Novel Membrane Catalytic Reactor for Waste Polylactic Acid Recycling and Valorisation

The disposal of plastic packaging represents a significant environmental problem; although recycling of plastics has increased in recent years, current recycling methods are mainly mechanical or chemical techniques that result in lower grade second life products and much material is also still disposed of to landfill. The introduction of plastics produced from biological sources such as plant derived sugars has potential to reduce reliance on fossil derived sources and decrease emissions of greenhouse gases associated with manufacture. Polylactide has emerged as one of the most promising biorenewable and biodegradable polymers which has uses in packaging, textile and biomedical applications. However the lack of a reliable method for recycling polylactide could limit its widespread application and market growth. A significant opportunity therefore exists to develop a process to depolymerise/degrade commodity PLA to produce value-added small molecules, such as lactate esters, via routes which have not previously been developed. Such molecules could be recycled to make new PLA or other value added chemicals, including solvents, fragrances and plasticizers.
We propose to address the above problems by developing a catalytic process for degradation/depolymerisation of PLA, integrated with a membrane separation to selectively isolate small molecule products within a specified molecular weight cut off range, as valuable products. Firstly the catalytic part of the process will be developed, building on previous work by Jones on salalen homogeneous catalysts, and including a work plan to select and design the best metal-support combinations to achieve a high conversion of PLA. Secondly, commercial membranes will be screened for the separation of product molecules, which will provide the necessary data to enable design and fabrication of bespoke membranes for a particular molecular weight cut off. We then aim to coat catalysts on to the membranes, so as to avoid the potential difficulties of working with, separating and reusing slurry catalysts. The tested catalyst and membrane designs will then be scaled up. A larger scale (1 litre) reactor will be constructed for carrying out crossflow membrane tests. The results of the studies will be used to develop kinetic models of the reaction and diffusion models for the membrane pore structure. A programme of activities for delivery of impact to the academic and industrial communities and the general public has been devised.
The work is expected to deliver new catalysts, supports and membrane designs and performance data. Laboratory scale up data will be used to determine how well these techniques work together and to deliver a process design that could be deployed to take the technology in to industrial production.
The proposed technologies are expected to deliver a number of potential benefits including reduced reliance on fossil derived plastics, potential to increase the market for bio-derived polymers, the production of value added chemicals such as ethyl lactate, novel catalyst and membrane designs, UK held intellectual property and patents.

This three year programme is designed to have a significant impact to all, through producing a new world leading process for the degradation/depolymerisation of PLA - that can be used to produce value added feedstocks which can be recycled to make new polymers. This should enable a superior pathway for recycling of plastics and packaging rather than landfilling or processing to lower quality 'second life' products. The main beneficiaries will be:
(1) PEOPLE AND SOCIETY: Polymers derived from plant based sugars and subsequently recycled via depolymerisation could replace a number of petrochemical derived substances, leading to reduced environmental impact (giving a better environment for all) and lower reliance on fossil fuels. They have the advantage of being near carbon neutral (carbon dioxide released during use is offset by consumption during plant growth). Further research, such as in this project, is needed to develop catalysts and processes that can make bio derived polymers economically competitive with fossil fuel derived chemicals.
(2) COMPANIES AND MANUFACTURERS: A number of UK (and international) companies are expected to benefit from this research, leading to enhanced wealth creation, as well as company and job creation. Primary engagement with most companies will be through publications, press releases and conference/workshop presentations. The companies include:
a. Catalyst manufacturers. This project will provide these companies to more effective and efficient catalysts for degradation.
b. Reactor, membrane reactor and membrane manufacturers: The new membrane reactor technology and membrane materials will enable new manufactures to be created or will become new product lines for existing manufacturers.
c. Chemical manufacturers and suppliers: The process developed will provide a superior way of producing value added molecules such as lactate esters (initial value to Natureworks).
d. Biofeedstock suppliers (including waste dealers): This project will provide a new market, opening a new pathway for the utilisation of further renewable bioresources, which will be of use to companies producing bio-based polymers, e.g Natureworks.
(3) KNOWLEDGE AND SCIENTIFIC ADVANCES: This research programme will initiate and develop new research skills and a novel research at the interface of chemical and process engineering, chemistry, materials science and environmental engineering. The depolymerisation of plastics as a replacement to the currently non-renewable fossil fuel derivatives is an internationally important research area of wide interest and applicability. This grant will provide the platform to develop and applying new research skills and novel techniques, both experimental and computational in this area. These are interdisciplinary research skills that will enable the researchers we train to work from the level of molecular science up to the applied engineering level. These skills are transferable and will be used as the basis of building and extending further innovative research on other renewable chemical feedstocks.
IP and technology transfer will occur through the appropriate offices of the three partner universities, using a collaboration agreement between all partners prior to project start.
(4) SKILLS, RESEARCH CAPABILITY AND PEOPLE PIPELINE: The project will deliver two research fellows, who will be highly trained in a wide range of skills associated with biofeedstock processing, characterisation and assessment. They will provide the foundation for the development of further work in this area, creating a platform for this project team to be leaders in this area into the foreseeable future.