Thermal Degradation and Organic Chlorine Removal from Mixed Plastic Wastes

Abstract

Plastic waste accumulation has been growing due to the increase in plastic generation and the lack of infrastructure for recycling. One of the approaches is to treat the mixed plastic waste (MPW) through thermal processes to produce feedstocks for other applications. However, the presence of polyvinyl chloride (PVC) in MPW would produce HCl during processing and has negative impacts (emission, catalyst poisoning, etc.). In addition, due to the high heterogeneity of MPW, it is difficult to generate consistent experimental data. In this study, MPW was homogenized through double compounding–extrusion and then formed into a sheet to be treated at 400 °C. The solid products at various mass losses were characterized by heat and chlorine content, Fourier-transform infrared (FTIR) spectroscopy, and elemental composition analysis. It was found that the thermal degradation of MPW started at ~260 °C. The chlorine removal efficiency increased with mass loss and reached an asymptotic value of ~84% at ~28% mass loss, and the remaining chlorine can be attributed to inorganic sources. A PVC de-chlorination model was developed for MPW using TGA data for PVC and MPW to determine organic chlorine removal efficiency. These results show that PVC de-chlorination was not affected by other plastics at this temperature. As the mass loss increases, the heat content first increases and then decreases. It was found that mass loss is a universal parameter for organic chlorine removal efficiency and heat content. The elemental composition analysis and FTIR spectroscopy also shed more light into the chemical changes during MPW thermal degradation.

Recent advances in polyvinyl chloride (PVC) recycling

“…The core concept of this investigation demonstrates the efficacy of torrefaction in reducing chlorine levels in waste feedstocks, rendering them more suitable for applications in power generation. [122][123][124] Shreyas S. Kolapkar et al have introduced a pilot-scale system that combines torrefaction and extrusion to transform a mixture of fiber and plastic waste into fuel pellets. These resultant pellets exhibit a range of desirable characteristics, including affordability, a high heating value, improved consistency, and minimal environmental impact.…”

“…The study also observed a significant decrease in organic chlorine content per unit heat content at around 30% mass loss, while ~90% of the energy was retained. The core concept of this investigation demonstrates the efficacy of torrefaction in reducing chlorine levels in waste feedstocks, rendering them more suitable for applications in power generation 122–124 …”