In China, relevant researchers have conducted some research on the production process of sodium citrate. In 1990, Zhang Danfeng et al. carried out a process for the preparation of sodium citrate by back extraction. The principle was to extract citric acid according to the solvent extraction method, and to extract the organic solvent containing citric acid by alkali, and directly prepare sodium citrate.
The solvent extraction method for extracting citric acid is to use trialkylphosphine oxide as an extractant from the fermentation broth.
Extracting citric acid, and then back-extracting the organic solvent with hot water to obtain an aqueous solution of citric acid and containing very little
A quantity of citric acid extraction solvent. The extraction solvent is returned to the extraction section for recycling. The aqueous citric acid solution is concentrated, crystallized, and dried to finally obtain a citric acid product. The literature indicates that if citric acid is extracted by extraction, sodium citrate can be obtained by replacing NaOH with pure water in the stripping section. Compared with the traditional sodium citrate production process, the process reduces the production cost; no calcium sulfate and carbon dioxide are produced in the production, and the environmental pollution problem caused by the old process is solved. The disadvantage of this process is the use of caustic soda in production, which is not safe to operate. In addition, the literature does not report the quality of the time product used for extraction and back extraction and the yield of sodium citrate. No reports on the trial production of this process have been seen so far.
In 1993, Peng Qijun found a new process for the production of sodium citrate by experiment. In the presence of an activator, the intermediate calcium citrate produced by fermentation to produce citric acid was directly reacted with sodium carbonate to prepare sodium citrate. The reaction formula is as follows. Activator
Ca3(C6H5O7)2. 4H2O + 3Na2CO3——→2Na3C6H5O7.2H2O + 3CaCO3↓
The activator which promotes the smooth progress of the reaction is a quaternary ammonium citrate material which can be used in foods and medicines as prescribed. The specific experimental process is as follows: take a certain amount of calcium citrate (the intermediate of fermentation to produce citric acid), add appropriate amount of water to stir it into a slurry, then add a certain amount of activator, then add sodium carbonate, filter and evaporate , crystallization, can get sodium citrate products in line with British Pharmacopoeia standards. The process reduces the steps of acid hydrolysis, ion exchange, citrate solution crystallization and drying in the old process, simplifies production conditions, reduces production equipment, shortens production cycle, and makes full use of by-product calcium carbonate. The shortcoming of this process is that the maximum yield of the product is only 97%, which can be further improved. In addition, a certain kind of catalyst must be used, and the price is not low, which leads to an increase in production cost, and also increases the production process and prolongs the production cycle.
In 1994, Pu Xiaohua and others conducted a small-scale test of sodium citrate. The basic method is: neutralization reaction with calcium citrate and sodium carbonate to form sodium carbonate and calcium citrate, and then sodium citrate is obtained by filtration, adjusting pH, removing iron, decoloring, crystallization, drying and the like. The process is still immature. For example, the reaction is carried out at 60 ° C, the reaction time is long, and the reaction is difficult to carry out sufficiently; when the pH of the solution before concentration is 7.2 to 7.5, the pH of the product is often not
Qualified; especially when the H value of the reaction end solution is controlled in the range of 9.7 to 10, the solution in the late stage tends to suddenly become milky white and continue to concentrate, failing to obtain sodium citrate crystals. This process is used for large production and some steps need to be improved.