Characterization of Product Fractions from Hydrothermal Liquefaction of Nannochloropsis sp. and the Influence of Solvents

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Abstract

We collected and analyzed the gas, crude bio-oil, dissolved aqueous solids, and insoluble residual solids product fractions arising from hydrothermal liquefaction of Nannochloropsis sp. at 350 °C for 60 min. Most of the carbon and hydrogen in the algal biomass appears in the crude bio-oil product, as desired. A majority of the original nitrogen appears as ammonia in the aqueous phase. We also determined how the solvent used to recover the crude bio-oil affected the yields and compositions of the product fractions. We used both nonpolar solvents (hexadecane, decane, hexane, and cyclohexane) and polar solvents (methoxycyclopentane, dichloromethane, and chloroform). Hexadecane and decane provided the highest gravimetric yields of bio-oil (39 ± 3 and 39 ± 1 wt %, respectively), but these crude bio-oils had a lower carbon content (69 wt % for decane) than did those recovered with polar solvents such as chloroform (74 wt %) and dichloromethane (76 wt %). We quantified the amount of 19 different individual molecular components in the crude bio-oil for the first time. Fatty acids were the most abundant components, but some aromatic and sulfur- and nitrogen-containing compounds were also quantified. The amount of free fatty acids in the crude bio-oil significantly depended on the solvent used, with polar solvents recovering more fatty acids than nonpolar solvents. The bio-oil recovered with chloroform, for example, had a fatty acid content equal to 9.0 wt % of the initial dry algal biomass.

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