Estimation of energy for hydrocarbon extraction in biofuel production from microalgae

Abstract

Energy requirements for extracting 1-MJ equivalent of hydrocarbons from dehydrated algae cake (water content: 70 %) of Botryococcus braunii was estimated for four feasible hydrocarbon extraction processes for biofuel production from microalgae; hexane extraction, hexane extraction with hydrothermal pretreatment, supercritical carbon dioxide extraction, and DME extraction. Input energy per 1 MJ-equivalent hydrocarbon extraction under the assumed reported conditions was 0.73-1.83 MJ/MJ-equivalent hydrocarbon for the 4 extraction processes, and the input energy required in the optimum case amounted to more than 70 % of the recovered energy. Consideration of methods to reduce the energy required for extraction in each process revealed that the following studies were important: research on increasing the extraction rate of wet microalgae, device design to minimize losses of extraction media, and increased efficiencies of the heat recovery and power recovery equipment.