Microalgae is seen as a sustainable source of chemicals and biofuels, but its processing to low value fuels is expensive, particularly due to drying, and thus the feasibility of a wet processing route is necessary. This thesis presents experimental research and life cycle assessment on the conversion of microalgal biomass to liquid biofuel (precursor) using high temperature and pressure processing technologies. The bulk of the work is related to Hydrothermal Liquefaction of algal biomass at various residence time (0.5 - 60 min) and temperatures within the Hydrothermal regime (275 - 380°C), using both batch and novel in-house built continuous flow reactor systems. Several analytical tools were deployed to assist with analysis of the formed biocrude to help understand the effect of the reaction conditions on the formed products.

Having analysed the biocrude, it became apparent that the aqueous phase contained substantial matter and as such an investigation to quantitate the inorganics in the aqueous phase was conducted. As for the biocrude, detailed analysis showed that further treatment was necessary to make it amenable for utility directly or as a blended fuel and thus, Hydrotreatment using commercially available catalyst under H2 in a batch reactor was conducted. Lastly, the conversion of algal lipids to biodiesel as well as other constituents was investigated under Hydrothermal conditions in presence of methanol, leading to in situ Supercritical Transesterification. The reaction conditions used were found to be too severe for stable yield of methyl esters and consequently degradation kinetics of methyl esters was calculated. Lastly, to understand the environmental profile of the investigated processes, a life cycle assessment was conducted based on experimental data combined with literature values for a conceptual biorefinery in 5 different countries with differing energy mixture. The thesis ends with concluding remarks on the investigation and potential direction for future work.