A Scalable Process for the Chemical Recycling of PET using Ionic Organocatalysts

Lead Research Organisation: University of Birmingham
Department Name: Chemical Engineering

Abstract

There is an urgent need to devise processes for recycling plastics, with an estimated total of 8300 million metric tonnes of plastics produced to date, of which less than 10% have been recycled overall. The end fate of polymers can include landfill, burning which contributes to CO2 production, global warming, and discarding into the environment, including rivers and oceans. Of the materials which are recycled, mechanical or thermal recycling techniques typically produce a lower grade of polymer which can be used in applications such as clothing, insulation, garden and road furniture for example, and also has inferior properties (e.g. colour and mechanical specification) and value compared with virgin polymers.
PET is selected as the principal polymer for depolymerisation studies in this proposal, owing to it being widely used, with typical applications in clothing, bottles and packaging. The world demand for PET resin is ~23.5 million tonnes and production capacity ~30.3 million tonnes, whilst only 30 % (US) - 52 %(EU) is currently recycled. However used PET bottles are priced £222.50/tonne whilst virgin PET resin is priced £1084/tonne, making a strong economic case for chemical recycling to produce the virgin polymer, rather than mechanical or thermal recycling to a lower grade product. Chemical recycling of PET can be achieved via methods such as alcoholysis, aminolysis, ammonolysis and glycolysis, including via catalytic methods such as ionic organocatalysts. Some drawbacks of currently available recycling methods such as glycolysis involve the separation and eradication of contaminants such as catalyst residue and dyes from the product, difficulty of separating the project BHET from the reaction mixture in case it repolymerises during vacuum distillation and requirement for high purity PET feed to make high grade recycled products.

This proposal aims to address these drawbacks by developing a scalable, continuous process for PET depolymerisation. In particular we aim to study the effect of polymer additives and food contaminants in real wastes upon the depolymerisation, to understand how the catalyst/process can be made resilient to these issues. Key considerations will be to fully understand reaction kinetics, enabling catalyst immobilisation to enable recycling of it and developing strategies for product recovery. The proposed technologies are expected to deliver potential benefits including reduced reliance on fossil derived virgin plastics, potential to increase the market for chemically recycled polymers, and deliver of a scalable process.

We have engaged Project Partners from across the recycling, polymer production and academic sectors including Suez, Avantium, Dupont Teijin Films, Process Systems Enterprise and University of Liverpool. They will provide or advise on samples for depolymerisation, catalyst supports, provide technical consultation on the work plan and advise on routes to commercialisation and impact delivery as outlined in their letters of support.

Publications

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