Development of cost-effective and benign lipid extraction system for microalgae

A laboratory-made continuous flow lipid extraction system (CFLES) was devised to extract lipids from microalgae Nannochloropsis sp., a potential feedstock for biodiesel fuel, with a focus to assess the workable temperatures and pressures for possible scale-up applications. Using conventional solvents, the CFLES recovered 100% of the lipids recovered with conventional Soxhlet extraction (USEPA method 3540) at moderate 50 psi pressure and 100°C temperature; conditions significantly lower than those normally used in pressurized liquid extractions requiring specialized equipment. Approximately 87% of the extracted oil was successfully transesterified into biodiesel fuel. For exploring the solvent potential of biodiesel, CFLES was also tested with 40% methyl-soyate (BD40) as co-solvent with ethanol. Both the solvents are less toxic to health and environment compared to conventional solvents. The system extracted 67% of lipids at 50 psi pressure and 100°C temperature. The system also extracted 64% and 65% lipids at pressure/temperature combinations of 50psi/120°C and 500psi/120°C respectively. Energy efficiency of CFLES was 48.9%. Compared to a lab-scale Soxhlet extraction system (150 mL), the solvents consumption in CFLES was reduced by 80% and 67% for conventional and biodiesel co-solvents, respectively, while extraction time was notably reduced from 8h to 0.25h and 0.67h, respectively. The estimated savings in extraction cost and energy at scaled-up CFLES systems are expected 57% and 60%, respectively, as compared to solvent extraction coupled with mechanical extractor. Based on previous studies, the total cost of microalgae oil production was estimated in the range of $13.73 to $44.60gal-1. The solvent potential of biodiesel was further investigated with the use of methyl-soyate in a closed-vessel microwave-assisted lipid extraction (MAE). Approximately 66%, 78%, and 116% lipids were extracted with BD40 at 80°C, 100°C, and 120°C temperatures, respectively, compared to that extracted with Soxhlet. Maximum efficiency for BD20 (20% methyl-soyate) was 34%. MAE using chloroform/ethanol mixture extracted 32%, 93%, and 108% of lipids at 80°C, 100°C and 120°C, respectively, compared to Soxhlet. Efficiency increased with increased biodiesel proportion in the co-solvent system and increased temperature. To our knowledge, this is the first study to report CFLES and the use of biodiesel as a co-solvent for extraction of biochemicals