JPS5942662B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing methacrylic acid by oxidizing methacrolein.

More specifically, when producing methacrylic acid by catalytic gas phase oxidation of methacrolein or methacrolein-containing gas with molecular oxygen or molecular oxygen-containing gas, Mo, P, V3W
and one of Mg, Ca, Cu, Ag, Ce, B
The present invention relates to a method for producing methacrylic acid, characterized in that a mixture containing one of i and oxygen as a catalyst is used. Many catalysts containing Mo and P as main constituents have been proposed as catalyst compositions for producing methacrylic acid by catalytic gas phase oxidation of methacrolein. However, the yield is still low and it cannot be used industrially. For example, Mo-
Catalysts consisting of PV are disclosed in JP-A-48-15817, JP-A-49-100027, and JP-A-26616-A.
However, its methacrylic acid selectivity and methacrylic acid yield are low. Also, Mo-PV type catalyst was used in Journal of the Chemical Society of Japan, Vol. 1975, No. 3, p. 481, but the methacrylic acid selectivity was only 58% and the methacrylic acid yield was only 43%. Moreover, this Mo
-When a PV catalyst is used, the selectivity is low and there are many side reactions, so a large amount of reaction heat is generated, and the temperature difference between the catalyst layer and the heating medium reaches 39°C (Comparative Example 1). It is difficult to control and extremely difficult to implement industrially. On the other hand, in Japanese Patent Application No. 51-7254, Mo, P and M
A catalyst comprising at least one member selected from the group consisting of G, Ca, Br, Ba, and Zn and oxygen has been proposed.

Although the methacrylic acid yield was significantly improved using this catalyst, the methacrylic acid selectivity was still insufficient. In order to further improve the catalytic activity of Mo-P-based catalysts, the present inventors have conducted research on multi-element catalysts and have investigated various types of catalyst constituent elements, atomic ratios, adjustment methods, etc. As a result, MO, P, V,
It has been found that a metal oxide consisting of W and Mg or one of the elements consisting of Ca and Cu, Ag, Ce, and Bi and oxygen has excellent catalytic activity in the catalytic gas phase oxidation reaction of methacrolein.

The characteristics of using the catalyst of the present invention are that the selectivity of methacrolein to methacrylic acid is very high, and therefore the amount of heat generated by the reaction due to the generation of excessive oxides such as acetic acid, carbon monoxide, and carbon dioxide is small, and the catalyst layer The temperature distribution is also uniform, making it easier to control the reaction.

Further, since there are few by-products, subsequent purification becomes extremely easy. These points have extremely great merits from an industrial perspective. In the process of completing the catalyst of the present invention, the present inventors discovered a new catalyst consisting of MO-P-V-W that is effective as an oxidation catalyst for methacrolein.
Although this catalyst has an improved yield compared to the MO-P-catalyst, as shown in Comparative Example 2, the selectivity is insufficient and it cannot be said to be a satisfactory catalyst.

The present invention improves the selectivity by further adding one of Mg and Ca and one of Cu, Ag, Ce, and Bl to the MO-P-V-W catalyst. This allows the aforementioned MO-PV catalyst and MO-P-
We were able to significantly improve the drawbacks of alkaline earth metal catalysts. For example, as shown in Example 1, MO-PV-
With the catalyst consisting of W-Mg-Cu oxide, methacrolein conversion rate was 84.1% and methacrylic acid selectivity was 88.3%.
%, and a single flow yield of methacrylic acid of 74.3% was obtained.

The by-products at this time were only acetic acid, carbon monoxide, and carbon dioxide gas, and the amount thereof was small, and the temperature of the catalyst layer was uniform, and the temperature difference with the heating medium was small. The catalyst used in the present invention is any one of MO, P, V, W, Mg, Ca,
It is a seven-component catalyst consisting of any one of Cu, Ag, Ce, Bi and oxygen, and the preferable atomic ratio of its constituent elements is expressed by the following general formula: If it is a-12,
b=1~3, c=0.5~3, d-0.5~3, e-0
．． 5 to 3, f-0.1 to 1, and g is the number of oxygen atoms sufficient to satisfy the valence of each element.

However, X represents Mg or Ca, and Y represents Cu, Ag, Ce.
, Bi represents one type of element. Increasing the values of c and d in the catalyst of the present invention to the above-mentioned extent increases the amount of CO2 by-product, which is not preferable.

Increasing the values of e and f beyond the above levels lowers the conversion rate, and conversely, decreasing these components lowers the selectivity, which is not preferable. As the Y component, Cu has the most effective effect. In producing the catalyst of the present invention, a molybdenum compound (preferably molybdenum nobdic acid, but molybdic acid, molybdenum trioxide, ammonium molybdate, etc.) can also be used as a raw material for each element.

As phosphorus compounds, orthophosphoric acid, ammonium phosphate, etc. can be used, as vanadium compounds, vanadium pentoxide, ammonium metavanadate, etc. can be used, as tungsten compounds, tungstic acid, tungsten trioxide, ammonium tungstate, etc. can be used, and magnesium and calcium compounds can be used. Hydroxides are particularly preferred, but nitrates can also be used. Further, copper nitrate, copper acetate, etc. can be used as a copper compound, silver nitrate can be used as a silver compound, cerium nitrate etc. can be used as a cerium compound, and bismuth compound (bismuth nitrate, bismuth oxide, etc.) can be used. Conventionally known evaporation to dryness methods, precipitation methods, oxide mixing methods, etc. can be used for preparation, but in order to prepare with good reproducibility, it is necessary to evaporate to dryness an aqueous solution or suspension of the catalyst raw material. Particularly preferred is an evaporation to dryness method in which baking is performed in air.

Further, the metal oxide itself can be used as a catalyst, but it can also be used by supporting it on a carrier. Preferred carriers include silicon carbide, zirconia,
Examples include celite, alumina, titania, and magnesia. The reactants used in the present invention are methacrolein or a gas containing metatalolein and molecular oxygen or a gas containing molecular oxygen.

Steam is used as a diluent for the raw material gas. The raw material gas composition is 1 to 10% by volume of methacrolein 2 to 2.
0% by volume of oxygen, 20-60% by volume of water vapor, and the rest is inert gas such as nitrogen and carbon dioxide. The reaction temperature when carrying out the method of the present invention is in the range of 200 to 400°C, but 2500 to 350°C is particularly preferred.

Further, the pressure is normal pressure to 10 atm, preferably normal pressure to 5 atm, and the space velocity is preferably 1000 to 3000 hr1. The type of catalytic reactor may be any conventionally known type such as a fixed bed, moving bed, or fluidized bed.

The reaction products can also be collected by known common methods. For example, a method of collecting the material by condensing it into a liquid using a condenser, a method of collecting it using a solvent, etc. are used. At this time, unreacted methacrolein can be separated and recovered from the collected material in a form depending on the respective collection method and recycled again as a raw material for the oxidation reaction. The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. In the examples, the definitions of methacrolein conversion rate, methacrylic acid selectivity, and methacrylic acid yield are as follows.

Example 1 Phosphormolybdic acid 1349 was dissolved in 200 ml of ion exchange water.

This solution contains 5.89% of 8.5% orthophosphoric acid and 3.8% of copper nitrate.
69, vanadium pentoxide 3.69, ammonium tungstate 13.09 and ngnesium hydroxide 2.99 were sequentially added thereto, and the mixture was stirred for 3 hours while heating to 70°C. Thereafter, the yellow-green solid obtained by evaporation to dryness was dried at 120° C. overnight and then molded into a sphere with a diameter of 3 mm. Change this to 42 "3 in C"
After time firing, composition ratio MOl2-P2-V1-W, -Mg
lCUO. A catalyst of No. 3 was obtained. This catalyst 50ml has an inner diameter of 2
An oxidation reaction was carried out by filling a 5 mm stainless steel fixed bed reaction tube with raw material gas having a composition of methacrolein: air: steam - 3:42:55 (volume %). The results are shown in Table 1. I got it. Comparative Example 1 A catalyst having the composition shown below was obtained in the same manner as in Example 1 except that ammonium tungstate, magnesium hydroxide, and copper nitrate were not used.

When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained. Comparative Example 2 A catalyst having the composition shown below was obtained in the same manner as in Example 1 except that magnesium hydroxide and copper nitrate were not used.

When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained.

Comparative Example 3 A catalyst having the composition shown below was obtained in the same manner as in Example 1 except that copper nitrate was not used.

When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained.

Example 2 The method of Example 1 was repeated except that 11.69 g of phosphoric acid, 9.69 g of copper nitrate, 7.29 g of vanadium pentoxide, and 5.8 g of magnesium hydroxide were used, and the composition shown below was obtained. A catalyst was obtained.

When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained.

Example 3 A catalyst having the composition shown below was obtained in the same manner as in Example 1, except that phosphoric acid was not used, copper nitrate was used at 1.29, and ammonium tungstate was used at 26.09.

4▼Todoroki V1 Otsu ^1 ▼L Dayz ▲▼↓6L
Vμυ. 1 The catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Example 4 Calcium hydroxide 3.7 instead of magnesium hydroxide
A catalyst having the composition shown below was obtained in the same manner as in Example 1 except that 9 was used.

When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained.

Examples 5 to 15 Catalysts were prepared according to the catalyst preparation method shown in Example 1 with the compositions shown in Table 1.

However, silver nitrate was used as silver, ceric ammonium nitrate was used as cerium, and bismuth nitrate was used as bismuth. When the catalyst thus obtained was subjected to a reaction in the same manner as in Example 1, the results shown in Table 1 were obtained.

Claims (1)

[Claims] 1. When producing methacrylic acid by catalytic gas phase oxidation of methacrolein with molecular oxygen or a gas containing molecular oxygen, the following general formula Moa-Pb-Vc-Wd-Xe-Y is used.
f-Og (in the above formula, Mo represents molybdenum, P represents phosphorus, V represents vanadium, W represents tungsten, X represents magnesium or calcium, and Y represents one of the elements consisting of copper, silver, cerium, and bismuth. a to g represent the atomic ratio of each element, and when a = 12, b = 1 to 3, c = 0.5 to 3, d = 0.5 to 3, e =
Each value is 0.5 to 3, f=0.1 to 1, and g is the number of oxygen atoms sufficient to satisfy the valence of each element. ) A selective method for producing methacrylic acid, characterized by using a metal oxide represented by as a catalyst.