Catalytic Upgrading of Polymer Waste into Value-Added Products

Plastics have played an instrument role in the development of modern day society, but growing environmental concerns associated with the industry has created an appetite for renewable alternatives. Indeed, it is clear the development of alternative waste management strategies is necessary to compliment the introduction of bio-based and biodegradable plastics as the industry shifts from a linear to circular economy. Thus, this project aims to:

- Investigate catalytic upgrading (via chemical recycling) of commercially bio-based plastics (e.g. PLA) into value-added products, such as lactate esters or acrylic acid, which have been cited as potential green substitutes for traditional petrochemical based solvents/chemicals. Key aspects to this process include:
Development of novel, industrially viable catalysts (i.e. using cheap/abundant metals and scalable ligands systems).
- High selectivity and yield under mild conditions, with metal-mediated degradation examples remaining limited. Indeed, current recycling methods rely on harsh reaction conditions, are resource/energy intensive and lead to eventual material 'downcycling' in the case of mechanical recycling 1 Chemical recycling has the potential to address these concerns.
- Demonstrate process scalability on a novel spinning disc reactor, adopting an interdisciplinary approach to research by working at the boundary between chemistry and engineering.
- Extend established methodologies to other commercially relevant polyesters, including PET and PEF, but also other polymer classes: polycarbonates, polyamides etc.
- Immobilize developed catalysts on a support to overcome industry concerns associated with catalyst recovery, a limiting feature of homogeneous catalysts. This will also assist in upscaling the established recycling technology.

Additionally, all novel catalysts prepared will also be investigated for their activity in the ROP of rac-LA in both solution and under industrially preferred melt conditions for PLA production and for polycarbonate formation (CO2/epoxide or anhydride/epoxide). Polymer of interest will be characterised using standard thermal/mechanical characterisation techniques.

Project strategy:
1. Preparation of scalable ligands, for example Schiff-Base.
2. Complexation to broad range of earth abundant metals e.g. Group (I), Group (II) and Zn.
3. Catalytic testing (batch and in flow).
4. Evaluate catalytic data to determine structural-activity relationships to understand catalytic upgrading processes through experimental and computational modelling.
5. Develop catalytic reactor to scale up the degradation and to prepare value-added products from waste materials.

References:
1. J. Payne, P. McKeown and M. D. Jones, Polym. Degrad. Stab., 2019, 165, 170-181.

The Centre for Doctoral Training (CDT) in Sustainable Chemical Technologies (SCT) at the University of Bath will place fundamental concepts of sustainability at the core of a broad spectrum of research and training at the interface of chemical science and engineering. It will train over 60 PhD students in 5 cohorts within four themes (Energy and Water, Renewable Resources and Biotechnology, Processes and Manufacturing and Healthcare Technologies) and its activities and graduates will have potential economic, environmental and social impact across a wide range of beneficiaries from academia, public sector and government, to industry, schools and the general public.

The primary impact of the CDT will be in providing a pool of highly skilled and talented graduates as tomorrow's leaders in industry, academia, and policy-making, who are committed to all aspects of sustainability. The economic need for such graduates is well-established and CDT graduates will enhance the economic competitiveness of the UK chemistry-using sector, which accounts for 6m jobs (RSC 2010), contributing £25b to the UK economy in 2010 (RSC 2013). The Industrial Biotechnology (IB) Innovation and Growth Team (2009) estimated the value of the IB market in 2025 between £4b and £12b, and CIKTN (BIS) found that "chemistry, chemical engineering and biology taken together underpin some £800b of activity in the UK economy".

UK industry will also gain through collaborative research and training proposed in the Centre. At this stage, the CDT has 24 partners including companies from across the chemistry- and biotechnology-using sectors. As well as direct involvement in collaborative CDT projects, the Centre will provide an excellent mechanism to engage with industrial and manufacturing partners via the industrial forum and the Summer Showcase, providing many opportunities to address economic, environmental and societal challenges, thereby achieving significant economic and environmental impact.

Many of the issues and topics covered by the centre (e.g., sustainable energy, renewable feedstocks, water, infection control) are of broad societal interest, providing excellent opportunities for engagement of a wide range of publics in broader technical and scientific aspects of sustainability. Social impact will be achieved through participation of Centre students and staff in science cafés, science fairs (Cheltenham Science Festival, British Science Festival, Royal Society Summer Science Exhibition) and other events (e.g., Famelab, I'm a Scientist Get Me Out of Here). Engagement with schools and schoolteachers will help stimulate the next generation of scientists and engineers through enthusing young minds in relevant topics such as biofuels, solar conversion, climate change and degradable plastics.

The activities of the CDT have potential to have impact on policy and to shape the future landscape of sustainable chemical technologies and manufacturing. The CDT will work with Bath's new Institute for Policy Research, through seminars, joint publication of policy briefs to shape and inform policy relevant to SCT. Internship opportunities with stakeholder partners and, for example, the Parliamentary Office of Science and Technology will provide further impact in this context.