JPS5824419B2 - Fuhouwa Carbon Sanno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing the corresponding unsaturated carboxylic acid by oxidizing an unsaturated aldehyde with air or molecular oxygen at high temperature in the gas phase.

Conventionally, many patents have been proposed regarding methods for producing corresponding unsaturated carboxylic acids by vapor phase catalytic oxidation of unsaturated aldehydes.

These mainly focus on methods for producing acrylic acid from acrolein, and if the catalysts proposed there are used for producing methacrylic acid, the selectivity is low due to large side reactions, and the life is short. It was thus impractical.

On the other hand, many catalysts have been proposed for the production of methacrylic acid from methacrolein, but all of them have poor reaction results, a large decline in catalyst activity over time, or too high reaction temperature. It has drawbacks and is not necessarily sufficient as an industrial catalyst.

The present inventors conducted intensive research on catalysts used to produce methacrylic acid from methacrolein, and found a catalyst that improved the above-mentioned drawbacks and had high practicality in terms of activity, selectivity, and lifespan. The present inventors have discovered that the present invention can also be applied to a method for producing acrylic acid from acrylic acid, and have completed the present invention.

In the present invention, when acrolein or methacrolein is catalytically oxidized with molecular oxygen to obtain acrylic acid or methacrylic acid, the general formula is PaMobXcYdzoOf, where P is phosphorus, Mo is molybdenum, 0 is oxygen, and X is potassium. , one or more selected from the group consisting of rubidium, cesium, and thallium, Y is one or two selected from the group consisting of vanadium and niobium, and 2 is iron, nickel, antimony, silicon, manganese, and uranium. and one or two selected from the group consisting of copper.
a, b, c, and del are the atomic ratios of each component, a = 0.5 to 6, b = 12
, c=0.2~6, d=o, oI~6, e-〇, 01~
6, f is a value determined by the oxidation state of the catalyst.

A method for producing an unsaturated carboxylic acid characterized by using a catalyst formed by:

According to the method of the present invention, it is possible to obtain unsaturated carboxylic acids from unsaturated aldehydes in high yield and high selectivity, and in particular, high catalytic activity is maintained over a long period of time, so it has extremely high industrial value. Thick.

Catalyst systems containing phosphorus and molybdenum are well known to be effective for gas phase catalytic oxidation of acrolein or methacrolein.

Phosphorus and molybdenum form extremely complex compounds depending on their mixing ratio and the temperature and atmosphere of heat treatment.

However, when conventionally proposed catalyst systems containing phosphorus and molybdenum are used for gas phase oxidation, their activity and selectivity often decrease over time in the reaction temperature range normally used, making them problematic as industrial catalysts. It had

In contrast, the catalyst of the present invention has extremely high thermal stability and can maintain high performance even when heat treated at 600°C.

In the catalyst of the present invention, added metals other than phosphorus and molybdenum have the property of forming extremely stable salts with phosphorus and molybdenum.
This seems to contribute to maintaining activity and selectivity.

The chemical state of existence of each component element of the catalyst used in the present invention is extremely complex and is not strictly clear, but it is likely that none of the components exists as an individual oxide, but rather is tightly bound. It will be done.

The method for preparing the catalyst does not need to be limited to a special method, and various well-known methods such as evaporation to dryness method, precipitation method, oxide mixing method, etc. can be used as long as the method does not involve significant uneven distribution of components. A method can be used.

As the raw material compounds used for preparing the catalyst, salts and oxides of each element such as nitrates, ammonium salts, and halides, or heteropolyacids such as phosphomolybdic acid or salts thereof can be used in combination.

For example, ammonium metavanadate is dissolved in an aqueous solution of ammonium molybdate, an aqueous solution of phosphoric acid is added thereto, an aqueous thallium nitrate solution and an aqueous iron nitrate solution are added, an appropriate carrier substance is added to the resulting slurry, and the mixture is evaporated to dryness. do.

The temperature of heat treatment is 300-650℃, preferably 350-650℃
The heat treatment time varies depending on the temperature within the range of 00°C, but is suitably 1 hour to several tens of hours.

The catalyst used in the method of the present invention can be supported on an inert carrier such as silica, alumina, silica-alumina, silicon carbide, etc., or can be used after being diluted with these.

The catalyst of the invention can be used in fixed beds, fluidized beds or moving beds.

Although the concentration of unsaturated aldehyde in the raw material gas can be varied within a wide range, a range of 1 to 20% by volume is appropriate, and a range of 3 to 15% is particularly preferred.

The raw material unsaturated aldehyde may contain small amounts of impurities such as water and lower saturated aldehydes, but these impurities do not substantially affect the reaction.

It is economical to use air as the oxygen source, but air enriched with pure oxygen can also be used if necessary.

The oxygen concentration in the raw material gas is defined by the molar ratio to the unsaturated aldehyde, and this value is between 0.3 and 4 and between 0.4 and 2.
5 is preferred.

The raw material gas may be diluted by adding an inert gas such as nitrogen, water vapor, or carbon dioxide gas.

The reaction pressure is preferably from normal pressure to several atmospheres.

The reaction temperature can be selected within the range of 240 to 450°C, with 270 to 400°C being particularly preferred.

The method of the present invention will be explained in more detail below with reference to Examples and Comparative Examples.

In the following, parts represent parts by weight, and unsaturated carboxylic acid selectivity is the ratio (percentage) of the number of moles of unsaturated carboxylic acid produced to the number of moles of unsaturated aldehyde reacted.
represents.

Example 1 42.4 parts of ammonium paramolybdate was dissolved in 200 parts of pure water at about 60°C.

To this is added 2.3 parts of 85% phosphoric acid.

Next, 4.04 parts of potassium nitrate and 2.87 parts of manganese nitrate.
1 part dissolved in 50 parts of pure water is added.

Finally, 1.33 parts of niobium pentoxide suspended in 20 parts of pure water was added, and the mixture was evaporated to dryness while heating and stirring.

The resulting cake was dried at 130° C. for 16 hours, compression molded, and calcined at 450° C. for 2 hours to be used as a catalyst.

The composition of the catalyst is Mo 12p1, 2Nb 1Mn in atomic ratio.
□, 5.

This catalyst was packed into a reactor, and 5% methacrolein and 10% oxygen were added.
%, water vapor 30%, and nitrogen 55% (volume %) mixed gas was passed through the reactor at a reaction temperature of 330°C and a contact time of 3.6 seconds.

When the product was analyzed by gas chromatography, the methacrolein reaction rate was 80.6%, and the methacrylic acid selectivity was 8.
It was 0.1%.

In addition, acetic acid, carbon dioxide gas, -carbon oxide, etc. were generated.

The reaction continued for about 1000 hours under the same conditions, but the methacrolein reaction rate was 79.3% and the methacrylic acid selectivity was 80.8%.
And it hasn't changed at all.

Example 2-13 The following catalysts were prepared in the same manner as in Example 1 and reacted under the same conditions as in Example '1 to obtain the results shown in Table 1.

Example 13-20 A catalyst was prepared in the same manner as in Examples 1 to 13 by replacing part or all of the niobium pentoxide with ammonium methanonadate, and the reaction was carried out under the same conditions as in Example 1 except for the reaction temperature. The results are shown in Table 2.

Examples 21-24 The catalysts of Examples 1.8, 13 and 16 were reacted with a mixed gas of 5% acrolein, 10% oxygen, 30% water vapor and 55% nitrogen at a predetermined reaction temperature and for a contact time of 3.6 seconds, Table 3
I got the result.

Comparative Example A catalyst was prepared using the method of Example 1 except that niobium pentoxide, manganese nitrate, or potassium nitrate was removed and tested using the method of Example 1. The results are shown in Table 4.

Claims (1)

[Claims] 1. When acrylic acid or methacrylic acid is obtained by catalytically oxidizing acrolein or methacrolein in a high-temperature gas phase with molecular oxygen, the following general formula % is used, where P is phosphorus and MO is Molybdenum, 0 represents oxygen, X is one or more selected from the group consisting of potassium, rubidium, cesium and thallium, Y is one or two selected from the group consisting of vanadium and niobium, Z represents one or more elements selected from the group consisting of iron, nickel, antimony, silicon, manganese, uranium, and copper, and a, b, c, d, e, and f represent the atomic ratio of each component. Hail, a = 0.5~6
, b=12, c=0.2~6, d=0.01~6,
e=0.01 to 6, and f is a value determined by the oxidation state of the catalyst. A method for producing an unsaturated carboxylic acid, characterized by using a catalyst formed by: