JPS5933576B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing methacrylic acid in good yield by catalytically oxidizing methacrolein with molecular oxygen or a molecular oxygen-containing gas in a high-temperature gas phase.

Many methods have already been proposed for producing unsaturated carboxylic acids by catalytic oxidation of unsaturated aldehydes in a high-temperature gas phase, but these methods mainly produce acrylic acid from acrolein. There are only a few articles related to methods for producing methacrylic acid from methacrolein.

In fact, a method for producing acrylic acid from acrolein has actually been industrialized, but a method for producing methacrylic acid from methacrolein has not yet been industrialized, despite the above proposals. The reason for this is that the yield when producing methacrylic acid from methacrolein is much lower than when producing acrylic acid. The lower yield in the case of methacrylic acid compared to acrylic acid production is due to the fact that methacrolein is more easily oxidized than acrolein.
This is thought to be due to the fact that complete oxidation (generation of carbon monoxide and carbon dioxide) is more likely to occur than partial oxidation. On the other hand, catalysts that can be used as oxidation catalysts for methacrolein to methacrylic acid either have low reaction performance or, although they show relatively good performance in the early stages of the reaction, their short active lifetimes make them impractical. It has a runner-up score that cannot be adopted as an industrial catalyst. The present invention produces methacrylic acid in high yield by using a catalyst consisting of molybdenum, phosphorus, vanadium, thallium, bismuth, copper, and oxygen, and the catalyst has a composition particularly shown by the following empirical formula. Favorable results are obtained when used within the range.

MoaPbVcTldBieCuf0g Here, a, b, c) d, e, f, and g represent the number of atoms of molybdenum, phosphorus, vanadium, thallium, bismuth, copper, and oxygen, respectively.

When a=12, b-0.1 to 6 (particularly preferably 0.5 to 3), c=0.1 to 6 (particularly preferably 0.5 to 3), d-0.01 to 3 (particularly preferably 0.
01-1), e=0.1-6 (particularly preferably 0.1-1), e=0.1-6 (especially preferably 0.1-1),
3), f-0.1 to 6 (particularly preferably 0.1 to 3), and g is a value naturally determined by the valence of the element other than oxygen and the values of a to f. In producing the catalyst used in the present invention, this type of oxide catalyst preparation method is generally used.

As starting materials used for producing catalysts, ammonium molybdate, molybdic acid, molybdenum oxide, phosphomolybdic acid, etc. are used for molybdenum, and phosphoric acid, phosphorous acid, phosphorus pentoxide, etc. are used as phosphorus raw materials. Ammonium metavanadate, vanadyl oxalate, vanadium pentoxide, vanadium sulfate, etc. are used as raw materials for vanadium, and raw materials for thallium and bismuth include their nitrates, carbonates, sulfates, organic acid salts, halides, Oxides etc. are used.

Among these raw materials, vanadyl oxalate prepared by dissolving vanadium pentoxide in an aqueous oxalic acid solution provides the best activity as the vanadium raw material. These raw material compounds are made into a liquid or slurry using a solvent such as water, mixed as uniformly as possible, and then the solvent is evaporated to dryness on a sand bath at 100 to 150°C. The resulting cake-like material is dried, preferably at 250-400°C.
After baking for 1 to 10 hours, the resulting solid is pulverized. This is compressed into tablets, or the powder is calcined in air at 300 to 500°C for 1 to 20 hours to obtain a catalyst. The catalyst of the present invention is extremely effective even without a carrier, but it is more convenient to support it on a carrier, such as silica gel, silica sol, alumina, alumina silicate, silicon carbide, diatomaceous earth, *titanium oxide, etc. used.

The methacrolein raw material used in the present invention does not need to be pure methacrolein, but methacrolein obtained by oxidizing isobutylene with air over a catalyst,
A mixed gas containing unreacted isobutylene, carbon monoxide, carbon dioxide, nitrogen gas, water vapor, etc. may be used.

Similarly, the oxygen source used may be pure oxygen, but air is generally used.

Alternatively, a gas obtained by diluting oxygen with an inert gas such as carbon dioxide or nitrogen may be used. The reaction temperature suitable for the reaction conditions using the catalyst of the present invention varies depending on the catalyst, raw material gas composition, space velocity, etc., but is the temperature normally used for this type of reaction, that is, 200 to 450°C, preferably 250°C. ~400'C.

Furthermore, although the present invention can be carried out either under pressure or reduced pressure,
It is convenient to carry out under normal pressure.

Space velocity is 100 to 12000 hr-1) preferably 2
It is 50 to 6000 hr-1.

The raw material gas composition is methacrolein 0.1 to 10 mol%, oxygen 0.1 to 20 mol%, and water vapor 0 to 90 mol%, preferably 10 to 80 mol%.

The coexistence of water vapor in the raw material mixed gas is extremely advantageous in terms of the yield of methacrylic acid, which is the target product. The catalyst of the present invention is generally used in a fixed bed, but it can also be used in a fluidized bed. It can also be used.

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

In addition, the methacrolein reaction rate, methacrylic acid selectivity, and acetic acid selectivity in the present specification are defined as follows.

The analysis was conducted using gas chromatography.

Example 1 Ammonium molybdate 105.9y 6
It was dissolved in 600 ml of water heated to 0°C, 11.57 of orthophosphoric acid (85 wt% concentration) was added to this solution, and 4.557 of vanadium pentoxide was dissolved in 25 wt% of an oxalic acid aqueous solution.
The solution dissolved in 0ml was mixed (solution A).

Separately, a solution was prepared in which 6.06 y of bismuth nitrate, 3.027 y of copper nitrate, and 1.33 y of thallium nitrate were dissolved in 50 ml of 3 wt % dilute nitric acid, and this was mixed into the above solution A. Next, this mixed solution was evaporated to dryness on a sand bath heated to 100-150°C, and the obtained solid was calcined in air at 200°C for 4 hours, and then ground into 10-16 meshes. I sieved it. Then, it was fired in air at 350°C for 5 hours. The catalyst thus completed has an atomic ratio (excluding oxygen) of MOL2
P2lTlO. lBlO. 25CUO. 10 ml of this catalyst having a composition of
1, a raw material gas having a composition of 2.5 mol% methacrolein, 5 mol% oxygen, 65 mol% nitrogen, and 27.5 mol% water vapor was supplied.

The results were that the methacrolein reaction rate was 95.3%, the methacrylic acid selectivity was 74.8%, and the acetic acid selectivity was 6.8%.
Reference Example 1 MOL2P2,T was prepared in the same manner as in Example 1 except that the amount of bismuth nitrate in Example 1 was changed to 4.85y and that 2.97% of cobalt nitrate was used instead of copper nitrate.
lO. , BiO. 2COO. A catalyst with an atomic ratio of 2 (excluding oxygen) was prepared.

When the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was 320°C, the methacrolein reaction rate was 92.
．． 5%, methacrylic acid selectivity 73.2%, acetic acid selectivity 8
．． The score was 0%. Reference Example 2 In Example 1, the amount of bismuth nitrate was set to 4.857, and aluminum nitrate was replaced with 3.757 of aluminum nitrate instead of copper nitrate.
MOL2P2Vl was prepared in the same manner as in Example 1 except that thallium nitrate was used and the amount of thallium nitrate was 2.66V.
TlO. 2BiO. 2AlO. A catalyst with an atomic ratio of 2 (excluding oxygen) was prepared.

When the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was 350°C, the methacrolein reaction rate was 86.
6%, methacrylic acid selectivity 73.8%, acetic acid selectivity 7.
The score was 1%.

Example 2 105.97 ammonium molybdate was dissolved in 600 ml of water heated to 60°C, and orthophosphoric acid (85
11.57 (wt% concentration) was added, and a solution prepared by dissolving 25 wt% of vanadium pentoxide (25 wt%) in 50 ml of an oxalic acid aqueous solution was mixed (solution A).

Separately, add 6.06y of bismuth nitrate and 3.027y of copper nitrate to 3w.
When it was dissolved in 50 ml of t% dilute nitric acid and mixed with the above solution A, a precipitate was formed. A solution of 13.3 y of thallium nitrate dissolved in 250 ml of water was added to this precipitate mixture, stirred, and then evaporated to dryness on a sand bath heated to 100 to 150°C. The obtained solid was calcined in air at 200° C. for 4 hours, then ground and sieved into 10 to 16 meshes. Then, it was fired in air at 350°C for 5 hours. The catalyst thus completed has an atomic ratio (excluding oxygen) of MOL2P.
2, TllBiO. 25CUO. It has 25 compositions.

Claims (1)

[Claims] 1. In producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen or molecular oxygen-containing gas, the general composition is MoaPbVcTldBieCuf.
Og (where a, b, c, d, e, f and g are respectively molybdenum, phosphorus, vanadium, thallium, bismuth,
Number of copper and oxygen atoms. And if a=12, b=0.1~6, c=0.1~
6, d=0.01~3, e=0.1~6, f=0.1~
6, g=represented by a number naturally determined by the valence of each atom and the values of a to f. ) A method for producing methacrylic acid, characterized by using a catalyst represented by: