Preparation method of methionine

Abstract

The invention belongs to the field of chemical engineering, and discloses a methionine preparation method, the method comprises a process of contacting a CeO2 solid catalyst with 2-amino-4-methylthio butyronitrile water-containing liquid flow, the CeO2 solid catalyst is in a rod-like crystal form, the crystal diameter is 10-80 nm, and the crystal length is 100-500 nm. Furthermore, according to the process disclosed by the invention, the step of catalyzing CeO2 is only put into an amidation reaction process of hydrolyzing 2-amino-4-methylthio butyronitrile into methionine amide, then the methionine amide hydrolysate is hydrolyzed by using solid acid to prepare the methionine hydrolysate, and finally the methionine is taken out by using a carbon dioxide acidification crystallization mode. The rod-like cerium dioxide catalyst used in the method has higher catalyst activity and better anti-pollution capacity, the production process does not generate low-value byproduct salt, the cerium dioxide catalyst has longer recycling period, the methionine is high in one-time crystal extraction rate and stable in yield, industrial adaptability is achieved, and the method is suitable for industrial production. The industrial popularization and application of methionine can be realized.

Description

technical field [0001] The invention belongs to the field of chemical industry, and in particular relates to an industrially adaptable method for preparing methionine by catalyzing 2-amino-4-methylthiobutyronitrile with rod-shaped ceria. Background technique [0002] The chemical synthesis of methionine (MET, scientific name 2-amino-4-methylthiobutyric acid) is currently mainly through the synthesis of 2-hydroxy-4-methylthiobutyronitrile (referred to as cyanohydrin) through methylthiopropionaldehyde and hydrocyanic acid. , cyanohydrin and carbon dioxide, ammonia to synthesize hydantoin intermediates, hydantoin intermediates are hydrolyzed by inorganic alkalis to obtain methionine alkali salts, and acidified methionine alkali salts to obtain methionine; or methionine is directly combined with sodium cyanide, carbon dioxide, Ammonia and other components are used to synthesize hydantoin intermediates, and hydantoin intermediates are hydrolyzed with alkali and acidified to obtai...

AI Technical Summary

Problems solved by technology

But it still has deficiencies, at first, the productive rate that prepares methionine with this patent method is not stable, can see that productive rate fluctuates in a large range from the examples; secondly, the preferred cerium oxide catalyst used is 20~ 30nm (specific surface area 100m 2 / g or more) is helpful to make the unit mass catalyst have higher catalytic activity, but in practical application, it is difficult to efficiently separate from the reaction system, and the catalytic efficiency is significantly reduced after 3-5 cycles of catalysis, and the appearance changes from off-white or light yellow to brown, it is difficult to achieve long-term cycle catalysis; again, it adopts atmospheric pressure concentration, reduced pressure concentration, etc. to carry out deamination treatment on the reaction feed liquid whose main component is methionine ammonium salt to obtain methionine, deamination treatment The method takes a long time and is difficult to remove the ammonia thoroughly, which will lead to some unnecessary side reactions of the original impurities and methionine in the system, making the system darker and difficult to completely remove the methionine. system, if it returns to the catalytic stage, it will further aggravate the degradation of the performance of the catalyst and the difficulty of separation

[0004] In summary, there are the following main problems in the prior art: traditional production will generate a large amount of unnecessary by-product salts, and it is difficult to separate the methionine product from the by-product salts; and the use of cerium oxide to catalyze the preparation of 2-amino-4-methylthiobutyronitrile The process of methionine also has the problems of long reaction time, unstable yield, difficulty in complete deamination, and inability to achieve long-term cycle catalysis of the catalyst; in addition, cerium oxide has various crystal forms such as spherical, octahedral, rod-shaped, and square. The exposed active surface of the type is different, and the crystal type has an important influence on the performance of the cerium oxide catalyst. However, in order to make more significant use of the catalytic activity of the cerium oxide, the existing process directly selects the cerium oxide particle catalyst with a smaller particle size and a larger surface area. Exacerbating its application defects, small particle or spherical catalysts of the above size are more likely to be contaminated by polymers, side reactants, pigment impurities, etc., resulting in reduced activity, and after pollution, a certain polymerization and flocculation effect will be formed, making it difficult to be efficient Separation, the catalyst filter cake often contains water as high as 30-50w%

Images