Lewis acid-catalyzed transesterification and esterification of high free fatty acid oil in subcritical methanol

Abstract

Lewis acid catalysts are active for both esterification and transesterification, but the reaction is very slow due to mass-transfer limitations between methanol and oil phase. Because oil, FFA and Lewis acid catalysts are all soluble in the subcritical methanol phase, the esterification and transesterification will be enhanced when they are carried out under subcritical conditions. In this work, the esterification and transesterification of high FFA oil to biodiesel via Lewis acid catalysts such as Pb(OOCCH₃)₂, Cd(OOCCH₃)₂ and Zn(OOCCH₃)₂ were carried out in the subcritical methanol phase (2 MPa, 180°C, reaction time 30 min). The results show that the esterification conversion reaches 79.8-96.4% with Palmitic acid as feedstock, and the transesterification conversion reaches 56.8-73.4% with soybean oil as feedstock. With the mixture of Soybean oil and Palmitic acid (FFA content of 20.3 wt%) as feedstock, the content of fatty acid methyl esters (FAME) in products reaches 67.3-83.4%.