Using switchable solvents for enhanced, simultaneous microalgae oil extraction-reaction for biodiesel production

Switchable solvents with hydrophobicities that can be reversibly changed were evaluated as single solvents for oil extraction from wet biomass. Three switchable solvents, N,N-dimethylcyclohexylamine (DMCHA), N-ethylbutylamine (EBA), and dipropylamine, were used to extract oil from the undisrupted wet paste of harvested Chlorella sp. microalgae. The oil extraction yields for the three solvents were 13.6%, 12.3%, and 7.0%, respectively. However, single hydrophobicity solvents n-hexane and [Bmim][PF₆] were unable to extract any oil, achieving yields of 0% and 0.7%, respectively. A parametric study was performed to evaluate the effects of temperature, cell disruption duration, and extraction duration on the effectiveness of oil extraction. The results were used to develop a statistical model to predict oil extraction effectiveness under different conditions. The switchable solvents were also evaluated in simultaneous extraction-reaction systems used to convert the oils extracted from wet microalgae into biodiesel. The use of enzymes was found to enhance the production yield of biodiesel by 33%. The highest biodiesel yield of 47.5% was achieved using DMCHA at 35 °C with a methanol/oil molar ratio of 6:1 and a 30% enzyme loading employing a solvent program comprising 1-h cell disruption, 1-h extraction/reaction, and 1-h phase separation steps. The proposed strategy of using a single solvent for simultaneous extraction and reaction could substantially simplify biodiesel production from wet microalgae.