JPS6136816B2 - - 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 when 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 wasn't practical. On the other hand, many catalysts have been proposed for the production of methacrylic acid from methacrolein, but all of them have problems such as low reaction product, large decrease in catalyst activity over time, or too high reaction temperature. However, it cannot be said to be 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 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} P _a Mo _b Molybdenum, Nb is niobium, V is vanadium, O is oxygen, X is one or more selected from the group consisting of potassium, rubidium, cesium and thallium, Y
represents one or more selected from the group consisting of silicon, manganese, and copper, and a, b,
c, d, e, f represent the atomic ratio of each component, a=0.5~6, b=12, c=0.2~6, d=
0.01-6, e=0.01-6, f=0.06-6, and g is a value determined by the oxidation state of the catalyst. This is a method for producing an unsaturated carboxylic acid, characterized by using a catalyst represented by: According to the method of the present invention, it is possible to obtain the corresponding 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 it has 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. 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, and 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 together. It can 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, niobium pentoxide is added to the resulting slurry, and a suitable carrier is added. Add the material and evaporate to dryness. The temperature of heat treatment is 300~650℃, preferably 350~
Although the heat treatment time varies depending on the temperature within the range of 600° C., one hour to several tens of hours is appropriate. 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, especially 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 several atmospheres. The reaction temperature can be selected within the range of 240 to 450°C, but 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 represents the ratio (percentage) of the number of moles of unsaturated carboxylic acid produced to the number of moles of reacted unsaturated aldehyde. Example 1 Ammonium paramolybdate was dissolved in pure water at about 60°C. To this add ammonium metavanadate and 85% phosphoric acid. Next, potassium nitrate and manganese nitrate dissolved in pure water are added.
Finally, niobium pentoxide suspended in 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, then compression molded and calcined at 450°C for 2 hours, and used as a catalyst. The composition of the catalyst _is Mo ₁₂ P ₂ K _{2 Nb 0.5 V 0.5 Mn 1 in} atomic ratio.
It was hot. This catalyst was packed in a reactor, and a mixed gas of 5% methacrolein, 10% oxygen, 30% steam, and 55% nitrogen (volume %) was passed through the reactor at a reaction temperature of 330°C and a contact time of 3.6 seconds. When the product was separated by gas chromatography, the methacrolein reaction rate was 80.2% and the methacrylic acid selectivity was 81.8%. In addition, acetic acid, carbon dioxide gas, carbon monoxide, etc. were generated. Examples 2-4 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. 【table】

Claims (1)

[Claims] 1. When acrolein or methacrolein is catalytically oxidized with molecular oxygen in a high temperature gas phase to obtain acrylic acid or methacrylic acid, then the general formula P _a Mo _b X _c Nb _d V _e Y _f O _gHowever , P is phosphorus, Mo is molybdenum, Nb is niobium, V is vanadium, O is oxygen, X is one or more selected from the group consisting of potassium, rubidium, cesium and thallium, Y
represents one or more selected from the group consisting of silicon, manganese and copper; a, b, c,
d, e, f and g represent the atomic ratio of each component, a=0.5-6, b=12, c=0.2-6,
d=0.01~6, e=0.01~6, f=0.01~6, g
is a value determined by the oxidation state of the catalyst. A method for producing an unsaturated carboxylic acid, characterized by using a catalyst represented by: