JPS6230177B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing methacrylic acid, which is characterized by using a novel catalyst having a long life, high activity, and high selectivity when producing methacrylic acid by gas-phase catalytic oxidation of methacrolein. It is something. In recent years, many catalyst systems have been proposed as catalytic catalysts for gas-phase catalytic oxidation of methacrolein. do not have. This is thought to be due to the fact that the yield of the target substance is not as high as in the acrylic acid production method, and the catalyst has a short lifespan and cannot maintain stable activity over a long period of time. Most of the catalysts for gas-phase catalytic oxidation of methacrolein that have been proposed to date are mainly composed of molybten-phosphorus; It is thought to have a heteropolyacid salt structure consisting mainly of alkali metal salts. However, the biggest drawback of these catalysts is that they have a short lifespan, and if the reaction is continued for a long time, the phosphomolybdate structure will gradually decompose, and the catalytic activity will decrease, making it impossible for industrial use. None of these systems have a catalyst life long enough to withstand commercial use, and in order to maintain catalytic activity over a long period of time in such systems, it is necessary to select extremely mild reaction conditions that are far from economic requirements. is the current situation. In addition to improving the low activity and low selectivity of the conventional catalyst for gas-phase catalytic oxidation of methacrolein, the present inventors
Attempting to improve the short life mentioned above, Mo-V-P-Cu-
We discovered that As-O or a composition with a heteropolyacid structure made by adding various elements to As-O is a highly active, highly selective, and especially stable catalyst with an unprecedented lifetime, and have filed a separate patent application (patent application). 153158 (1972), Japanese Patent Application Publication No. 79341 (1982)). The present inventors further investigated the improvement of the above-mentioned system, and as shown below, a heteropolyacid catalyst consisting mainly of phosphovanadomolybdic acid and various elements added thereto as needed was developed. The present inventors have discovered that by coexisting acid salts (potassium, rubidium, cesium, thallium), the activity and selectivity can be further improved without losing their long-life properties, leading to the completion of the present invention. . That is, the present invention oxidizes methacrolein in the gas phase with molecular oxygen or a gas containing molecular oxygen to produce methacrylic acid using the general formula (Mo) _a (V) _b (P) _c (Cu ) _d (As) _e (X) _f (Y) _g (O) _h (In the formula, Mo, V, P, Cu, As and O each represent molybdenum, vanadium, phosphorus, copper, arsenic and oxygen, are tin, lead, cerium, cobalt,
Iron, zirconium, thorium, tungsten, germanium, nickel, rhenium, bismuth, antimony, chromium, boron, magnesium, silver,
Represents at least one element selected from the group consisting of aluminum, zinc, and titanium. Y represents at least one element selected from the group consisting of potassium, rubidium, cesium, and thallium.
Also, the subscripts a, b, c, d, e, f, g and h indicate the atomic ratio of each element, and when a is fixed at 10, b
is a value of 3 or less, not including 0, preferably 0.5 to 2
, c is a value of 0.5 to 6, preferably a value of 0.5 to 3, and d is a value of 3 or less, not including 0, preferably
A value of 0.01 to 1.0, e is a value of 3 or less, not including 0,
Preferably a value of 0.01 to 1.0, f is a value of 0 to 3, preferably a value of 0 to 1.0, g is a value of 1.5 or less, not including 0, preferably a value of 0.01 to 1.0, h is an atom of another element It is a naturally determined value depending on the valence and atomic ratio, and usually takes a value of 32 to 75. The present invention relates to a method for producing methacrylic acid characterized by using a catalyst having a composition shown in () and containing a mixture of a heteropolyacid and a salt of the heteropolyacid containing the above-mentioned elements as constituent components. The catalyst of the present invention is a catalyst in which copper and arsenic occupy part of the structure of the catalyst in which phosphovanadomolybdic acid and its Y metal salt are mixed when the catalyst does not contain the X component. When the X component is included, the catalyst is a catalyst in which copper, arsenic, and the X element occupy part of the structure of the catalyst, which is a mixture of phosphovanadomolybdic acid and its Y metal salt. As mentioned above, the catalyst used in the present invention is a catalyst in which phosphorus vanadomolybdic acid or a heteropolyacid mainly composed of phosphovanadomolybdic acid and salts of these heteropolyacids coexist. When viewed by X-ray diffraction, the heteropolyacid has characteristic diffraction peaks of 2θ = 8.0°, 8.9°, 9.3°, etc., and its salt has a characteristic diffraction peak of 2θ = 26.6°. Both peak groups such as 10.8° are observed. However, only acid-based peaks are observed in regions where the amount of coexisting salts in the catalyst is small. As will be shown in Examples and Comparative Examples to be described later, catalysts in which the amount of the Y component added is too large and only salt-based peaks are observed, especially when viewed from X-ray diffraction, do not give good results. It is important to control the amount of the Y component added within the range of the present invention, and a significant feature of the present invention is that significant effects can only be achieved within this range. As described above, the catalyst of the present invention is a catalyst containing a mixture of a heteropolyacid and a salt such as an acid salt of the heteropolyacid, but may also contain oxides of catalyst constituent elements. When the oxidation reaction of methacrolein is also carried out using the catalyst of the present invention, it is thought that the catalyst is reduced by the reaction gas in the early stage of the reaction and shifts to a reduced form. It is clear from the examples shown later that the catalyst of the present invention is a highly active and highly selective catalyst, and at the same time has a long life and is an excellent industrial catalyst unlike any before. For example, as shown in Example ₁ , using _a catalyst with the composition Mo ₁₀ V ₁ P ₁ Cu _{0.2 As 0.2 Cs 0.1} , the reaction temperature was 310°C, and the SV (space velocity) was 1600 hr ^-1.
Continuous reactions were carried out at Initially, the methacrolein conversion rate was 96.7% and the methacrylic acid yield was 80.5%, but even after 120 days, the activity remained completely stable with a methacrolein conversion rate of 96.9% and a methacrylic acid yield of 80.7%. When the catalyst was extracted and X-ray diffraction was measured,
No crystal growth of molybdenum trioxide due to decomposition of the heteropolyacid structure was observed, and there was no change in the catalyst structure. Regarding other Examples, continuous reactions were carried out for 30 days due to time constraints, but no substantial change was observed in the reaction results. Naturally, it is considered that the catalyst has the same lifespan as Example 1. The catalyst of the present invention can be prepared by a conventional method for preparing heteropolyacids and salts of heteropolyacids, but it must be avoided that the resulting catalyst becomes an ammonium salt of a heteropolyacid. (A) Examples of methods for preparing heteropolyacids include the following methods. That is, a method of dispersing an appropriate compound of the constituent elements in water etc., heating it while adding hydrogen peroxide if necessary, reacting and dissolving it, and evaporating to dryness, or a method of dispersing a suitable compound of the constituent elements in water etc. A method of reacting with compounds of constituent elements. (B) Examples of methods for preparing heteropolyacid salts include the following methods. That is, a method of dispersing an appropriate compound of the constituent elements in water etc., heating and reacting while adding hydrogen peroxide as necessary, and evaporating to dryness, or a method of dispersing phosphovanadomolybdic acid and Y
A method of reacting compounds such as (potassium, etc.). Similarly, the catalyst of the invention can be prepared, for example, as follows. That is, by dispersing an appropriate compound of the constituent elements in water etc., heating and reacting while adding hydrogen peroxide as necessary, and evaporating to dryness, or by methods such as (A) and (B) above. A method of mixing the prepared heteropolyacid and a salt of the heteropolyacid in a certain ratio in water or other suitable solvent and evaporating to dryness, or adding Y (potassium etc.) to the heteropolyacid prepared by method (A) etc. ), etc., and evaporation to dryness. However, as long as the catalyst of the present invention is finally obtained, any preparation method may be used, and the method is not limited to the above method. isn't it. Various compounds of constituent elements can be used as starting materials in preparing the catalyst. For example, molybdenum compounds include molybdenum trioxide, molybdic acid or its salts, heteromolybic acid or its salts, etc., and phosphorus compounds include orthophosphoric acid, phosphorous acid, hypophosphorous acid or their salts, anhydrous phosphorus. Examples of vanadium compounds include vanadium pentoxide, vanadyl oxalate, vanadic acid, and salts thereof. In addition, starting raw materials for copper include copper oxide, copper phosphate, copper sulfate, copper nitrate,
Copper molybdate, copper metal, etc., starting materials for arsenic include arsenic oxide, orthoarsenic acid, metaarsenic acid, pyriarsenic acid, or their salts, and compounds of X and Y include nitrates, sulfates, carbonates, phosphorus, etc. Acid salts, organic acid salts, halides, hydroxides, oxides, etc. can be used. The catalyst of the present invention exhibits high catalytic performance even without a carrier, but it does not show any effect even if it is molded or supported on a common carrier such as silicon carbide, α-alumina, aluminum powder, zeolite, diatomaceous earth, or titanium oxide. More desirable effects such as improved heat resistance and longer life can be expected than in the case of a carrier. When carrying out the catalytic gas phase oxidation reaction of the present invention, the molar ratio of molecular oxygen to methacrolein is 0.5 to 0.
It is preferable to use 20, particularly preferably 1 to 10. It is also preferred to add water in the form of steam in a molar ratio of 1 to 20 to methacrolein. The feedstock gas may also contain other inert gases such as nitrogen, carbon dioxide, saturated hydrocarbons, and the like. Also, isobutylene or tertiary
It is also possible to use the reaction product gas containing methacrolein obtained by catalytically oxidizing butanol as the raw material gas. The reaction temperature when carrying out the method of the present invention is 200 to 400
°C is preferred. The feed rate of the raw material mixed gas is preferably 100 to 5000 hr ^-1 based on the NTP standard in terms of space velocity (SV), and more preferably 500 to 3000 hr ^-1 , but when the catalyst according to the present invention is used, the SV can be increased. However, there is no significant change in reaction results, and it is possible to perform high SV reactions. Although the catalytic reaction of the present invention can be carried out under increased pressure or reduced pressure, a pressure near atmospheric pressure is generally suitable. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples unless it goes against the spirit of the invention. Note that in the examples, description of oxygen in the catalyst composition was omitted since it was a value naturally determined from the valences and atomic ratios of other elements. The definitions of the conversion rate of methacrolein, methacrylic acid yield, and methacrylic acid selectivity are as follows. Methacrolein conversion rate (%) = Number of moles of methacrolein reacted / Number of moles of methacrolein supplied × 100 Methacrylic acid yield (%) = Number of moles of methacrylic acid produced / Number of moles of methacrolein supplied × 100 Methacrylic acid selectivity (%) = methacrylic acid yield / methacrolein conversion rate x 100 Example 1 Molybdenum trioxide 100g, vanadium pentoxide 6.3
g, copper oxide 1.1g, orthophosphoric acid 8.0g, pyroarsenic acid 1.8g
Disperse or dissolve in 1000ml of deionized water. After heating and stirring this for about 3 hours, cesium hydroxide
Add 1.0 g to this solution and boil and reflux for about 3 hours. This aqueous solution is distilled to dryness on a hot water bath. The composition of the obtained dry solid ₍ catalyst) was Mo ₁₀ V ₁ P ₁ Cu _{0.2 As 0.2 Cs 0.1} , and X-ray diffraction showed that it had heteropolymerization at 2θ = 8.0°, _8.9 °, 9.3°, etc. A diffraction peak due to acid was observed, and 2θ = 26.6°,
A slight peak due to the heteropolyacid salt was observed at 10.8°. Therefore, it can be seen that phosphorus vanadomolybdic acid is the main ingredient, and salts thereof also coexist. After crushing this to a size of 24 to 48 meshes, it was filled into a Pyrex glass reaction tube with an inner diameter of 18 mm.
Immerse in a fluid bath. Methacrolein: Oxygen: Nitrogen: Water vapor = 1:2.5:14:7 (mole ratio) raw material gas was passed through the reaction tube so that SV = 1600hr ^-1 (NTP standard) at a reaction temperature of 310°C. The reaction was carried out for 120 days. The results are shown in Table 1. Examples 2-4 According to the method of Example 1, 1.0 g of cesium hydroxide
Instead, 0.45 g of potassium hydroxide, 0.7 g of rubidium hydroxide, and 1.6 g of thallium oxide were added to obtain a dried product (catalyst) having the composition shown in Table 1. The reaction was carried out under the same reaction conditions. The results are shown in Table 1. It was confirmed by X-ray diffraction that these catalysts mainly contained phosphorus vanadomolybdic acid and salts thereof.

[Table] Examples 5 to 11 In the same manner as in Examples 1 to 4, dried products (catalysts) having the composition shown in Table 2 were obtained, and using these, a reaction was carried out in the same manner as in Example 1. Summer. The result is second
As shown in the table.

[Table] Comparative Example 1 In Example 1, 1.0 g of cesium hydroxide was added, but without adding this, the aqueous solution was boiled and refluxed for about 6 hours, then dried on a hot water bath, and the composition was determined.
_A dried product (catalyst) of Mo ₁₀ V _{1 P 1} Cu _0.2 As _0.2 was obtained. Using this, a reaction was carried out under the same reaction conditions as in Example 1 except that the reaction temperature was 320°C.
The following values were obtained. Methacrolein conversion rate 93.4% Methacrylic acid selectivity 83.6% Methacrylic acid yield 78.1% Comparative example 2 The method of Example 1 was followed except that 9 g of potassium hydroxide was added instead of 1 g of cesium hydroxide.
A catalyst was prepared in the same way, and the composition
A catalyst of Mo ₁₀ V _{1 P 1} Cu _{0.2 As 0.2 K 2} was obtained. Example 1
When the reaction was carried out under the same reaction conditions, the following values were obtained. Methacrolein conversion rate: 76.9% Methacrylic acid selectivity: 75.2% Methacrylic acid yield: 57.8% It was observed from X-ray diffraction that this catalyst was mainly composed of potassium salt of heteropolyacid. Example 12 Mo ₁₀ V ₁ P _{1 Cu 0.2 As 0.2} catalyst prepared in Comparative Example 1 and Mo ₁₀ V _{1 P 1} Cu _{0.2 As 0.2 Cs 1 prepared} in Example 7
Mix the catalyst at a ratio of 9:1 and add 50g to 200ml.
The mixture was dispersed in water and evaporated to dryness on a hot water bath to obtain a dried product (catalyst). Using this, a reaction was carried out under the same reaction conditions as in Example 1, and the following values were obtained. Methacrolein conversion rate 97.1% Methacrylic acid selectivity 82.7% Methacrylic acid yield 80.3% Example 13 Molybdenum trioxide 100g, vanadium pentoxide 6.3
g, copper oxide 1.1g, orthophosphoric acid 8.0g, pyroarsenic acid 1.8g
It was prepared in the same manner as in Example 1 using 0.45 g of potassium hydroxide and 2.1 g of tin oxide as raw materials.
_A reaction was carried out under the same conditions as in Example ₁ using a dried product of Mo ₁₀ V _{1 P} 1 Cu _0.2 As _{0.2 K 0.1} Sn _{0.2 .} The results are shown in Table 3. In addition, this dried product (catalyst) was determined by X-ray diffraction as 2
Diffraction peaks due to heteropolyacid mainly composed of phosphovanadomolybdic acid are observed at θ=8.0°, 8.9°, 9.3°, etc. In addition, peaks due to heteropolyacid salts are slightly observed at 2θ=26.6°, 10.8°, etc. Therefore, it can be seen that this catalyst contains a mixture of a heteropolyacid mainly composed of phosphovanadomolybdic acid and a salt of the heteropolyacid. Examples 14-32 In Example 13, instead of tin oxide, 3.2 g of trilead tetroxide, 2.4 g of cerium oxide, 1.1 g of tricobalt tetroxide, 1.1 g of iron oxide, 1.7 g of zirconium oxide,
3.7g of thorium oxide, 3.2g of tungsten trioxide,
Germanium oxide 1.5g, nickel oxide 1.0g, rhenium heptoxide 3.4g, bismuth oxide 3.2g, antimony trioxide 2.0g, chromium trioxide 1.4g, boric acid 0.9
g, magnesium oxide 0.6g, silver oxide 1.6g, aluminum oxide 0.7g, zinc oxide 1.1g, titanium oxide
1.1 g of each was added to obtain dried solids having the composition shown in Table 3, and a reaction was conducted using these under the same reaction conditions as in Example 1. The results are shown in Table 3. It was confirmed by X-ray diffraction that these dried solids (catalysts) contained a mixture of heteropolyacids mainly composed of phosphovanadomolybdic acid and salts of heteropolyacids. Examples 33-35 According to the method of Example 13, 0.45 g of potassium hydroxide
Instead of, 1.0 g of cesium hydroxide, 0.7 g of rubidium hydroxide, and 1.6 g of thallium oxide were added,
The dried solids (catalysts) shown in Table 3 were obtained, and a reaction was carried out using them under the same reaction conditions as in Example 13. The results are shown in Table 3. Examples 36 to 39 Dried products having the composition shown in Table 3 were obtained in the same manner as in Example 1, and a reaction was carried out under the same reaction conditions as in Example 1 using these. The results are shown in Table 3. In addition, it was confirmed from X-ray diffraction that these dried products (catalysts) contained a mixture of heteropolyacids mainly composed of phosphovanadomolybdic acid and salts of heteropolyacids.

【table】

[Table] Examples 40 to 45 Dried products having the compositions shown in Table 4 were obtained in the same manner as in Example 1, and a reaction was conducted using these under the same reaction conditions as in Example 1. The results are shown in Table 4. In addition, it was confirmed from X-ray diffraction that these dried products (catalysts) contained a mixture of heteropolyacids mainly composed of phosphovanadomolybdic acid and salts of heteropolyacids.

[Table] Examples 46 to 47 Using the catalyst of Example 21, a reaction was carried out at the space velocity (SV) shown in Table 5 under the same conditions as in Example 1 except for the reaction conditions. The results are shown in Table 5, and there is no significant difference in reaction performance even if the SV is increased.

[Table] Example 48 The reactions of Examples 2 to 4 and 13 to 39 were carried out continuously for 30 days, but no substantial change was observed in the reaction results.

Claims (1)

[Claims] 1. When producing methacrylic acid by oxidizing methacrolein with molecular oxygen or a gas containing molecular oxygen, the general formula (Mo) _a (V) _b (P) _c (Cu) _d (As) _e (X) _f (Y) _g (O) _h (wherein, X is tin, lead, cerium, cobalt, iron,
Represents at least one element selected from the group consisting of zirconium, thorium, tungsten, germanium, nickel, rhenium, bismuth, antimony, chromium, boron, magnesium, silver, aluminum, zinc, and titanium. Y represents at least one element selected from the group consisting of potassium, rubidium, cesium, and thallium. Also, subscripts a, b, c, d, e, f, g and h
represents the atomic ratio of each element, when a is fixed at 10, b is a value of 3 or less not including 0, and c is 0.5 to 0.
6, d is a value of 3 or less, not including 0, e is a value of 3 or less, not including 0, f is a value of 0 to 3, g is a value of 1.5 or less, not including 0, h is an atom of another element The value is determined by the valence and atomic ratio. 1. A method for producing methacrylic acid, which is characterized by using a catalyst having a composition shown in (a) and containing a mixture of a heteropolyacid and a salt of the heteropolyacid having the above-mentioned elements as constituent components.