A novel strategy of biodiesel production from wet microalgae by direct saponification–esterification conversion (DSEC)

Microalgae has become a potential resource of biodiesel in recent years for its fast growth, non-food source, and CO2 capture ability. However, efficient and economic production of biodiesel from microalgae is still a challenge. In this study, we presented a novel strategy of direct saponification–esterification conversion (DSEC) from wet microalgae (Chlorella vulgaris) to biodiesel and its associated kinetic model. The process was accomplished with two consecutive additions into wet algae. Firstly, addition of NaOH/methanol solution, lipids including triglycerides (TG) and free fatty acids (FFA) of wet algae were released from disrupted algae and primarily converted into soaps by means of saponification. Then with further HCl/methanol addition, soaps were acidified into FFA and esterified into fatty acid methyl ester (biodiesel). The experimental results supported the proposed mechanism and observed several advantages of DSEC process. Primarily, DSEC eliminates lipid extraction/purification step in the conventional process, which usually accounts for more than half of production cost. Secondly, compared with the alkali catalyzed transesterification process, DSEC completely alleviates the restriction of incapable of dealing with high content of water and FFA. On the other hand, compared with acid catalyzed transesterification process, the production time of DSEC was only a fraction, less than 15 mins.