Control of chlorine migration in catalytic co-pyrolysis of PVC with other plastics

Abstract Polyvinyl chloride (PVC) present in mixed plastic waste poses a significant challenge to chemical recycling processes. This is due to the potential release of chlorine as HCl and its subsequent migration into oils, solids, and catalysts in both inorganic and organic forms. This review deals with the current understanding of chlorine behavior during the co-pyrolysis of PVC with major polymer classes, focusing on (i) dechlorination pathways and the phase-wise distribution of chlorine, (ii) interaction mechanisms in representative blends (PVC/polyolefins, PVC/PS, and PVC/PET), and (iii) catalytic and process-engineering strategies for chlorine management. Research within the field suggests that polyolefins can postpone the apparent dehydrochlorination process through mechanisms of melt encapsulation and transport limitation. In contrast, aromatic or polar matrices may enhance chlorine retention in condensable products via radical-mediated or functional-group-assisted pathways. The most consistent results in mitigation are observed with staged (two-stage/stepwise) approaches that separate low-temperature dehydrochlorination from high-temperature catalytic upgrading. This is particularly effective when combined with appropriate sorbents and specifically designed zeolite catalysts, such as ZSM-5. These findings reveal the synergistic and antagonistic roles of polymer mixtures and catalysts in governing chlorine migration, thereby offering practical insights for developing cleaner and more efficient PVC valorization routes.