FR2903620A1 - MEMBRANE CATALYST FOR THE SYNTHESIS OF ACRYLIC ACID FROM GLYCEROL - Google Patents

Abstract

The present invention relates to a membrane catalyst for the synthesis of acrylic acid from glycerol, the preparation of the membrane catalyst and its use for the preparation of acrylic acid from glycerol. Said membrane catalyst comprises a first layer A consisting of a phase capable of selectively converting acrolein to acrylic acid, and a second layer B formed on said first layer A, consisting of an acid phase having a Hammett acidity H0 less than +2, capable of selectively performing the dehydration reaction of glycerol to acrolein.

Description

TECHNICAL FIELD The present invention relates to a catalyst

  membrane for the synthesis of acrylic acid from glycerol, the preparation of the membrane catalyst and its use for the preparation of acrylic acid from glycerol. PRIOR ART AND TECHNICAL PROBLEM There are numerous references in the literature on membrane reactors, but paradoxically few references describe membrane catalysts.

  In a membrane reactor, the catalyst is deposited on a porous membrane. One of the reagents or products diffuses through the membrane to react on the catalyst, or to be removed from the reaction medium. By membrane catalyst is meant a catalyst consisting of at least two layers of active material, obtained for example by depositing a layer of active material B on a grain of active material A. US Pat. No. 6,177,381 describes a catalyst composed of a inner heart and an outer layer bound to the heart. The core consists of an inorganic refractory oxide such as alpha alumina, teta alumina, cordierite, zirconia, titania or mixtures thereof, or silicon carbide or a metal. The outer layer consists of an inorganic refractory oxide, which is different from that used for the core, chosen from gamma, delta or eta aluminas, silica / alumina mixtures, zeolites or non-zeolite molecular sieves, titanium, zirconia or mixtures thereof. The inorganic refractory oxide of the outer layer is deposited in the form of a paste on the inorganic refractory oxide of the core, the paste additionally containing an organic or inorganic binding agent to facilitate the adhesion of the two layers. On the outer layer, a platinum group metal is dispersed with, on the one hand, a promoter selected from tin, germanium, rhenium, gallium, bismuth, lead, indium, cerium, zinc or mixtures thereof, and on the other hand, an modifier selected from alkali or alkaline earth metals or mixtures thereof. The catalyst thus obtained is used for alkylation, cracking, hydrocracking, isomerization, hydrogenation, dehydrogenation or oxidation reactions. It shows in particular improved durability and selectivity for the dehydrogenation of hydrocarbons.

Patent application EP 1 008 378 describes a catalyst for the treatment of exhaust gases. The catalyst comprises a first catalytic layer formed on a substrate, comprising a NOx absorption component based on at least one element selected from alkali metals, alkaline earth metals and rare earth elements. The exhaust gases are first contacted with a component, other than that absorbing NOx, selected from sodium or potassium, and a transition metal, constituting a second catalytic layer deposited on the first. This second layer has the role of absorbing sulfur and oxidizing nitrogen oxide to NOx and unsaturated hydrocarbons, before the exhaust gas is in contact with the NOx absorption component. This results in an improvement of the catalyst efficiency in terms of sulfur resistance and NOx conversion. International application WO 03/033625 describes catalysts for the selective oxidation of one or more compounds in a stream of gaseous or liquid fluids. More particularly, there is disclosed a catalyst for selective oxidation of CO in a hydrocarbon stream. The oxidation catalyst, comprising at least one platinum group element supported on a material, is covered with a molecular sieve layer acting as a semi-permeable membrane. Carbon monoxide, which is a small molecule, diffuses more easily through the molecular sieve layer than hydrocarbons and thus oxidizes preferentially in contact with the internal oxidation catalyst. It has now been found a membrane catalyst comprising two superimposed layers A and B of different active material, the outer surface layer B having the role of catalyzing a first reaction in contact with one or more reagents, the (or the) product ( s) formed at the end of this first reaction then diffusing to the inner layer A whose function is to catalyze a second reaction to give the expected final product. More particularly, a membrane catalyst has been found for the synthesis of acrylic acid from glycerol. This membrane catalyst 5 comprises two layers of superimposed solids, a surface layer B having the role of selectively catalyzing the dehydration reaction of glycerol to acrolein, another internal layer A having the role of selectively catalyzing the oxidation reaction of the acrolein to acrylic acid. The main advantage is to have a single catalyst and to be able to guarantee a homogeneous filling of the reactor, while effectively combining the energy of the two consecutive reactions used. Another advantage lies in the possibility of having catalysts having layers A and B with thicknesses and / or modulable particle sizes, thus leading to gradients of activity in the reactor.

SUMMARY OF THE INVENTION The present invention therefore relates to a membrane catalyst for the synthesis of acrylic acid from glycerol, characterized in that it comprises a first layer A consisting of a phase capable of selectively converting the acrolein to acrylic acid comprising at least one element selected from the list molybdenum, vanadium, tungsten, rhenium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, tellurium, antimony, bismuth, platinum, palladium, ruthenium, rhodium, present in the metal form or in the form of oxide, sulphate or phosphate, and a second layer B formed on said first layer A, consisting of an acid phase having a Hammett Ho acidity of less than +2, capable of selectively effecting the dehydration reaction of glycerol to acrolein. The invention also relates to a method for preparing a membrane catalyst for the synthesis of acrylic acid from glycerol, characterized in that it comprises the following steps: (a) forming a first layer A on a inert substrate from a phase capable of selectively converting acrolein to acrylic acid, comprising at least one element selected from the list 290 mol molybdenum, vanadium, tungsten, rhenium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, tellurium, antimony, bismuth, platinum, palladium, ruthenium, rhodium, present in metallic form or in oxide, sulphate or phosphate form, said first layer being formed by suspension or powder coating, or by impregnating the substrate, (b) forming a second layer B on said first layer from an acidic phase having a Hammett Ho acid of less than +2, capable of effecting the glyde dehydration reaction acrolein. The subject of the invention is also a process for producing acrylic acid from glycerol, in the gas phase and in the presence of molecular oxygen, characterized in that a membrane catalyst as defined previously or obtained according to the invention is used. the preparation method described above. DETAILED DESCRIPTION OF THE INVENTION Synthesis of acrylic acid from glycerol is based on 2 consecutive reactions, a dehydration reaction of glycerol to acrolein and an acrolein oxidation reaction to acrylic acid, according to the following reaction scheme , called oxydeshydration of glycerol to acrylic acid: CH 2 OH -CHOH-CH 2 OH CH 2 = CH-CHO + 2H 2 O CH 2 = CH-CHO + 1/2 - CH 2 = CH-COOH The membrane catalyst according to the invention is suitable for oxidation reaction of glycerol to acrylic acid. The catalyst according to the invention comprises two layers A and B consisting of different phases, each being suitable for one of the two reactions of the glycerol oxidation hydration reaction scheme. The main advantage is to combine the exothermicity of the oxidation reaction with the endothermicity of the dehydration reaction. This combination makes it possible to better manage the temperature of the catalyst, which contributes to a better thermal equilibrium of the synthesis of acrylic acid from glycerol. The first layer A constitutes a catalytic layer in the core of the catalyst and the second layer B constitutes a catalytic layer at the periphery, formed on the first layer A. In contact with the catalyst according to the invention, the glycerol passes through the solid layer B. on which it turns into acrolein. Acrolein diffuses to the core of the catalyst to react with the solid layer A to produce acrylic acid. Layer B consists of an acidic phase having a Hammett's acidity of less than +2, preferably less than -3. Hammett acidity for a solid is defined in US Pat. No. 5,387,720 which refers to the article by K. Tanabe et al in "Studies in Surface Science and Catalysis", Vol 51, 1989, Chapters 1 and 2. Hammett's acidity is determined by amine titration using indicators or adsorption of a gas phase base. Advantageously, the layer B consists of an acid phase having a Hammett Ho acidity of between -9 and -18, more particularly between -10 and -16. Suitable acidic solids for layer B are natural or synthetic siliceous materials or acidic zeolites; inorganic carriers, such as oxides, coated with inorganic acids, mono, di, tri or polyacids; oxides or mixed oxides or heteropolyacids. Advantageously, the layer B consists of an acid phase chosen from zeolites, Nafion composites (based on fluorosulphonic acid of fluoropolymers), chlorinated aluminas, acids and salts of phosphotungstic and / or silicotungstic acids, and various metal oxide solids such as tantalum oxide Ta2O5, niobium oxide Nb2O5, alumina Al2O3, titanium oxide TiO2, zirconia ZrO2, tin oxide SnO2, silica SiO2 or silico-aluminate SiO2-Al2O3 impregnated with functions acids such as BO3 borate, SO4 sulfate, WO3 tungstate, PO4 phosphate, SiO2 silicate, or MoO3 molybdate.

Preferably, the layer B consists of a sulfated zirconia, a phosphatized zirconia, a tungsten zirconia, a silicified zirconia, an oxide of titanium or of sulphated tin or tungsten. The layer A consists of a solid phase comprising at least one element selected from the list molybdenum, vanadium, tungsten, rhenium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, tellurium, antimony, bismuth, platinum, palladium, ruthenium, rhodium, present in the metal form or in the form of oxide, sulphate or phosphate. Advantageously, the layer A consists of a solid phase of mixed metal oxide type that can respond to the following composition (I): ## STR1 ## in which: Mo is molybdenum; - V is vanadium; O is oxygen; X 'is at least one element selected from tungsten, titanium, tantalum and niobium; - X2 is at least one element selected from copper, antimony, tellurium and bismuth; X3 is at least one member selected from alkaline earth metals; - X4 is at least one element selected from alkali metals; and - 0 <a <_10, preferably 3 <_a <_6; -0 <_b <_4, preferably 0.5 <_b <_3; - 0 <c <_5, preferably 0 <c <_4; 25 - 0 <_d <_2; - 0 <_e <_2; and x is the amount of oxygen bound to the other elements and depends on their oxidation states. Copper and antimony are preferred as X2.

The alkaline earth metal X 3 is preferably selected from magnesium, calcium, strontium and barium.

The alkali metal X4 is preferably selected from potassium, rubidium and cesium. The layer A may have a single-component structure. It can also have a multi-component structure, in particular a two-component or three-component structure. Such structures are described for example in US 6,737,545, US 2004/0249183, DE 10360058 or US 6,921,836. The layer A may be obtained according to the methods well known to those skilled in the art for the preparation of catalysts in general, and may have the following steps: preparation of a suspension of oxides or compounds capable of forming oxides, drying, pre-calcination, calcination, grinding, shaping ... Various metal oxides used in the composition of layer A can be used for the preparation of this composition, but the raw materials are not limited to oxides, other raw materials can be used, such as solutions of metal salts in the form of sulphates, phosphates, nitrates for example. Advantageously, the layer A is formed on an inert substrate such as alumina, silica, silico-alumina, silicon carbide, titanium oxide, soapstone, without this list being considered exhaustive. Suitable solids for layer A are, for example, the solids marketed by companies such as Nippon Shokubai, Nippon Kayaku, Mitsubishi Chemical or BASF. The layer A according to the invention may be in the form of beads, or in the form of cylinders, multilobes, rings, half-rings or saddles. A process for preparing a membrane catalyst suitable for the synthesis of acrylic acid from glycerol, another subject of the invention, comprises the following two steps (a) and (b): Step (a) consists in forming a first layer A, as defined above, on an inert substrate which may consist, for example, of alumina, silica, silico-alumina, silicon carbide, titanium oxide, steatite.

The step (a) can be carried out according to various ways well known to those skilled in the art, which result in a homogeneous and controlled deposition of active material on a support. According to one embodiment of the invention, the layer A is obtained by coating the substrate in suspension. In this case, the active ingredient constituting the layer A is prepared by coprecipitation of various metal salts in solution, in the presence or absence of the substrate. When the coprecipitation of the metal salts is carried out in the absence of the substrate, the final phase of evaporation of the solvent is then carried out in the presence of the substrate. The final solid is obtained after drying and calcination. The active material constituting the layer A is then fixed at the periphery of the substrate. According to one embodiment of the invention, the layer A is obtained by powder coating of the substrate. In this case, the substrate, for example in the form of beads, is brought into contact with the powder of active material. A binder is then added gradually, for example dropwise, or by spraying. The binder can be water, but also aqueous solutions of glycerol, polyvinyl alcohol, carboxymethylcellulose or methylcellulose for example. Preferably, the assembly is rotated so that the balls progressively overlap with the active material homogeneously. The final solid is obtained after a drying step. A calcination step may be performed to improve the attachment of the active ingredient to the ball. According to one embodiment of the invention, the layer A is obtained by impregnating the substrate with a solution or suspension containing the active material. For example, the substrate is placed in a rotated capacity and a solution or suspension containing the active material is atomized on the substrate. This operation can be carried out in the presence of a hot gas stream or by heating the substrate so as to gradually evaporate the solvent. The active ingredient is deposited as and homogeneously on a solid which remains dry.

Step (b) consists in forming on the solid resulting from step (a) a second layer B from an acidic active material as defined above. The acidic active material is generally in the form of a powder which is used in step (b) to coat the solid from step (a). Advantageously, a prior heat treatment of the acidic active material makes it possible to obtain a compromise of strength and density of the acidic sites. Indeed, for the selectivity of the dehydration reaction to be optimal, it is necessary that the strength of the acidic sites be adjusted to the reaction. The strength of the acid sites can be characterized by the temperature at which a probe molecule such as ammonia, desorbs from the catalyst. The higher this temperature, the stronger the acid site. The average strength of the acid sites can be controlled in various ways, for example by heat treatment at a sufficiently high temperature, or by selective poisoning, for example by a base (such as an alkaline, alkaline earth ...) having the effect of preferentially neutralizing the strongest acid sites. The layer B can also be obtained by preparing a suspension of acidic active material in a solvent and then depositing this suspension on the solid resulting from step (a) according to the techniques well known to those skilled in the art. It may be advantageous to control the particle size distribution of the acidic solid particles, and thus control the porosity of the layer B. The porosity of the layer B can be adjusted according to several methods well known to those skilled in the art: for example, the addition of porogenic agents (such as cellulose, starch, surfactants, amminium nitrate, etc.) makes it possible to generate a controlled porosity in layer B. Another method which can be used in combination with the previous one is to control the particle size distribution. Indeed, if the particles have a high average size, the voids created between these particles also have a high average size. It is thus possible to control the porosity of the layer B. Indeed, it is essential that the layer B, having the role of performing the dehydration reaction of glycerol to acrolein, does not allow to diffuse glycerol to the layer A. This is possible in particular by decreasing the size and the distribution of the particles constituting the acid phase, according to the techniques of the art.

The membrane catalyst according to the invention or obtained according to the process of the invention is advantageously used in a process for producing acrylic acid from glycerol, in the gas phase, and in the presence of molecular oxygen.

The molecular oxygen may be present as air or as a mixture of gases containing molecular oxygen. The amount of oxygen is chosen to be outside the flammability range at any point in the installation. The oxygen content in the process according to the invention will generally be chosen so as not to exceed 20% relative to the reaction gas mixture (glycerol / H2O / oxygen / inert gas mixture). The term "inert gas" means a gas that does not participate in the reactions, water in the form of vapor having a special role, especially as a product of oxidation reactions. Glycerol is available in concentrated form, but also in the form of more economical aqueous solutions. Advantageously, an aqueous glycerol solution with a concentration of between 10% and 100%, preferably between 10% and 70% by weight, is used in the reactor, more particularly between 20% and 50%. The concentration should not be too high in order to avoid parasitic reactions such as formation of glycerol ethers or reactions between acrolein or acrylic acid produced and glycerol. In addition, the glycerol solution should not be diluted too much because of the energy cost induced by the evaporation of the aqueous glycerol solution. In any case, the concentration of the glycerol solution can be adjusted by recycling the water produced by the reaction. In order to reduce the costs of transporting and storing glycerol, the reactor can be fed with a concentrated solution of 40 to 100% by weight of glycerol, a dilution that can be carried out in the reactor by recycling part of the water vapor produced by the reaction and dilution water. Similarly, the heat recovery at the outlet of the reactor can also make it possible to vaporize the glycerol solution feeding the reactor. Glycerol from the methanolysis of vegetable oils in a basic medium may contain certain impurities such as chloride or sodium sulfate, non-glycerol organic materials, and methanol. The presence of sodium salts is particularly detrimental to the catalytic dehydration reaction because these salts are capable of poisoning the acidic sites of the catalyst. Pre-treatment of glycerol by ion exchange for example may be considered. A temperature of between 250 ° C. and 350 ° C. and a pressure of between 1 and 5 bar is preferably used. The process according to the invention can be carried out according to different technologies, such as fixed bed, fluidized bed or circulating fluidized bed, or in a plate exchanger type reactor. Compared with the conventional process for preparing acrylic acid by selective oxidation of propylene, the acrylic acid produced according to the process of the invention may contain impurities of different nature or in different amounts. Depending on the use envisaged, it may be envisaged to purify the acrylic acid according to the techniques known to those skilled in the art.

Claims (12)

  Membrane catalyst for the synthesis of acrylic acid from glycerol, characterized in that it comprises a first layer A consisting of a phase capable of selectively converting acrolein to acrylic acid comprising at least one element chosen from list of molybdenum, vanadium, tungsten, rhenium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, tellurium, antimony, bismuth, platinum, palladium, ruthenium, rhodium, present in metallic form or in oxide form , sulphate or phosphate, and a second layer B formed on said first layer A, consisting of an acid phase having a Hammett Ho acid of less than +2, capable of selectively effecting the dehydration reaction of glycerol to acrolein.   2. Catalyst according to claim 1, characterized in that the first layer A is formed on an inert substrate such as alumina, silica, silicoaluminum, silicon carbide, titanium oxide, steatite.   3. Catalyst according to claim 1 or 2, characterized in that the first layer A consists of a solid phase of mixed metal oxide type corresponding to the composition (I): M012 Va X1b X2c X3d X4eOX (I) in which : Mo is molybdenum; V is vanadium; O is oxygen; X 'is at least one member selected from tungsten, titanium, tantalum and niobium; X 2 is at least one member selected from copper, antimony, tellurium and bismuth; X3 is at least one member selected from alkaline earth metals; X4 is at least one member selected from alkali metals; and 0 <a <_10, preferably 3 <_a <_6; 0 <_b <_4, preferably 0.5 <_b <_3; 2903620 13 0 <c <_5, preferably 0 <c <_4; 0 <_d <_2; 0 <_e <_2; and x is the amount of oxygen bound to the other elements and depends on their oxidation states.   4. Catalyst according to one of claims 1 to 3, characterized in that said second layer consists of an acid phase having a Hammett acidity Ho between -9 and -18, preferably between -10 and -16. 10   5. Catalyst according to one of claims 1 to 4, characterized in that said second layer consists of an acid phase selected from natural or synthetic siliceous materials or acidic zeolites; inorganic carriers, such as oxides, coated with inorganic acids, mono, di, tri or polyacids; oxides or mixed oxides or heteropolyacids.   6. Catalyst according to one of claims 1 to 5, characterized in that said second layer consists of an acid phase selected from zeolites, Nafion composites (based on sulfonic acid fluoropolymers), chlorinated aluminas , phosphotungstic and / or silicotungstic acids and salts, and various metal oxide solids such as tantalum oxide Ta2O5, niobium oxide Nb2O5, alumina Al2O3, titanium oxide TiO2, zirconia ZrO2, tin oxide SnO2 SiO 2 silica or silico-aluminate SiO 2 -Al 2 O 3, impregnated with acid functions such as BO 3 borate, SO 4 sulfate, WO 3 tungstate, PO 4 phosphate, SiO 2 silicate, or MoO 3 molybdate.   7. Catalyst according to one of claims 1 to 6, characterized in that said second layer is a sulfated zirconia, a phosphatized zirconia, a tungsten zirconia, a silicified zirconia, an oxide of titanium or tin or sulfated tungsten. 30   8. Process for the preparation of a membrane catalyst for the synthesis of acrylic acid from glycerol, characterized in that it comprises the following steps: 2903620 14 a. forming a first layer A on an inert substrate from a phase capable of selectively converting acrolein to acrylic acid, comprising at least one element selected from the list of molybdenum, vanadium, tungsten, rhenium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, tellurium, antimony, bismuth, platinum, palladium, ruthenium, rhodium, present in the metallic form or in the form of oxide, sulphate or phosphate, said first layer being formed by coating with suspension or powdered, or by impregnation of the substrate, b. forming a second layer B on said first layer from an acid phase having a Hammett Ho acid of less than +2, capable of performing the dehydration reaction of glycerol to acrolein.   9. Process according to claim 8, characterized in that step (b) is carried out by powder coating from a solid acid phase that has been previously treated thermally.   10. Process for producing acrylic acid from glycerol, in the gas phase and in the presence of molecular oxygen, characterized in that a membrane catalyst defined according to one of Claims 1 to 7 or obtained according to the method of claim 8 or 9.   11. Process according to claim 10, characterized in that an aqueous solution of glycerol with a concentration of between 10% and 100% by weight is used in the reactor.   12. Process according to claim 10 or 11, characterized in that the reactor is fed with concentrated solutions of 40 to 100% by weight of glycerol, a dilution of the glycerol solution that can be carried out in the reactor by recycling the product. part of the water vapor produced by the reaction and the dilution water.