Insight into dechlorination of pyrolysis oil during fast co-pyrolysis of high-alkali coal and polyvinyl chloride (PVC)

Abstract

Thermal treatment can utilize polyvinyl chloride (PVC) in a high-value, eco-friendly method, but HCl generation and high oil chlorine content are key pyrolysis issues. Therefore, this research extensively characterized fast co-pyrolysis of PVC and high-alkali coal (HAC) using XPS, TG-FTIR-GC/MS, and GC-MS. This explored alkali metal catalysis and volatile reforming effects on Cl transfer and utilizing PVC as a hydrogen donor to improve the quality of pyrolysis oil. According to the GC-MS results, increasing the PVC ratio to 40 % raised monocyclic (MAHs) and polycyclic aromatic hydrocarbons (PAHs) to 59.1 % and 33.4 % respectively. However, co-pyrolysis of PVC and HAC inhibited the polyene reconstruction of the carbon skeleton, leading to a decrease of oxygenates, such as phenolic, acid, and ester. The XPS results showed that the inorganic chlorine in the solid product increased from 1 % to 66 % after co-pyrolysis at 600 °C, indicating the high fixed chlorine effect of HAC. Fast heating almost merges the PVC dechlorination stage with the conjugated polyene reconstruction stage, creating a liquid–gas synergy. Abundant coal α-carbon selectively binds with H+, dechlorinated PVC, and polyene fragments, rather than binding with Cl-. This study provides valuable insights into coal-PVC interactions and the dechlorination of pyrolysis oil during fast co-pyrolysis processes and advances the sustainable management of PVC waste.