Physicochemical characterizations of microalgal methyl esters extracted with hexane and refined by vacuum distillation at different temperatures

Abstract To prepare quality biodiesel from microalgal lipids in pilot-scale reactors, methyl esters from microalgal cells were extracted with hexane after direct transesterification and then refined by vacuum distillation. The refined methyl esters were comprehensively characterized via gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and thermogravimetric analysis. The methyl ester refined at 255 °C–259 °C was found to be the ideal fuel with a high fatty acid methyl ester content of 94.6%, a low combustion activation energy of 42.1 kJ/mol, and a proper carbon-chain length distributed in C14–C18. Impurities extracted with hexane, such as alkanes and short-chain esters, were separated at 105 °C–254 °C owing to their low polarity and molecular weight. Highly unsaturated methyl esters with a long carbon-chain were collected at 260 °C–280 °C owing to their high boiling point. Separation of alkanes, short-chain esters, and highly unsaturated methyl esters through vacuum distillation effectively improved the properties of the methyl esters extracted with hexane as a fuel and enhanced the economic feasibility of microalgal lipids.