JPS5842176B2 - Fuhouwa Carbon Sanno Seizouhou - 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.

The main focus is on the method of producing acrylic acid from acrolein, and when the catalyst proposed there is used for producing methacrylic acid, the selectivity is low due to large side reactions, and the life is short, making it impractical for practical use. It wasn't on point.

Many proposals have been made regarding methods for producing methacrylic acid from methacrolein.
etc.), PMo alkaline system (JP-A-48-61416)
．． 61417, 67216゜72116 etc.), PM
OAs-based catalysts (Japanese Patent Publication No. 49-10652, etc.) are known.

Although each of these catalysts has its own characteristics, they also have drawbacks such as poor reaction results, a marked decline in catalytic activity over time, and too high reaction temperatures, so they cannot necessarily be said to be sufficient as industrial catalysts. .

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 an unsaturated aldehyde is catalytically oxidized with molecular oxygen to obtain a corresponding unsaturated carboxylic acid, the general formula P a Mo b X c Y d Z e Of, where P is phosphorus, MO is molybdenum, O represents oxygen;
Further, X is at least one selected from the group consisting of potassium, rubidium, and cesium, Y is at least one selected from the group consisting of iron, nickel, and uranium, and Z is at least one selected from the group consisting of tungsten, zinc, cadmium, cobalt, and antimony. At least one selected one, a t b
+ C+ d + e y f represents the atomic ratio of each component, a=0.5~6 + b= 12 t c=0
．． 2-6 y d=0.01-6+e-0-6. f is a value determined by the oxidation state of the catalyst.

This is a production method using a catalyst represented by

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

It is well known that catalyst systems containing phosphorus and molybdenum are effective for the 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.

Therefore, when a catalyst system containing phosphorus and molybdenum is used for gas phase oxidation, it becomes active over time in the reaction temperature range normally used.
A decrease in selectivity often occurs.

The catalyst containing phosphorus, molybdenum, and arsenic that the present inventors proposed earlier (Japanese Patent Application No. 48-91976) has high activity, high selectivity, and high performance, but has the drawback of low thermal stability of the catalyst. are doing.

In contrast, the catalyst of the present invention, which does not contain any arsenic, 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 in the preparation of the catalyst, salts and oxides of each element such as nitrates, ammonium salts, and halides, or heteropolyacids such as phosphorus and molybdic acid, or their salts can be used in combination.

For example, an aqueous solution of phosphoric acid is added to an aqueous solution of ammonium molybdate, an aqueous solution of thallium nitrate is added, and an aqueous solution of iron nitrate is further added to the resulting slurry, an appropriate carrier material is added, and the slurry is evaporated to dryness.

The temperature of heat treatment is 300-650°C, preferably 350-650°C
The heat treatment time is within the range of 6000C and varies depending on the temperature, but is suitable for one 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 0.3 to 4, particularly 0.4 to 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 diffused pressure.

Although the reaction temperature can be selected within the range of 240 to 450°C, 270 to 400°C is 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.

Reaction time means the elapsed time measured from the time when the reaction conditions were set.

Example 1 To an aqueous solution in which 88.3 g of ammonium paramolybdate was dissolved in 400 parts of pure water at about 60° C., an aqueous solution in which 9.7 parts of 85% phosphoric acid was dissolved in 10 parts of pure water was added.

Furthermore, a solution of 16.4 parts of cesium nitrate dissolved in 200 parts of pure water and an aqueous solution of 16.8 parts of ferric nitrate dissolved in 50 parts of pure water were added to this solution, and the mixture was evaporated to dryness while stirring.

The resulting cake was dried at 130° for 16 hours and then ground.

This was pressure-molded, crushed into 10 to 20 meshes, and then calcined at 450°C for 5 hours to be used as a catalyst.

The composition of this catalyst is P2Mo12C52Fel in atomic ratio.
Met.

This catalyst was packed into a reactor, and 5% methacrolein and 1% oxygen were added.
A mixed gas of 0% water vapor, 30φ water vapor, and 55% nitrogen (volume %) was passed through the reactor at a reaction temperature of 335° C. and a contact time of 3.6 seconds.

When the product was analyzed by gas chromatography, the following results were obtained.

Methacrolein reaction rate 78.6% *Methacrylic acid selectivity 81.2φ In addition, acetic acid, carbon dioxide gas, -carbon oxide, etc. were produced.

After continuous reaction for about 1000 hours under the same conditions, the following results were obtained.

Methacrolein reaction rate 78.6% Methacrylic acid selectivity 81.3% Examples 2 to 4 In the same manner as in Example 1, cesium nitrate or rubidium nitrate was used as the X component, and ferric nitrate was substituted for the Y component. A catalyst was prepared in the same manner as in Example 1 except that nickel nitrate and uranyl nitrate were used.

However, the firing temperature and opening were changed as shown in Table 1.

These catalysts were reacted in the same manner as in Example 1 except for the reaction temperature.

Table 1 summarizes the catalyst, reaction conditions, and reaction results.

Examples 10 to 11 Using the catalysts of Examples 1 and 6, 5% acrolein and 1% oxygen
A mixed gas containing 0% water vapor, 30% water vapor, and 55% nitrogen was reacted for a contact time of 3.6 seconds.

Table 3 summarizes the catalyst, reaction conditions, and reaction results.

Example 12 The same procedure as in Example 1 was carried out except that cesium nitrate in Example 1 was replaced with potassium nitrate, and ferric nitrate was replaced with nickel nitrate and cobalt nitrate.

However, the composition ratio, firing temperature, and time were changed as shown in Table 4.

The reaction of this catalyst was carried out under the same conditions as in Example 1 except for the reaction temperature.

Table 4 shows the catalyst and the main points of the reaction results.

Comparative Examples 1 to 3 Catalysts were prepared except for using cesium nitrate in Example 2, nickel nitrate in Example 4, and nickel nitrate in Example 2, and the reactions were carried out in the same manner as in Example 1 except for the reaction temperature.

The results of the reaction are shown in Table 4.

Claims (1)

[Claims] 1. When an unsaturated aldehyde is catalytically oxidized with molecular oxygen to obtain a corresponding unsaturated carboxylic acid, the following general formula % is used. However, P is phosphorus, MO is molybdenum, and O is oxygen. represented by At least one selected from the group, a, b, c, d
, e. f represents the atomic ratio of each component, a=0.5~6゜b
= 12 p c = 0.2 ~ 6 t d = 0.01 ~ 6
teO~6. f is a value determined by the oxidation state of the catalyst. A manufacturing method using a catalyst represented by