(363e) Co-Solvent Hydrothermal Liquefaction of a Microbial Yeast Biomass

Direct hydrothermal liquefaction (HTL) is an effective route that converts whole, wet biomass into an energy-dense liquid fuel precursor, called â??biocrudeâ??. HTL represents a promising alternative to conventional lipid extraction methods as it does not require a dry feedstock or additional steps for lipid extraction. HTL is normally performed in hot-compressed (subcritical) water at a 280-370 ^oC temperature and 5-25 MPa (700-3000 psi) pressure, although the actual operating conditions largely depend on the desired end product and the initial feedstock type and composition. High working pressure can create challenges in reactor sizing and overall operating costs. Through the use of co-solvents the HTL operating pressure can be reduced. The present study reports results from low-temperature co-solvent HTL treatment of oleaginous yeast, Cryptococcus curvatus, conducted at 240-300 ^oC using laboratory batch reactors. Isopropanol-water was used for the co-solvent HTL experiments and Na₂CO₃ was used as a catalyst. Co-solvent HTL produced significantly higher yield of biocrude (56.4±0.1%) than that of HTL performed without a co-solvent (49.1±0.4%). Addition of Na₂CO₃ as a catalyst marginally increased the biocrude yields, by 7.1% in HTL without a co-solvent and 2.7% in HTL with co-solvents. The energy content of the produced biocrude was ~37 MJ kg^-1, which is significantly higher than that of the original feedstock, 24 MJ kg^-1. Gas chromatographyâ??mass spectrometry of the biocrude suggested that the HTL process was successful in removing carboxyl groups from fatty acids and creating their associated alkanes (eicosane and heptadecane). Experimental results were leveraged to inform techno-economic analysis (TEA) of the baseline HTL conversion pathway to evaluate the commercial feasibility. Results from TEA models show a renewable diesel price of $4.12 per gallon with the HTL processing accounting for approximately 15% of the total cost.