Feedstock Recycling via Waste Plastic Pyrolysis

Abstract

Recycling of waste plastics is essential for reducing environmental degradation and ensuring future resource security. The quantity of domestic plastic waste recycled is increasing yearly, reaching 83 % in 2014. However, only 26 % and 4 % of the recycled waste plastic is treated by mechanical and feedstock recycling, respectively, whereas 70 % is treated by energy recovery (incineration). Therefore, the mechanical and feedstock recycling rates must be improved. This review examines the pyrolysis of waste plastics, which is a treatment method classed as feedstock recycling. Pyrolysis can convert waste plastics, which cannot be treated by mechanical recycling, into oils and gases. However, polyvinylchloride (PVC) and poly(ethylene terephthalate) (PET) produce corrosive gases and sublimating substances during pyrolysis, resulting in reduced quality of pyrolysis products, and damage to the treatment plant. Dehydrochlorination and dechlorination of PVC, in addition to catalytic pyrolysis of PET using Ca-based catalysts, have been developed. Recent studies into the pyrolysis of major plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are summarized here, together with research on the dry and wet treatment of PVC and the catalytic pyrolysis of PET.