Dechlorination of waste polyvinyl chloride (PVC) via its co-pyrolysis with Ca(OH)₂: A TG-IR-GCMS investigation

Being the most deployed thermoplastic worldwide, waste polyvinyl chloride (PVC) generation is expected to increase by about 80% over the next couple of decades. Chlorine toxication during the incineration process is a menace for waste handling facilities though various PVC management is in place. Hence, effective chloride capture is considered the primary focus during PVC pyrolysis rather than harnessing the latent hydrocarbons in any form of energy. In order to simulate a real-world situation wherein the chlorine content is proficiently removed from waste PVC using affordable additives, the state-of-the-art online TG-IR-GCMS approach was used to examine the PVC thermal degradation products in the presence and absence of Ca(OH)₂. In both cases, the TG analysis revealed twin degradation phases with the simultaneous IR spectral analysis verifying that the HCl release was limited to the first stage with a mass loss of ∼60%; most notably benzene being the other major product with 81.59% relative area as endorsed by GCMS analysis. In the second stage, further PVC chains unzipping generated several other aromatic products upon the Diels–Alder reactions of intramolecular cyclization such as toluene, xylene and other benzene derivatives. The PVC co-pyrolysis with Ca(OH)₂ reduced the HCl formation significantly due to the dissociative adsorption of HCl gradually over the calcium surface converting Ca(OH)₂ into calcium oxide and eventually into CaCl₂ as verified by the XRD crystallinity analysis and surface morphology and elemental mapping via SEM-EDX analysis.