Triflate-catalyzed (trans)esterification of fatty acids, triglycerides, and lipids within carbonized algal biomass

The production of biodiesel from microalgae is complicated by the energy and cost associated with biomass harvesting, dewatering, and oil separation. We previously reported on a two-step method to produce biodiesel from wet algal biomass through hydrothermal carbonization and in situ supercritical ethanol (trans)esterification. Here we demonstrate the use of rare-earth metal triflates (Sc(OTf) ₃ and In(OTf) ₃) to catalyze the conversion of fatty acids (FAs) and glycerides in both model systems and carbonized algal solids to ethyl esters. High yields (>90%) were obtained at moderate temperatures (190-235 °C), in short times (5-30 min), and with industrially relevant amounts of ethanol (10:1-15:1 molar ratio EtOH:FA), catalyst (1 mol% to FA), and water (2-10 wt%).