The industrial production methods of Glycerine Usp can be divided into two categories: the method using natural oils and fats as the raw material, and the obtained glycerin is commonly known as natural glycerin;
1. Production of natural Glycerine Usp Before 1984, Glycerine Usp was all recovered from the by-products of animal and vegetable fat soaps. Until now, natural oils and fats are still the main raw material for glycerin production. About 42% of the natural Glycerine Usp in the base comes from soap by-products, and 58% comes from fatty acid production. Saponification of oils and fats in the soap industry. The saponification reaction product is divided into two layers: the upper layer mainly contains fatty acid sodium salt (soap) and a small amount of glycerin, and the lower layer is waste lye, which is a dilute solution of glycerol containing salts and sodium hydroxide, generally containing 9-16% glycerol, inorganic salts 8-20%. Grease reaction. Glycerine water (also known as sweet water) obtained by oil hydrolysis has a higher Glycerine Usp content than soap-making waste liquor, about 14-20%, and inorganic salts 0-0.2%. In recent years, continuous high-pressure hydrolysis has been widely used, and the reaction does not use catalysts. Whether it is soap-making waste liquid or glycerin water obtained by oil hydrolysis, the amount of glycerin is not high, and they all contain various impurities. The production process of natural Glycerine Usp includes purification and concentration to obtain crude glycerin, and crude glycerin distillation and decolorization. The refining process of deodorization.
2. Production of Synthetic Glycerine Usp The various routes for synthesizing Glycerine Usp from propylene can be classified into two categories, namely chlorination and oxidation. Now the industry is still using propylene chlorination and propylene irregular acetic acid oxidation.
(1) Propylene chlorination method This is the most important production method in the synthesis of Glycerine Usp. It consists of four steps, namely, high temperature chlorination of propylene, hypochlorination of propylene chloride, saponification of dichlorohydrin and hydrolysis of epichlorohydrin. The hydrolysis of epichlorohydrin to glycerol is carried out at 150°C and 1.37MPa carbon dioxide pressure in an aqueous solution of 10% hydrogen peroxide and 1% sodium carbonate to generate a sodium chloride-containing glycerol aqueous solution with a glycerin content of 5-20%. After concentration, desalination and distillation, glycerol with a purity of more than 98% can be obtained.
(2) Propylene Peracetic Acid Oxidation Method Propylene and peracetic acid act to synthesize propylene oxide, and propylene oxide is isomerized to alkene to propanol. The latter reacts with peracetic acid to form glycidol (ie glycidol), which is finally hydrolyzed to Glycerine Usp.Acetaldehyde and oxygen are oxidized in gas phase. Under the conditions of normal pressure, 150-160 ° C, and contact time of 24 s, the conversion rate of acetaldehyde is 11%, and the selectivity of peracetic acid is 83%. The above-mentioned last two-step reactions are carried out continuously in a special-structured reactive distillation column. After the raw material allyl alcohol and the ethyl acetate solution containing peracetic acid are sent into the tower, the tower still is controlled at 60-70°C and 13-20kPa. The ethyl acetate solvent and water are evaporated from the top of the tower, and the tower still obtains an aqueous glycerin solution. This method has high selectivity and yield, uses peracetic acid as the oxidant, does not need a catalyst, has a faster reaction speed, and simplifies the process. At present, the output of natural Glycerine Usp and synthetic Glycerine Usp account for almost 50% each, and the propylene chlorination method accounts for about 80% of the output of Hezhi glycerin. my country’s natural Glycerine Usp accounts for more than 90% of the total output.