Z. Zailan, H. Ali, J.W. Chau, M. Jusoh, M. Tahir, Z.Y. Zakaria, Development of Sulphonated Sago Pith Waste Catalyst for Esterification of Palm Fatty Acid Distillate to Methyl Ester, Chemical Engineering Transactions. 78 (2020) 31-36. doi:10.3303/CET2078006.