Large amounts of residues are obtained after lipid extraction when producing biodiesel from microalgae. From these residues, animal feed or bioethanol production may be obtained. Another alternative biofuel that can be obtained from microalgae biomass residues is bio-oil from pyrolysis or hydrothermal processes. Out of these, microalgae for biofuel production stand out due to the high thermal value of Algal biomass of around 24 MJ / kg. The organic components of the biological mass can be thermally decomposed in the production of fuel by thermochemical applications, such as direct combustion, gasification, pyrolysis, and liquefaction. With the hydrothermal liquefaction process, microalgae are converted into liquid crude oil with or without a catalyst. The reaction takes place at 280-370 °C and 10-25 MPa pressure on wet biomass in water. Biological oil production by hydrothermal liquefaction method from microalgae has gained considerable attention in recent years. Compared to the biodiesel obtained mainly due to the lipid content, hydrothermal liquefaction converts not only the lipid content but also carbohydrates and proteins.
Keywords: Algae, Algae to oil, Biofuel production, Catalytic process, Liquefaction.