(681a) Hydrothermal Dechlorination of Municipal Solid Waste

Plastics are a ubiquitous material in modern society due to their low cost, versatility, and durability, however traditional recycling is unable to meet the current demands of waste plastic disposal. As a result, as much as 85% of all waste plastic ends up in landfills. This is because most plastic waste is a mix of plastics and contaminated with food, dyes, and impurities. The expense to separate and decontaminate plastic waste is often prohibitive. Moreover, recycled plastic is often inferior to virgin plastic and therefore less valuable on the open market.

Thermochemical methods, like gasification, represent a feedstock-agnostic method to process mixed plastics and other waste to produce fuels and chemicals. However, halogenated plastics are a significant obstacle. It has been estimated that polyvinyl chloride (PVC) accounts for 12–15% of all plastic manufactured. Gasifying waste containing PVC releases chlorine gas that damages equipment and is a pollutant that has to be captured post-gasification. A pretreatment method that can remove chlorine prior to gasification has the potential to significantly improve gasification economics and reduce landfilling.

In this work, we examine the feasibility of using a hydrothermal treatment to remove chlorine from plastic in mixed waste, specifically PVC. Chlorine is captured as acid in subcritical water and the remaining solid materials are carbonized and highly amenable to gasification. We tested conditions to maximize chlorine removal and to retain energy in the solids for gasification. Products were analyzed to better understand hydrothermal dechlorination mechanisms and to evaluate the potential as a gasification feedstock. Finally, the results of the experiments were used in a technoeconomic analysis to determine the potential for treated mixed waste as an additional feedstock to improve gasification economics. We will discuss the effects of temperature, reaction time, solids to water ratio, and various catalysts on the treatment of pure PVC and mixed waste.