Magnetic material comprising iron and a clay matrix

Abstract

The invention relates to a magnetic material comprising at least iron, in metal form and / or in oxide form, and at least one clay matrix, the iron content being between 15% and 70% by weight of iron element relative to the total weight of said material, characterized in that said material has a specific surface area greater than 1 m² / g and less than 50 m² / g, and said material is in the form of beads or extrudates, and in that said material comprises at most 25% by weight of hematite relative to the total weight of said material.

Description

[0001] MAGNETIC MATERIAL COMPRISING IRON AND A CLAY MATRIX

[0002] Scope of the invention

[0003] The invention relates to a novel composite magnetic material containing metallic iron and / or iron oxide and a clay matrix. The magnetic material is capable of providing induced heating in response to an applied alternating magnetic field. The material can advantageously be used as a heating material in a catalytic reactor, as a catalyst support, or as a catalyst in catalytic processes, particularly processes for the conversion of bio-based molecules and the conversion of carbon dioxide.

[0004] Previous art

[0005] Electromagnetic induction heating technology is used in numerous fields of application, such as metallurgy, biomedical applications, and more recently, catalytic oxidation reactions. This technology enables significant, locally targeted heating, very close to the active sites. It is therefore particularly advantageous for endothermic reactions of heat-sensitive compounds with short reactor lifetimes, such as bio-based oxygenated products.

[0006] This heating technology typically uses magnetic materials (superparamagnetic, ferromagnetic, ferrimagnetic) as heating agents. These magnetic materials generally consist of a magnetic core composed of one or more metals or oxides. Examples include iron, cobalt, nickel, copper, and the alloys FeCo, NiCo, NiFe, CuNi, and CuCo.

[0007] Such a material can be used pure or incorporated into an oxide matrix, for example, by impregnating a powder or a pre-formed oxide matrix. With this preparation method, the amount of magnetic material incorporated is small, generally less than 20% by weight, and distributed exclusively on the surface of the oxide matrix. The heating, being inhomogeneous, does not occur at the core of the oxide grain.

[0008] Exxon patents US 4,252,679 and US 4,255,289 disclose a magnetic catalyst composed of an iron or cobalt alloy dispersed in an alumina oxide matrix by spray-drying with the addition of phosphoric acid. The grain size of the magnetic catalyst is less than 800 µm. US patent application US2023 / 0356198 describes the use of a catalytic composition consisting of a magnetic material containing ferrite and a catalytic agent, in powder form, coated onto ceramics, particularly for NOx oxidation reactions.

[0009] Patent application WO2017 / 186608 discloses a porous ferromagnetic material, in powder form, with a spinel, inverted spinel, or perovskite-type structure for vapor reforming with induction heating. Patent application WO2020 / 254184 describes a ceramic-type catalyst support comprising particles with a ferromagnetic core and an oxide shell, said particles being dispersed in an oxide matrix. The particle size is less than 500 pm, preferably less than 10 pm. The support has a specific surface area greater than 1 m². 2 / g, preferably between 5 and 50 m 2 / g.

[0010] Patents FR3100990 and FR3100988 disclose a methanation process in the presence of a ferromagnetic material in the form of micrometric powder and / or wires based on iron or an iron alloy, said material being suitable for heating by magnetic induction using a magnetic field inductor.

[0011] Therefore, there is still a strong interest in developing new magnetic materials that can be used as a heating material for energy-intensive endothermic catalytic reactions.

[0012] The Applicant has developed a novel shaped magnetic material capable of providing induced heating in response to an applied alternating magnetic field. This material can be used as a heating material for the dehydration reaction of a charge containing an alcohol, and as both a heating material and a catalyst for the CO2 reduction reaction. Furthermore, the material according to the invention is stable under hydrothermal conditions, i.e., conditions combining water pressure and temperature. Its textural and magnetic properties are preserved.

[0013] Objects of the invention

[0014] The present invention relates to a magnetic material comprising at least iron, in metallic form and / or in oxide form, and at least a clay matrix, the iron content being between 15% and 70% by weight as elemental iron relative to the total weight of said material, characterized in that said material has a specific surface area greater than 1 m² 2 / g and less than 50 m 2 / g, said material is in the form of beads or extrudates, and said material comprises at most 25% by weight of hematite relative to the total weight of said material.

[0015] According to one or more embodiments of the invention, the volume of the macropores is between 30% and 100% by volume relative to the total porous volume of the material.

[0016] According to one or more embodiments of the invention, the macroporous median diameter of the material is greater than 50 nm and less than or equal to 500 nm.

[0017] According to one or more embodiments of the invention, the material has a macroporous volume of between 0.05 and 0.5 cm 3 / g.

[0018] According to one or more embodiments of the invention, said material has a mechanical resistance value measured by grain-by-grain crushing greater than 0.6 daN / mm.

[0019] According to one or more embodiments of the invention, said material has a specific absorption rate of between 2 W / g and 120 W / g after activation by a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

[0020] Another object according to the invention relates to a process for preparing a magnetic material according to the invention comprising at least the following steps: a) at least one source of iron in metallic or oxide or oxyhydroxide form, a clay source and at least one solvent are brought into contact to obtain a paste, said iron source being in the form of a powder with a grain size between 1 and 500 pm; b) the paste obtained at the end of step a) is shaped to obtain a material precursor; c) the material precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried material precursor; d) the dried material precursor obtained at the end of step c) is calcined at a temperature between 250°C and 1000°C.

[0021] According to one or more embodiments of the invention, the process comprises a step e) in which the material obtained at the end of step d) is reduced at a temperature between 200°C and 600°C for a duration between 1 and 10 hours in the presence of a reducing gas. According to one or more embodiments of the invention, the material obtained at the end of step d) is subjected to hydrothermal treatment at a temperature between 100°C and 1100°C.

[0022] According to one or more embodiments of the invention, step e) is carried out in the presence of a reducing gas comprising between 25 vol% and 100 vol% of hydrogen, the hydrogen flow rate being between 0.01 and 100 NL / hour / gram of material.

[0023] According to one or more embodiments of the invention, the iron source is chosen from metallic iron, magnetite, maghemite, goethite, lepidocrocite and hematite, taken alone or in mixture.

[0024] According to one or more embodiments of the invention, the clay source is chosen from kaolin, kaolinite, metakaolin, and montmorillonite, taken alone or in mixture.

[0025] Another object according to the invention comprises an active phase based on at least one metal selected from groups 6 to 11 of the periodic table, preferably selected from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, and a support in the form of a magnetic material according to the invention or prepared according to the material preparation process according to the invention.

[0026] According to one or more embodiments of the invention, said metal is chosen from Co, Ni, and Cu, and in which the content of said metal is between 0.5% and 30% by weight of the element of said metal relative to the total weight of the catalyst.

[0027] According to one or more embodiments of the invention, said metal is chosen from Pt, Pd, Au, Ag, Ru, and in which the content of said metal is between 0.01% and 10% by weight of the element of said metal relative to the total weight of the catalyst.

[0028] Another object of the invention relates to a process for preparing a catalyst according to the invention comprising at least the following steps: f1) a liquid solution in aqueous or organic phase is prepared comprising at least one precursor of the active phase based on at least one metal selected from groups 6 to 11 of the periodic table, preferably selected from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, preferably at a temperature between 5°C and 80°C, more preferably between 10°C and 70°C; f2) the solution prepared in step f1) is impregnated onto the material according to the invention or prepared according to the invention, the volume of the solution advantageously being between 0.9 and 1.1 times the porous volume of said material; f3) optionally, the catalyst precursor obtained in step f2) is subjected to maturation in order to obtain a catalyst precursor;f4) the catalyst precursor obtained in step f2), optionally f3), is dried at a temperature greater than or equal to 15°C and less than 250°C; f5) the catalyst precursor obtained in step f4) is calcined at a temperature between 250°C and 600°C.

[0029] Another object according to the invention relates to a CO2 hydrogenation process carried out at a temperature between 180°C and 800°C, at a pressure between 0.1 MPa and 13 MPa, at a hydrogen / CCh molar ratio between 0.1 and 10 and at an hourly volumetric rate between 100 h' 1 and 40,000 h' 1 in the presence of a catalyst according to the invention, said process being implemented under the action of a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

[0030] Another object of the invention relates to a process for dehydrating a feed comprising at least one alcohol, carried out at a temperature between 180°C and 450°C, at a pressure between 0.1 MPa and 12 MPa, at a mass flow rate ratio of the feed divided by the total mass of the material and the catalyst of between 0.01 and 12 MPa. -1 and 100 h- 1 in the presence of a dehydration catalyst and a magnetic material according to the invention, said process being carried out under the action of a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

[0031] Detailed description of the invention

[0032] Definitions

[0033] In what follows, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC Press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII (or VIIIB) according to the CAS classification corresponds to the metals in columns 8, 9, and 10 according to the new IUPAC classification.

[0034] Mass percentages are expressed relative to the anhydrous mass of the final composite material. This anhydrous mass is determined by a measurement called Loss on Ignition (LOI), which corresponds to the mass change resulting from heating the sample to 1000°C for 2 hours. Loss on ignition is expressed as a percentage by mass of the dry matter. The BET specific surface area is measured by nitrogen physisorption according to ASTM D3663-03, a method described in the book by Rouquerol F.; Rouquerol J.; Singh K. "Adsorption by Powders & Porous Solids: Principle, methodology and applications", Academic Press, 1999.

[0035] In this description, according to the IUPAC convention, micropores are defined as pores with a diameter less than 2 nm, i.e. 0.002 pm; mesopores are pores with a diameter greater than or equal to 2 nm, i.e. 0.002 pm and less than or equal to 50 nm, i.e. 0.05 pm; and macropores are pores with a diameter greater than 50 nm, i.e. 0.05 pm.

[0036] The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example using a Microméritics™ Autopore III™ instrument.

[0037] To obtain better accuracy, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with the mercury porosimeter measured on the sample less the value of the total pore volume measured by intrusion with the mercury porosimeter measured on the same sample for a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0038] The volume of macropores and mesopores is measured by mercury intrusion porosimetry according to ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°. The value at which mercury fills all intergranular voids is set at 0.2 MPa, and beyond this point, mercury is considered to penetrate the pores of the sample.

[0039] The macroporous volume of the material according to the invention is defined as the cumulative volume of mercury introduced at a pressure between 0.2 MPa and 30 MPa, corresponding to the volume contained in pores with an apparent diameter greater than 50 nm.

[0040] The mesoporous volume of the material according to the invention is defined as the cumulative volume of mercury introduced at a pressure between 30 MPa and 400 MPa, corresponding to the volume contained in pores with an apparent diameter between 2 nm and 50 nm. The mesoporous median diameter is also defined as the diameter such that all pores, among all the pores constituting the mesoporous volume, smaller than this diameter constitute 50% of the total mesoporous volume determined by mercury porosimeter intrusion.

[0041] The metal content is measured by X-ray fluorescence or by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0042] The crystallographic structure of metallic iron or oxide is determined by the X-ray diffraction (XRD) technique. More specifically, in the case of a copper source, the 20 lines at 44.69° and 65.05° are associated with the crystallographic form of metallic iron, the 20 lines at 30.08°, 35.43°, 56.94°, and 62.53° are associated with the magnetite crystallographic form, the 20 lines at 30.26°, 35.65°, 43.33°, 57.31°, and 62.95° are associated with the maghemite crystallographic form, and the 20 lines at 33.16°, 35.64°, and 49.47° are associated with the maghemite crystallographic form. 54.08° and 62.95° are associated with the hematite crystallographic form.

[0043] Throughout this text, lateral crush resistance refers to the mechanical resistance of the material according to the invention as determined by the grain-by-grain crush (GBC) test. This is a standardized test (ASTM D4179-01) that involves subjecting a material in the form of a millimeter-sized object, such as a ball, pellet, or extrudate, to a compressive force that causes it to break. This test is therefore a measure of the material's tensile strength. The analysis is repeated on a number of individual solids, typically between 10 and 200. The average of the measured lateral fracture forces constitutes the average GBC, which is expressed in units of force (N) for granules and in units of force per unit length (daN / mm or decaNewtons per millimeter of extrudate length) for extrudates.

[0044] In the following text, the grain size or particle size distribution of the constituents of the materials obtained according to the invention is measured using laser scattering particle size analysis. This indirect measurement technique allows the determination of the particle size distribution (on the micron to millimeter scale). This analytical method uses the principle of light scattering (Mie theory) and / or diffraction (Fraunhofer theory and Mie theory). Particles illuminated by the laser light deflect the light from its principal axis. The amount of light deflected and the magnitude of the deflection angle allow for the precise measurement of the particle size. The powder is conveyed by a solvent (water, isopropanol) or by air before passing in front of the laser beam. Two paths are thus distinguished: the wet path and the dry path.

[0045] The wet method allows for the characterization of dispersions (elementary particle size distribution after dispersion) or suspended solids (aggregate particle size distribution). The measured particles range from 0.02 pm to 2000 pm.

[0046] Dry particle size analysis allows for the characterization of powders without disrupting their initial aggregation. The measurement range extends from 0.2 µm to 2000 µm. In the present invention, the dry method is used to measure the grain size of the constituents of the material of the invention.

[0047] The heating capacity of a material is defined by its specific absorption rate (SAR). It corresponds to the amount of energy absorbed per unit mass as a function of the intensity of the applied alternating magnetic field and is expressed in watts per gram of material. SAR is measured by calorimetry. More precisely, it involves measuring the temperature rise per unit time when the sample is heated by magnetic induction. To do this, a quantity of material is weighed and placed in a tube in the presence of water and a thermocouple. The tube is then placed at the center of a coil that applies an alternating magnetic field of 47.1 mT at a frequency of 93 kHz. The SAR value is then determined by the following equation: with Cpi and mi representing respectively the specific heat capacities and the masses introduced of the elements of the system.

[0048] By hourly volumetric velocity “PPH”, we mean the mass flow rate of the feed at the reactor inlet in kg / h at 15°C and 0.1 MPa, divided by the mass of material in kg contained in the reactor.

[0049] For the purposes of this invention, a clay matrix is ​​defined as a matrix comprising one or more silicate or aluminosilicate-based materials, which may, for example, be kaolin, kaolinite, metakaolin, or montmorillonite. Magnetic material

[0050] A first object of the invention relates to a magnetic material comprising at least iron, in metallic form and / or in oxide form, and at least a clay matrix, the iron content being between 15% and 70% by weight as elemental iron relative to the total weight of said material, characterized in that said material has a specific surface area greater than 1 m² 2 / g and less than 50 m 2 / g, said material is in the form of beads or extrudates, and said material comprises at most 25% by weight of hematite relative to the total weight of said material.

[0051] The magnetic material according to the invention is capable of providing induced heating in response to an applied alternating magnetic field. Heating is thus initiated within a reaction chamber itself, rapidly and with minimal energy input, resulting in significant energy cost savings.

[0052] The said material has an iron content of between 15% and 70% by weight, preferably between 20% and 65% by weight, and even more preferably between 25% and 60% by weight in iron element relative to the total weight of the material.

[0053] According to an essential feature of the invention, the magnetic material comprises at most 25% by weight of hematite relative to the total weight of said material, preferably at most 10% by weight, more preferably at most 5% by weight, and even more preferably at most 3% by weight relative to the total weight of the material. In one embodiment of the invention, said magnetic material does not comprise hematite. In another embodiment of the invention, said material comprises between 0.1% and 25% by weight of hematite relative to the total weight of said material, preferably between 0.5% and 10% by weight, and even more preferably between 1% and 5% by weight. Above 25% by weight, the magnetic properties of the material are degraded, making it impossible to provide effective heating when an alternating magnetic field is applied.

[0054] Preferably, said material has a total pore volume (TPV) between 0.01 and 0.5 cm³ 3 / g, more preferably between 0.01 and 0.45 cm 3 / g, even more preferably between 0.01 and 0.40 cm 3 / g, and even more preferably between 0.05 and 0.40 cm 3 / g.

[0055] Preferably, said material has a mesoporous volume between 0.01 and 0.3 cm³ 3 / g, more preferably between 0.01 and 0.25 cm 3 / g, even more preferably between 0.02 and 0.20 cm 3 / g, and even more preferably between 0.02 and 0.15 cm 3 / g. Preferably, the volume of the mesopores represents between 1% and 55% by volume of said total porous volume of said material, preferably between 2% and 50%, and even more preferably between 5% and 40%.

[0056] Preferably, said material has a macroporous volume between 0.05 and 0.5 cm³ 3 / g, more preferably between 0.07 and 0.45 cm 3 / g, even more preferably between 0.10 and 0.40 cm 3 / g, and even more preferably between 0.15 and 0.35 cm 3 / g.

[0057] Preferably, the volume of macropores represents between 30% and 100% by volume of said total porous volume of said material, preferably between 35% and 99%, and even more preferably between 40% and 98%.

[0058] Preferably, the macroporous median diameter of the material is greater than 50 nm and less than or equal to 500 nm, preferably between 60 nm and 400 nm, and even more preferably between 65 nm and 350 nm.

[0059] The said material has a specific surface area greater than 1 m² 2 / g and less than 50 m 2 / g, preferably between 2 m 2 / g and 45 m 2 / g, more preferentially between 2 m 2 / g and 40 m 2 / g.

[0060] Advantageously, said material has a mechanical resistance value measured by grain-by-grain crushing greater than 0.6 daN / mm, preferably greater than 0.65 daN / mm, more preferably greater than 0.7 daN / mm.

[0061] According to one or more embodiments, said material exhibits a SAR between 2 W / g and 120 W / g after activation by a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

[0062] The said material is in the form of beads or extrudates.

[0063] When the material 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.

[0064] When the material is in extruded form, the length of the extruded piece is generally between 2 mm and 10 mm, preferably between 2 mm and 8 mm, and more preferably between 3 mm and 6 mm. When the material is in extruded form, the extruded pieces generally have a diameter between 0.5 mm and 10 mm, preferably between 1.0 mm and 2.5 mm, and a length between 1.0 mm and 2.0 mm.

[0065] The aspect ratio of an object is defined as the ratio between its length and width. Preferably, the material has an aspect ratio greater than 2.

[0066] Material preparation process

[0067] According to the invention, the present invention relates to a process for preparing a magnetic material according to the invention comprising at least the following steps: a) at least one source of iron in metallic or oxide or oxyhydroxide form, a clay source and at least one solvent are brought into contact to obtain a paste, said iron source being in the form of a powder with a grain size between 1 µm and 500 µm; b) the paste obtained at the end of step a) is shaped to obtain a material precursor; c) the material precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried material precursor; d) the dried material precursor obtained at the end of step c) is calcined at a temperature between 250°C and 1000°C.

[0068] Steps a) to d) are described in detail below. Additional optional steps may be performed. These optional steps are also described below.

[0069] According to the invention, the process includes a step a) of bringing into contact at least one source of iron in metallic or oxide or oxyhydroxide form, a source of clay and at least one solvent to obtain a paste.

[0070] Advantageously, the iron source is chosen from metallic iron, magnetite, maghemite, goethite, lepidocrocite, and hematite, taken alone or in mixtures. Preferably, the iron source is metallic iron, magnetite, maghemite, and goethite, taken alone or in mixtures. The iron source in metallic, oxide, or oxyhydroxide form added in step a) advantageously has a grain size between 1 µm and 50 µm, preferably between 1 µm and 40 µm, and even more preferably between 1 µm and 10 µm. The grain size of the metallic iron, oxide, or oxyhydroxide is advantageously measured by dry laser granulometry.

[0071] Advantageously, the clay source is chosen from kaolin, kaolinite, metakaolin, or montmorillonite. Preferably, the clay source is kaolin.

[0072] Preferably, the clay source added in step a) is chosen without restriction from the following commercial sources: ARGICAL™ M1000 (Imerys), ARGICAL™ M1200S (Imerys), MetaStar® 501 (Imerys), MetaStar® 501 HP (Imerys), Sorbix® (Imerys).

[0073] Within the framework of the invention, it is entirely possible to proceed with mixtures of several different iron powders and / or different clay powders.

[0074] According to the invention, at least one solvent is added in step a). Said solvent is advantageously chosen from water, ethanol, alcohols and amines. Preferably, said solvent is water.

[0075] In one embodiment according to the invention, at least one organic adjuvant is also added during step a). Said organic adjuvant may be chosen from all additives known to those skilled in the art. Preferably, said organic adjuvant is chosen from cellulose derivatives, polyethylene glycols, monocarboxylic aliphatic acids, alkylated aromatic compounds, sulfonic acid salts, fatty acids, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, polyacrylates, polymethacrylates, polyisobutene, polytetrahydrofuran, starch, polysaccharide-type polymers (such as xanthan gum), scleroglucan, hydroxyethylated cellulose-type derivatives, carboxymethylcellulose, lignosulfonates, and galactomannan derivatives, taken alone or in mixtures.

[0076] Preferably, said organic adjuvant may be mixed in powder form or in solution in said solvent.

[0077] Preferably, step a) is carried out by mixing, either batch or continuous. If step a) is carried out batch, it is preferably performed in a mixer equipped with Z-arms, cams, or any other type of mixer, such as a planetary mixer. This mixing step a) results in a homogeneous paste or mixture of the components.

[0078] In the case of the implementation of a "Z-arm" type mixer, the rotation speed of the mixer arms is advantageously between 10 and 75 revolutions per minute, preferably between 25 and 50 revolutions per minute.

[0079] In the case of implementation in a centrifugal planetary mixer, the rotation speed is advantageously between 300 and 2000 revolutions per minute, preferably between 1500 and 2000 revolutions per minute in order to obtain a paste.

[0080] Preferably, the following quantities are introduced in step a):

[0081] - 10% to 90% by weight, preferably 20% to 80% by weight, preferably 30% to 70% by weight, and most preferably 35% to 65% by weight and even more preferably 40% to 60% by weight of at least one metallic iron powder or oxide;

[0082] - 10% to 90% by weight, preferably 20% to 80% by weight, preferably 30% to 70% by weight, and most preferably 35% to 65% by weight and even more preferably 40% to 60% by weight of at least one clay powder;

[0083] - 0% to 20% by weight, preferably 1% to 15% by weight, preferably 1% to 10% by weight, and most preferably 1% to 7% by weight of at least one organic adjuvant, the percentages by weight being expressed in relation to the total weight of said material and the sum of the contents of each of the compounds of said material being equal to 100%.

[0084] According to the invention, said process includes a step b) of shaping the dough obtained at the end of step a).

[0085] Preferably, the paste obtained at the end of step a) is advantageously shaped by extrusion.

[0086] If the shaping of the mixture from step a) is carried out by extrusion, step b) is advantageously performed in a piston, single-screw, or twin-screw extruder. In this case, an organic additive may optionally be added in step a) as described above. The presence of this organic additive facilitates shaping by extrusion. This organic additive is described above and is introduced in step a) in the proportions indicated above.

[0087] Extrusion can be performed either by extruding directly from the end of a continuous mixer, such as a twin-screw type, or by connecting one or more batch mixers to an extruder. The die geometry, which gives the extruded products their shape, can be chosen from among the dies well-known to those skilled in the art. These can be, for example, cylindrical or multilobed (e.g., trilobed or quadrilobed).

[0088] In the case where the shaping of the mixture from step a) is carried out by extrusion, the quantity of solvent added in step a) of mixing is adjusted so as to obtain, at the end of this step and whatever the variant implemented, a mixture or paste which does not flow but is not too dry either in order to allow its extrusion under suitable pressure conditions well known to the person skilled in the art and dependent on the extrusion equipment used.

[0089] Preferably, said step b) of shaping by extrusion is carried out at an extrusion pressure greater than 1 MPa and preferably between 3 MPa and 10 MPa.

[0090] The preparation process according to the invention includes a step c) of drying the precursor material obtained at the end of step b). Said drying step is advantageously carried out at a temperature below 250°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.

[0091] Preferably, this drying stage 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 stage ensures good hydration of the material, which is necessary to limit the appearance of cracks that would be detrimental to mechanical strength.

[0092] Step d) According to the invention, the dried material precursor obtained at the end of step c) undergoes a calcination step d) at a temperature between 250°C and 1000°C, preferably between 300°C and 900°C, and even more preferably between 400°C and 600°C. Step d) is carried out for a duration advantageously between 1 and 12 hours, and preferably between 1 and 4 hours. This calcination step is particularly useful for removing the organic additives used to facilitate shaping the material.

[0093] The calcination step (d) is advantageously carried out under a gas stream comprising oxygen; for example, preferably the material precursor is calcined under dry air or with varying humidity levels, or alternatively, treated at temperature in the presence of a gas mixture comprising an inert gas, preferably nitrogen, and oxygen. The gas mixture used preferably comprises at least 5% by volume, or even more preferably at least 10% by volume, oxygen.

[0094] At the end of step d), a material is obtained according to an embodiment of the invention. However, the preparation process may include additional steps which are described in detail below.

[0095] In one embodiment of the invention, the process includes a hydrothermal treatment step in the presence of steam. The hydrothermal treatment is carried out by any technique known to those skilled in the art. Hydrothermal treatment is understood to mean contacting the material or material precursor with water in vapor or liquid phase at any stage of its preparation. Hydrothermal treatment may include, in particular, curing, steam treatment (or steaming, according to Anglo-Saxon terminology), autoclaving, calcination under humid air, and rehydration.

[0096] Preferably, the hydrothermal treatment step is carried out between step d) calcination and any step e) reduction. In a preferred embodiment, said hydrothermal treatment step may, where appropriate, replace step d) calcination entirely or partially.

[0097] In a highly preferred embodiment, the hydrothermal treatment step is carried out at atmospheric pressure, at a temperature between 200°C and 1100°C, preferably between 400°C and 1000°C, for a period of between 30 minutes and 5 hours. The water content in the gas is between 5% and 100%, preferably between 10% and 90%.

[0098] In another highly preferred embodiment, the hydrothermal treatment step is carried out under partial water pressure. The material or material precursor can thus advantageously undergo hydrothermal treatment in a confined atmosphere or by autoclaving. Hydrothermal treatment in a confined atmosphere is defined as treatment by autoclaving in the presence of water at a temperature above ambient temperature.

[0099] According to this highly preferred embodiment of the invention, the hydrothermal treatment is a treatment under a flow containing water vapor and a gas, at a specific temperature and pressure. The gas is advantageously air or nitrogen. The water content in the gas is between 5% and 100%, preferably between 10% and 90%. The temperature during the hydrothermal treatment can be between 100°C and 1100°C, preferably between 100°C and 450°C, and preferably between 200°C and 450°C, for a period of between 30 minutes and 24 hours, and preferably between 30 minutes and 4 hours. The partial pressure of water is between 0.1 MPa and 10 MPa, preferably between 0.11 MPa and 7.5 MPa, and even more preferably between 0.1 MPa and 5 MPa.

[0100] Step e) reduction (optional)

[0101] The calcination, or hydrothermal treatment, stage is advantageously followed by a temperature reduction treatment. This heat reduction treatment is advantageously carried out at a temperature between 200°C and 600°C, preferably between 220°C and 500°C, and even more preferably between 250°C and 475°C, under a flow or atmosphere containing hydrogen. This reduction process is particularly useful for reducing iron oxide to metallic iron.

[0102] The reduction is carried out in the presence of a reducing gas advantageously comprising between 25 vol% and 100 vol% hydrogen, preferably 100 vol% hydrogen. The hydrogen may optionally be supplemented with an inert gas for the reduction, preferably argon, nitrogen, or methane.

[0103] The duration of the reduction treatment is between 1 and 10 hours, preferably between 2 and 8 hours. The hydrogen flow rate, expressed in NL / hour / gram of material, is between 0.01 and 100 NL / hour / gram of material, preferably between 0.05 and 10 NL / hour / gram of material, and even more preferably between 0.1 and 5 NL / hour / gram of material.

[0104] Another object according to the invention relates to a catalyst comprising an active phase based on at least one metal chosen from groups 6 to 11 of the periodic table, preferably chosen from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, and a support in the form of a material according to the invention.

[0105] In an embodiment according to the invention, said metal is chosen from the metals Co, Ni, Cu, taken alone or in mixture.

[0106] The content of the metal chosen from Co, Ni, Cu is preferably between 0.5% and 30% by weight, preferably between 1% and 20% by weight, even more preferably between 2% and 15% by weight and even more preferably between 3% and 12% by weight of the element of said metal in relation to the total weight of the catalyst.

[0107] In another embodiment according to the invention, said metal is chosen from the metals Pt, Pd, Au, Ag, Ru, taken alone or in mixture.

[0108] The content of the metal chosen from Pt, Pd, Au, Ag, Ru is preferably between 0.01% and 10% by weight, preferably between 0.05% and 5% by weight of the element of said metal relative to the total weight of the catalyst.

[0109] Catalyst preparation process

[0110] Another object according to the invention relates to a process for preparing a catalyst according to the invention. In an embodiment according to the invention, the preparation process comprises at least the following steps: f1) a liquid solution in aqueous or organic phase is prepared comprising at least one precursor of the active phase based on at least one metal selected from groups 6 to 11 of the periodic table, preferably selected from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, preferably at a temperature between 5°C and 80°C, more preferably between 10°C and 70°C; f2) the solution prepared in step f1) is impregnated onto the material according to the invention or obtained according to the process of preparing the material according to the invention, the volume of the solution being advantageously between 0.9 and 1.1, preferably between 0.8 and 1.05 times the porous volume of the material;f3) Optionally, the catalyst precursor obtained in step f2) is subjected to maturation in order to obtain a catalyst precursor; f4) the catalyst precursor obtained in step f2), optionally f3), is dried at a temperature greater than or equal to 15°C and less than 250°C; f5) the catalyst precursor obtained in step f4) is calcined at a temperature between 250°C and 600°C; f6) Optionally, the catalyst obtained at the end of step f5) is reduced at a temperature between 200°C and 600°C for 1 hour and 10 hours in the presence of a reducing gas.

[0111] The impregnation solution of step f1) is preferably prepared by dissolving in aqueous or organic phase one or more precursors of the active phase based on at least one metal chosen from groups 6 to 11 of the periodic table, preferably from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, alone or in mixtures. The precursors are preferably chosen from salts of carbonate, nitrate, sulfate, formate, acetate, citrate, lactate, chloride, hydroxide, oxide, or metal organic complexes.

[0112] Preferably, a maturation step f3) is carried out for a duration of between 1 minute and 72 hours, preferably between 30 minutes and 72 hours, most preferably between 1 hour and 48 hours, and even more preferably between 1 hour and 24 hours. Advantageously, step f3) is carried out at atmospheric pressure, in a water-saturated atmosphere, and at a temperature between 17°C and 50°C, preferably at ambient temperature.

[0113] Preferably, drying step f4) is advantageously carried out at a temperature greater than or equal to 15°C and less than 250°C, preferably between 15°C and 180°C, more preferably between 30°C and 160°C, even more preferably between 50°C and 150°C, and even more preferably between 70°C and 140°C, for a duration typically between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 5 hours. Longer durations are not excluded, but do not necessarily provide any improvement. The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gases and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure.Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

[0114] Preferably, calcination step f5) is carried out at a temperature between 250°C and 600°C, preferably between 350°C and 550°C, for a duration typically between 0.5 hours and 24 hours, preferably between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 10 hours, preferably under an inert atmosphere or an atmosphere containing oxygen. Longer durations are not excluded, but do not necessarily provide any improvement.

[0115] The calcination step (f5) can optionally be followed by a temperature reduction treatment (step f6). The reduction heat treatment is advantageously carried out at a temperature between 200°C and 600°C, preferably between 220°C and 500°C, and even more preferably between 250°C and 475°C, under a flow or atmosphere containing hydrogen. This reduction process is particularly effective in reducing iron oxide to metallic iron.

[0116] The reduction is carried out in the presence of a reducing gas advantageously comprising between 25 vol% and 100 vol% hydrogen, preferably 100 vol% hydrogen. The hydrogen may optionally be supplemented with an inert gas for the reduction, preferably argon, nitrogen, or methane.

[0117] The duration of the reduction treatment is between 1 hour and 10 hours, preferably between 2 hours and 8 hours.

[0118] The hydrogen flow rate, expressed in NL / hour / gram of material, is between 0.01 and 100 NL / hour / gram of material, preferably between 0.05 and 10 NL / hour / gram of material, even more preferably between 0.1 and 5 NL / hour / gram of material.

[0119] CO2 conversion process using hydrogenation

[0120] The catalyst according to the invention can advantageously be used in a CO2 hydrogenation conversion process.

[0121] The CO2 hydrogenation process, which operates in the presence of the catalyst according to the invention, is advantageously carried out at a temperature between 180°C and 800°C, preferably between 190°C and 750°C, most preferably between 250°C and 700°C, and most preferably between 250°C and 600°C, at a pressure between 0.1 and 12 MPa, preferably between 0.11 MPa and 10 MPa, most preferably between 0.13 MPa and 9 MPa, and most preferably between 0.15 MPa and 8 MPa, at a hydrogen / carbon dioxide molar ratio between 0.1 and 10, and at an hourly volumetric rate between 100 and 40,000 h / s -1 in the presence of the catalyst according to the invention or prepared by the process according to the invention described above.

[0122] The heat required for the catalytic reaction is supplied by radiation from the material according to the invention, induced in response to an applied alternating magnetic field. The magnetic field can, in particular, be generated by a field inductor and have an amplitude between 1 mT and 80 mT, preferably between 1 mT and 50 mT, with a frequency between 30 kHz and 500 kHz, preferably between 90 and 300 kHz.

[0123] In the process according to the invention, carbon dioxide is hydrogenated to carbon monoxide, methane or methanol depending on the operating conditions.

[0124] The effluents consist mainly of carbon monoxide, water, hydrogen, methanol, methane, and unconverted carbon dioxide. By-products of the reaction, such as alcohols, alkenes, ethers, and alkanes, may also be observed.

[0125] The carbon dioxide in the gas mixture feed can come from various sources. Preferably, the CO2 comes from process exhaust gases or the environment. The hydrogen / carbon dioxide molar ratio is between 0.1 and 10, preferably between 0.5 and 5, and even more preferably between 1 and 3.

[0126] The gaseous mixture constituting the charge may contain, in addition to carbon dioxide and hydrogen, other gaseous elements such as water vapor, alkanes such as methane, propane, isobutane.

[0127] The 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.

[0128] Preferably, the catalyst is heat-treated in the reactor under a reducing atmosphere, before the injection of the feed, at a temperature between 100°C and 600°C, preferably between 150°C and 500°C, and for a duration of 30 minutes and 12 hours.

[0129] Dehydration process for an alcoholic feedstock The material according to the invention can advantageously be used in a mixture with a dehydration catalyst in a dehydration process for a feedstock comprising at least one alcohol.

[0130] The dehydration catalyst is chosen from materials known to those skilled in the art. Preferably, the catalyst is chosen from acidic solids such as amorphous or crystalline aluminosilicates, zeolites such as ZSM-5, Y, Mordenite, Ferrierite, and Beta, aluminas, phosphorus-modified aluminas, solid or oxide-supported heteropolyacids, modified silicas, and resins.

[0131] The dehydration process operates in the presence of the material prepared according to the invention and a dehydration catalyst, is advantageously carried out at a temperature between 180°C and 450°C, preferably between 190°C and 430°C, most preferably between 250°C and 420°C and most preferably between 270°C and 420°C, at a pressure between 0.1 MPa and 12 MPa, preferably between 0.11 MPa and 10 MPa, most preferably between 0.13 MPa and 9 MPa and most preferably between 0.15 MPa and 8 MPa, and at a mass flow rate ratio of feed to total mass of the material and catalyst between 0.01 h' 1 and 100 hours 1 , preferably between 0.02 h' 1 and 50 hours 1 , more preferably between 0.03 h' 1 and 30 hours 1 and in a highly preferred manner of 0.05 h -1 and 8 p.m. -1 .

[0132] The mass ratio [mass of dehydration catalyst : mass of material according to the invention] is preferably between 90:10 and 35:55, preferably between 80:20 and 40:60 and even more preferably between 75:25 and 45:55.

[0133] The loading of the reactor between the dehydration catalyst and the material according to the invention is either homogeneous or by stacking of beds of variable thickness between the catalyst and the material according to the invention.

[0134] The heat required for the catalytic reaction is supplied by radiation from the material according to the invention, induced in response to an applied alternating magnetic field. The magnetic field can, in particular, be generated by a field inductor and have an amplitude between 1 mT and 80 mT, preferably between 1 mT and 50 mT, with a frequency between 30 kHz and 500 kHz, preferably between 90 kHz and 300 kHz.

[0135] The said process makes it possible to selectively obtain a mixture of products comprising established compounds such as ethylene, propylene, or butadiene.

[0136] The said process can advantageously be carried out under a neutral or oxidizing atmosphere.

[0137] The 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, with the liquid feed being injected into the process preferably in the liquid phase. The feed for the dehydration process comprises at least one molecule with at least one alcohol functional group, such as ethanol, propanol, isopropanol, butanol, propylene glycol, butane diols, or hydroxypropanoic acids. Preferably, the feed comprises ethanol.

[0138] Said charge advantageously comprises between 1% and 99.9% by weight, preferably between 5% and 99.5% by weight, most preferably between 7% and 99% by weight and even more preferably between 8% and 98% of a molecule with at least one alcohol function.

[0139] The said charge may also include impurities related, in particular, to the processes of obtaining molecules with at least one alcohol function.

[0140] The molecules with at least one alcohol function included in said charge can be of any origin, chemical, petrochemical and / or bio-based.

[0141] Said charge advantageously comprises between 0.1% and 99% by weight, preferably between 0.5% and 90% by weight, most preferably between 1% and 80% by weight and even more preferably between 2% and 70% by weight of water.

[0142] Said charge advantageously comprises between 0.1% and 99% by weight, preferably between 0.5% and 90% by weight, most preferably between 1% and 80% by weight and even more preferably between 2% and 70% by weight of organic solvent.

[0143] The main products obtained by said process are molecules with at least one unconverted alcohol function, and unsaturated compounds resulting from the dehydration reaction.

[0144] The examples below illustrate the invention without limiting its scope.

[0145] Examples

[0146] Example 1: Preparation of materials Ax

[0147] Materials A1, A2, A5, A6 and A7 according to the invention

[0148] A powdered iron and clay source is introduced and mixed in the bowl of a Thinky™ centrifugal planetary mixer (see Table 1 for the iron sources used and the target Fe and alumina content of the material). The rotation speed is set at 1500 rpm for 30 seconds. Water is gradually added until a paste is obtained. The rotation speed is then set at 2000 rpm for 30 seconds. The resulting paste is then extruded using an MTS piston extruder with a 1.6 mm diameter cylindrical die. The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 550°C. Material A3 according to the invention (additional reduction step)

[0149] A powdered iron and clay source is introduced and mixed in the tank of a Thinky™ centrifugal planetary mixer (see Table 1 for the iron sources used and the target Fe and clay contents of the material). The rotation speed is set at 1500 rpm for 30 seconds. Water is gradually added until a paste is obtained. The rotation speed is then set at 2000 rpm for 30 seconds. The resulting paste is then extruded using an MTS piston extruder with a 1.6 mm diameter cylindrical die. The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 550°C. After calcination, the extrudates undergo a reduction step under pure H2 at atmospheric pressure for 4 hours at a temperature of 450°C with a ramp rate of 5°C / min. The reduction gas flow rate is 1 Lh / g of catalyst. The cooling step is carried out under nitrogen.

[0150] Material A4 conforming to the invention (additional hydrothermal treatment step)

[0151] A powdered iron and clay source is introduced and mixed in the tank of a Thinky™ centrifugal planetary mixer (see Table 1 for the iron sources used and the target Fe and clay contents of the material). The rotation speed is set at 1500 rpm for 30 seconds. Water is added dropwise until a paste is obtained. The rotation speed is then set at 2000 rpm for 30 seconds. The resulting paste is then extruded using an MTS piston extruder with a 1.6 mm diameter cylindrical die. The extrudates are dried for 16 hours at 120°C in a ventilated oven and then calcined for 4 hours at 550°C. Following calcination, the extrudates undergo a hydrothermal treatment at atmospheric pressure for 4 hours at a temperature of 450°C. The volumetric composition of water in the air for hydrothermal treatment is 50%.

[0152] Table 1

[0153] *Magma: mixture of Magnetite (54% by weight), Hematite (40% by weight), Geothite (6% by weight)

[0154] Example 2: Use of Ax materials for the dehydration of ethanol.

[0155] The experimental setup for implementing this reaction consists of a fixed-bed reactor with walls permeable to magnetic fields. The reactor is surrounded by a coil with a helical winding and is connected to an alternating current generator, which produces the alternating magnetic field necessary for induction heating. The coil is cooled by a water circuit to prevent overheating.

[0156] Materials A2, A3, and A4 are mixed with zeolite dehydration catalyst D at iso-mass ratio (e.g., 50% by weight of material A2 and 50% by weight of the dehydration catalyst). The mixture is active and stable for gas-phase dehydration with a water:ethanol gas mixture at a volumetric rate per hour (PPH) of 10 h -1 .

[0157] Table 2

Claims

Demands 1. Magnetic material comprising at least iron, in metallic and / or oxide form, and at least a clay matrix, the iron content being between 15% and 70% by weight as elemental iron relative to the total weight of said material, characterized in that said material has a specific surface area greater than 1 m² 2 / g and less than 50 m 2 / g, said material is in the form of beads or extrudates, and said material comprises at most 25% by weight of hematite relative to the total weight of said material.

2. Material according to claim 1, characterized in that said material comprises macropores having a diameter greater than 50 nm, and in that the volume of the macropores is between 30% and 100% by volume relative to the total porous volume of the material.

3. Material according to claim 1 or 2, characterized in that the macroporous median diameter of the material is greater than 50 nm and less than or equal to 500 nm.

4. Material according to any one of the preceding claims, characterized in that the material has a macroporous volume of between 0.05 and 0.5 cm³ 3 / g.

5. Material according to any one of the preceding claims, characterized in that said material has a mechanical resistance value measured by grain-by-grain crushing greater than 0.6 daN / mm.

6. Material according to any one of the preceding claims, characterized in that said material has a specific absorption rate of between 2 W / g and 120 W / g after activation by a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

7. A method for preparing a magnetic material according to any one of claims 1 to 6, comprising at least the following steps: a) contacting at least one source of iron in metallic or oxide or oxyhydroxide form, a clay source and at least one solvent to obtain a paste, said iron source being in the form of a powder with a grain size between 1 µm and 500 µm; b) shaping the paste obtained at the end of step a) to obtain a material precursor; c) drying the material precursor obtained at the end of step b) at a temperature below 250°C to obtain a dried material precursor; d) the dried material precursor obtained at the end of step c) is calcined at a temperature between 250°C and 1000°C.

8. Process according to claim 7, wherein said material obtained at the end of step d) is subjected to hydrothermal treatment at a temperature between 100°C and 1100°C.

9. A process according to claim 7, comprising a step e) in which the material obtained at the end of step d) is reduced at a temperature between 200°C and 600°C and for a period of between 1 hour and 10 hours in the presence of a reducing gas.

10. A method according to the preceding claim, wherein the iron source is chosen from metallic iron, magnetite, maghemite, goethite, lepidocrocite and hematite, taken alone or in mixture.

11. A method according to any one of claims 7 to 10, wherein the clay source is selected from kaolin, kaolinite, metakaolin, and montmorillonite, taken alone or in mixture.

12. Catalyst comprising an active phase based on at least one metal selected from groups 6 to 11 of the periodic table, preferably selected from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, and a support in the form of a magnetic material according to any one of claims 1 to 6 or prepared according to any one of claims 7 to 11.

13. Catalyst according to claim 12, characterized in that said metal is selected from Co, Ni, and Cu, and in which the content of said metal is between 0.5% and 30% by weight of element of said metal relative to the total weight of the catalyst.

14. Catalyst according to claim 12, characterized in that said metal is selected from Pt, Pd, Au, Ag, Ru, and in which the content of said metal is between 0.01% and 10% by weight of element of said metal relative to the total weight of the catalyst.

15. A process for preparing a catalyst according to any one of claims 12 to 14 comprising at least the following steps: f1) a liquid solution in aqueous or organic phase is prepared comprising at least one precursor of the active phase based on at least one metal selected from groups 6 to 11 of the periodic table, preferably selected from Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt, Re, Au, Ag, Mo, W, Cr, taken alone or in mixture, preferably at a temperature between 5°C and 80°C, more preferably between 10°C and 70°C; f2) the solution prepared in step f1) is impregnated onto the material according to any one of claims 1 to 6 or prepared according to any one of claims 7 to 11, the volume of the solution being advantageously between 0.9 and 1.1 times the porous volume of said material; f3) optionally, the catalyst precursor obtained in step f2) is subjected to maturation in order to obtain a catalyst precursor; f4) the catalyst precursor obtained in step f2), optionally f3), is dried at a temperature greater than or equal to 15°C and less than 250°C; f5) the catalyst precursor obtained in step f4) is calcined at a temperature between 250°C and 600°C.

16. CO2 hydrogenation process implemented at a temperature between 180°C and 800°C, at a pressure between 0.1 MPa and 13 MPa, at a hydrogen / CO2 molar ratio between 0.1 and 10 and at an hourly volumetric rate between 100 h' 1 and 40,000 h' 1in the presence of a catalyst according to any one of claims 12 to 14, said process being carried out under the action of a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

17. A process for dehydrating a feed comprising at least one alcohol, carried out at a temperature between 180°C and 450°C, at a pressure between 0.1 MPa and 12 MPa, at a mass flow rate ratio of feed divided by the total mass of the material and catalyst between 0.01 h' 1 and 100 hours 1 in the presence of a dehydration catalyst and a magnetic material according to any one of claims 1 to 6, said process being carried out under the action of a magnetic field of amplitude between 1 mT and 80 mT at a frequency between 30 kHz and 500 kHz.

Images