Increased bio-oil yield from Nannochloropsis salina through tuning the polarity of subcritical water

Abstract Changing solvent polarity at subcritical conditions, by an appropriate co-solvent, may be used to enhance oil extraction from different raw materials. As a newly commercially interested process, oil extraction from Nannochloropsis salina as a valuable bio-resource, by subcritical water-ethanol mixture as a polarity altered solvent, was investigated. Response surface methodology (RSM) was applied to achieve the best operating conditions. Three factors including temperature (90–150 °C), water-ethanol concentration (25–75 wt%) and flow rate (1.0–4.0 ml/min) were investigated. The best separation conditions were determined at 90 °C, 75 wt% ethanol and 4 ml/min. The oil composition was compared with four other methods including subcritical water extraction (SCWE), ultrasound-assisted extraction (UAE), Soxhlet (SOX) and Folch methods. The main fatty acids were identified as C16:0, C18:0, C18:1c and C18:3c. The highest extraction efficiency of 33.93 wt% was achieved for subcritical water/ethanol mixture.