Effect of Process Variables on Food Waste Valorization via Hydrothermal Liquefaction

We examined hydrothermal liquefaction (HTL) of simulated food waste over a wide range of temperatures (200-600 degrees C), pressures (10.2-35.7 MPa), biomass loadings (2-20 wt %), and times (1-33 min). These conditions included water as vapor, saturated liquid, compressed liquid, and supercritical fluid and explored both isothermal and fast HTL. The highest biocrude yields (similar to 30 wt %) were from HTL near the critical temperature. The most severe reaction conditions (600 degrees C, 35.3 MPa, 30 min) gave biocrude with the largest heating value (36.5 MJ/kg) and transfer of up to 50% of the nitrogen and 68% of the phosphorus in the food mixture into the aqueous phase. Energy recovery in the biocrude exceeded 65% under multiple reaction conditions. Saturated fatty acids were the most abundant compounds in the light biocrude fraction under all the reaction conditions. Isothermal HTL gave a higher fraction of heavy compounds than fast HTL. A kinetic model for HTL of microalgae predicted 2/3 of the experimental biocrude yields from HTL of food waste to within +/- 5 wt %, and nearly 90% to within +/- 10 wt %. This predictive ability supports the hypothesis that biochemical composition of the feedstock is important input for a predictive HTL model.

Automated summary

The study found that hydrothermal liquefaction of food waste near the critical temperature can achieve the highest biocrude yields, while the most severe reaction conditions can produce biocrude with the highest heating value.