Pyrolysis Characteristics of Hailar Lignite in the Presence of Polyvinyl Chloride: Products Distribution and Chlorine Migration

Abstract

This study investigated the effects of polyvinyl chloride (PVC) addition on low-rank coal’s pyrolysis characteristics, especially the products distribution and chlorine migration. Hailar lignite (HLE) with different industrial, pure, PVC-content additions were prepared (the mass percentage of PVC addition was from 5% to 25%), and the co-pyrolysis characteristics of HLE and PVC were performed on a fixed-bed reactor and thermogravimetric analyzer. The chars were characterized with X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier-transform infrared (FT-IR) spectroscopy analysis. The gas and tar compositions were analyzed by using gas chromatography (GC) and a gas chromatography–mass spectrometry (GC–MS) system, respectively. The results indicate that the addition of PVC can increase the release amounts of CH4, C2H4, and C2H6, simultaneously reducing the release amount of CO2 and CO; the quality of pyrolysis tar was also improved, especially the alkane content in tar, which increased by 6.9%. The migration of chlorine in PVC was analyzed with the different PVC additions and terminal pyrolysis temperatures. It showed that the content of chlorine in the gas phase first increased with the increasing pyrolysis temperature, but at the terminal temperature of 600 °C, the chlorine in the gas phase began to decrease. The results of the co-pyrolysis char characterization show that the content of the alkali metal oxide gradually decreases in the char, and metal chloride appears during the pyrolysis process. In the co-pyrolysis reaction of coal and PVC, chlorine was fixed in the char, thereby reducing the distribution of chlorine in the gas phase. This also proves that the PVC pyrolysis process, with the participation of low-rank coal, can enrich chlorine into the solid phase, thus reducing the emission of chlorine in the gas phase.

Recent Advancements in Pyrolysis of Halogen-Containing Plastics for Resource Recovery and Halogen Upcycling: A State-of-the-Art Review

“…Hong et al applied the reactive molecular dynamics (ReaxFF MD) simulations to study the copyrolysis of PVC and coal, demonstrating two distinct stages of positive synergistic effects. Coal promotes the release of HCl from PVC pyrolysis, which is subsequently trapped by the minerals in coal, as documented elsewhere . The copyrolysis of PVC and the hazardous oil-based drill cuttings reveals synergistic effects that suppress HCl release from PVC and reduce SO 2 formation from oil-based drill cuttings .…”

“…Coal promotes the release of HCl from PVC pyrolysis, which is subsequently trapped by the minerals in coal, as documented elsewhere. 70 The copyrolysis of PVC and the hazardous oilbased drill cuttings reveals synergistic effects that suppress HCl release from PVC and reduce SO 2 formation from oil-based drill cuttings. 73 The research indicates that the interactions among pyrolyzates resulting from halogen-plastics/feedstock copyrolysis exhibit synergistic effects that effectively mitigate both halogens and other undesired (N/S/O) substances.…”

“…When over 40 wt % coal is mixed with PCBs, the added coal stabilizes Br in the residues rather than evaporation. Research on the copyrolysis of PVC and low-rank coal reveals synergistic effects that promote an increase in the tar yield with increased alkaline content in mixed feedstocks. , Alkaline metals in coal suppress the release of Cl during PVC pyrolysis, fixing Cl within the char. Hong et al applied the reactive molecular dynamics (ReaxFF MD) simulations to study the copyrolysis of PVC and coal, demonstrating two distinct stages of positive synergistic effects.…”