Improvement in biodiesel production from soapstock oil by one-stage lipase catalyzed methanolysis

• Soapstock is a less expensive feedstock reservoir for biodiesel production.
• Addition of tert-alcohol can enhance the yield of fatty acid methyl ester significantly.
• One-stage lipase catalyzed methanolysis of soapstock oil was successfully developed.
• FAME yield of 95.2% was obtained with low lipase loading in a shorter reaction time.

A major obstacle in the commercialization of biodiesel is its cost of manufacturing, primarily the raw material cost. In order to decrease the cost of biodiesel, soapstock oil was investigated as the feedstock for biodiesel production. Because the soapstock oil containing large amounts of free fatty acids (FFAs) cannot be effectively converted to biodiesel, complicated two-stage process (esterification followed by transesterification) was generally adopted. In this study, simple one-stage lipase catalyzed methanolysis of soapstock oil was developed via one-pot esterification and transesterification. Water produced by lipase catalyzed esterification of FFAs affected the lipase catalyzed transesterification of glycerides in the soapstock oil severely. Addition of tert-alcohol could overcome this problem and enhance the fatty acid methyl ester (FAME) yield from 42.8% to 76.4%. The FAME yield was further elevated to 95.2% by optimizing the methanol/oil molar ratio, lipase amount, and water absorbent. The developed process enables the simple, efficient, and green production of biodiesel from soapstock oil, providing with a potential industrial application.