Microwave-assisted solubilization of microalgae in high-temperature ethylene glycol

Abstract Four types of microalgae (Chlorella vulgaris, Nannochloropsis oculata, Fistsulifera solaris (JPCC DA0580), and Phaeodactylum tricornutum Strain NRIA-065) were liquefied through noncatalytic solvothermal solubilization under microwave (MW) irradiation using ethylene glycol (EG) as a reaction media. C. vulgaris and N. occulata exhibited higher solubilization rates and bio-crude oil yields in a temperature range at 300 °C while diatoms (Fistsulifera. Solaris and Phaeodactylum tricornutum) were recalcitrant to MW treatment owing to its high ash content. Bio-crude oil yield increased depending on the reaction temperature and reaction time. In particular, nearly 38% bio-crude oil was obtained under a reaction at 300 °C for 40–60 min from C. vulgaris. Higher heating values of bio-crude oil of 39 and 28 MJ kg−1 were attained in the chloroform and ethyl acetate layers in EG soluble fraction, respectively. Dielectric measurement of the reaction system indicated the effectiveness of ethylene glycol as a medium for absorbing MW energy. EG was efficient reaction medium for rapid heating up by MWs to facilitate solubilization of microalgae at low pressure.