Effect of Process Variables on Food Waste Valorization via Hydrothermal Liquefaction

Abstract

We examined hydrothermal liquefaction (HTL) of simulated food waste over a wide range of temperatures (200–600 °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 (∼30 wt %) were from HTL near the critical temperature. The most severe reaction conditions (600 °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.

Screening Potential Catalysts for the Hydrothermal Liquefaction of Food Waste

“…We chose conditions that gave the highest oil yields in prior work. 35 It is possible that HTL at these conditions is already generating the highest oil yield physically possible, so there could be little opportunity for a potential catalyst to increase the biocrude yields further. Another potential factor could be metal poisoning (e.g., by sulfur 42 ).…”

“…A simulated food waste was made from a mixture of food items as discussed in previous work. 35 The mixture was 27.5% protein, 36.5% nonstructural carbohydrates, 14.9% fiber, and 15.7% lipids, by mass. Its elemental composition was 47.8% carbon, 5.11% hydrogen, 4.78% nitrogen, 0.23% sulfur, and 42.1% oxygen, by mass.…”

“…Details have been reported previously. 35 The NIST mass spectral library was used to tentatively identify molecular species, with a similarity index >85% being required for a tentative identification.…”

Hydrothermal Liquefaction of Food Waste: Effect of Process Parameters on Product Yields and Chemistry

“…HTL of food waste has been studied by a number of researchers (Viganó et al, 2015;Motavaf and Savage, 2021). The highest bio-crude oil obtained from HTL of food residues at 300 • C was 90, 75, and 10 wt.% for meats, cheeses, and fruits, respectively (Kostyukevich et al, 2018).…”

“…HTL temperature showed a strong effect on bio-crude oil yield and properties during HTL of fruit peel at 300-350 • C and 30-120 min; the bio-crude oil yield obtained at 350 • C was relatively low . Motavaf and Savage (2021) studied a wide range of temperatures (200-600 • C) to investigate isothermal and fast HTL. The highest bio-crude oil yield from fast HTL was as high as the highest yields from isothermal HTL (28-30 wt.% at 300-400 • C).…”