Catalytic Hydrothermal Liquefaction of Horse Manure: Impact of Catalyst Type and Concentration on Biocrude Yield

Catalytic hydrothermal liquefaction (CAT-HTL) offers a powerful strategy for converting wet biomass into energy-dense biocrude. This study systematically investigates the CAT-HTL of horse manure at 300 °C for 40 minutes, evaluating the performance of four homogeneous catalysts: KOH, NaOH, H₃PO₄, and NH₃·H₂O at 10% and 20% concentrations by dry feedstock weight. Compared to a non-catalytic baseline yield of 15.4 wt%, alkaline catalysts dramatically enhanced biocrude production. At a 20% loading, NaOH and KOH achieved observed yields (n = 1) of 55.7 wt% and 54.3 wt%, respectively. In contrast, the acidic (H₃PO₄) and ammoniacal (NH₃·H₂O) catalysts proved ineffective, yielding only 9.3 to 11.0 wt% biocrude. While the high catalyst dosages present economic challenges for scale-up, these results clearly demonstrate the potent efficacy of alkaline agents in promoting biomass liquefaction. This work provides a fundamental basis for catalyst selection and process optimization in the design of future waste-to-energy biorefineries.