Hydrothermal Liquefaction of Food Waste and Model Food Waste Compounds

Solid waste is generated at a rate of more than 4 lb per person per day. A significant portion of the non-recyclable waste is food waste, with high water content and low energy density. While most thermochemical conversion processes require a relatively dry feedstock, hydrothermal liquefaction uses subcritical water as the reaction medium and is therefore compatible with high-moisture feedstocks. We have studied the viability of converting high-moisture food waste into a liquid fuel. A surrogate food waste stream was formulated and the yield and bio-oil quality were measured at various process conditions. Yields as high as 45% on a dry mass basis were observed at a reactor temperature of 315 °C. To further understand hydrothermal liquefaction of food waste, three model food compounds were studied—starch, soybean oil, and casein. The reaction mechanism, product distribution, and product yields for each compound were investigated at reactor temperatures ranging from 250–315 °C, using a sodium carbonate catalyst and a syngas head gas. The pure-component data were compared to data collected for the surrogate food waste under the same operating conditions. A lumped kinetic model describing the hydrothermal liquefaction of starch is also proposed.