Optimised pyrolysis strategies for energy-dense bio-oil from Chlorella sp

Microalgae are promising feedstocks for sustainable biofuels due to rapid growth, CO₂ fixation, and non-reliance on arable land. This study investigates the pyrolysis of Chlorella sp. under non-catalytic, catalytic, and microwave-assisted configurations to optimise bio-oil composition and energy density. Response surface methodology identified optimal conditions at 550 °C and 60 °C/min, yielding 43 wt% bio-oil. Catalytic pyrolysis with HZSM-5 and Na₂CO₃ improved deoxygenation and increased higher heating value (HHV) to 30.8 MJ/kg. Microwave-assisted pyrolysis at 80 W (∼80 W/g for 1 g sample) produced the best bio-oil, with 68.3 % C, 16.1 % O, and HHV of 33.4 MJ/kg. Carbon-rich biochar (∼80 wt% C) was also obtained, suitable for soil amendment or activation. Catalyst-dependent gas profiles were observed, with Na₂CO₃). Yielding 24.7 vol% H₂. These results highlight the potential of tuning pyrolysis configuration to upgrade algal biomass without post-treatment. The study supports the development of drop-in microalgal biofuels and reinforces their role in circular, carbon-neutral energy systems.