Transesterification of Bio-Oils in a Binary Supercritical Mixture of Methanol and Carbon Dioxide: Parametric Effects On Yield and Selectivity

Biodiesel is an oxygenated fuel created from renewable bio-oils and is usable in unmodified diesel engines. The conventional process for biodiesel production proceeds through transesterification of triglycerides using an alcohol, most often methanol, and a small amount of base to catalyze the reaction. This work illustrates a novel route for continuous biodiesel production that proceeds non-catalytically in a mixture of carbon dioxide and methanol at elevated temperatures and pressures. The process utilizes carbon dioxide’s ability to act as a solvent at high pressures and temperatures to reduce the amount of methanol necessary for the transesterification to proceed non-catalytically. The experiments were conducted in a 0.1 L Haynes® 282® alloy tubular reactor with a fixed molar ratio of 28:1 methanol to triglyceride and a carbon dioxide flow rate of 3 SLPM. The space time varied from 30 seconds to 90 seconds, the reactor pressure from 1500 psig to 4500 psig, and the temperature ranged from 240°C to 320°C.