Preparation process of catalysts for producing methacrylic acid

Abstract: A process for preparing a multi-component catalyst for producing methacrylic acid containing phosphorus, molybdenum and vanadium comprising using in preparing the catalyst, at least one member selected from the group consisting of the oxide, carbonates, acetates and hydroxides of each catalyst-constituting element as a source of the element; dissolving or dispersing the selected sources of the catalyst-constituting elements in water; adding at least one member selected from the group consisting of ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and ammonium hydrogensulfate to the resulting aqueous solution or dispersion; removing water therefrom and then heat-treating the residual product. The catalyst obtainable by this process and its use are also disclosed.

Description: The present invention relates to a process for preparing a catalyst in producing methacrylic acid by the gas-phase catalytic oxidation of methacrolein. Hitherto, in producing methacrylic acid by the gas-phase catalytic oxidation of methacrolein, it is advantageous to keep the yield high at a low reaction temperature from standpoints such as the life of catalysts, inhibition of side reactions and cost of equipments. However, when catalysts prepared by the conventional methods are used, satisfactory results are not always obtained. One possible reason for this is that the specific surface area and distribution of micropores of the catalyst which are important to the oxidation reaction have not sufficiently been controlled. In order to improve these defects, the following various trials have been made at the time of preparation of the catalyst: Addition of carboxylic acids or polyhydric alcohols (refer to Japanese Patent Application Kokai No. 51-136615), addition of an alcohol and a glycol (refer to ibid. No. 55-73347), addition of a pyridine compound (refer to ibid. No. 47-38591, No. 57-171444), addition of a quinoline compound (refer to ibid. No. 60-209258), addition of ammonium ions (refer to ibid. No. 57-165040), for instance. However, these methods have various defects, for example, reaction results are not satisfactory; catalytic activity largely lowers with the lapse of time; reaction temperature is too high; and the heat-treatment method which is a catalyst-activating treatment is troublesome because of organic substances being used. The catalysts thus obtained, therefore, are not always satisfactory as industrial catalysts. Specifically, when organic substances such as quinoline compounds, pyridine compounds and carboxylic acids are used, there are defects that a burning phenomenon is easy to appear to result in the collapse of a catalyst structure when the catalyst after shaping is subjected to the heat treatment, and also that the distribution of micropores is difficult to control. When alcohols are added, the catalyst structure is easy to change and those giving satisfactory reaction results are difficult to obtain. When ammonia is added as an ammonium ion source, there is a defect of the catalyst structure being easy to change. Further, when ammonium nitrate is added as the ammonium ion source, there is a defect of catalyst-shaping machines and/or catalyst-drying equipments being injured because of its corrosive action. EP-A-0 350 862 discloses a process for producing methacrylic acid by a gas-phase catalytic oxidation of methacrolein and describes a method for preparing a multi-component catalyst used for the process. However, the catalyst obtained by this method is not satisfactory in conversion of methacrolein and selectivity of methacrylic acid. An object of the present invention is to provide a catalyst and a process for preparing it and its use for advantageously producing methacrylic acid from methacrolein. In order to improve the conventional catalyst-preparation methods, the present inventors have studied with particular notice given to the physical properties of the catalyst, and as a result have found a novel process for preparing a catalyst which works effectively at lower reaction temperatures and yet gives methacrylic acid in higher yields than when catalysts prepared by the conventional methods are used. The present invention relates to a process for preparing a multi-component catalyst for producing methacrylic acid, the catalyst being represented by the formula P a Mo b V c Cu d X e Y f (NH₄) g O h wherein P, Mo, V, Cu, NH₄ and O are phosphorus, molybdenum, vanadium, copper, ammonium group and oxygen, respectively, X is at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, Y is at least one element selected from the group consisting of silver, magnesium, zinc, arsenic, germanium, silicon, tungsten, boron, bismuth, chromium, lanthanum, barium, antimony, iron, zirconium, tellurium and cerium, a, b, c, d, e, f and h are an atomic ratio of each element, g is the number of ammonium molecules, being 0.01 to 2, and when b is 12, a is 0.5 to 3, c is 0.01 to 3, d is 0.01 to 2, e is 0.01 to 2 and f is 0 to 5, and h is the number of oxygen atoms necessary to satisfy the valence of each component, which process comprises using in preparing the catalyst at least one member selected from the group consisting of molybdenum trioxide and molybdic acid, and at least one member selected from the group consisting of the oxides, carbonates, acetates and hydroxides of each of the catalyst constituting elements V, Cu, X and Y, dissolving or dispersing the selected sources of the catalyst constituting components in the corresponding amounts in water, adding at least one member selected from the group consisting of ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and ammonium hydrogensulfate in an amount of 1 to 50 wt.-% based on the total weight of all the materials for the catalyst to the resulting aqueous solution or dispersion; removing water therefrom and then heat-treating the residual product at a temperature of 300°C to 430°C while streaming air and/or a gas containing 5 vol.-% or more of oxygen. The catalyst obtainable by this process is useful for the production of methacrylic acid. The catalyst according to the present invention is represented by the following formula P a Mo b V c Cu d X e Y f (NH₄) g O h wherein P, Mo, V, Cu, NH₄ and O are phosphorus, molybdenum, vanadium, copper, ammonium group and oxygen, respectively, X is at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, Y is at least one element selected from the group consisting of silver, magnesium, zinc, arsenic, germanium, silicon, tungsten, boron, bismuth, chromium, lanthanum, barium, antimony, iron, zirconium, tellurium and cerium, a , b, c, d, e, f and h are an atomic ratio of each element, g is the number of ammonium molecules, being 0.01 to 2, and when b is 12, a is 0.5 to 3, c is 0.01 to 3, d is 0.01 to 2, e is 0.01 to 2 and f is 0 to 5, and h is the number of oxygen atoms necessary to satisfy the valence of each component. Materials for molybdenum used to prepare the catalyst include molybdenum trioxide and molybdic acid. Particularly, good results are obtained when molybdenum trioxide is used. Materials for other catalyst-constituting elements include the oxides, carbonates, acetates and/or hydroxides of said elements. In practicing the present invention, for example, the following procedure is taken: The materials for molybdenum, vanadium and phosphorus are dissolved or dispersed in water, the resulting aqueous solution or dispersion is heated to carry out a reaction sufficiently and then other materials for the catalyst are added at the same time or successively. In the present invention, ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and/or ammonium hydrogensulfate may be added at the time of addition of other materials for the catalyst. Particularly, however, good results are obtained when ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and/or ammonium hydrogensulfate dissolved in water is added after all of other materials for the catalyst are added. The amount of ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and/or ammonium hydrogensulfate is 1 to 50 wt.%, particularly preferably 3 to 30 wt.% based on the total weight of all the materials for the catalyst. Next, water is removed from a mixture containing the materials for the catalyst and ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and/or ammonium hydrogensulfate, and on heat-treating the residual product, the desired catalyst is obtained. The heat treatment is carried out, for at a temperature of 300° to 430°C while streaming air and/or a gas containing 5 vol.% or more of oxygen. The catalyst used in the present invention works effectively without a carrier, but it is preferred to use the catalyst supported on or diluted with an inert carrier such as silica, alumina, silica-alumina and silicon carbide. When methacrylic acid is produced with the catalyst obtained by the present invention, the methacrolein concentration of the gas used as a material can be changed in a wide range, but 1 to 20% by volume, particularly 3 to 10% by volume is preferably used. Methacrolein, a material, may contain small amounts of impurities such as water and a saturated lower aldehyde, for example. These impurities give substantially no effect to the reaction. As an oxygen source, the use of air is economical, but air made rich in pure oxygen may be used if necessary. The oxygen concentration of the gas used as a material is determined by the molar ratio to methacrolein. The value of this molar ratio is 0.3 to 4, particularly preferably 0.4 to 2.5. The gas, a material, may be diluted with an inert gas such as nitrogen, steam and carbon dioxide. Reaction pressure is preferably atmospheric pressure to several atmospheres. Reaction temperature is 200° to 420°C, particularly preferably 230° to 400°C. The reaction can be carried out by using either a fixed bed or fluidized bed. In the following examples and comparative examples, the conversion of methacrolein and the selectivity of methacrylic acid produced are defined as follows: Conversion of methacrolein (%) = Number of moles of reacted methacrolein Number of moles of supplied methacrolein x 100 Selectivity of methacrylic acid (%) = Number of moles of produced methacrylic acid Number of moles of reacted methacrolein x 100 In the following examples and comparative examples, parts are weight, and analyses were carried out by gas chromatography. Example 1 100 Parts of molybdenum trioxide, 2.6 parts of vanadium pentoxide and 6.7 parts of 85% phosphoric acid were added to 800 parts of pure water, and the resulting mixture was heated under reflux for 6 hours. Thereafter, 1.2 parts of copper acetate was added, and refluxing was continued for further 3 hours with heating. After refluxing, 11.2 parts of cesium hydrogencarbonate dissolved in 100 parts of pure water and then 5.6 parts of ammonium carbonate dissolved in 100 parts of pure water were added, and the resulting mixed solution was evaporated to dryness with heating. The solid product obtained was dried at 120°C for 16 hours, shaped by applying pressure and heat-treated at 380°C for 5 hours under air stream. The composition of components except oxygen of the resulting catalyst was P₁Mo₁₂V 0.5 Cu 0.1 Cs₁(NH₄) 0.3 (catalysts described hereinbelow also are represented by the composition of components except oxygen). A reactor was filled with this catalyst, and a mixed gas consisting of 5 vol.% of methacrolein, 10 vol.% of oxygen, 30 vol.% of steam and 55 vol.% of nitrogen was passed through the reactor at a reaction temperature of 285°C for a contact time of 3.6 seconds. The product was collected and analyzed by gas chromatography to find that the conversion of methacrolein was 84.1% and the selectivity of methacrylic acid was 83.8%. Comparative Example 1 A catalyst having the same composition as in Example 1 was prepared without adding ammonium carbonate. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 290°C. As a result, it was found that the conversion of methacrolein was 80.0% and the selectivity of methacrylic acid was 81.6%. Example 2 A catalyst having the composition, P₁Mo₁₂V 0.5 Cu 0.1 K₁Si 0.3 As 0.2 (NH₄) 0.2 , was prepared according to Example 1 except that ammonium hydrogencarbonate of 9.2 parts based on 100 parts of molybdenum trioxide was added in place of ammonium carbonate, and that potassium carbonate, silica sol and arsenic acid were used. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 270°C. As a result, it was found that the conversion of methacrolein was 84.3% and the selectivity of methacrylic acid was 86.6%. Comparative Example 2 A catalyst having the same composition as in Example 2 was prepared without adding ammonium hydrogencarbonate. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 280°C. As a result, it was found that the conversion of methacrolein was 78.9% and the selectivity of methacrylic acid was 84.2%. Example 3 A catalyst having the composition, P 1.5 Mo₁₂V 0.8 Cu 0.2 Rb₁Ce 0.1 Fe 0.2 Sb 0.8 (NH₄) 0.4 , was prepared according to Example 1 except that a part of ammonium carbonate was replaced by ammonium sulfate and a mixed solution containing 2.8 parts of ammonium carbonate and 3.8 parts of ammonium sulfate based on 100 parts of molybdenum trioxide was added, and that rubidium acetate, cerium oxide and iron oxide were used. In this case, antimony trioxide was used as the source of antimony. Using this catalyst, the reaction was carried out under the same conditions as in Exmaple 1 except that the reaction temperature was changed to 270°C. As a result, it was found that the conversion of methacrolein was 89.6% and the selectivity of methacrylic acid was 88.7%. Comparative Example 3 A catalyst having the same composition as in Example 3 was prepared without adding ammonium carbonate and ammonium sulfate. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 270°C. As a result, it was found that the conversion of methacrolein was 77.2% and the selectivity of methacrylic acid was 87.0%. Example 4 A catalyst having the composition, P 1.1 Mo₁₂V 0.8 Cu 0.2 K 0.7 Cs 0.3 Bi 0.2 Sb 0.7 (NH₄) 0.4 , was prepared according to Example 1 except that a part of ammonium carbonate was replaced by ammonium hydrogensulfate and a mixed solution containing 2.8 parts of ammonium carbonate and 11.5 parts of ammonium hydrogensulfate based on 100 parts of molybdenum trioxide was added, and that potassium carbonate, cesium hydrogencarbonate and bismuth oxide were used. In this case, antimony pentoxide was used as the source of antimony. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 270°C. As a result, it was found that the conversion of methacrolein was 90.5% and the selectivity of methacrylic acid was 88.7%. Comparative Example 4 A catalyst having the same composition as in Example 4 was prepared without adding ammonium carbonate and ammonium hydrogensulfate. Using this catalyst, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 290°C. As a result, it was found that the conversion of methacrolein was 87.1% and the selectivity of methacrylic acid was 87.3%. Examples 5 to 7 Catalysts shown in Table 1 were prepared according to Example 1. Part in the table which represents the amount of an ammonium salt added means part by weight based on 100 parts by weight of molybdenum trioxide. Using these catalysts, the reaction was carried out in the same manner as in Example 1 except that the reaction temperature was changed. The results also are shown in Table 1. Composition of catalyst Amount of ammonium salt added (part) Reaction temperature (°C) Conversion of methacrolein (%) Selectivity of methacrylic acid (%) Example 5 P₁Mo₁₂V 0.5 Cu 0.1 Tl 0.8 Fe 0.3 Zr 0.1 Cr 0.2 (NH₄) 0.3 Ammonium sulfate, 10 280 88.8 86.7 Example 6 P 1.1 Mo₁₂V 0.5 Cu 0.1 K 0.8 Cs 0.3 Fe 0.3 Mg 0.2 Te 0.2 (NH₄) 0.2 Ammonium hydrogencarbonate, 8 280 89.0 87.1 Example 7 P 1.2 Mo₁₂V 0.8 Cu 0.1 K₁Fe 0.2 Ge 0.2 B 0.3 (NH₄) 0.2 Ammonium carbonate, 8 275 89.5 87.7 Examples 8 to 10 Catalysts shown in Table 2 were prepared according to Example 3. Part in the table which represents the amount of an ammonium salt added means part by weight based on 100 parts by weight of molybdenum trioxide. Using these catalysts, the reaction was carried out in the same manner as in Example 1 except that the reaction temperature was changed. The results also are shown in Table 2. Composition of catalyst Amount of ammonium salt added (part) Reaction temperature (°C) Conversion of methacrolein (%) Selectivity of methacrylic acid (%) Example 8 P 1.2 Mo₁₂V 0.6 Cu 0.2 K₁Bi 0.3 Sb 0.3 Ba 0.2 (NH₄) 0.3 Ammonium carbonate, 7 280 88.3 88.9 Example 9 P₁Mo₁₂V 0.5 Cu 0.2 Cs₁Fe 0.3 Sb 0.6 La 0.1 Ag 0.05 (NH₄) 0.5 Ammonium sulfate, 10 280 89.1 88.1 Example 10 P₁Mo₁₂V 0.8 Cu 0.1 Rb₁Zn 0.2 Fe 0.2 Sb 0.7 W 0.1 (NH₄) 0.1 Ammonium carbonate, 3 + ammonium sulfate, 7 280 90.1 88.8

Claims: A process for preparing a multi-component catalyst for producing methacrylic acid containing phosphorous, molybdenum and vanadium, which process comprises using in preparing the catalyst at least one member selected from the group consisting of molybdenum trioxide and molybdic acid, and at least one member selected from the group consisting of the oxides, carbonates, acetates and hydroxides of each of the catalyst constituting elements V, Cu, X and Y, wherein X is at least one member selected from the group consisting of potassium, rubidium, cesium and thallium, Y is at least one element selected from the group consisting of silver, magnesium, zinc, arsenic, germanium, silicon, tungsten, boron, bismuth, chromium, lanthanum, barium, antimony, iron, zirconium, tellurium and cerium, dissolving or dispersing the selected sources of the catalyst constituting components in water, adding at least one member selected from the group consisting of ammonium carbonate, ammonium hydrogencarbonate, ammonium sulfate and ammonium hydrogensulfate in an amount of 1 to 50 wt.-% based on the total weight of all the materials for the catalyst to the resulting aqueous solution or dispersion; removing water therefrom and then heat-treating the residual product at a temperature of 300°C to 430°C while streaming air and/or a gas containing 5 vol.-% or more of oxygen. A process for preparing a multi-component catalyst for producing methacrylic acid according to Claim 1, wherein the catalyst being represented by the formula P a Mo b V c CU d X e Y f (NH₄) g O h wherein P, Mo, V, Cu, NH₄ and O are phosphorus, molybdenum, vanadium, copper, ammonium group and oxygen, respectively, X is at least one element selected from the group consisting of potassium, rubidium and cesium, Y is at least one element selected from the group consisting of silver, zinc, germanium, tungsten, boron, bismuth, lanthanum, barium, antimony, iron and cerium, a, b, c, d, e, f and h are an atomic ratio of each element, g is the number of ammonium molecules being 0.01 to 2, and when b is 12, a is 0.5 to 3, c is 0.01 to 3, d is 0.01 to 2, e is 0.01 to 2 and f is 0 to 5, and h is the number of oxygen atoms necessary to satisfy the valence of each component.

Inventors: KINOSHITA YUTAKA, OH-KITA MOTOMU, YAMAMOTO SHINJI, KINOSHITA, YUTAKA, OH-KITA, MOTOMU, YAMAMOTO, SHINJI, KINOSHITA, YUTAKA, C/O CENTRAL RESEARCH LAB., OH-KITA, MOTOMU, C/O CENTRAL RESEARCH LAB., YAMAMOTO, SHINJI, C/O CENTRAL RESEARCH LAB.
Applicants: MITSUBISHI RAYON CO, MITSUBISHI RAYON CO., LTD.
Application year: 1991
Main classification: B01J27
IPC codes: C07C57, B01J27, C07C51, C07B61