Catalytic alcohothermal liquefaction of wet microalgae with supercritical methanol

Abstract

Microalgae are promising feedstock for the production of biofuel due to their high productivity and low interference with food production for their cultivation and usage. Owing to their aquatic production environment, however, energy-intensive dewatering and drying processes may be required before their conversion to biofuel. In order to avoid these processes, their liquefaction through hydrothermal means has attracted attention, with extensive research works. The present research proposes and examines alcohothermal liquefaction of wet microalgae, in an attempt to modify and improve microalgae liquefaction characteristics. Thus supercritical methanol was employed as a reaction media for liquefaction of wet Chlorella vulgaris, and the effects of water presence as well as the effects of heterogeneous oxide catalysts were examined. This methanothermal liquefaction gave high bio-oil yield of 54.5 C% (feed microalgae basis) compared to 30.5 C% by hydrothermal for non-catalytic reaction at 385 °C. With Zr(WO4)2 catalyst methanothermal bio-oil yield increased further to 65.6 C%. The presence of water in the methanol medium somewhat decreased the bio-oil yield, while some of the catalysts mitigated the decrease: at 50 wt% water content in methanol, MnO2, ZnO2 and ZrO2 gave bio-oil yield of 55.5 C%, 59.5 C% and 57.6 C%, respectively. Possible mechanism of catalytic methanothermal liquefaction of wet microalgae is discussed.