PAHs formation and distribution: Mechanistic insights from pyrolysis of chlorine-rich waste polyvinyl dichloride

The pyrolysis of waste polyvinyl dichloride (PVDC), a halogenated plastic with high chlorine content (∼64.68 wt%), poses considerable environmental risks due to the formation of toxic and persistent polycyclic aromatic hydrocarbons (PAHs). This study systematically investigated the effects of pyrolysis temperature (500-900°C), reaction duration (10-50 min), and heating rate (5-25 °C·min^-1) on the yield, congener profile, and phase distribution of 16 PAHs from the slow pyrolysis of waste PVDC plastics. The results indicated that pyrolysis temperature exhibited the most significant effect among all investigated parameters. The maximum total PAHs concentration was 3129.08 μg·g^-1, obtained at 800 °C, 40 min, and a heating rate of 10 °C·min^-1, of which the liquid phase contained the dominant fraction (∼95.8%). The yield of medium-ring PAHs showed a distinct maximum at a heating rate of 15 °C·min^-1, linked to optimized ring-growth kinetics. The formation pathways, initiated by chlorine-mediated de-chlorination and propagated via HACA/HAVA mechanisms, were elucidated. This work provides essential quantitative data and mechanistic insights for assessing environmental risks and designing control strategies during the co-pyrolysis of halogenated and traditional plastic wastes.