In China, industrially, sodium citrate is generally produced by fermentation to produce citric acid, followed by neutralization with a base to obtain sodium citrate. According to the different raw materials, the process methods are generally divided into the following
(1) The principle of citric acid + caustic soda reaction is as follows:
C6H8O7+NaOH→Na3C6H5O7+ H2O
The basic process is: dissolving citric acid in water, adding to the caustic soda under stirring, neutralizing reaction, and generating a large amount of heat, the reaction liquid is subjected to a process of concentration, crystallization, drying, etc., and finally a finished sodium citrate product is obtained. The process is simple, and the obtained product has good purity; the only disadvantage is that the production cost is high, and it is only used in the laboratory.
(2) The principle of citric acid + soda ash is as follows: C6H8O7+ Na2CO3→C6H5O7Na3+ CO2↑+ H2O
Because soda ash has the advantages of low price, easy purchase, and convenient storage, it quickly replaced caustic soda. The preparation method is an improvement of the former method and is currently widely used by domestic sodium citrate production enterprises.
(3) The principle of citric acid + baking soda is as follows:
C6H8O7+NaHCO3→C6H5O7Na3+ CO2↑+H2O
The method is mainly to solve the improved method of the sodium citrate produced by the previous preparation method which is not suitable for the needs of the pharmaceutical industry. The raw material is made of high-quality baking soda, dissolved in water according to the specified amount, and neutralized with citric acid to obtain a pharmaceutical grade product sodium citrate. The preparation method has the advantages that the reaction conditions are mild, the production is easy to handle, and the product quality is good. At present, this process is mainly used by some pharmaceutical manufacturers. Taking the second process method generally adopted by the current sodium citrate manufacturer as an example, the process mainly comprises filtering the citric acid fermentation liquid, and the filtrate is neutralized with calcium carbonate, and the obtained calcium citrate is acidified with sulfuric acid. After both tubes were cleaned, filtration, decolorization and ion exchange were carried out to obtain citric acid. The citric acid and sodium carbonate are neutralized, and then separately subjected to filtration, decolorization, pH adjustment, concentration, crystallization, separation, drying, etc., and finally a sodium citrate product is obtained.