Optimization and characterization of biocrude produced from hydrothermal liquefaction of food waste

Abstract

This study investigates the valorization of restaurant-derived food waste into biocrude using hydrothermal liquefaction (HTL). The selected feedstocks, including carrot, parsnip, and other vegetables, were evaluated for their physicochemical properties, showing low ash (9.1–22.0 wt%) and fixed carbon content (5.3–18.4 wt%) with high moisture levels (79–95% wet basis), suitable for HTL without additional drying. Carrot emerged as the optimal feedstock due to its elevated carbon (44.9 wt%), hydrogen (7.8 wt%), cellulose (15.3 wt%), and hemicellulose (4.1 wt%) content. Reaction parameters optimized via response surface methodology (280 °C, 1500 psi, 42 minutes) yielded 18.8 wt% biocrude with a carbon recovery of 55.9–72.8%. Quality analyses such as gas chromatography-mass spectrometry and Fourier-transform infrared spectroscopy highlighted the complex composition of biocrude, including esters, hydrocarbons, and oxygenated compounds, confirming its potential for biofuel applications. Solvent optimization experiments demonstrated that methanol was the most effective, yielding 19.6 wt% biocrude. Additionally, methanol actively participated in the extraction process by promoting esterification, generating methyl esters, as evidenced in gas chromatography-mass spectrometry analysis. These reactions enhance product yield and quality by forming bioactive compounds like methyl esters, which improve the bio-oil stability and calorific value. Despite high oxygen content (20.7 wt%), the biocrude properties can be upgraded via deoxygenation techniques, paving the way for its use as a sustainable transportation fuel. This research underscores hydrothermal liquefaction as an effective approach to manage food waste while addressing global energy challenges through renewable bioenergy production. By integrating statistical optimization and comprehensive characterization, this study contributes to advancing biofuel technology and sustainable energy solutions.