Two-step separation of bio-oil from condensed products of hydrothermal liquefaction of microalgae

Abstract

Present paper is devoted to the study of the process of bio-oil separation from condensed products of hydrothermal liquefaction (HTL) of microalgae (MA). In this work we proposed a two-step separation. Proposed separation method produces separately “light” (with density less than 1 g/cm3) and “heavy” (with density more than 1 g/cm3) fractions of bio-oil. “Light” bio-oil is separated mechanically from the aqueous solution. “Heavy” bio-oil is produced by solvent (dichloromethane) extraction and subsequent solvent evaporation. The solvent in the proposed method doesn’t contact with aqueous solution. The last makes the utilization of aqueous solution safer. The total yield of “light” and “heavy” bio-oil is 34.7 % (at 330 °C and hour). It is almost the same as the yield of bio-oil obtained by the “standard” solvent separation method (35.1 %). The elemental composition of “light” bio-oil differs from the “standard” bio-oil by a lower content of carbon, and a greater content of hydrogen and oxygen. “Light” bio-oil contains more easily boiled compounds than “standard” bio-oil. In particular, the content of the fraction with boiling point less than 200 °C in “light” bio-oil is 7 % higher than in “standard” bio-oil (28 vs. 21 %).