Dechlorination during pyrolysis of plastics: The potential of stepwise pyrolysis in combination with metal sorbents

Pyrolysis liquid is a valuable product that could be re-introduced into the refinery or petrochemical industry following circular economy principles. However, halogens in the liquid product hinder this approach by causing corrosion of subsequent technologies. Dehalogenation is, therefore, a necessary step that aims to reduce halogen content below the set limit of 10 ppm. Research on this topic often includes contradictory results, and dehalogenation is still not widely used in large-scale operations. The present study explores the possibility of chlorine removal from a model plastic mixture, including 10% PVC utilizing various pyrolysis conditions, stepwise pyrolysis, and sorbents based on Ca(OH)2, Fe3O4, and Fe. Results suggest that it is not suitable to use sorbents in-situ as the captured Cl in the form of chlorides was released at higher temperatures increasing the chlorine content in the liquid products. The limit of 10 ppm for refinery introduction was reached by combining stepwise pyrolysis and sorbents ex-situ. Fe3O4 displayed the best efficiency, while its reduced form was the most efficient considering its low surface area. The obtained results are a necessary preliminary step for the development of a reliable dehalogenation procedure for municipal plastic waste being underway.