Study On The Improvement Of Ammonium Sulfate By-product Process In Glycine Production

The hydrocyanic acid process used for the production of glycine, with natural gas for raw material, has the strong competitiveness in the international market due to its lower production costs. One company in chongqing uses the process to product glycine. In the manufacture process of hydrocyanic cyanide, the company uses 25% sulfuric acid to absorb the excessive ammonia and product ammonium sulfate. But because ammonium sulfate products are gray, it is much difficult to sell the products and results in product backlog. Moreover, a lot of wastewater containing cyanide is generated in ammonium sulfate crystallization and brings the company serious environmental pressures.By analyzing the existing problems of manufacture process of ammonium sulfate, the paper finds out that the HCN in ammonium sulfate solutions is the major factor that causes the problems in the process. By compared hydrogen peroxide oxidation of cyanide with the solvent extraction of cyanide, the later was determined as the experimental program. In the solvent extraction experiments, Different extractants were discussed and TBP was an ideal extractant.In the extraction experiments, the optimum operating conditions were obtained by using single factor experiments & orthogonal experiments which were showed as: volume phase ratio, 2; TBP concentration, 35%; initial pH, 3.0. Under the optimum conditions, the concentration of cyanide in raffinate was less than 0.5mg/L after a five-stage countercurrent extraction and the purpose of recovering cyanide deeply was achieved when the mother liquor contained 1.71g/L cyanide.In stripping experiments, the optimum operating conditions were obtained by using single factor experiments which were showed as: volume phase ratio, 1; concentration of sodium hydroxide,≥0.6mol/L; equilibrium pH, >13. Under the optimum conditions, the concentration of cyanide in loaded organic phase was less than 0.001g/L when loaded organic phase contained 0.78g/L cyanide after a two-stage countercurrent stripping. Poor organic phase could be reused without treatment.Under the existing conditions of evaporation crystallization in the company, ammonium sulfate solution treated by solvent extraction was used to crystallize. The obtained ammonium sulfate products were white crystal and had greatly improved in color compared with the product of factory. The improved production process has obvious improvement on material consumption, product yield and wastewater amount of product. So it is a technological and feasible process.