Purification Of Glycerol From Biodiesel Production

Biodiesel is a clean and renewable energy,and glycerol is the main by-product from biodiesel production.The purification and recovery of glycerol can greatly improve the economic efficiency and enhance the competitiveness of enterprises.Since the component of biodiesel-derived glycerol is complex,a glycerol purification process was developed in this study.Crude glycerol was obtained after the pretreatment of glycerol feedstock,followed by vacuum distillation to get refined glycerol.The main contents and conclusions are as follows:1.Crude glycerol was obtained after the pretreatment of glycerol feedstock including acidification demulsification,deolysis,dehydration,and desalination.The effects of pH,reaction temperature,and methanol account in the acidification demulsification process on the production of crude glycerol were investigated.The results showed that the optimal pH,reaction temperature,and methanol account were 4,60?,and 0.7~1 times of glycerol volume.After the pretreatment,the glycerol yield reached 89%,with glycerol purity of 78%.The water and potassium contents in the glycerol phase were determined for each stage during the pretreatment.The results provide the basis for the design of dehydration and desalination equipments.2.High purity glycerol product was obtained after the vacuum distillation of crude glycerol.The effects of reflux ratio and cooling water temperature on glycerol purity and distillation efficiency was investigated.The results showed that glycerol product with purity of 99.5% was obtained at the reflux ratio of 3:1 and cooling water temperature of 60?.The steady state simulation of high vacuum distillation of crude glycerol was conducted using Aspen Plus software.A two-column distillation model was developed and the optimal process conditions were determined by sensitivity analysis.The trace moisture in crude glycerol can be removed when the pressure,tray number of B1 distillation tower,and reflux ratio were 0.05 bar,6,and 0.1,respectively.The purity of glycerol at column top was higher than 99% when the tray number of B3 distillation tower,feed position,and reflux ratio were 7,the fourth tray from the top,and 0.4,respectively.3.The refined glycerol was tested according to the GB/T13206-91.The indexes including glycerin color,chloride content,sulfated ash,acidity,alkalinity,saponification equivalent,reducing substance,heavy metals,and glycerol content reached the standards of second-class glycerol.