A review of recent developments of pre-treatment technologies and hydrothermal liquefaction of microalgae for bio-crude oil production

Microalgae have been widely considered as the potential sources for bio-fuel production without affecting the environment. Hydrothermal liquefaction (HTL) is a suitable technology for converting high water-containing feedstocks (e.g., microalgae) to liquid fuel. However, the structural diversity and rigidity of the microalgal cell wall remains as the major techno-economic bottlenecks for the recovery of intramolecular compounds (e.g., lipid) from microalgae. In this paper, the recent developments in cell disruption technologies and HTL for various microalgae strains are reviewed. The available literature investigating the effect of microalgal pre-treatment on the production of microalgae-derived bio-crude oil are presented. Furthermore, this article provides an extensive review of the recent studies on the HTL of microalgae, including the influences of feedstock characteristics and various operating conditions, underlying reaction mechanism, and physicochemical properties of liquefaction products.