A review on recent advances in clean microalgal bio-oil production via catalytic hydrothermal deoxygenation

Converting microalgae biomass into bio-oil in hydrothermal condition is a suitable and promising way to produce alternative liquid fuel yet challenging in high oxygen content of resultant oil product for further commercial application. Deoxygenation mechanism in hydrothermal condition has significant difference with that in organic solvent due to unique physicochemical property of water in sub- and supercritical state. Accordingly, this paper reviews recent advances on hydrothermal catalytic deoxygenation of microalgal bio-crude oil. The specific role of high-temperature water played on deoxygenation process is discussed. And the effects of several experimental variables including temperature, reaction time, solvent and hydrothermal processing technology on deoxygenation are systematically illustrated. Finally, catalytic activity and mechanism of metal and acid-based catalysts involved in deoxygenation of typical aliphatic and aromatic oxygen-containing model compounds under hydrothermal conditions are elaborated as well. This review summarizes the process of HDO of microalgae bio-oil from HTL and provides a general scientific reference for further studies.