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

10 25 50
 
Description A series of small molecule and polymeric supported dual ionic organocatalysts were developed in Chemistry. These were characterised using techniques such as NMR. The catalysts were deployed for the depolymerisation of a range of polyethylene terephthalate (PET) samples, via glycolysis with ethylene glycol (EG). The reaction occurred at temperature of 180 degrees Celsius. Polymer samples included virgin powder and pellets from a commercial manufacturer, consumer products such as films, shredded drinks bottles and felt board produced from an industrial partner. The samples could be fully converted in reaction times typically ranging from 1-4 hours to yield product Bis(2-Hydroxyethyl) terephthalate (BHET). Preliminary kinetic modelling indicated a shrinking core reaction model of the polymer particles, as they react with liquid EG.

Studies of process scalability were carried out in Chemical Engineering, including experimental and modelling studies of BHET crystallisation in EG using a batch crystalliser. These were modelled using gFormulated Products (gFP) software with Project Partner Siemens. Good agreement of the model results with cooling crystallisation curves was achieved. A membrane separator rig was developed to study the retention of the reaction mixture and catalyst, whilst separating the product. Good initial separations were achieved using polymeric membranes to retain small molecule ionic organocatalysts. However, the membranes appear to have a temperature limit of about 150 degrees Celsius and thus may have limited applicability at the reaction temperature of 180 degrees Celsius.
Exploitation Route The work will be of interest to Chemists and Chemical Engineers working on chemical depolymerisation. The data generated from the project could potentially used to develop a pilot scale and then industrial scale process, for example equipment sizing and techno-economic calculations for the treatment of particular waste plastic flows.
Sectors Agriculture

Food and Drink

Chemicals

Education

Environment

Manufacturing

including Industrial Biotechology

Retail

 
Description We are working with two industrial partners. The first is a major plastics company who produce films and industrial products manufactured from PET. The second is a building design company who are interested to recycle felt board used in interior design projects. Both companies have supplied us with samples for depolymerisation, which we have tested in our reactors, showing good results with the developed catalysts. We are feeding back results to them and exploring the best ways of taking these forward, for example, at trade exhibitions. These have wider societal implications for the removal of plastics from waste and landfill, for recycling in the circular economy.
First Year Of Impact 2023
Sector Manufacturing, including Industrial Biotechology
Impact Types Societal

 
Description Thermally Responsive Supports for Enhanced Efficiency in PET Depolymerisation
Amount £923,700 (GBP)
Funding ID EP/Y003667/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2024 
End 03/2027
 
Description Dupont Teijin Films 
Organisation DuPont Teijin Films
Country Global 
Sector Private 
PI Contribution Researchers are testing the depolymerisation of film samples to be supplied by Dupont Teijin Films using ionic organocatalysts developed in the project.
Collaborator Contribution Dupont Teijin Films take part in online technical meetings to offer advice and supply of industrial films of varying molecular weight, application and additives, for testing as 'real world' materials for depolymerisation and recycling in the circular economy.
Impact The outcomes of this work are ongoing.
Start Year 2022
 
Description Siemens Process Systems Engineering 
Organisation Siemens Process Systems Engineering Ltd
Country United Kingdom 
Sector Private 
PI Contribution Using gFormulated Products software to model crystallisation processes, e.g. BHET product from ethylene glycol.
Collaborator Contribution Supply of software licences and consultancy advice.
Impact Ongoing.
Start Year 2022
 
Description A poster presentation at the UK Catalysis Conference 2023 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Poster presentation: 'Scalable process for PET chemical recycling with thermally stable organocatalysts'
by Joseph Sutton, Guido Grause, Ali Al Rida Hmayed, Andrew Dove, Joseph Wood
Year(s) Of Engagement Activity 2023
URL https://www.ukcatalysisconference.co.uk/conference-information
 
Description ChemEngDay 2023 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Oral presentation: 'Crystallisation of Bis(2-hydroxyethyl) Terephthalate from Ethylene Glycol after the Chemical Recycling of Poly(ethylene Terephthalate)', by G. Grause, J. Sutton, A. Dove, N. Mitchell, J. Wood
Year(s) Of Engagement Activity 2023
URL https://www.icheme.org/knowledge-networks/communities/special-interest-groups/education/events/30-31...
 
Description Factories for the Future, an IChemE Catalysis SIG Symposium at the University of Birmingham 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Short talk 'Concept for a Novel Process for the Glycolysis of PET' by G. Grause, J. Sutton, A. Dove, J. Wood at the University of Birmingham.
Year(s) Of Engagement Activity 2023
URL https://www.icheme.org/knowledge-networks/communities/special-interest-groups/catalysis/events/28-03...
 
Description Oral presentation at the International Symposium on Industrial Crystallization, Glasgow 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Poster presentation: 'Purification of bis(2-hydroxyethylene) terephthalate as a part of a bottle-to-bottle recycling concept for PET', by Guido Grause, Joe Sutton, Andrew Dove, Niall Mitchell and Joseph Wood
Year(s) Of Engagement Activity 2023
URL https://www.isic2023.com/
 
Description Purification of bis(2-hydroxyethylene) terephthalate as a part of a bottle-to-bottle recycling concept for PET at Process Systems Engineering Advanced Process Modelling Forum meeting, London, 18-19 October 2022 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact A poster presentation of the project concept was made to a group of over 100 software and process modelling industry professionals at the Siemens Advanced Process Modelling Forum event in London, October 2022.
Year(s) Of Engagement Activity 2022