Screening Potential Catalysts for the Hydrothermal Liquefaction of Food Waste

We examined the effect of supported metals (Ni/C, Pt/C, Ru/C, Pd/C, Ni/SiO2–Al2O3, Pt/Al2O3, and Ru/Al2O3), bulk metal oxides (CaO, Al2O3, CeO2, La2O3, and SiO2), and a set of salt, acid, and base additives on the hydrothermal liquefaction (HTL) of simulated food waste. Supported metals and the additives did not increase biocrude yields, but three of the metal oxides did lead to higher yields, with the following order: SiO2 > La2O3 > CeO2. The elemental compositions and heating values of the biocrudes were sensitive to the type of potential catalyst used, especially in the presence of high-pressure hydrogen. The higher heating values (HHVs) of the biocrude from HTL were higher with added H2 and supported metal. Of all the potential catalysts tested, K3PO4 produced oil with the greatest HHV (37.5 MJ/kg). Fatty acids were the major GC-elutable compounds in most of the oils, save that produced with added CaO, where amides and N-containing compounds dominated. Thermogravimetric analysis showed that the distribution of the volatilities of the molecules in the biocrude oils is sensitive to the type of metal oxide used. HTL with CaO and no metal oxide recovered the most nitrogen and phosphorus, respectively, in the aqueous phase.