Co-hydrothermal carbonization of food wastes and lignocellulose-derived kitchen wastes: Product characteristics, synergistic mechanism and pyrolysis kinetics of hydrochars

This work investigated the physicochemical properties of bio-oil and hydrochars obtained from co-hydrothermal carbonization (co-HTC) of food wastes (FW) and lignocellulose-derived kitchen wastes (LKW), and based on thermogravimetric (TG) data, the pyrolysis behavior of hydrochars was evaluated by kinetic. The results showed that co-HTC promoted the intermolecular polymerization reaction, resulting in the increase of the content of aromatic compounds and other long-chain macromolecular compounds in bio-oil. The co-HTC of FW and LKW was conducive to the formation of microcrystalline structures and increase in aromaticity of hydrochars. The higher LKW ratio promoted the ring-opening reaction of hemicellulose, cellulose and lignin, and then increased the relative content of -OH and C-O-C in hydrochars. And the synergistic mechanism and reaction path of co-HTC were speculated. TG results showed that higher LKW ratio promoted the condensation and carbonization reaction between raw materials, thus increasing the stability of hydrochars. The activation energy of hydrochars calculated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) gradually increased from 187.54 and 190.10 kJ/mol in FLHC-1:0 to 221.82 and 227.04 kJ/mol in FLHC-0:1, respectively. With the increase of conversion rate (x), the activation energy of hydrochars increased first and then decreased, and the activation energy reached the maximum value at x = 0.7.