Evolution of structure and pyrolysis characteristics of coal tar residue after extraction

Coal tar residue (CTR) is a type of hazardous waste with potential utilization value. Pyrolysis is a promising thermal conversion technology, and a comprehensive knowledge regarding the pyrolysis behavior of CTR is crucial. In this study, the extract fraction (ECTR) and solid residual fraction (RCTR) of CTR are separated by toluene Soxhlet extraction. The structure features and pyrolysis characteristics of raw CTR, ECTR, and RCTR are investigated. The results shows that the ECTR is primarily composed of small molecule aromatics, aliphatic and aromatics with long alkyl side chains, branched alkyl or alicyclic structures. The condensed macromolecular aromatic carbon skeleton is remained in RCTR with some of the oxygenated structures exposed. The low volatile content and high aromaticity results in high thermal stability of RCTR, while the high fixed carbon content and carbonization product yield demonstrates its potential for high value-added applications. When postulated by Z (alpha) master plot, the reaction-order model fit best with the pyrolysis experimental data of CTR and its isolates. Both the Coats-Redfern (CR) model and Arrhenius model validate the reaction-order mechanism. The kinetic analyses reveals that the reaction order, activation energy and pre-exponential factor for RCTR all increased after extraction.