Thermal behaviour of hydrochar derived from hydrothermal carbonization of food waste using leachate as moisture source: Kinetic and thermodynamic analysis

Abstract

The effect of leachate (L) as a reaction medium in hydrothermal carbonization (HTC) of food waste (FW) on the thermal behaviour of the resulting hydrochar (H) was investigated. The physicochemical and structural characterization of FW hydrochar produced using leachate (FWH-L) at different process temperatures (180/210/240 °C) confirmed the improved properties over raw FW. Kinetic analysis using Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods revealed that FWH-L have a lower activation energy (Ea) than raw FW. The average Ea values for raw FW by FWO, KAS and Friedman methods were 196.18, 196.85, 206.34 kJ/mol, respectively, while for FWH-L they were 127.89, 124.22 and 134.5 kJ/mol, respectively. The computed thermodynamic parameters showed that FWH-L has improved combustion behaviour. The results of FWH-L are well comparable to FW hydrochar produced using distilled water (FWH-DW). These findings demonstrated that residual ions in leachate would act as a catalyst, benefiting the HTC degradation reaction path.