Triflate-catalyzed (trans)esterification of lipids within carbonized algal biomass

This study demonstrates the utility of rare-earth metal triflate catalysts (i.e., Sc(OTf)(3) and In(OTf)(3)) in the (trans)esterification of oleic acid as well as the lipids contained within carbonized algal biomass using ethanol in the presence of water. Both catalysts are highly active between 200 and 235°C with an ethanol:fatty acid (EtOH:FA) molar ratio of 10-20:1 and showed a high tolerance for moisture. Lipids within hydrochars produced by reacting Chlorella protothecoides paste (25% solids) in high temperature water (220-250°C) were successfully converted into fatty acid ethyl esters (FAEE). The highest FAEE yields (85-98%) were obtained when hydrochars were reacted for 60 min at 215°C with about 11-13 mol% Sc(OTf)(3), a 17-19:1 EtOH:FA molar ratio, and without water. FAEE yields remained as high as 93% in the presence of 9 wt.% water. Our preliminary results warrant further work to optimize triflate-catalyzed in situ (trans)esterification at low catalyst and ethanol loadings.