Hydrothermal Liquefaction of Model Food Waste Biomolecules and Ternary Mixtures under Isothermal and Fast Conditions

We subjected potato starch, casein, and sunflower oil to both isothermal and fast hydrothermal liquefaction (HTL), both individually and as ternary mixtures in different proportions. Fast HTL (15 wt % biomass loading, 600 °C set-point temperature, 1 min) of sunflower oil produced the highest biocrude yield (91 wt %), followed by casein (23 wt %) and potato starch (19 wt %). Up to 21% of the phosphorus and 57% of the nitrogen in casein are distributed to the aqueous phase after fast HTL and can potentially be recovered as fertilizer for growing more food. Fast HTL (600 °C, 1 min) provided higher biocrude energy recoveries than did isothermal HTL (350 °C, 60 min) for all three feedstocks. Potato starch showed the greatest increase in energy recovery with fast (46%) vs isothermal (32%) HTL, and fast HTL of the ternary mixture rich in potato starch produced biocrude with the largest higher heating value (HHV) (42 MJ/kg). The results indicate that fast HTL is particularly beneficial for polysaccharides compared to the other biomolecules. Biocrude yields produced from fast HTL of ternary model mixtures were within two standard deviations of the yields estimated on the basis of individual biomolecules. The presence of pyrrolidines, pyrazines, fatty acid alkyl esters, and fatty acid amides indicate that chemical reactions occur between molecules derived from the different feedstocks during HTL of mixtures.