Using CO2 in cultivation of microalgal biomass and thermo-chemical process

Microalgal biomass is a promising candidate for next generation biorefinery resources because of its rapid growth rate and efficiency in carbon assimilation. Recent studies have reported successful microalgal cultivation using exhaust gases rich in CO2 as the carbon source. This study focuses on optimising carbon utilisation by incorporating CO2 into the pyrolysis process of microalgae, particularly Scenedesmus sp., cultivated under elevated CO2 concentrations. Under the influence of CO2, homogeneous reactions occurred between the volatile pyrolysates and CO2. These reactions result in enhanced CO levels and a reduction in polycyclic aromatic hydrocarbons (PAHs) in pyrolytic oil through the simultaneous reduction of CO2 and oxidation of volatile pyrolysates. To accelerate the kinetics of these homogeneous reactions, catalytic pyrolysis was performed using Ni-based catalysts. The catalytic effects of The Ni catalyst significantly boosted CO production by promoting homogeneous reactions. The evolution of CO from catalytic pyrolysis under CO2 conditions was 2.92 times higher than that from double-stage pyrolysis. Thus, these experimental findings underscore the technical advantages of strategically utilising CO2 in both microalgal biomass cultivation and the thermochemical conversion of microalgal biomass.