Proposal for a Circular Recycling of Hydrocarbon Plastics

Abstract

Over 430 million tons of plastic were produced in the year 2022, and 2/3rd of them were of short-term use. Besides good successes in recycling PET (No 1) and HDPE (No 2), most of them end up in landfills or waterways and oceans. Even recycling of plastic by mixing them with virgin plastic has problems, as they contain large amounts of pharmaceuticals and other undesirable chemicals. One of the desirable ways to chemically recycle a plastic is to take it back to its starting monomers, which can then be re-polymerized into virgin plastic—a circular recycling. A polyester (PET) polymer can be hydrolyzed back to diacids and diols, and after cleaning, polymerized back to PET with the same characteristics as the original polymer. There are catalytic pyrolytic ways to produce naphtha (C₄–C₇) that can be a starting material for ethylene and propylene to be repolymerized to PE and PP. Inductively coupled depolymerization of plastic can, under the right conditions (Eco Fuel Technology, US Patent 9 505 901), take the polymer all the way to its monomer (85–90 + % yield). Mixtures of plastic can be reacted, and the resulting ethylene, propylene, or styrene can be separated to get pure monomers that can be re-polymerized. This will be a true circular chemical recycling and this paper will propose ways to scale up the process to industrial scale. This cycle can be repeated indefinitely and the process by itself does not add any CO₂.