Refining methods and characteristics of crude glycerol

High purity glycerol is an important industrial raw material and one of the ways of large-scale utilization of glycerol. Taking crude glycerol, a byproduct of biodiesel, as an example, its quality is greatly affected by the raw materials and process of biodiesel. Crude glycerol generally contains residual impurities such as methanol, methyl ester, oil, water, catalyst, salt, soap, free fatty acid and pigment.The presence of impurities has a great influence on the subsequent utilization of glycerol. Therefore, the refinement of crude glycerol is the prerequisite for the conversion and utilization of glycerol. Industrial grade crude glycerol containing 80%-85% can be obtained by simple neutralization, dealcoholization, degreasing, dehydration, decolorization and decolorization of crude glycerol.There are two main methods for refinement of industrial crude glycerol. One is vacuum distillation, which has the disadvantages of high energy consumption and high cost of glycerol purification. The other is ion exchange method, which is low energy consumption and easy to operate, but for crude glycerol with too many harmful impurities, it is easy to cause resin deactivation. At present, the cost of crude glycerol purification in China is higher. The reason is that the raw materials of domestic biodiesel are poor, especially waste oils, such as ditch oils, which are generally treated at high temperature. The internal structure of oils has changed, and the quality of by-product glycerol is poor.The raw materials for biodiesel production abroad are relatively pure and the cost of purification is low. The purification cost of glycerol can reach more than 90% of the production cost of essential glycerol, and the lowest production cost is US$150 per ton.

With the rapid development and large-scale production of biodiesel industry, the output of crude glycerol is excessive. At present, the purity of crude glycerol is high in medicine, food, cosmetics and other industries. Therefore, crude glycerol usually needs to be purified by separation or distillation. The refining process is relatively complex, and the current market price of glycerol is low, the economic feasibility of refining process is still insufficient. Therefore, it is necessary to develop the application space of crude glycerol and improve the added value of crude glycerol.