A two-step process was developed to refine biodiesel with oleic acid (C18H34O2) and triolein (C57H104O6) mixture (acid value 42.52 mgKOH/g). The whole process was simulated by Aspen Plus V10. Firstly, crude biodiesel was prepared by ultrasound-assisted deep eutectic solvent enzymatic method, and then free fatty acids were separated by distillation with ethanol and glycerol as carrier agent, and the distillation process was optimized. The results showed that the conversion rates of oleic acid and triolein were 88.19% and 92.71% respectively, and the acid value of crude biodiesel was 5.07 mgKOH/g. The optimal distillation process conditions were obtained as follows: pressure 0.9 MPa, reflux ratio 0.7, theoretical tray number 31, crude biodiesel feed from the 14th tray and carrier agent feed from the second tray. Under the optimal conditions, the acid value of refined biodiesel reduced to 0.36 mgKOH/g, and the yield of distillation was 95.27%. |