Hydrothermal liquefaction of starch using homogeneous and heterogeneous co-catalysts

We examined the hydrothermal liquefaction (HTL) of potato starch with K₂HPO₄, which dissolves in hot, compressed water, along with metal-containing co-catalysts, which present a separate solid phase in the reaction system. Co-catalytic HTL with K₂HPO₄ and either Mo₂C or Co-Mo/γ-Al₂O₃ produced more biocrude than did HTL with no catalyst or either catalyst alone. The synergistic effect of co-catalysis was greatest when the masses of K₂HPO₄ and Co-Mo/γ-Al₂O₃ were equal. At this condition, HTL with the two catalysts produced a biocrude that contained more than 90% of the chemical energy originally in the biomass feedstock. This biocrude also had a larger portion (61 wt%) of desirable lighter components (volatilized below 343 ℃) than did the biocrudes from HTL with either catalyst individually at the same conditions (38 and 41 wt%). With the addition of catalysts, there was less aliphatic content in the biocrude, and more ethers and aromatics appeared. The use of K₂HPO₄ and Co-Mo/γ-Al₂O₃ together for HTL led to greater fractions of alcohols, aldehydes/ketones, hydrocarbons, and phenolic compounds in the biocrude. In addition, less of the organic carbon in the feedstock migrated to the aqueous products. We identify catalysis of different HTL pathways to account for the experimental observations.