PROCESS FOR PRODUCING METHACRYLIC ACID AND CATALYSTS FOR THE PROCESS

Abstract: A catalyst for the production of methacrylic acid by the oxidation of methacrolein with oxygen in the gas phase has the formula: PaMobVcFedCueZfXgYhOi where X is K, Rb, Cs and/or Tl- Y is Te, La, B, Ag, Cr, Mg and/or Ba; Z is Zr or Sb; a = 0.3-4; b = 12; c = 0.01-3; d = 0.01-4; e = 0.01-3; f = 0.01-3; g = 0.01-3; h = 0.001-5; i is the number of oxygen atoms required to satisfy the valencies of the other elements present. The catalyst is prepd. by pyrolysis of a mixt. of cpds. of the elements present in appropriate ratio. The prepn. of methacrylic acid is carried out by passing methacrolein (1-20% by wt.) and oxygen (0.3-4 moles per mole of methacrolein) in an inert carrier gas (such as nitrogen, steam or carbon dioxide) over the catalyst at 230-450 deg. C.

Description: TECHNICAL FIELD This invention relates to a process for the production of methacrylic acid by vapor phase catalytic oxidation of methacrolein and a catalyst to be used for the process. BACKGROUND ART There have hitherto been disclosed in patents enormous methods with reference to processes of unsaturated carboxylic acids by vapor phase catalytic oxidation of unsaturated aldehydes, for example, a process for the production of methacrylic acid by vapor phase catalytic oxidation of methacrolein. These patents put emphasis on the method of producing acrylic acid from acrolein, and the method was impractical because of a low rate of selectivity due to severe side reaction and short life of the catalysts disclosed in the patents on using the catalysts as the ones for producing methacrylic acid. On the other hand, many catalysts have been proposed for producing methacrylic acid from methacrolein. But these catalysts have problems that they are insufficient in reactivity, catalyst activity decreases largely with the passage of time or high temperature is required for the reaction, so that a further improvement for the use as an industrial catalyst is required. US-A-4 558 029 discloses compositions of the empirical formula: Mo₁₂P 0.1-3 M₀ .1 ₋₃Cu 0.1-2 V 0.1-2 Sb₀ .01-2 X₀ .01 ₋₂Y a O x where M is at least one of K, Rb and Cs; X is at least one of Ba, La, Ga, Al, Ag, Cd, Ti, Tl, Hg, Pb and Zn; Y is at least one of Fe, Co, Ni, Sr, Mn, In, Ta, Ge, S and Be when a>0; a is a number of 0 to about 2; and x is a number that satisfies the valance requirements of the other elements present, as catalysts for the oxidation of oxygenated C₄ hydrocarbons, such as methacrolein, to methacrylic acid. In said reference the yield of methacrylic acid in using the above catalyst is up to 75.5%. DISCLOSURE OF THE INVENTION The object of this invention is to provide a process for producing advantageously methacrylic acid from methacrolein. In particular, the object of this invention is to provide a catalyst which is excellent in activity, selectivity and life and thus has high practicability for producing methacrylic acid and a process for producing methacrylic acid by using said catalyst. BEST MODE FOR PRACTISING THE INVENTION This invention relates to a catalyst practicable for producing methacrylic acid by the vapor phase oxidation of methacrolein with molecular oxygen, which is represented by the general formula P a Mo b V c Fe d Cu e Z f X g Y h O i wherein X represents at least one or more of the elements selected from the group consisting of potassium, rubidium, cesium and thallium, Y represents at least one or more of elements selected from the group consisting of tellurium, boron, chromium and magnesium, Z represents any one of the elements of zirconium or antimony, a to i denote atomic ratios of respective elements, and when b = 12, a = 0.3 - 4, c = 0.01 - 3, d = 0.01 - 4, e = 0.01 - 3, f = 0.01 - 3, g = 0.01 - 3, h = 0.001 - 5 and i denotes the number of oxygen required for satisfying the valence number of the aforementioned ingredients, and a process for producing methacrylic acid characterized by using said catalyst. The catalyst of this invention has a basic composition of phosphorus, molybdenum, vanadium, iron and copper, and comprises additionally anyone of the elements of zirconium or antimony, at least one or more of the elements selected from the group consisting of potassium, rubidium, cesium and thallium, and at least one or more of specific elements selected from the group consisting of tellurium, boron, chromium and magnesium. The catalyst may be used industrially very advantageously and thus the catalyst activity can be maintained at a high level over a long period of time, because the catalyst is high in activity and selectivity for producing methacrylic acid from methacrolein and it can accomplish sufficient rate of reaction even at low reaction temperature owing to its high activity. The atomic ratios of respective elements may be any one of the aforementioned ratios and may be suitably selected from the aforementioned ranges of the ratios. The ratios are preferably in the ranges 1 - 2.5 for a, 0.05 - 1.5 for c, 0.05 - 2 for d, 0.05 - 2 for e, 0.1 - 1.5 for f, 0.1 - 2 for g and 0.01 - 2 for h when b is 12. As the process for preparing the catalyst of this invention, a variety of methods such as evaporation to dryness, precipitation and the like may be used provided that components will not distribute unevenly departing from the aforementioned atomic ranges. As the raw materials used for preparing the catalyst, there may be used nitrates, carbonates, ammonium salts, halides, oxides or the like of respective elements in combination thereof. The catalyst of this invention may be used as a bare catalyst or carried or diluted with such known inert carriers as silica, alumina, silica-alumina, silicon carbide or the like. The catalyst of this invention is further possible to be used for producing the acrylic acid from acrolein by controlling the reaction conditions. According to the process for producing methacrylic acid by using the aforementioned catalyst as another aspect of this invention, it is possible to obtain methacrylic acid from methacrolein in high yield and high selectivity and to maintain the catalyst activity over a long period of time, so that the process of this invention has great industrial advantages. On the practice of the process according to this invention, the concentration of methacrolein in the raw material gases may be varied over a wide range. However, it is preferably in the range of 1 - 20% by volume, particularly 3 - 10%. Methacrolein as the raw material may contain a small amount of impurities such lower aldehydes or the like, and these impurities will not affect substantially on the reaction. It is economical to use air as oxygen source, and it is also possible to use air enriched with pure oxygen, if necessary. The content of oxygen in the feed gas is defined by a mole ratio to methacrolein and preferably in the range of 0.3 - 4, particularly in the range of 0.4 - 2.5. The raw material gases may be diluted by mixing with inert gases such as nitrogen, steam, carbon dioxide or the like. The reaction is preferably carried out in the pressure range from normal pressure to several atmospheric pressures. The reaction temperature can be selected from the range of 230 - 450°C, particularly preferably 250 - 400°C. The reaction may be carried out either in a fixed bed or in a fluidized bed. The process for preparing the catalyst of this invention and the preparation examples with the catalyst thus prepared are specifically explained below. In Examples and Comparative Examples, part means part by weight, and analysis was carried out by gas chromatography. The conversion of methacrolein and the selectivity for methacrylic acid will be defined as follows. Example 1 Hundred parts of ammonium paramolybdate, 1.7 parts of ammonium metavanadate and 4.8 parts of potassium nitrate were dissolved in 300 parts of pure water. To this mixture was added a solution of 8.2 parts of 85% phosphoric acid in 10 parts of pure water. Then, a solution of 1.1 parts of telluric acid in 10 parts of pure water was further added, and the temperature of the mixture was raised with stirring up to 95°C. Next, a solution of 2.3 parts of copper nitrate, 3.8 parts of ferric nitrate and 2.5 parts of zirconyl nitrate in 40 parts of pure water was added, and the mixture was heated with stirring up to a temperature of 100°C and evaporated to dryness. The solid obtained was dried at 130°C for 16 hours and subjected to pressure molding and then to thermal treatment at 380°C for 5 hours under the stream of air, whereupon the solid was used as a catalyst. The catalyst thus obtained had a composition of elements other than oxygen (referred to as composition hereinafter) P 1.5 Mo₁₂V 0.3 Fe 0.2 Cu 0.2 Zr 0.2 K₁Te 0.1 . The catalyst was charged in a reactor and the mixed gas comprising 5% of methacrolein, 10% of oxygen, 30% of steam and 55% of nitrogen (by volume) was flown at a reaction temperature of 290°C for a contact time of 3.6 seconds. Products were collected and upon gas chromatographical analysis the conversion of methacrolein was 87.0% and the selectivity for methacrylic acid was 86.2%. When the reaction was continued for about 1000 hours under the same condition, the conversion of methacrolein was 86.8% and the selectivity for methacrylic acid was 86.3%. Example 2 In accordance with Example 1, a catalyst having a composition of P 1.5 Mo₁₂V 0.5 Fe₀ .4 Cu 0.3 Zr 0.1 K 0.5 Rb 0.6 B 0.2 was prepared and reaction was carried out in the same condition as in Example 1. The conversion of methacrolein was 86.8% and the selectivity for methacrylic acid was 86.1%. Example 3 Hundred parts of ammonium paramolybdate, 1.7 parts of ammonium metavanadate and 9.2 parts of cesium nitrate were dissolved in 300 parts of pure water. A solution of 5.4 parts of 85% phosphoric acid in 10 parts of pure water was added to the mixture, and the temperature of the whole mixture was raised with stirring up to 95°C. Next, a solution of 1.1 parts of copper nitrate, 5.7 parts of ferric nitrate, 3.8 parts of zirconyl nitrate and 0.4 parts of silver nitrate in 60 parts of pure water was added, and the mixture was heated with stirring up to a temperature of 100°C and evaporated to dryness. The solid obtained was dried at 130°C for 16 hours and subjected to pressure molding and then to thermal treatment at 380°C for 5 hours under the stream of air, whereupon the solid was used as a catalyst. The catalyst thus obtained had a composition of elements P₁Mo₁₂V 0.3 Fe 0.3 Cu 0.1 Zr 0.3 Cs₁Ag 0.05 . Using the catalyst, reaction was carried out under the same condition as in Example 1. The conversion of methacrolein was 88.1% and the selectivity for methacrylic acid was 84.9%. This catalyst was not according to the invention. Examples 4 - 5 In accordance with Example 3, inventive catalysts shown in Table 1 were prepared, and the reaction was carried out in the same manner as in Example 1 to obtain results listed in Table 1. Example 6 Hundred parts of ammonium paramolybdate, 5.5 parts of ammonium metavanadate and 4.8 parts of potassium nitrate were dissolved in 300 parts of pure water. To this mixture was added a solution of 9.8 parts of 85% phosphoric acid in 15 parts of pure water. Then a solution of 1.1 parts of telluric acid in 10 parts of pure water and 0.6 part of boric acid were further added, and the temperature of the mixture was raised with stirring up to 95°C. Next, a solution of 3.4 parts of copper nitrate, 7.6 parts of ferric nitrate, 6.3 parts of zirconyl nitrate and 1.2 parts of barium nitrate in 80 parts of pure water was added, and the mixture was heated with stirring up to a temperature of 100°C and evaporated to dryness. The solid obtained was dried at 130°C for 16 hours and subjected to pressure molding and then to thermal treatment at 380°C for 5 hours under the stream of air, whereupon the solid was used as a catalyst. The catalyst thus obtained, which was not according to the invention, had a composition of elements P 1.8 Mo₁₂V₁Fe 0.4 Cu 0.3 Zr 0.5 K₁Te 0.1 B 0.2 Ba 0.1 . Using the catalyst, reaction was carried out under the same condition as in Example 1. The conversion of methacrolein was 86.7% and the selectivity for methacrylic acid was 86.5%. Examples 7 - 8 In accordance with Example 6, catalysts shown in Table 2 were prepared, and reaction was carried out in the same manner as in Example 1 to obtain the results listed in Table 2. Example 9 Using the catalyst prepared in Example 1, reaction was carried out under the same condition as in Example 1 except that the reaction temperature was changed to 305°C. The conversion of methacrolein was 97.0% and the selectivity for methacrylic acid was 80.8%. Example 10 Using the catalyst prepared in Example 2, reaction was carried out under the same condition as in Example 1 except that the reaction temperature was changed to 305°C. The conversion of methacrolein was 96.8% and the selectivity for methacrylic acid was 80.8%. Example 11 Using the catalyst prepared in Example 3, reaction was carried out under the same condition as in Example 1 except that the reaction temperature was changed to 305°C. The conversion of methacrolein was 97.3% and the selectivity for methacrylic acid was 80.6%. Comparative Examples 1 - 3 In accordance with Example 1, catalysts shown in Table 3 were prepared, and reaction was carried out under the same condition as in Example 1 to obtain the results listed in Table 3. Example 12 Hundred parts of ammonium paramolybdate, 2.8 parts of ammonium metavanadate and 4.8 parts of potassium nitrate were dissolved in 300 parts of pure water. To this mixture was added a solution of 8.2 parts of 85% phosphoric acid in 10 parts of pure water. Then, a solution of 3.3 parts of telluric acid in 20 parts of pure water and 3.4 parts of antimony trioxide were further added, and the temperature of the mixture was raised with stirring up to 95°C. Next, a solution of 3.4 parts of copper nitrate and 5.7 parts of ferric nitrate in 30 parts of pure water was added, and the mixture was heated with stirring up to a temperature of 100°C and evaporated to dryness. The solid obtained was dried at 130°C for 16 hours and subjected to pressure molding and then to thermal treatment at 380°C for 5 hours under the stream of air, whereupon the solid was used as a catalyst. The catalyst thus obtained had a composition of elements P 1. ₅Mo₁₂V 0.5 Fe 0.3 Cu 0.3 Sb 0.5 K₁Te 0.3 . The catalyst was charged in a reactor and the mixed gas comprising 5% of methacrolein, 10% of oxygen, 30% of steam and 55% of nitrogen (by volume) was flown at a reaction temperature of 290°C for a contact time of 3.6 seconds. Products were collected and upon gas chromatographical analysis conversion of methacrolein was 87.5% and the selectivity for methacrylic acid was 87.3%. When the reaction was continued for about 1000 hours under the same condition, the Conversion of methacrolein was 87.3% and the selectivity for methacrylic acid was 87.0%. Example 13 In accordance with Example 12, a catalyst having a composition of P₁Mo₁₂V₁Fe 0.2 Cu 0.1 Sb₁Cs₁B 0.3 was prepared, and reaction was carried out under the same condition as in Example 12. The conversion of methacrolein was 86.5% and the selectivity for methacrylic acid was 87.9%. Example 14 Hundred parts of ammonium paramolybdate, 2.8 parts of ammonium metavanadate and 4.8 parts of potassium nitrate were dissolved in 300 parts of pure water. To this mixture was added a solution of 5.4 parts of 85% phosphoric acid in 10 parts of pure water. Then, 4.8 parts of antimony trioxide was further added to the mixture, and the temperature was raised with stirring up to 95°C. Next, a solution of 1.1 parts of copper nitrate, 9.5 parts of ferric nitrate and 0.4 part of silver nitrate in 40 parts of pure water was added, and the mixture was heated with stirring up to 100°C and evaporated to dryness. The solid obtained was dried at 130°C for 16 hours and subjected to pressure molding and then to thermal treatment at 380°C for 5 hours under the stream of air, whereupon the solid was used as a catalyst. The catalyst thus obtained, which was not according to the invention, had a composition of elements P₁Mo₁₂V 0.5 Fe 0.5 Cu 0.1 Sb 0.7 K₁Ag 0.05 . Using the catalyst, reaction was carried out under the same condition as in Example 12. The conversion of methacrolein was 88.0% and the selectivity for methacrylic acid was 86.7%. Examples 15 - 16 In accordance with Example 14, inventive catalysts shown in the following Table were prepared. Reaction was carried out under the same condition as in Example 12, and the results shown in Table 4 were obtained. Example 17 Using the catalyst prepared in Example 12. Reaction was carried out under the same condition as in Example 12 except that the reaction temperature was changed to 305°C. The conversion of methacrolein was 97.3% and the selectivity for methacrylic acid was 81.5%. Example 18 Using the catalyst prepared in Example 13, reaction was carried out under the same condition as in Example 12 except that the reaction temperature was changed to 305°C. The conversion of methacrolein was 97.3% and the selectivity for methacrylic acid was 81.2%. Comparative Examples 4 - 6 In accordance with Example 12, comparative catalysts shown in Table 5 were prepared, and reaction was carried out under the same condition as in Example 12 to obtain the results listed in Table 5.

Claims: 1. A catalyst represented by the general formula P a Mo b V c Fe d Cu e Z f X g Y h O i wherein X represents at least one or more of the elements selected from the group consisting of potassium, rubidium, cesium and thallium, Y represents at least one or more of the elements selected from the group consisting of tellurium, boron, chromium and magnesium, Z represents any one of the elements of zirconium or antimony, a to i denote atomic ratios of respective elements, and when b = 12, a = 0.3 - 4, c = 0.01 - 3, d = 0.01 - 4, e = 0.01 - 3, f = 0.01 - 3, g = 0.01 - 3, h = 0.001 - 5 and i denotes the number of oxygen required for satisfying the valence number of said ingredients. 2. A catalyst according to Claim 1, wherein Z represents zirconium. 3. A catalyst according to Claim 1, wherein Z represents antimony. 4. A process for the production of methacrylic acid comprising a vapor phase catalytic oxidation of methacrolein using molecular oxygen in the presence of a catalyst represented by the general formula P a Mo b V c Fe d Cu e Z f X g Y h O i wherein X represents at least one or more of the elements selected from the group consisting of potassium, rubidium, cesium and thallium, Y represents at least one or more of the elements selected from the group consisting of tellurium, boron, chromium and magnesium, Z represents any one of the elements of zirconium or antimony, a to i denote atomic ratios of respective elements and when b = 12, a = 0.3 - 4, c = 0.01 - 3, d = 0.01 - 4, e = 0.01 - 3, f = 0.01 - 3, g = 0.01 -3, h = 0.001 - 5 and i denotes the number of oxygen required for satisfying the valence number of said ingredients. 5. A process for the production of methacrylic acid according to Claim 4, wherein Z in the general formula of said catalyst is zirconium. 6. A process for the production of methacrylic acid according to Claim 5, wherein Z in the general formula of said catalyst is antimony. 7. A process for the production of methacrylic acid according to Claim 4, wherein the concentration of methacrolein contained in said raw material gas is in the range of 1 - 20% by volume. 8. A process for the production of methacrylic acid according to Claim 4, wherein the molar ratio of molecular oxygen contained in said raw material to methacrolein is in the range of 0.3 - 4. 9. A process for the production of methacrylic acid according to Claim 4, wherein said raw material gas is the one diluted with an inert gas selected from nitrogen, steam and carbon dioxide gas. 10. A process for the production of methacrylic acid according to Claim 5, wherein said vapor phase oxidation is carried out at a temperature selected from the range of 230 - 450°C under pressure.

Inventors: KATO, MASAAKI, KOBAYASHI, MASAO, OH-KITA, MOTOMU
Applicants: MITSUBISHI RAYON CO., LTD.
Application year: 1987
Main classification: B01J27
IPC codes: B01J27, C07C51, C07C57