Engineering of Plastic Degrading Enzymes

The misuse of manmade plastics has resulted in an accumulation of non-degradable materials in the biosphere. It is now widely recognized that these plastics pose a serious global pollution threat, especially in marine ecosystems (Science 2010, 329, 1185-1188. Science 2015, 347, 768-771). Consequently, there is a pressing demand for new catalytic strategies to efficiently deconstruct these anthropogenic contaminants to minimize and reverse their environmental impact and to allow valuable raw materials to be recovered in an environmentally sustainable manner. In this studentship we will develop integrated and scalable catalytic processes for the efficient recycling of single polymer feedstock of PVC and complex laminated products, such as blister packs. In 2018, PVC made up about 10% of the polymer resin demand and over 12,000 tonnes of blister pack packaging were shipped into the UK for use in medicine delivery and toothbrush packaging.
This project aims to address the recycling difficulties associated with PVC and the separation problems associated with mixed composite materials. PVC is problematic as it is readily unzips to yield HCl between 250-400oC producing a highly unsaturated C rich "poly-ene" with low levels of organo-chlorine (0.1%) remaining, problematic for on-processing. The efficiency of Cl removal is further reduced by the use of additives in the packaging, such as dioctylphthalate (Energy & Fuels 2003, 17, 896).
Ionic liquids have the capability of dissolving a wide range of materials and we will examine the potential to selectively solubilise the component parts of problematic polymers to allow the downstream processing to value added products more tractable. This will involve the synthesis of ionic liquids which will allow the breakdown of binders as well as potentially reduce the molecular mass of the polymer materials. The development and optimisation of low temperature dehydrochlorination of PVC using ionic liquids, will facilitate the potential recycling of PVC by addition to hydrogen-rich polyolefin mixed polymer streams using slurry and spinning basket reactors, (Garforth, Patent EP 2437886 -2019).
Enzymatic deconstruction of unsaturated C rich "poly-ene". Our lab has recently developed automated high-throughput directed evolution workflows to engineer enzymes that efficiently deconstruct plastics with hydrolysable backbones (e.g. PET, unpublished data). These workflows will now be extended to discover and engineer enzymes that efficiently operate on the C-rich poly-ene fraction generated following the dehydrochlorination of PVC. Several families of oxidative enzymes have been discovered which are active towards varying hydrocarbon chain lengths (Sci. Rep. 2014, 4968), which serve as attractive starting points for enzyme engineering to afford commercially viable biocatalysts for PVC deconstruction to allow valuable raw materials to be recovered in an environmentally sustainable fashion.
Hydrocracking of unsaturated C rich "poly-ene" comingled with PP initially will be studied under hydrotreating and hydrocracking conditions using a batch reactor. Heterogeneous catalysts established in our lab based on noble metals (Pt, Pd and Ni), or bimetallic sulphides, such as, Co/MoS or Ni/MoS with the acidic supports being alumina or zeolites (Garforth). Traditional ion exchange and impregnation techniques will be supplemented with aerosol-assisted chemical vapour deposition (AACVD) where a single source precursor has been used to produce a range of thin film Mo1-xWxS2 (0<-x<-1) alloys. This inexpensive ambient pressure CVD technique will be extended to Co and Ni. As noted above, the presence of halides, for example in PVC transformations, have the potential to poison the catalysts and this will be examined in detail.
The project takes a truly innovative approach to merge the fields of biocatalysis, ionic liquids and heterogeneous bifunctional catalysis, and thus is perfectly aligned to iCAT's priorities.

iCAT will work with industry partners to create an holistic approach to the training of students in biocatalysis, chemocatalysis, and their process integration. Traditional graduate training typically focuses on one aspect of catalysis and this approach can severely restrict innovation and impact. Advances in technology and fundamental reaction discovery are rendering this silo-approach obsolete, and a new training modality is needed to produce the next generation of chemists and engineers who can operate across a far broader chemical continuum. iCAT will meet this challenge with a state-of-the-art CDT, equipping the next generation of scientists and engineers with the skills needed to develop future catalytic processes and create the functional molecules of tomorrow.

The UK has one of the world's top-performing chemical industries, achieving outstanding levels of growth, exports, productivity and international investment. The UK's chemical industry is a significant provider of jobs and creator of wealth, with a turnover in excess of £50 billion and a contribution of over £15 Billion of value to the UK economy [2015 figures]. iCAT will deliver highly skilled people to lead this industry across its various sectors, achieving impact through the following actions:

1. Equip the next generation of science and engineering leaders with the interdisciplinary skills and knowledge needed to work across the bio and chemo catalytic remit and build the functional molecules we need to structure society.

2. Provide a highly skilled workforce and research base, skilled in the latest methodologies, strategies and techniques of catalysis and engineering that is crucial for the UK's Chemical Industry.

3. Build the critical mass necessary to support effective cohort-based training in a world-class research environment.

4. Develop and disseminate new catalytic technologies and processes that will be taken up by industrial and academic teams around the world.

5. Encourage Industry to promote research challenges within the CDT that are of core relevance to their business.

6. Provide cohesion in the integration of biocatalysis, engineering and chemocatalysis to create a more unified voice for strategic dialogue with industry, funders and policy makers, and more generally outreach and public engagement.

7. Draw-in and bring together Industrial partners to facilitate future Industrial collaborations.

8. Benefit Industrial scientists through interactions with the CDT (e.g. training and supervisory experience, exposure to cutting-edge synthesis and catalysis etc).

9. Link with other activities in the landscape: bringing unique expertise in catalysis to, for example, externally-funded University-led initiatives, EPRSC Grand Challenge Networks, and the National Catalysis Hub.