Pyrolysis kinetics and thermodynamic parameters of the hydrochars derived from co-hydrothermal carbonization of sawdust and sewage sludge using thermogravimetric analysis

The thermal behavior of the hydrochars from co-hydrothermal carbonization (co-HTC) of sawdust (SD) and sewage sludge (SS) was investigated using thermogravimetric analysis. The comprehensive devolatilization index indicated that the devolatilization performance of SS was decreased by HTC, while it was significantly improved 7.38-23.69 times by co-HTC. The kinetic analysis showed that HTC of SS decreased the average activation energy from 308.96 and 314.78 kJ mol(-1) to 220.86 and 221.27 kJ mol(-1) by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS), respectively, while it was increased from 182.37 to 207.06 kJ mol(-1) and from 181.06 to 207.05 kJ mol(-1) with the increasing proportion of SD from 25% to 75% during co-HTC, respectively. The thermodynamic parameters revealed that pyrolysis reactivity of the hydrochar derived from SD was improved by co-HTC of SD and SS. Kinetic and thermodynamic findings were useful for the design of pyrolysis process using hydrochar as solid fuel.