Analysis of energy conversion characteristics in liquefaction of algae

Abstract The water environment and aquaculture in lakes have recently been influenced by the abnormal appearance of unpleasant water-bloom or eutrophication problems. It is the source reason of producing odors and being obstacles of water purification systems. Physical and chemical methods can remove algae from water and transform it to become algae sludge. Generally such algae sludge could be disposed as municipal wastes. However, algae and other biomass have become focal points as alternative energy resources, since they are renewable by fixation of CO2 through photosynthesis from the atmosphere. This study applies a thermochemical liquefaction process to convert the biomass of algae into oil in the presence of water at high temperature (about 300–340 °C) and high pressure (about 20 MPa), with or without an alkali catalyst. Thermochemical liquefaction has the merit of not requiring a drying process for feedstock. The oil and energy yields were analyzed in a batch reactor with the 30 and 60 min holding times. The elemental composition was investigated in each product to clarify the energy conversion efficiency in the thermochemical liquefaction of algae. The maximum oil and energy yields were obtained at 33 and 40% on an organic basis. The mass balance of carbon and hydrogen was analyzed based on elemental composition. The following suitable operational conditions for thermochemical liquefaction of algae were suggested: reaction temperature of 340 °C, holding time of 30 min, and catalyst dosage of 5 wt.%.