JPH064558B2 - Method for producing methacrylic acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing methacrolein by gas phase catalytic oxidation of methacrolein.

[Conventional technology]

Conventionally, an extremely large number of patents have been proposed regarding a method for producing an unsaturated carboxylic acid by vapor-phase catalytic oxidation of an unsaturated aldehyde. These mainly focus on the method of producing acrylic acid from acrolein, and when the catalyst proposed there is used for the production of methacrolein acid, the side reaction is large and the selectivity is low, and the life is short. It was not practical.

On the other hand, many catalysts have been proposed for the method of producing methacrylic acid from methacrolein, but all of them are
It has drawbacks such as insufficient reaction results, a large decrease in catalyst activity over time, and an excessively high reaction temperature, and further improvement is desired when it is used as an industrial catalyst.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for producing methacrylic acid from methacrolein in an advantageous manner, and particularly to provide a method for producing methacrylic acid using a catalyst having high activity, selectivity and long life.

[Means for solving problems]

In the present invention, when methacrolein is subjected to vapor-phase catalytic oxidation with molecular oxygen to produce methacrylic acid, a general formula P _a Mo _b V _{c F d} Cu _e Sb _f X _g Y _h Z _i O _j (wherein 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 tellurium, lanthanum and boron, Z is silver and / or Represents magnesium, a to i represent atomic ratios of respective elements, and when b = 12, a = 0.3 to 4, c = 0.01 to
3, d = 0.01 to 4, e = 0.01 to 3, f = 0.01 to 3, g =
0.01-3, h = 0.001-5, i = 0-5, and j is the number of oxygen atoms required to satisfy the valence of each component. The method for producing methacrylic acid is characterized in that the catalyst represented by the formula (1) is used, and the catalyst constituent component is a heteropolyacid salt structure.

The catalyst used in the present invention has large peaks at 2θ = 26.4 ° and 10.8 °, which are peculiar to the heteropolyacid salt, when observed by X-ray diffraction, and 2θ = 8.0 peculiar to the heteropolyacid.
Since almost no peaks are observed at °, 8.9 °, and 9.3 °, it is considered that substantially all have a heteropolyacid salt structure. There is also a view that a catalyst having a heteropolyacid salt structure gradually decomposes and its catalytic activity decreases, and it does not have an industrially endurable lifetime. This is not the case for catalysts with a heteropolyacid salt structure.

In the present invention, by adding a specific amount of iron, antimony and other specific elements to a catalyst containing phosphorus, molybdenum, vanadium and copper, the activity and the selectivity are increased, and the activity is high, so that the reaction temperature is sufficient. A reaction rate can be achieved, and as a result, a high catalytic activity is maintained over a long period of time, so that a method for producing methacrylic acid having an extremely high industrial value can be provided.

The method for producing the catalyst used in the present invention is not limited to a special method, and unless a significant uneven distribution of the components is involved, a conventionally well-known method such as an evaporation-drying method,
Various methods such as a precipitation method can be used.

As the raw material compound used for the preparation of the catalyst, nitrates, carbonates, ammonium salts, halides, oxides and the like of each element can be used in combination.

Although the catalyst used in the method of the present invention is effective without a carrier,
It can also be used by supporting it on an inert carrier such as silica, alumina, silica-alumina, or silicon carbide, or by diluting it.

In carrying out the present invention, the concentration of methacrolein in the raw material gas can be varied over a wide range, but the volume of methacrolein is 1 to 20
% Is suitable, and particularly preferably 3 to 10%.

The raw material methacrolein may contain a small amount of impurities such as water and lower saturated aldehydes, and these impurities do not substantially affect the reaction.

It is economical to use air as the oxygen source, but pure oxygen-enriched air can be used if desired.

The oxygen concentration in the raw material gas is defined by the molar ratio with respect to methacrolein, and this value is preferably 0.3 to 4, particularly 0.4 to 2.5.

The raw material gas may be diluted by adding an inert gas such as nitrogen, steam or carbon dioxide gas. The reaction pressure is preferably atmospheric pressure to several atmospheres. The reaction temperature can be selected in the range of 230 to 450 ° C, but particularly preferably 250 to 400 ° C. The reaction can be carried out in a fixed bed or a fluidized bed.

〔Example〕

Hereinafter, a method for preparing the catalyst according to the present invention and a reaction example using the same will be specifically described.

In the examples and comparative examples, “part” means “part by weight”, and analysis was carried out by gas chromatography. In addition, the reaction rate of methacrolein and the selectivity of methacrylic acid produced are defined as follows.

Example 1 100 parts of ammonium paramolybdate, 2.8 parts of ammonium metapanazinate and 4.8 parts of potassium nitrate were added to 30 parts of pure water.
Dissolved in 0 parts. To this, 8.2 parts of 85% phosphoric acid was added to pure water 10
Add the dissolved part to 3.3 parts of telluric acid and add 2 parts of pure water.
What was melt | dissolved in 0 part and 3.4 antimony trioxide were added, and it heated up at 95 degreeC, stirring.

Next, a solution prepared by dissolving 3.4 parts of copper nitrate and 5.7 parts of ferric nitrate in 30 parts of pure water was added, and the mixed solution was evaporated to dryness while heating and stirring at 100 ° C.

The obtained solid product was dried at 130 ° C. for 16 hours, pressure-molded, and then heat-treated at 380 ° C. for 5 hours in an air stream to be used as a catalyst.

The composition of elements other than oxygen in the obtained catalyst (the same applies hereinafter) is P
_{It was 1.5} Mo ₁₂ V _0.5 Fe _0.3 Cu _0.3 Sb _0.5 K ₁ Te _0.3 . The catalyst was packed in a reactor and methacrolein 5%,
A mixed gas of oxygen 10%, water vapor 30%, and nitrogen 55% (volume%) was passed at a reaction temperature of 290 ° C. and a contact time of 3.6 seconds.
When the product was collected and analyzed by gas chromatography, the reaction rate of methacrolein was 87.5% and the selectivity of methacrylic acid was high.
It was 87.3%.

When the reaction was continued for about 1000 hours under the same conditions, the methacrolein conversion rate was 87.3% and the methacrylic acid selectivity was 87.0%.

Example 2 P ₁ Mo ₁₂ V ₁ Fe _0.2 Cu _0.1 Sb ₁ C according to Example 1
When a catalyst having a composition of s ₁ B _0.3 was prepared and reacted under the same conditions as in Example 1, the methacrolein conversion was 86.5% and the methacrylic acid selectivity was 87.9%.

Examples 3 to 6 According to Example 1, except that the addition of silver and magnesium corresponding to the Z component was carried out by dissolving in pure water together with copper nitrate and ferric nitrate to prepare each catalyst in the following table, The reaction was carried out under the same conditions as in Example 1, and the results shown in the following table were obtained.

Example 7 P _1.7 Mo ₁₂ V _0.7 Fe _0.4 Cu _0.1 Sb according to Example 1
A catalyst having a composition of _0.9 K ₁ La _0.05 was prepared and reacted under the same conditions as in Example 1. The reaction result shows that the methacrolein reaction rate is
The selectivity was 87.6% and the methacrylic acid selectivity was 87.0%.

Example 8 Using the catalyst of Example 1, the reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 305 ° C., resulting in a methacrolein conversion of 97.3% and methacrylic acid selectivity of 81.5%.

Example 9 The reaction was conducted under the same conditions as in Example 1 except that the reaction temperature was changed to 305 ° C. using the catalyst of Example 2, and the methacrolein conversion was 97.3% and the methacrylic acid selectivity was 81.2%. .

Comparative Examples 1 to 3 Comparative catalysts shown in the following table were prepared according to Example 1, and Example 1
The following results were obtained by reacting under the same conditions as.

[Brief description of drawings]

 FIG. 1 is an X-ray diffraction diagram of the catalyst obtained in Example 1.

Continuation of front page (56) References JP-A-55-2619 (JP, A) JP-A-59-115750 (JP, A)

Claims (1)

[Claims] 1. When producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, a compound represented by the general formula: P _a Mo _b V _c Fe _d Cu _e Sb _f X _g Y _h Z _i O _j Where 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 tellurium, lanthanum and boron, Z is silver and / Or magnesium, a to i represents the atomic ratio of each element, when b = 12, a = 0.3 to 4, c = 0.01 to
3, d = 0.01 to 4, e = 0.01 to 3, f = 0.01 to 3, g =
0.01-3, h = 0.001-5, i = 0-5, and j is the number of oxygen atoms required to satisfy the valence of each component. A method for producing methacrylic acid, characterized in that the catalyst represented by the formula (4) is used, and the catalyst constituent component is a heteropolyacid salt structure.