A Scalable Process for the Chemical Recycling of PET using Ionic Organocatalysts

目前迫切需要设计回收塑料的工艺，据估计，迄今为止，全球共生产了83亿吨塑料，其中只有不到10%被回收利用。聚合物的最终命运可能包括填埋，燃烧，导致二氧化碳的产生，全球变暖，以及丢弃到包括河流和海洋在内的环境中。在回收的材料中，机械或热回收技术通常会产生较低等级的聚合物，可用于诸如服装，绝缘材料，花园和道路家具等应用，并且与原始聚合物相比，其性能（例如颜色和机械规格）和价值也较差。本提案选择PET作为解聚研究的主要聚合物，因为它被广泛使用，典型应用于服装，瓶子和包装。世界对PET树脂的需求量约为2350万吨，生产能力约为3030万吨，而目前只有30%（美国）- 52%（欧盟）被回收利用。然而，用过的PET瓶的价格为222.50英镑/吨，而原始PET树脂的价格为1084英镑/吨，这就为化学回收生产原始聚合物提供了强有力的经济理由，而不是机械或热回收生产较低等级的产品。PET的化学回收可以通过醇解、氨解、氨解和糖酵解等方法来实现，包括通过离子有机催化剂等催化方法。目前可用的回收方法（如糖酵解）的一些缺点包括从产品中分离和消除催化剂残留物和染料等污染物，难以从反应混合物中分离出项目BHET，以防其在真空蒸馏过程中再聚合，并且需要高纯度的PET饲料来制造高质量的回收产品。本提案旨在通过开发一种可扩展的、连续的PET解聚过程来解决这些缺点。特别是，我们的目标是研究实际废物中聚合物添加剂和食品污染物对解聚的影响，以了解催化剂/过程如何能够适应这些问题。关键的考虑因素将是充分了解反应动力学，使催化剂固定化，使其能够回收利用，并制定产品回收策略。拟议的技术有望带来潜在的好处，包括减少对化石衍生原生塑料的依赖，增加化学回收聚合物市场的潜力，以及提供可扩展的工艺。我们已经与来自回收、聚合物生产和学术领域的项目合作伙伴合作，包括苏伊士、Avantium、杜邦帝人电影、过程系统企业和利物浦大学。他们将提供解聚样品或提供建议，催化剂支持，就工作计划提供技术咨询，并就其支持信中概述的商业化路线和影响交付提供建议。

There is an urgent need to devise processes for recycling plastics, with an estimated total of 8300 million metric tonnes of plastics produced to date, of which less than 10% have been recycled overall. The end fate of polymers can include landfill, burning which contributes to CO2 production, global warming, and discarding into the environment, including rivers and oceans. Of the materials which are recycled, mechanical or thermal recycling techniques typically produce a lower grade of polymer which can be used in applications such as clothing, insulation, garden and road furniture for example, and also has inferior properties (e.g. colour and mechanical specification) and value compared with virgin polymers. PET is selected as the principal polymer for depolymerisation studies in this proposal, owing to it being widely used, with typical applications in clothing, bottles and packaging. The world demand for PET resin is ~23.5 million tonnes and production capacity ~30.3 million tonnes, whilst only 30 % (US) - 52 %(EU) is currently recycled. However used PET bottles are priced £222.50/tonne whilst virgin PET resin is priced £1084/tonne, making a strong economic case for chemical recycling to produce the virgin polymer, rather than mechanical or thermal recycling to a lower grade product. Chemical recycling of PET can be achieved via methods such as alcoholysis, aminolysis, ammonolysis and glycolysis, including via catalytic methods such as ionic organocatalysts. Some drawbacks of currently available recycling methods such as glycolysis involve the separation and eradication of contaminants such as catalyst residue and dyes from the product, difficulty of separating the project BHET from the reaction mixture in case it repolymerises during vacuum distillation and requirement for high purity PET feed to make high grade recycled products.This proposal aims to address these drawbacks by developing a scalable, continuous process for PET depolymerisation. In particular we aim to study the effect of polymer additives and food contaminants in real wastes upon the depolymerisation, to understand how the catalyst/process can be made resilient to these issues. Key considerations will be to fully understand reaction kinetics, enabling catalyst immobilisation to enable recycling of it and developing strategies for product recovery. The proposed technologies are expected to deliver potential benefits including reduced reliance on fossil derived virgin plastics, potential to increase the market for chemically recycled polymers, and deliver of a scalable process. We have engaged Project Partners from across the recycling, polymer production and academic sectors including Suez, Avantium, Dupont Teijin Films, Process Systems Enterprise and University of Liverpool. They will provide or advise on samples for depolymerisation, catalyst supports, provide technical consultation on the work plan and advise on routes to commercialisation and impact delivery as outlined in their letters of support.