Thermally Responsive Supports for Enhanced Efficiency in PET Depolymerisation

目前迫切需要设计回收塑料的工艺，仅在2019年，全球估计就使用了4.6亿公吨塑料，其中只有10%在全球范围内回收，其余的将被焚烧，填埋或出口。燃烧聚合物会产生二氧化碳，导致全球变暖，并通过向环境中丢弃而污染河流和海洋。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、花园和道路设施，但与原始聚合物相比，这些产品的颜色或机械性能较差，因此需要进行化学回收以生产原始单体。在本提案中选择用于研究的主要聚合物是PET，其在瓶子、包装和服装中具有广泛的工业和消费应用。在美国，目前有30%的PET被回收，在欧盟，这一数字为52%，而全球对PET树脂的需求量约为2350万吨，生产能力约为3030万吨，这是一种潜在的大型回收原料。与价格为222.50英镑/吨的旧PET瓶相比，原生PET树脂的价值高得多，为1084英镑/吨，这使得化学回收生产原生聚合物比机械或热回收更经济。PET的化学回收可以遵循许多途径，包括与醇、二醇、胺和氨的反应，有时通过碱性材料如碳酸氢钠或最近开发的离子有机催化剂或金属盐/有机碱双催化剂催化。然而，从产物混合物中分离催化剂和有效再循环的困难阻碍了工业生产的潜在规模扩大。此外，需要从可能含有来自聚合物的污染物（包括染料和添加剂）的混合物中分离和纯化产物BHET。该提案旨在通过开发负载型催化剂和分离技术来解决这些问题，以实现PET解聚的规模化工艺，这可能会在工业上得到应用。将基于热响应聚合物开发催化剂载体，热响应聚合物可以溶解以接触反应混合物，或者通过简单的温度循环固化以帮助通过过滤回收。关键考虑因素将包括理解系统的反应动力学，包括任何传质阻力，以及优化反应条件以实现有吸引力的反应速率。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混合基质膜纳入沸石，以提高渗透流量。拟议的技术将为化学品回收提供更具吸引力和商业可行的解决方案。为了实现研究的好处，我们聘请了来自回收和聚合物生产部门的项目合作伙伴，包括杜邦帝人电影公司和西门子PSE，以及学术合作伙伴宾夕法尼亚州立大学。他们将提供或建议解聚样品，提供软件，工作计划的技术咨询，设施的使用，并就支持信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.