Natural glycerol
Before 1984, glycerol was recovered from by-products of soap making from animal fat or vegetable oil.Until now, natural oils and fats are still the main raw materials for the glycerol production. About 42% natural glycerol is produced from the by-product of soap making and 58% by fatty acid production.Saponification of oils and fats in soap making industry，the product of saponification reaction is divided into two layers: the upper layer mainly contains salt (soap) and a small amount of glycerol, the lower layer is waste lye, a dilute glycerol solution containing salt, sodium hydroxide, generally containing 9-16% glycerol, inorganic salt 8-20%.In recent years, the continuous high pressure hydrolysis method has been widely used, the reaction does not use catalyst, the purification method is simpler than the waste alkali solution.The glycerol content in the waste liquor of soap making or the glycerol water obtained by hydrolysis of oil and fat is not high, and it contains various impurities. The production process of natural glycerol includes purification, concentration to crude glycerol, and distillation, decolorization and deodorization of crude glycerol.
Synthetic glycerol
Many ways to synthesize glycerol from propylene can be classified into two main categories, chlorination and oxidation. Acrylonitrile and propylene oxidation are still used in industry.
Industrial grade glycerin
Industrial grade glycerol is diluted with 1/2 star distilled water, stirred sufficiently, activated carbon is added, and heated to 60~70 ℃for decolorization.Then vacuum filtration is used to ensure that the filtrate is clear and transparent.The filtrate was added to the pre-treated 732 strong acid positive resin and 717 strong alkali negative and negative resin column to remove electrolytes and impurities in glycerol by controlling the dropping acceleration.After removing impurities, the glycerol solution is distilled by vacuum distillation, and the vacuum degree is more than 93326Pa. The temperature of the kettle is between 106 and 108 ℃. After evaporating most of the water, the kettle temperature is raised to 120 ℃ for rapid dehydration. When the kettle is not in water, it stops heating. The materials in the kettle are finished products, and are used as automobile and aircraft fuel and antifreeze in oil field.
