Value-added products from pyrolysis of hydrochar derived from polyvinyl chloride and alkali coal

Abstract This work targets to produce multi value-added products by pyrolysis of hydrochars obtained from co-hydrothermal carbonization (co-HTC) of PVC and alkali coal. The hydrochars pyrolysis was carried out with a downdraft fixed bed reactor. The results indicate that HTC promoted the damage of oxygen functional groups, and the fixed carbon content and calorific value were considerably improved after co-HTC. The entire pyrolysis was delayed for coal hydrochar due to the increase of stable compositions in coal structure and improvement of coal rank. Besides, the PVC addition weakened this delay because of its instability, which could be verified by the activation energy. The H2 and CH4 yields increased in syngas, while the CO2 yield was concurrently reduced because of the removal of oxygen by decarboxylation. The obtained H2/CO ratio of syngas from hydrochar pyrolysis ranged from 1.34 to 4.33 depending on the pyrolysis parameters. The tar yield from hydrochar pyrolysis was lower than that of raw coal, which was ascribed to the lower degree of crosslinking in hydrochar facilitating the release of tar. The aromatic degree and rich pore structures of char indicated its great potential for contaminants adsorption which was further confirmed by the malachite green adsorption experiments. These findings could provide comprehensive knowledge on producing multi value-added products (hydrogen-rich syngas, poly-aromatic tar and adsorbent-char) from hydrochar pyrolysis, which would promote the economical utilization of high alkali coal and chlorinated wastes.