JPS5929570B2 - Production method of unsaturated carboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acrylic acid or methacrylic acid by contacting a mixed gas containing acrolein or methacrolein and oxygen with a catalyst in a high temperature gas phase.

Regarding the method of producing acrylic acid from acrolein, there is a method using a catalyst consisting of P, Mo, and As (Japanese Patent Publication No. 19260/1983), a method using a catalyst consisting of Mo, Ri, W, and silica (Japanese Patent Publication No. 1973-19260), 12129) and many others have been proposed.

Furthermore, many other methods have been proposed for producing methacrylic acid from methacrolein, including a method using a catalyst consisting of Mo, Ni, and Ti (Japanese Patent Publication No. 47-6605). However, from the standpoint of industrialization, they all have drawbacks in terms of selectivity, lifespan, etc., which currently hinders industrialization. As a result of various studies on catalysts used to produce (meth)acrylic acid from (meth)acrolein, the present inventors discovered a new catalyst that is extremely practical in terms of activity, selectivity, and life. invention has been achieved.

The present invention provides a mixed gas containing acrolein or methacrolein and molecular oxygen according to the general formula PaM0bXCYd0e [where P is phosphorus, Mo is molybdenum, o is oxygen, and X is one or more of potassium, rubidium, and cesium. ,
Y is one or two of rhodium, cerium, and zirconium
species or more (however, two or more species when containing cerium or zirconium), a, b, c, d, e represent the atomic ratio of each component, a■0.5-6, b=12, c= 0.2～
6, d ■ 0.001 to 6, e is a value determined by the oxidation state of the catalyst] is a method for producing acrylic acid or methacrylic acid, which is characterized by bringing it into contact in a high temperature gas phase. .

The state of existence of phosphorus, molybdenum, and additional metals in the catalyst used in the present invention is complex and not strictly clear, but it is likely that none of the components exists as a single oxide but is tightly bound together. It will be done.

The atomic ratio of phosphorus and metal elements in the catalyst used in the present invention is 0.5 to 6 for phosphorus when molybdenum is 12, 0.2 to 6 for potassium, rubidium, and cesium in total, and 0.2 to 6 for phosphorus in total, and 0.2 to 6 in total for potassium, rubidium, and cesium, and 12 for molybdenum. Total is 0.0
The range is from 01 to 6.

The present catalyst may also contain other metal elements such as thallium. It is well known that catalysts containing phosphorus and molybdenum are effective for gas-phase oxidation of acrolein or methacrolein, but complex and highly active substances may vary depending on the mixing ratio of phosphorus and molybdenum, heat treatment temperature and atmosphere. generate.

Excellent activity and selectivity can be obtained from this catalyst even by heat treatment in air, which is commonly carried out. However, the atmosphere during heat treatment has a large effect on catalytic activity. For example, when heat treatment is performed in a substantially oxygen-free gas atmosphere such as nitrogen gas or ammonia gas, the catalytic activity is surprisingly improved. Its high activity is maintained for a long time. Other preferred atmospheres for heat treatment include CO. CO2, hydrocarbons, He. Gases such as Ar may also be used. Although the details of the cause of this improvement in activity are not clear, this catalyst containing phosphorus and molybdenum exhibits a yellow-green color when heat-treated in air, and turns dark blue after being used in the method of the present invention, indicating that phosphomolybdate is It will be slightly refunded.

On the other hand, if the catalyst is heat-treated in nitrogen gas instead of air, the color of the catalyst exhibits a black edge color due to further reduction, and after being used in the method of the present invention, it is slightly oxidized by the oxygen in the mixed gas and returns to a deep blue color. From this fact, in the catalyst of the present invention containing phosphorus and molybdenum, the semi-reduced form of phosphomolybdate has catalytic activity, and moreover, the reduction is more advanced than changing from an oxidized catalyst to a semi-reduced catalyst. It is thought that the catalytic activity increases when a type catalyst is modified to a semi-reduced type catalyst.
When a catalyst containing phosphorus and molybdenum is used for gas phase oxidation, the catalyst structure often changes over time, resulting in a decrease in activity and selectivity, and these phenomena are more likely to occur as the reaction temperature is higher.

Therefore, for example, by heat-treating the catalyst under a nitrogen atmosphere, the activity can be significantly increased, as a result of which the reaction temperature can be lowered and the catalyst life can be extended.
This is of practical significance. As a method for producing the catalyst used in the present invention, for example, an evaporation to dryness method, a precipitation method, an oxide mixing method, etc. can be used.

The heat treatment temperature of the catalyst is preferably 300 to 600°C. The heat treatment time varies depending on the temperature, but is preferably from one hour to several tens of hours. The catalyst component may be supported on a known inert carrier such as silica, alumina, silica alumina, or silicon carbide, or may be diluted with the carrier. In carrying out the present invention, a mixed gas containing acrolein or methacrolein and molecular oxygen is brought into contact with a catalyst in a high temperature gas phase. The raw material unsaturated aldehyde may contain a small amount of impurities such as water and lower saturated aldehyde. Although the unsaturated aldehyde concentration in the feed gas can be varied within a wide range,
A range of 20% by volume is preferred. The oxygen concentration in the raw material gas is defined by the molar ratio to the unsaturated aldehyde, and this molar ratio is preferably in the range of 0.3 to 4. The raw material gas is nitrogen,
It may be diluted with an inert gas such as water vapor or carbon dioxide. The reaction temperature is preferably 250 to 450°C, and 250 to 400°C.
C. is particularly advantageous. According to the method of the present invention, there are no drawbacks of conventional methods in terms of selectivity, lifespan, etc., and (meth)acrylic acid can be produced from (meth)acrolein with high reaction rate and selectivity. Parts in the following examples mean parts by weight.

The unsaturated carboxylic acid selectivity is the unsaturated aldehyde (
It is expressed as the ratio (%) of the unsaturated carboxylic acid (mol) produced to the unsaturated carboxylic acid (mol). Example 1 42.4 parts of ammonium paramolybdate was dissolved in 85 parts of water, to which was added 9.75 parts of cesium nitrate dissolved in 50 parts of water, and further 0.56 parts of rhodium chloride was added as a solid. After dissolving the mixture, 4.61 parts of 85% phosphoric acid was added, and the mixture was evaporated to dryness while heating and stirring.

The residue was dried at 130°C for 16 hours, then pressure-molded, crushed, sieved to 10 to 20 mesh, and placed under air circulation to
The catalyst was heat treated at 0°C for 2 hours. The composition of this catalyst is P2MOl2CS2.5RhO. It was l. This catalyst was packed into a reactor, and a mixed gas consisting of 5% methacrolein, 10% oxygen, 30% water vapor, and 55% nitrogen by volume was introduced into the catalyst bed at a reaction temperature of 325°C and a contact time of 3.6 seconds. . When the product was collected and analyzed by gas chromatography, the methacrolein reaction rate was 8.
The selectivity for methacrylic acid was 3.4% and 82.4%. Other substances produced include acetic acid, acetone, carbon dioxide gas, and carbon monoxide. When the reaction was continued for about 1600 hours under the same conditions, the methacrolein reaction rate was 83.0% and the methacrylic acid selectivity was 82.2%. Example 2 The 10 to 20 meshes sieved in the catalyst manufacturing process of Example 1 were heat treated at 500° C. for 2 hours under nitrogen gas flow, and used as a catalyst.

The reaction was carried out in the same manner as in Example 1 except that the reaction temperature was 295°C, and the methacrolein reaction rate was 82.1%.
, the methacrylic acid selectivity was 83.1%.

When the reaction was continued for about 1600 hours under the same conditions, the methacrolein reaction rate was 82.3% and the methacrylic acid selectivity was 83.
It was 0%. Example 3 The material sieved into 10 to 20 meshes in the catalyst manufacturing process of Example 1 was sieved at 500°C under ammonia gas flow for 2 hours.
This was heat treated for a period of time and used as a catalyst.

The reaction was carried out in the same manner as in Example 1 except that the reaction temperature was 300°C, and the methacrolein reaction rate was 82.0.
%, and the methacrylic acid selectivity was 82.5%.

When the reaction was continued for about 1600 hours under the same conditions, the methacrolein reaction rate was 82.1% and the methacrylic acid selectivity was 83.
It was 0%. 5 Examples 4 to 5 Using each catalyst obtained by using 5.05 parts of potassium nitrate or 7.38 parts of rubidium nitrate in place of cesium nitrate in Example 1, and otherwise treating in the same manner as in Example 1. The reaction was carried out in the same manner as in Example 1 at the reaction temperatures shown in Table 1.

The results are shown in Table 1. Examples 6 to 13 Using each catalyst shown in Table 2 obtained in the same manner as in Example 1, a reaction was carried out in the same manner as in Example 1 at the reaction temperature shown in Table 2.

The results are shown in Table 2. Example 14 Using the same catalyst as in Example 1, 5% acrolein by volume,
A mixed gas consisting of 10% oxygen, 30% water vapor and 55% nitrogen was introduced into the catalyst bed at a reaction temperature of 335° C. and a contact time of 3.6 seconds.

The product was collected and analyzed by gas chromatography, and the acrolein reaction rate was 90.1% and the acrylic acid selectivity was 91.0%. Example 15 Using the same catalyst as in Example 2, the reaction temperature was 315°C,
The rest was treated in the same manner as in Example 14, and the acrolein reaction rate was 91.0% and the acrylic acid selectivity was 90.8%.

Claims (1)

[Claims] 1 A mixed gas containing acrolein or methacrolein and molecular oxygen is expressed by the general formula P_aMo_bX_cY_dO_
e [In the formula, P is phosphorus, Mo is molybdenum, O is oxygen, and X is one or more of potassium, rubidium, and cesium,
Y is one or two of rhodium, cerium, and zirconium
species or more (however, two or more species when containing cerium or zirconium), a, b, c, d, e represent the atomic ratio of each component, a = 0.5 to 6, b = 12, c = 0.2～
6, d=0.001 to 6, e is a value determined by the oxidation state of the catalyst] A method for producing acrylic acid or methacrylic acid, which is characterized by contacting the acrylic acid or methacrylic acid in a high temperature gas phase.