said solvent is water.

[0113] Preferably, at least one organic adjuvant can also be added during stage ii').

[0114] Said organic adjuvant can be chosen from all the additives known to a person skilled in the art.

[0115] In the case where at least one organic adjuvant is added in stage ii'), said organic adjuvant is advantageously chosen from cellulose derivatives, polyethylene glycols, aliphatic monocarboxylic acids, alkylaromatic compounds, sulfonic acid salts, fatty acids, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, polyacrylates, polymethacrylates, polyisobutene, polytetrahydrofuran, starch, polymers of polysaccharide type (such as xanthan gum), scleroglucan, derivatives of hydroxyethylcellulose type, carboxymethylcellulose, lignosulfonates and galactomannan derivatives, taken alone or as a mixture.

[0116] Preferably, said organic adjuvant can be mixed in powder form or in solution in said solvent.

[0117] Stage i') and stage ii') can advantageously be carried out in the same item of equipment and preferably in a planetary centrifugal mixer.

[0118] In another embodiment, stage i') and stage ii') can advantageously be carried out in different items of equipment. In this case, stage i') is preferably carried out in a planetary centrifugal mixer and then the suspension obtained on conclusion of stage i') is transferred into a batch kneader of Z-shaped arm type in which a powder of at least one precipitated silica or silica gel or zeolite and at least one solvent are added to said suspension, according to stage ii').

[0119] In the case where stage i') and stage ii') are not carried out in the same item of equipment, preferably, the source of silica (precipitated silica, silica gel or zeolite with an Si/ Al ratio > 100), at least one solvent and optionally at least one organic adjuvant are preferably added first, preferably in the batch kneader of Z-shaped arm type, before the introduction of the suspension obtained in stage i'). [0120] In the case where a powder of caesium phosphate salt is used, an addition of aqueous ammonia can be carried out so as to obtain an extrudable mixture in stage ii').

[0121] Preferably, said mixing stage ii') is carried out by batchwise or continuous kneading.

[0122] In the case where said stage ii') is carried out batchwise, said stage ii') is advantageously carried out in a kneader preferably equipped with Z-shaped arms, or a cam mixer, or in any other type of mixer, such as, for example, a planetary' mixer. Said mixing stage ii') makes it possible to obtain a paste or a homogeneous mixture of the constituents.

[0123] In the case of the use of a kneader of “Z-arm” type in stage ii'). the rotational speed of the arms of the kneader is advantageously of between 10 and 75 revolutions/minute, preferably between 25 and 50 revolutions/minute.

[0124] In the case of the implementation of stage ii') in a planetary⁷ centrifugal mixer, the rotational speed is advantageously of 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 caesium phosphate salt ground and sieved to a particle size of less than 100 pm in stage i'), combined w ith the use of a silica source (precipitated silica or silica gel or zeolite with an Si/ Al ratio > 100) exhibiting a reduced size preferably of less than 10 pm, in a preferred way of less than 5 pm, more preferably of less than 1 pm, in stage ii'), makes possible a significant improvement in the mechanical strength of the materials obtained according to the invention.

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

1% to 99% by weight, preferably from 5% to 99% by weight, in a preferred way from 5% to 95% by weight, very preferably from 5% to 40% by weight and more preferably still from 5% to 20% by weight of at least one colloidal silica sol;

1% to 99% by w eight, preferably from 5% to 99% by w eight, in a preferred way from 10% to 95% by weight and very⁷ preferably from 10% to 60% by weight of at least one potassium and/or caesium phosphate salt;

1% to 99% by weight, preferably from 5% to 99% by weight, in a preferred way 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 an Si/ Al ratio > 100;

- 0% to 20% by weight, preferably from 1% to 15% by weight, in a preferred way from 1% to 10% by weight and very preferably from 1% to 7% by weight of at least one organic adjuvant; the percentages by weight being expressed with respect 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%.

[0127] In accordance with the second embodiment, said process comprises a stage iii') of shaping the paste obtained on conclusion of the mixing stage ii').

[0128] Preferably, the paste obtained on conclusion of stage ii') is advantageously shaped by extrusion.

[0129] In the case where the shaping of the mixture resulting from stage ii') is carried out by extrusion, said stage ii') is advantageously carried out in a single-screw or twin-screw piston extruder.

[0130] In this case, an organic adjuvant can optionally be added in the mixing stage ii'). The presence of said organic adjuvant facilitates the shaping by extrusion. Said organic adjuvant is described above and is introduced in stage ii') in the proportions indicated above.

[0131] The extrusion of the mixture, also called “kneaded paste'’, can be carried out either by directly extruding at the end of a twin-screw continuous kneader, for example, or by connecting one or more batch kneaders to an extruder. The geometry of the die, which gives the extrudates their shape, can be chosen from dies well known to a person skilled in the art. They can thus, for example, be of cylindrical, multilobe, fluted or slotted shape.

[0132] In the case where the shaping of the mixture resulting from stage ii') is carried out by extrusion, the amount of solvent added in the mixing stage ii') is adjusted so as to obtain, on conclusion of this stage and whatever the alternative form employed, a mixture or a paste which does not run but which is not too dry either, so as to make possible its extrusion under suitable pressure conditions well known to a person skilled in the art and dependent on the item of extrusion equipment used.

[0133] Preferably, said stage iii¹) of shaping by extrusion is carried out at an extrusion pressure of greater than 1 MPa and preferably of between 3 MPa and 10 MPa.

Embodiment 3:

[0134] In a third embodiment according to the invention, stage a) comprises the following substages: i") a liquid solution in the aqueous or organic phase comprising at least one phosphate precursor and at least one potassium and/or caesium precursor is supplied, the preparation temperature advantageously being between 5°C and 80°C, preferably between 10°C and 70°C; ii") said solution obtained on completion of stage i") is impregnated on a silica-containing support, the volume of the solution advantageously being between 0.9 and 1.1 times the pore volume of the support, preferably betw een 0.8 and 1.05 times the pore volume of the support, and the phosphate concentration of the solution preferably being of between 50 g/1 and 2000 g/1.

[0135] The impregnation solution of stage i") is preferably prepared by dissolution in an aqueous or organic phase of one or more precursors of phosphate and of potassium (K) or caesium (Cs) element. The impregnation solution can advantageously be prepared by mixing phosphorus and alkaline elements introduced independently. In this case, the precursor of alkali metal M chosen from K or Cs is chosen, for example, from one or more of the carbonate M2CO3, nitrate MNO3, sulfate, formate HCOOM, acetate CH3COOM, citrate, lactate, chloride MCI, hydroxide MOH or oxide M2O salts.

[0136] The precursor(s) of phosphate can advantageously be chosen, for example, from H3PO4. (NH₄)H₂PO4, (NH₄)2HPO4, (NH₄)PO₄ or P2O5.

[0137] The phosphate concentration of the solution is preferably of between 50 g/1 and 2000 g/1.

[0138] The support supplied in stage ii") advantageously comprises an amorphous phase SiO2 which can be characterized by X-ray diffraction. Said support preferably exhibits a specific surface of greater than or equal to 5 m²/g, preferably of between 5 m²/g and 500 m²/g and more preferably of between 10 m²/g and 450 m²/g.

[0139] The pore volume of the support is advantageously of between 0.05 cm³/g and 1.5 cm³/g, preferably of between 0.2 cm³/g and 1.2 cm³/g and more preferably of between 0.25 cm³/g and 1.1 cm³/g.

[0140] The macropore volume of the support is advantageously of between 0.01 cm³/g and 0.5 cm³/g, preferably of between 0.01 cm³/g and 0.4 cm³/g, and more preferably of between 0.01 cm³/g and 0.3 cm³/g.

[0141] The manufacture of supports of amorphous silicon oxide type and their shaping is well known and taught to a person skilled in the art, for example in the Handbook of Porous Solids, Wiley-VCH (Volume 3, pages 1543-1590).

[0142] Preferably, the support supplied in stage ii") is provided in the form of beads, extrudates (preferably cylindrical, trilobe or quadrilobe), pellets or irregular and non-spherical agglomerates.

[0143] Very advantageously, said support is provided in the form of beads or extrudates. [0144] When the support is provided in the form of beads, the diameter of the beads is generally of between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm. When the support is provided in the form of an extrudate, the extrudates have a diameter generally of between 0.5 mm and 10 mm, preferably between 1.0 mm and 2.5 mm, and with a length of between 1.0 mm and 2.0 mm.

[0145] Preferably, the impregnation stage ii") can be preceded by a heat treatment stage carried out at a temperature of between 80°C and 550°C.

[0146] Preferably, the impregnation stage ii") can be followed, optionally, by other impregnation stages. The impregnation stages following the first can advantageously be carried out after the maturation stage b).

Stage b)

[0147] The preparation process according to the invention comprises a stage b) of maturation of the material obtained on conclusion of stage a). Said maturation stage is advantageously carried out at a temperature of between 0°C and 300°C, preferably between 20°C and 200°C and in a preferred way between 20 and 150°C, for a period of time of advantageously between 1 minute and 72 hours, preferably between 30 minutes and 72 hours, in a preferred way between 1 hour and 48 hours and more preferably between 1 hour and 24 hours.

[0148] Preferably, said maturation stage is earned out under air and preferably under moist air with a relative humidity between 20% and 100% and preferably between 70% and 100%. This stage makes possible good hydration of the material necessary to limit the appearance of cracks which are harmful to the mechanical strength. On conclusion of stage b), a matured material precursor is obtained.

Stage c)

[0149] According to an essential stage of the preparation process, the matured material precursor resulting from stage b) is subjected to a stage c) of calcination at a temperature of between 800°C and 1200°C, preferably between 800°C and 1 100°C and very preferably between 800°C and 900°C. Stage c) is carried out for a period of time of advantageously between 1 hour and 12 hours, preferably between 1 hour and 4 hours. This stage is essential for the formation of the cristobalite and/or tridymite crystallographic phases. This stage makes it possible in addition to remove the organic adjuvants used in order to facilitate the shaping of the material. [0150] Said calcination stage c) is advantageously carried out under an oxygencomprising gas stream; for example, preferably, the matured material precursor obtained on conclusion of stage b) is calcined under air which is dry or with various degrees of humidity or also 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, indeed even preferably at least 10% by volume, of oxygen, with respect to the total volume of said gas mixture.

Stage d)

[0151] According to stage d) of the preparation process, the calcined material obtained on conclusion of stage c) is brought into contact with at least one second phosphate precursor and at least one second potassium and/or caesium precursor in order to obtain a second material precursor.

[0152] Advantageously, stage d) comprises the following substages: dl) a liquid solution in the aqueous or organic phase comprising at least one second phosphate precursor and at least one second potassium and/or caesium precursor is prepared, at a temperature of preferably between 5°C and 80°C, more preferentially between 10°C and 70°C; d2) the solution prepared in stage dl) is impregnated on the calcined material obtained on conclusion of stage c), the volume of the solution being advantageously of between 0.9 and 1.1, preferably between 0.8 and 1.05, times the pore volume of the calcined material obtained on conclusion of stage c); d3) optionally, a stage of maturation of the second material precursor obtained on conclusion of stage d2); d4) optionally, a stage of drying of the second matured material precursor obtained on conclusion of stage d3).

[0153] Preferably, the phosphate concentration of the solution supplied to stage dl) is of between 50 g/1 and 2000 g/1.

[0154] The impregnation solution of stage dl) is preferably prepared by dissolution in an aqueous or organic phase of one or more precursors of phosphate and of potassium (K) or caesium (Cs) element. The impregnation solution can advantageously be prepared by mixing phosphorus and alkaline elements introduced independently. In this case, the precursor of alkali metal M chosen from K or Cs is chosen, for example, from one or more of the carbonate M2CO3, nitrate MN03. sulfate, formate HCOOM. acetate CH3COOM. citrate, lactate, chloride MCI, hydroxide MOH or oxide M2O salts.

[0155] The precursor(s) of phosphate can advantageously be chosen, for example, from H3PO4, (NH₄)H₂PO4, (NH₄)2HPO4, (NH4)PO4 or P2O5.

[0156] The phosphate concentration of the solution is preferably of between 50 g/1 and 2000 g/1.

[0157] Preferably, a maturation stage d3) is carried out at a temperature of between 0°C and 300°C, preferably between 20°C and 200°C and in a preferred way between 20 and 150°C, for a period of time of between 1 minute and 72 hours, preferably between 30 minutes and 72 hours, in a preferred way between 1 hour and 48 hours and more preferably between 1 hour and 24 hours.

[0158] Preferably, said maturation stage is carried out under air and preferably under humid air with a relative humidity of between 20% and 100% and preferably between 70% and 100%. This stage makes possible good hydration of the material necessary to limit the appearance of cracks which are harmful to the mechanical strength.

[0159] Preferably, after the maturation stage d3), a drying stage is carried out at a temperature of less than 250°C, preferably of between 15°C and 180°C, more preferentially between 30°C and 160°C, more preferentially still between 50°C and 150°C and in an even more preferential way between 70°C and 140°C, for a period of time typically of between 0.5 hour and 12 hours and more preferably for a period of time of between 0.5 hour and 5 hours. Longer periods of time are not ruled out but do not necessarily contribute an improvement.

[0160] Preferably, the impregnation stage d) can be followed, optionally, by other impregnation stages.

Stage e)

[0161] According to the process for the preparation of the material, the second material precursor obtained on conclusion of the impregnation stage d) is subjected to a stage e) of calcination at a temperature of between 300°C and 600°C, preferably between 300°C and 550°C and very preferably between 300°C and 525°C, for a period of time of advantageously between 1 hour and 12 hours, preferably of between 1 hour and 4 hours.

[0162] Said calcination stage e) is advantageously carried out under an oxygencomprising gas stream; for example, preferably, the extrudates are calcined under air which is dry or with various degrees of humidity or also heat treated in the presence of a gas mixture comprising an inert gas, preferably nitrogen, and oxygen. The gas mixture used preferably compnses at least 5% by volume, indeed even preferably at least 10% by volume, of oxygen.

[0163] On conclusion of stage e), the material according to the invention is obtained.

4. Conversion process

[0164] The material according to the invention can advantageously be used as catalyst in a process for the dehydration of hydroxy propanoic acid and its derivatives.

[0165] The process for the dehydration of hydroxypropanoic acid and its derivatives is carried out in the presence of the material prepared according to the invention, which is advantageously employed as 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, in a preferred way between 0.13 MPa and 9 MPa and very preferably between 0.1 MPa and 8 MPa, and at a flow rate by weight of feedstock to weight of material ratio of between 0.01 and 100 h’¹, preferably between 0.02 and 50 h’¹, more preferentially between 0.03 and 30 h"¹ and very preferably between 0.05 and 20 h’¹.

[0166] Said process makes it possible to selectively obtain a mixture of products comprising acrylic acid.

[0167] During the dehydration of hydroxypropanoic acid and its derivatives to give aery' lie acid, a mixture of different products, called by-products, is obtained, comprising in particular propanoic acid, carbon monoxide, carbon dioxide, acetaldehyde and heavy compounds containing more than 3 carbon atoms.

[0168] Said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0169] Said process is preferably carried out continuously, in a fixed bed, preferably at a pressure adjusted in order for the products and the reactants to be in the gas phase, the feedstock being injected into the process preferentially in the liquid phase.

5, Feedstock

[0170] The feedstock feeding the process for the conversion of 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 more preferably still between 8% and 98% by weight of hydroxypropanoic acid and its derivatives.

[0171] Said feedstock can also comprise impurities linked, in particular, to the processes for obtaining hydroxypropanoic acid and its derivatives, such as fermentation. The content of impurities is preferably less than 10% by weight of said feedstock. The hydroxypropanoic acid(s) and its (their) derivatives included in said feedstock can be of any origin, chemical, petrochemical or biobased.

[0172] Said feedstock 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 more preferably still between 2% and 70% by weight of water.

[0173] Said feedstock 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 more preferably still betw een 2% and 70% by weight of organic solvent, such as, for example, an alcohol.

[0174] The sum of the contents of hydroxypropanoic acid and its derivatives, of water, of organic solvent and of possible impurities represents 100% by weight of the feedstock.

[0175] The main products obtained by said process are the unconverted hydroxypropanoic acids and its (their) derivatives, and the acrylic acid resulting from the dehydration reaction. [0176] The examples below illustrate the invention without limiting the scope thereof.

EXAMPLES

[0177] In order to exemplify the invention, several methods of preparation of materials are described. The contents are expressed as percentages by weight.

[0178] The examples below illustrate the invention without limiting the scope thereof.

Example 1 : Preparation of materials A based on the embodiment 1 in the presence of a precipitated silica powder

[0179] A precipitated silica powder (Siliaflash P6040-63 pm; Silicycle) (38%), a colloidal silica sol (36%), potassium phosphate (KPCh, Aldrich) (26%) and Methocel™ (K15M) (3%) are introduced into and premixed in a kneader of Brabender trademark. Water is added dropwise until a paste is obtained and the kneading is continued for 20 minutes. The paste obtained is subsequently extruded on a piston extruder of MTS trademark using a cylindrical die with a diameter of 1.6 mm. The extrudates obtained (extrudates A) are subsequently matured at 120°C for 16 hours in a ventilated oven.

[0180] Finally, the extrudates A are subj ected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are called materials Al and the extrudates calcined at 800°C are called material precursors A2.

[0181] Subsequently, 2.6 g of potassium hydrogenphosphate (K2HPO4, M = 174 g/mol) and 2.0 g of ammonium hydrogenphosphate ((NHfJJTPC , M = 132 g/mol) are first of all dissolved in 5 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added dropwise to 20 g of material precursor A2. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. It is subsequently calcined under air at 450°C for 4 hours in order to obtain the material A3 (in accordance with the invention).

[0182] The compositional analysis of the material A3 by X-ray fluorescence gives a content by weight of K of 12% and of P of 10%. The mean equivalent content by weight of KPO3 of the material A3 after calcination is 36%.

[0183] The material Al (not in accordance with the invention) exhibits, in X-ray diffraction, diffraction peaks of the metaphosphate KPO3 phase.

[0184] The material A3 (in accordance with the invention) exhibits, in X-ray diffraction, diffraction peaks of the metaphosphate KPO3 phase and of the cristobalite crystalline silica.

Example 2: Preparation of materials B based on the embodiment 1 in the presence of a precipitated silica powder

[0185] A precipitated silica powder (Nyasil 20 1.5 pm; Nyacol) (53%), a colloidal silica sol (32%), potassium phosphate (KPO3, Aldrich) (15%) and Methocel™ (K15M) (3%) are introduced into and premixed in a kneader of Brabender trademark. Water is added dropwise until a paste is obtained and the kneading is continued for 20 minutes. The paste obtained is subsequently extruded on a piston extruder of MTS trademark using a cylindrical die with a diameter of 1.6 mm. The extrudates obtained (extrudates B) are subsequently matured at 120°C for 16 hours in a ventilated oven. Finally, the extrudates B are subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are called materials Bl and the extrudates calcined at 800°C are called material precursors B2.

[0186] Subsequently, 1,6 g of potassium hydrogenphosphate (K2HPO4, M = 174 g/mol) and 1.2 g of ammonium hydrogenphosphate ((NFE^HPCh, M = 132 g/mol) are first of all dissolved in 5.6 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added dropwise to 20 g of material precursor B2. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. It is subsequently calcined under air at 450°C for 4 hours in order to prepare the material B3 (in accordance with the invention).

[0187] The compositional analysis of the material B3 by X-ray fluorescence gives a content by weight of K of 7.3% and of P of 6.4%. The mean equivalent content by weight of KPCh of the material B3 after calcination is 22%.

[0188] The material B 1 (not in accordance) exhibits, in X-ray diffraction, diffraction peaks of the metaphosphate KPOs phase.

[0189] The material B3 (in accordance) exhibits, in X-ray diffraction, diffraction peaks of the cristobalite cry stalline silica and also diffraction peaks of the metaphosphate KPO3 phase.

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

[0190] A colloidal silica sol (12.4%) and a potassium dihydrogenphosphate (KH2PO4; Aldrich) powder (15.2%), which powder is ground and sieved to 100 pm, are introduced into and mixed in the container of a planetary centrifugal mixer of Thinky brand. The rotational speed is set at 1500 revolutions/minute for 30 seconds. The suspension obtained, a Methocel™ (K15M) powder (3%) and a precipitated silica powder (Nyasil 20; Nyacol) (72.4%) are introduced into and premixed in a kneader of Brabender trademark. Water is added drop wise until a paste is obtained and the kneading is continued for 20 minutes. The paste obtained is subsequently extruded on a piston extruder of MTS trademark using a cylindrical die with a diameter of 1.6 mm. The extrudates are dried at 120°C for 16 h in a ventilated oven. The extrudates obtained (extrudates C) are subsequently matured at 120°C for 16 hours in a ventilated oven. Finally, the extrudates C are subjected to different calcination temperatures (450°C and 800°C) in a muffle furnace for 4 hours. The extrudates calcined at 450°C are called materials Cl and the extrudates calcined at 800°C are called material precursors C2.

[0191] Subsequently, 2,8 g of potassium hydrogenphosphate (K2HPO4, M = 174 g/mol) and 2.1 g of ammonium hydrogenphosphate ((NH^HPCfi, M = 132 g/mol) are first of all dissolved in 4.2 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added dropwise to 20 g of material precursor C2. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. It is subsequently calcined under air at 450°C for 4 hours in order to prepare the material C3 (in accordance with the invention).

[0192] The compositional analysis of the material C3 by X-ray fluorescence gives a content by weight ofKof 8.8% and of P of 7.5%. The mean equivalent content by weight ofKPCh of the material C3 after calcination is 27%.

[0193] The material C 1 (not in accordance) exhibits, in X-ray diffraction, diffraction peaks of the metaphosphate KPCh phase.

[0194] The material C3 (in accordance) exhibits, in X-ray diffraction, diffraction peaks of the cristobalite crystalline silica and also diffraction peaks of the metaphosphate KPOs phase.

[0195] For each of the materials obtained (in accordance or not in accordance), the structural characteristics (total pore volume, macropore volume, median macropore diameter, specific surface, SPC) and the cry stalline phases observed by X-ray diffraction are shown in Table 1 below.

Table 1.

Example 4: Preparation of materials D according to the embodiment 3

[0196] The materials DI and D3 are prepared from an amorphous silica DO in the form of beads with a diameter of 2 mm, with a specific surface, measured by mercury porosimetry, of 90 m²/g and with a total pore volume of 0.92 cm7g and the structural properties of which are shown in Table 2 below.

Table 2.

[0197] For the preparation of the materials DI and D3, 100 grams of commercial amorphous silica DO are calcined under air in a muffle furnace, as a thin layer, at 450°C for 2 hours.

[0198] 10 g of potassium hydrogenphosphate (K2HPO4, M = 174 g/mol) and 8.6 g of ammonium hydrogenphosphate ((NFEfiHPCfi, M = 132 g/mol) are first of all dissolved in 30 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added drop wise to the SiCh beads. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. [0199] 20 g of the material are calcined under air at 450°C for 4 hours in order to prepare the material DI (not in accordance with the invention).

[0200] 20 g of the material are calcined under air at 900°C for 4 hours in order to prepare the material precursor D2.

[0201] 3.3 g of potassium hydrogenphosphate (K2HPO4. M = 174 g/mol) and 2.5 g of ammonium hydrogenphosphate ((NH^HPC M = 132 g/mol) are first of all dissolved in 5.3 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added dropwise to 20 g of beads of material precursor D2. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. It is subsequently calcined under air at 450°C for 4 hours in order to obtain the material D3 (in accordance with the invention).

[0202] The compositional analysis of the material D3 by X-ray fluorescence gives a content by weight of K of 14% and of P of 12%. The mean equivalent content by weight of KPO3 of the material D3 after calcination is 44.5%.

[0203] The material DI (not in accordance) exhibits, in X-ray diffraction, diffraction peaks of the metaphosphate KPCh phase.

[0204] The material D3 (in accordance) exhibits, in X-ray diffraction, diffraction peaks of the cristobalite crystalline silica and also diffraction peaks of the metaphosphate KPCh phase.

[0205] The specific surface (Hg porosimetry) of the material DI is 46 m²/g and its macropore volume is 0.07 ml/g. After calcination at a temperature of greater than or equal to 800°C and impregnation, the specific surface of the material D3 is 3 m²/g and the macropore volume is 0.30 ml/g.

Example 5: Use of the materials Al. A3, Cl and C3 as catalyst for the gas-phase dehydration of lactic acid to give acrylic acid

[0206] The materials Al, A3, Cl and C3 are tested with an Avantium® unit comprising 16 reactors, with an internal diameter of 2 mm and with 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 top. The evaporation of the feedstock is carried out in the first part of the reactor using a cord. The pph of lactic acid is 0.2 h'¹ with a charged weight of catalyst of approximately 190 mg. At the unit outlet, all of the products are analysed by gas chromatography. The results are presented in Table 3 below. Table 3.

[0207] The catalysts Al, A3, Cl and C3 convert a feedstock of lactic acid into acrylic acid with a carbon yield of greater than or equal to 70%. The catalysts A3 and C3 in accordance with the invention have an acrylic acid (AA) carbon yield which is greater than those obtained respectively by the not-in-accordance catalysts Al and Cl. After 150 hours with feedstock, it is easier to discharge the catalysts A3 and C3 than the catalysts Al and Cl , which are stuck to the walls of the reactor. The catalysts A3 and C3, which are in accordance and for which a calcination at a temperature of greater than 800°C is applied, are more stable under operating conditions and after a time with feedstock of 150 hours can be easily discharged.

Example 6: Use of the materials Bl. B3. DI and D3 as catalyst for the gas-phase dehydration of lactic acid to give acrylic acid

[0208] The materials Bl, B3, DI and D3 are tested with a single-reactor unit with an internal diameter of 10 mm and with a volume of 50 ml. The tubular reactor with an internal diameter of 10 mm is charged with approximately 10 cubic centimetres of shaped catalyst (approximately 6 g of catalyst), which is located between two beds of solids validated as reaction inert substances (quartz extrudates). The feedstock, composed of 20% of lactic acid and 80% by weight of water, is co-injected with nitrogen at the reactor top. The reactor is located in an oven using several temperature maintenance zones, a barrier mechanical pressure regulator and two gas-liquid separation stages, the first making possible the condensation of the water contained in the reaction effluent and the second separator being located on the residual vapour from the first separator in order to ensure the post-condensation thereof (T = -5°C).

[0209] The gases from the unit are analysed (under hot conditions for the total effluent and under cold conditions for the separator top gases) by gas chromatography. The liquid effluent is regularly weighed and analysed by high pressure liquid chromatography (HPLC).

[0210] The reaction is operated 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 feedstock flow rate is 5 g/h.

Conversion

[0211] The conversion of the lactic acid (LA) is calculated according to the following formula:

LA conversion (%) = 100 x ([LA]c feedstock - [LA]c effluent)/[LA]c feedstock with [LA]c = LA carbon concentration in gC/1, determined by HPLC.

[0212] The acrylic acid (AA) carbon yield is determined according to the following formula:

AA Yield (%) = 100 x [AA]c effluent/[LA]c feedstock

[0213] The results are presented in Table 4 below.

Table 4.

[0214] The catalysts Bl, B3, DI and D3 convert a feedstock of lactic acid into acrylic acid with a carbon yield of greater than 50%, 160 hours with feedstock. The catalysts B3 and D3 in accordance with the invention have an acrylic acid (AA) yield which is greater than those obtained respectively by the not-in-accordance catalysts Bl and DI . During the discharging of the catalysts Bl and DI, the latter are no longer integrated and a part of the KPO3 is found again in the reactor. The catalysts B3 and D3 are identical in appearance to the charged catalyst after 160 hours under operating conditions.

[0215] The catalysts B3 and D3 in accordance with the invention are thus more active and stable during the reaction for the dehydration of lactic acid to give acrylic acid than the not-in- accordance catalysts Bl and DI.

Claims

1. Macroporous material based on at least one potassium phosphate salt and/or on at least one caesium phosphate salt and on silica, characterized in that the silica is provided at least partially in the cristobalite and/or tridymite crystalline form.

2. Material according to claim 1 , characterized in that said potassium phosphate salt and/or said caesium phosphate salt is chosen from potassium metaphosphate (KPO3) and/or caesium metaphosphate (CsPCh).

3. Material according to claim 2, characterized in that said material exhibits an MPCh/CMPCh + SiCh) ratio by weight of between 13 and 50 with M being potassium and/or caesium.

4. Material according to any one of claims 1 to 3, characterized in that said material exhibits a total pore volume of between 0.01 and 0.6 cm³/g.

5. Material according to any one of claims 1 to 4, characterized in that said material exhibits a macropore volume of between 0.01 and 0.6 cm³/g.

6. Material according to any one of claims 1 to 5, characterized in that the macropore volume represents between 50% and 100% of the total pore volume of said material.

7. Material according to any one of claims 1 to 6, characterized in that said material exhibits a specific surface of greater than 1 m²/g and less than 50 m²/g.

8. Material according to any one of claims 1 to 7, characterized in that said material exhibits a mechanical strength value, measured by single pellet crushing, of greater than 0.5 daN/mm.

9. Material according to any one of claims 1 to 8, characterized in that said material comprises between 1% and 99% by weight of at least one potassium or caesium phosphate salt, w ith respect to the total weight of said material.

10. Material according to any one of claims 1 to 9, characterized in that said material exhibits between 50% and 90% by weight of silica, with respect to the total weight of said material.

11. Material according to any one of claims 1 to 10, characterized in that the silica is provided in the cristobalite crystalline form.

12. Material according to any one of claims 1 to 11, characterized in that said material comprises a median macropore diameter of between 80 nm and 7000 nm.

13. Material according to any one of claims 1 to 12, characterized in that said material is provided in the form of beads, extrudates, pellets or irregular and non-spherical agglomerates.

14. Process for the dehydration of a feedstock comprising at least one hydroxypropanoic acid and its derivatives in the presence of the material according to any one of claims 1 to 13 as catalyst, at a temperature of between 180°C and 450°C. at a pressure of between 0.1 MPa and 12 MPa, and at a flow rate by weight of feedstock to weight of material ratio of between 0.01 h ¹ and 100 h ¹.

15. Process according to claim 14, characterized in that said feedstock comprises a hydroxypropanoic acid chosen from 2-hydroxypropanoic acid and 3-hydroxypropanoic acid.