High yield bio-oil production by hydrothermal liquefaction of a hydrocarbon-rich microalgae and biocrude upgrading

A green colonial microalgae Botryococcus braunii was hydrothermally processed under subcritical water conditions without the addition of catalysts, obtaining an oil yield as high as 68%. The higher heating value of liquefaction products is close to that of petroleum crude oil. The oil fraction from Botryococcus braunii liquefaction was specified for the first time, and the liquefaction mechanism was proposed. Due to the high lipid content of Botryococcus braunii, the liquefaction product distribution is quite distinct from other microalgae. The produced biocrudes contain ∼9% oxygen, with oleic acid as the main source. Amides derived from oleic acid and proteins are the major nitrogenates in the biocrudes. The biocrude was processed using catalytic cracking and hydrotreating. Catalytic cracking mostly produces aromatics, while the majority of hydrotreating products are straight and branched hydrocarbons. The oxygen content in the catalytic cracking products was very low. The presence of amides in the hydrotreating feed changes the reaction pathway from hydrodecarboxylation to hydrodeoxygenation as a result of the competitive adsorption of amides on the active sites for hydrodecarboxylation. Both processes show satisfactory denitrogenation performance. Catalytic cracking displays superior ability than hydrotreating with regards to the removal of oxygen. Keywords: Hydrothermal liquefaction, Botryococcus braunii, Biocrude upgrading, Fluidized catalytic cracking, Unsupported CoMoS nano catalys