Co-hydrothermal carbonization of food wastes and waste plastic bottles: Physicochemical properties, pyrolysis kinetics and thermodynamic of hydrochars

This work investigated the physicochemical properties of hydrochars obtained from co-hydrothermal carbonization (co-HTC) of food wastes (FW) and waste plastic bottles (WPB), and the pyrolysis kinetic and thermodynamic of hydrochars based on Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods were analyzed. The results showed that co-HTC of FW and WPB showed synergistic effect on hydrochars, the increase of WPB fraction enabled demethylation to gradually play a dominant role in co-HTC. The results of XPS and FT-IR showed that the higher proportion of WPB increased the aromaticity of hydrochars and enhanced the stretching vibration of C-H. The higher proportion of WPB increased the initial decomposition temperature of hydrochars, decreased the final residues, causing the TG curve to shift to the lower right. The average activation energy of the hydrochars calculated by FWO and KAS gradually increased from 126.79 and 130.43 kJ/mol of FPHC-1:0 to 178.73 and 183.74 kJ/mol of FPHC-0:1, respectively. And thermodynamic analysis indicated that the increase of WPB fraction led to a decrease in the reactivity of hydrochars as the reaction proceeds. HTC enhanced the orderliness of the raw materials during the pyrolysis process. The Δ S value of hydrochars showed a trend of first increasing and then decreasing with the increase of the WPB fraction.