Utilizing the self-stabilizing stage of ZIF-8 for highly efficient in situ Cl capture during PVC pyrolysis

This paper explores the application of zeolitic imidazolate framework-8 (ZIF-8) in pyrolytic disposal of poly(vinyl chloride) (PVC), with the goal of assessing the in situ catalytic removal and capture effect of ZIF-8 on Cl, elucidating the migration pattern of Cl, revealing the mechanism of in situ Cl capture by ZIF-8. The results demonstrate that excellent catalytic and Cl trapping properties are exhibited by ZIF-8, and an additional 311.1 mg/g of organic Cl from PVC is facilitated to be removed at 250 ºC. The catalytic effect enhances Cl trapping at low temperatures. The solid-solid reaction between PVC and ZIF-8 during in situ pyrolysis significantly improves Cl capture compared to ex situ pyrolysis. During in situ pyrolysis, ZIF-8 shows excellent Cl capture between 250 and 350 ºC, where Cl is primarily captured in the solid phase as inorganic Cl. ZIF-8 achieves optimal Cl capture at 300 ºC, reaching a peak HCl removal rate of 89.5 %. At this temperature, the content of solid-phase inorganic Cl reaches a maximum of 442.0 mg/g, accounting for 78.7 wt% of the total Cl content. The key to Cl capture lies in the chemical adsorption sites of Zn²⁺ and organic ligands in the ZIF-8 structure, which can react with Cl in both solid-solid and gas-solid reactions. Additionally, crystals formed during pyrolysis create an adsorption barrier, ultimately enabling efficient Cl capture.