Method for preparing methionine

Abstract

The invention discloses a method for preparing methionine. The method for preparing the methionine concretely comprises the steps that cyanohydrins, carbon dioxide and ammonia or sodium cyanide, 3-(Methylthio)propionaldehyde, carbon dioxide and ammonia serve as raw materials to prepare hydantoin; alkaline hydrolysis is conducted on the hydantoin and then the hydantoin is acidized to pH 3.0-6.0 to obtain a compound of the methionine and salts; crystallization is conducted under the condition of temperature ranges from 8 DEG C to 45 DEG C, then the compound is separated to obtain a methionine crystal and salt mother liquor, the methionine crystal is washed by water and dried, and washing liquor is standby; finally, the salt mother liquor is concentrated under the condition of temperature which is lower than 60 DEG C, and then the salt mother liquor passes through a chromatographic column to obtain an inorganic salt and the methionine; the preparation method can efficiently separate the methionine and the salts, the recovery rate of the methionine can reach 99%, and the method is green and protects the environment, no methionine is resolved, no large number of acid and stink wastewater is discharged, and the purity of the inorganic salt is high and can be sold as a commodity.

Description

technical field [0001] The invention belongs to the field of chemical industry, and in particular relates to a method for preparing methionine. Background technique [0002] D, L-methionine, also known as methionine, is one of the basic units of protein and the only amino acid containing sulfur among the essential amino acids. In addition to participating in the transfer of methyl groups in animals, phosphorus metabolism and adrenaline, choline, In addition to the synthesis of creatine, it is also a raw material for the synthesis of protein and cystine. Methionine is widely used in the fields of medicine, food, feed and cosmetics, among which it is used in a large amount as a feed additive. The global demand for methionine has reached 1.6 million tons per year, and the demand for methionine in China in 2014 exceeded 130,000 tons. At present, in addition to the 110,000 tons of methionine produced by Chongqing Ziguang Chemical Industry Co., Ltd., my country also needs to impor...

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Problems solved by technology

[0003] Companies that use the Heine method to prepare methionine mainly include Evonik, Adisseo, Sumitomo, Ziguang Chemical and Russia Volga, among which Evonik and Sumitomo use hydrocyanic acid instead of traditional sodium cyanide or potassium cyanide and 3-methyl sulfide Propionaldehyde reacts to generate cyanohydrin, then reacts with carbon dioxide and ammonia to generate hydantoin, potassium carbonate hydrolyzes hydantoin, carbon dioxide neutralizes potassium methionine, separates methionine and potassium bicarbonate, and the mother liquor of potassium bicarbonate containing methionine is recycled to hydantoin hydrolysis step , the whole process hardly discharges a large amount of waste water and waste residue, which is a relatively clean and low-cost production process of methionine; Sodium, 3-methylthiopropionaldehyde, carbon dioxide, and ammonia are used as raw materials to prepare hydantoin, and then under the action of sodium hydroxide, hydrolyze to generate a saponified solution containing sodium carbonate and sodium methionine, acidify and crystallize with sulfuric acid, and obtain methionine respectively and sodium sulfate, the biggest disadvantage of this process is the separation and purification of methionine and sodium sulfate, that is, when sulfuric acid is added to acidify to about pH=5.0, methionine crystallizes at about 40°C, separates methionine, and dries to obtain methionine products, which are the largest methionine products The impurity is sodium sulfate; the sodium sulfate mother liquor containing methionine is then concentrated at high temperature, especially heated to about 90°C, and then a large number of sodium sulfate crystals are precipitated (at this time, the solubility of methionine is the highest, and the solubility of sodium sulfate is the lowest), and suction filtration while it is hot , the filtrate is cooled to 40°C, methionine is crystallized, washed with water, and dried to obtain methionine product, but nearly 10% of the total amount of methionine remains in the sodium sulfate mother liquor, and the mother liquor is recycled to the saponified solution acidification step, and the above steps are repeated , in the circulation process of sodium sulfate mother liquor containing methionine, in order to avoid the loss of methionine, the mother liquor should not be discharged as much as possible, resulting in the thermal decomposition of part of methionine under long-term high-temperature cooking, resulting in a foul-smelling substance Dimethyl disulfide, this substance will remain in the sodium sulfate mother liquor and the drained condensed water, causing the long-term circulating sodium sulfate mother liquor to have a foul smell. The operating environment of the sodium sulfate workshop is harsh, affecting the surrounding environment, and also causing Partial decomposition of methionine, high COD of the discharged mother liquor, difficult to carry out biochemical treatment, long-term circulation of sodium sulfate mother liquor containing methionine, resulting in a decline in the quality of subsequent methionine products. The main reasons for the decline are: first, the decomposition of methionine and The polymerization of methionine, especially the dimer formation of methionine, and the accumulation of organic impurities after the decomposition of methionine in the system, and the methionine obtained by crystallization has an unpleasant smell; the second is sodium formate and 2-hydroxy-4-methylsulfide in the saponification solution Sodium methionine accumulates in the system, thus affecting the quality of methionine products, which will eventually affect the quality of sulfuric acid. Sodium sulfate products not only contain methionine but also sodium formate, which affects the use of sodium sulfate, especially if it contains about 0.5%. Methionine

All of the above have led to the biggest outstanding problem in the methionine production process of companies such as Adisseo, Ziguang Chemical and Volga, which is environmental protection. At present, the best way to solve this problem is incineration, which inevitably consumes more energy and increases the production capacity of methionine. Losses and Production Costs

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