Amino acid feed additive-glycine synthesis process
[alias] glycine; glycine; aminoacetic acid
[chemical name] glycine; aminoacetic acid
[English name] Glycine
[Molecular formula] C2H5NO2
[Structural formula] H2N-CH2-COOH
[CAS number] 56-40-6
ã€Properties】 This product is white monoclinic or hexagonal crystal or white crystalline powder. Glycine is an uncharged polar amino acid, odorless and has a special sweet taste. Soluble in water, insoluble in ethanol and ether. The melting point of 232 ~ 236 ° C (decomposition). The relative density of 1.1607 can react with hydrochloric acid to form a hydrochloride.
ã€Method】
The methods for chemically synthesizing glycine include chloroacetic acid ammoniation, Strecker and Hydantion. At present, the domestic chloroacetic acid ammonia hydrolysis technology has been adopted in the country, while the foreign countries adopt the improved Strelker method and the Haiin method. Due to the difference in raw materials and processes, the chloroacetic acid ammoniation method has the characteristics of high production cost and poor product quality. Most of the glycine produced is industrial grade, and the purity is generally about 95%, which seriously restricts its downstream application, while most foreign manufacturers The use of acrylonitrile by-product hydrogen cyanide and hydroxyacetonitrile to produce glycine, the method has low production cost, good product quality, and the general purity can reach more than 99%.
Chloroacetic acid ammoniation
The method is obtained by reacting chloroacetic acid as a raw material with ammonia water in the presence of a catalyst urotropine. The reaction temperature is 50-60 ° C, atmospheric pressure, and the reaction material is subjected to alcohol precipitation in an ethanol solution, and the reaction time is 14 to 15 hours. It is a traditional glycine synthesis process, the process is simple, the equipment requirements are not high, and the environmental pollution pressure is not large; but there are also many shortcomings. First, the by-products such as ammonium chloride are difficult to separate, resulting in poor product quality and cannot meet the pharmaceutical and food industries. The need, if refined, the production cost is higher; the second is that the urotropine as a catalyst can not be recycled, resulting in a large waste of resources; the third is long reaction time, difficult to operate continuously. At present, this method is the main industrialization method in China. In order to overcome the shortcomings and improve the quality and yield of glycine, domestic and foreign chemists have conducted in-depth research on this synthesis technology. The research focus is on the selection and use of new catalysts. In addition, a lot of work has been done in strengthening process control and optimizing reaction conditions.
ClCH2COOH+2NH3 → H2NCH2COOH+N4Cl
2. Strecke method
The traditional Strakr method is carried out by reacting formaldehyde, sodium cyanide and ammonium chloride, adding acetic acid, and precipitating to obtain methylene aminoacetonitrile. The methylene aminoacetonitrile is decomposed in ethanol in the presence of sulfuric acid to obtain aminoacetonitrile. Sulfate, the sulfate is decomposed with cesium hydroxide to obtain a glycine strontium salt, then sulfuric acid is added to precipitate hydrazine, and the filtrate is concentrated and cooled to obtain glycine crystals. The product is easy to refine and the product quality is good, but it requires the use of highly toxic chemical raw materials, high operating conditions, complex desalination after reaction, and long process route. At present, many foreign companies adopt the Stryker method, but most of them are improved. Technical route.
3 direct Hydantion process
The development of the Hydantion process stems from the search for alternatives to hydrocyanic acid to eliminate the geographical limitations of glycine production. Hydroxyacetonitrile is an addition product of hydrocyanic acid and formaldehyde. Its boiling point is 183 ° C, and it is easily decomposed into hydrocyanic acid and formaldehyde at high temperature. Therefore, from the production and chemical point of view, the production of glycine by using hydroxyacetonitrile as a raw material not only solves the defect that the hydrocyanic acid is difficult to handle, but also maintains the advantages of the improved Strecker process, which is currently becoming the most popular technology in foreign countries. One of the routes.
4 Improved Strecker and Hydantion processes
In order to improve the quality of glycine, reduce production costs and reduce environmental pollution, the Strecker process has been developed to replace sodium cyanide or potassium cyanide with hydrocyanic acid. The reaction is based on hydrocyanic acid, formaldehyde, ammonia and carbon dioxide. It is carried out in a tubular reactor. Glycine is precipitated at a low temperature, and the mother liquor is recycled. By changing the concentration of by-products in the reaction system, the equilibrium is shifted toward the target product, thereby achieving the purpose of improving the reaction yield. Although the process has many advantages such as short process, high yield and no pollution, but due to the toxicity and volatility of hydrocyanic acid, it cannot be transported over long distances, and the device can only be placed near the raw material device, which restricts glycine. The development of production.
5 Biological process
The bio-process of glycine preparation is still in the stage of technology development. Some Japanese companies are active in this field and have applied for many patents. It uses glycine as a raw material to hydrolyze the aqueous solution of glycinonitrile under the action of microbial enzyme, thereby converting into glycine, accompanied by ammonia production, and the system contains at least one organic substance inhibiting the microbial enzyme during hydrolysis.
6 Glycine refining
The glycine content obtained by the chloroacetic acid ammoniation method is between 90% and 95%, the impurity content is 4% to 10%, and has a deep color. If it is not refined, it cannot satisfy the food and pharmaceutical grade glycine. Claim. At present, the method for purifying glycine in the industry is to carry out recrystallization after adsorption and decolorization by activated carbon. Firstly, the crude glycine is dissolved in hot water, added to the powdered activated carbon for adsorption and decolorization, and then the activated carbon is separated by filtration and then heated and concentrated. When the volume of the concentrated liquid is one-half of the original volume, it is cooled to room temperature, and then added 3 to 4 times. The volume of ethanol or methanol causes the glycine to crystallize, and in order to achieve the required quality index of glycine, the purification needs to be repeated 2 to 3 times. Usually, the purification yield is 60% to 70%, and a large amount of ethanol and activated carbon are consumed, and the production cost is high. For this reason, an improved crude glycine refining process using a strong basic anion resin and a weakly basic anion as an adsorbent has been reported in the literature, which simplifies the refining process and improves the yield of refining.
[process flow]
Take the chloroacetic acid ammoniation method as an example.
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