Nutrient Flows and Quality of Bio-crude Oil Produced via Catalytic Hydrothermal Liquefaction of Low-Lipid Microalgae

Five heterogeneous and two alkaline catalysts were applied into the hydrothermal liquefaction (HTL) of Chlorella pyrenoidosa, a low-lipid microalgal species. The effects of catalysts on the bio-crude oil yield were more substantial at 280 ºC (bio-crude oil yield was increased by 10 %) than at 240 ºC although bio-crude oil formation had already occurred at the low temperature. At 240 ºC, additions of catalyst could improve the boiling point distribution of bio-crude oil. At 280 ºC, addition of alkaline catalysts increased the fractions of compounds with high boiling points due to the formation of nitrogen and oxygen heterocyclic compounds. The majority of nitrogen (59∼68 %) and phosphorus (52∼86 %) content in the feedstock remained in the aqueous phase after the HTL process, implying the possible feasibility to reuse the nutrients in the post-HTL water. Carbon deposition and mineral mixing were found on the surface of metal catalysts after HTL.