Dehydrochlorination of PVC at low-temperatures and the pyrolysis behavior of dechlorinated PVC

Abstract

In this study, the dehydrochlorination reaction of polyvinyl chloride (PVC) was thoroughly investigated at various temperatures and reaction times. Ultraviolet–visible (UV–Vis) and Raman spectroscopies were employed to analyze the conjugated polyene sequences, and Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the functional groups present in the intermediates. The results reveal that in the very initial stages, the dehydrochlorination reaction forms soluble and colored intermediates, primarily consisting of conjugated polyene sequences without crosslinking. As dehydrochlorination progresses, the products become completely insoluble and transform into highly crosslinked black hard chucks. The obtained dehydrochlorinated intermediates were then pyrolysed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) to reveal their structures and decomposition mechanism. The core structure of the crosslinked intermediates is likely composed of cyclohexenes or cyclohexadienes. Among the aromatic compounds, benzenes and naphthalenes are the predominant categories with benzene being the most abundant. The crosslinking reaction inhibits benzene formation, leading to increased production of alkyl-aromatic compounds. This study proposes the structure of dehydrochlorinated intermediates and their decomposition mechanism, providing valuable insights for PVC recycling.

Graphical abstract