Effect of water content on [Bmim][HSO4] assisted in-situ transesterification of wet Nannochloropsis oceanica

1-Butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]) was employed to catalyze the in-situ transesterification of wet Nannochloropsis oceanica. Algal cell wall was dissolved by [Bmim][HSO4] according to TEM analysis of untreated Nannochloropsis sp. cells and lipid extracted algae (LEA). The temperature and time are favorable to biodiesel production in 100–200 °C, time of 0–70 min, with methanol: algae, however, it decreased to 10.64% at time of 90 min. The biodiesel and energy production of [Bmim][HSO4] catalyzed in-situ transesterification varied due to the competition of catalytic property and algal dissolution ability with variation of water content. The catalytic property of [Bmim][HSO4] was the dominate parameter affecting biodiesel production, therefore, total energy production of in-situ transesterification, as a parameter of biodiesel production, was slightly increased from 13.12 kJ to 14.51KJ with water content of wet algae varied from 0 to 15 wt%. However, it decreased to 8.37 at water content of 20 wt% due to the weakened algal dissolution ability, which was proved by the decrease of hydrogen bond acceptor capacity(β) from 0.942858 to 0.942851 in water content of 0–30 wt%. The decomposition of carbohydrates and proteins in IL – water mixtures enhanced biodiesel production according to elemental analysis of LEA.