Thermally Responsive Supports for Enhanced Efficiency in PET Depolymerisation

迫切需要设计回收塑料的工艺，仅2019年全球估计就有4.6亿公吨塑料被利用，其中只有10%被全球回收，其余的被焚烧、填埋或出口。燃烧聚合物会产生二氧化碳，导致全球变暖，河流和海洋的污染是通过对环境的丢弃而发生的。目前的机械和热回收技术可用于生产较低等级的产品，如服装、绝缘材料、花园和道路家具，但与原始聚合物相比，这些产品的颜色或机械性能较差，需要进行化学回收来生产原始单体。在这项提案中选择研究的主要聚合物是PET，它在瓶子、包装和服装中具有广泛的工业和消费应用。在美国，目前30%的聚酯被回收，在欧盟，这一数字为52%，而世界对聚酯树脂的需求约为2350万吨，生产能力约为3030万吨，这可能是一个巨大的回收原料。与价格为GB 222.50/吨的旧聚酯瓶相比，原始聚酯树脂的价格为GB 1084/吨，这使得化学回收生产原始聚合物比机械或热回收更具经济吸引力。PET的化学循环可以遵循许多路线，包括与醇、乙二醇、胺和氨的反应，有时由碳酸氢钠等基本材料催化，或最近开发的离子有机催化剂或金属盐/有机碱双重催化剂。然而，催化剂从产品混合物中分离和有效回收的困难阻碍了工业化生产的潜在规模扩大。此外，还需要从可能包含来自聚合物的污染物的混合物中分离和提纯产品BHET，包括染料和添加剂。这项提议旨在通过开发支撑型催化剂和分离技术来创造解决这些问题的方案，以实现放大的PET解聚过程，这可能会在工业上部署。催化剂载体将以热响应性聚合物为基础开发，这种聚合物可以溶解以接触反应混合物，或通过简单的温度循环进行固化，以帮助过滤回收。关键的考虑因素将包括了解系统的反应动力学，包括任何质量传输阻力，以及优化反应条件以获得吸引人的反应速度。我们将对聚合物结构进行实验，以找到最佳的催化剂/载体组合。除了通过温度循环回收催化剂外，我们还将研究通过膜分离回收BHET产品。战略将包括测试商业膜和开发含有沸石的混合基质膜以增强渗透流动。拟议的技术将为化学品回收提供更具吸引力和商业可行性的解决方案。为了实现这项研究的好处，我们聘请了回收和聚合物生产行业的项目合作伙伴，包括杜邦帝人薄膜公司和西门子PSE，以及学术合作者宾夕法尼亚州立大学。他们将提供解聚样品或就解聚提供建议，提供软件，就工作计划提供技术咨询，进入设施，并就其支持函中概述的商业化和影响交付的路线提供建议。

There is an urgent need to devise processes for recycling plastics, with an estimated 460 million metric tonnes of plastics being utilised worldwide in 2019 alone, of which only 10% is recycled globally, the remainder going to incineration, landfill or export. Burning of polymers contribute to CO2 production, causing global warming, and pollution of rivers and oceans occurs through discarding to the environment. Current mechanical and thermal recycling techniques can be used to produce lower grade products such as clothing, insulation, garden and road furniture, but these have inferior colour or mechanical properties, in comparison to virgin polymer, necessitating chemical recycling to produce virgin monomer. The principal polymer selected for study in this proposal is PET, with its wide industrial and consumer applications in bottles, packaging and clothing. In the USA 30 % of PET is currently recycled, in the EU the figure is 52 %, whilst world demand for PET resin is ~23.5 million tonnes and production capacity ~30.3 million tonnes, making a potentially large feedstock for recycling. Virgin PET resin has a much higher value at £1084/tonne compared with used PET bottles priced at £222.50/tonne, making chemical recycling to produce the virgin polymer the more economically attractive route than mechanical or thermal recycling. Chemical recycling of PET can follow a number of routes including reaction with alcohols, glycols, amines and ammonia, sometimes catalysed by basic materials like sodium bicarbonate, or more recently developed ionic organocatalysts or metal salt/organic base dual catalysts. However potential scale up for industrial production is hampered by the difficulties of separating the catalyst from the product mixture and efficient recycling. Also, there is a need to isolate and purify the product BHET from a mixture which may contain contaminants from the polymer, including dyes and additives. This proposal aims to create solutions to these problems by developing supported catalysts and separation technologies to enable a scaled-up process for PET depolymerisation, which could potentially be deployed industrially. Catalyst supports will be developed based on thermally responsive polymers, which can be solubilised to contact the reacting mixture, or solidified via simple temperature cycling to aid recovery by filtration. Key considerations will include understanding the reaction kinetics of the system, including any mass transport resistances, and optimisation of reaction conditions to achieve an attractive rate of reaction. We will experiment with polymer structures to find the optimal catalyst/support combination. In addition to catalyst recovery by temperature cycling, we will study recovery of BHET product via membrane separation. Strategies will include testing of commercial membranes and development of mixed matrix membranes incorporating zeolites to enhance the permeate flow. The proposed technologies will provide more attractive and commercially viable solutions for chemical recycling. In order to realise the benefits of the research, we have engaged Project Partners from across the recycling and polymer production sectors including Dupont Teijin Films and Siemens PSE, and academic collaborator Pennsylvania State University. They will provide, or advise on, samples for depolymerisation, provide software, technical consultation on the work plan, access to facilities and advise on routes to commercialisation and impact delivery as outlined in their letters of support.