From Plastics to Rings and Back Again: Catalytic Recycling of Waste Oxygenated Plastics

从塑料到环再返回：废氧化塑料的催化回收

• 批准号: 2581224
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2581224
• 关键词: Plastics; Rings; Back; Again; Catalytic

Despite the exponential increase in plastic usage in the past century, little attention has been paid to dealing with the huge amount of plastic left at the end of life. A solution to the growing plastic waste is desperately needed. The majority of plastics are derived from petrochemicals and whilst mechanical recycling is well developed, it is typically associated with high energy costs and material degradation. Chemical recycling has the potential to create a circular plastic economy as the original starting materials can be recovered under mild conditions, allowing for their reincorporation into new plastics and avoiding the need for new raw materials.Plastics are made up from long, chain-like molecules called polymers. These in turn are built up from a series of monomers. The order in which the monomers are connected, how they are connected and the individual structure of each monomer determines the properties of the polymer and which types of plastic they are used for. Chemical recycling breaks down the polymers in the plastic to their starting monomers which can then be reused.Chemical recycling faces many challenges. Many commercial plastics are incompatible with chemical recycling due to their chemical make-up and therefore alternative plastics which can be chemically recycled are needed to replace these. Polymers which contain oxygen linkers, such as polycarbonates, are particularly promising as they can be broken down much more readily. Polycarbonates can be produced by combining carbon dioxide with an epoxide. Epoxides are three-membered rings which contain an oxygen atom. Altering the epoxide used affects the properties of the resulting polycarbonate. Whilst previous research has shown that various polycarbonates can be broken down to recover the starting epoxide, the selectivity towards these starting epoxides is a major issue as a cyclic carbonate product is often formed instead. Catalysts are key tools in overcoming this challenge as they can help to favour the epoxide formation as well as speed up the decomposition reaction. Although the catalysed decomposition of several different polycarbonates to their starting epoxides has been successfully demonstrated, for polycarbonates to be adopted on an industrial scale their properties must be competitive with current commercial polymers. Poly(cyclohexene carbonate) (PCHC) and poly(propylene carbonate) (PPC) are two types of polycarbonate which have the greatest potential to replace current commercial polymers. Unfortunately the chemical recycling of these polycarbonates has proven more difficult due to selectivity issues. Recent work by the Williams group has developed a new and highly effective catalyst to chemically recycle PCHC to its epoxide1 but the chemical recycling of PPC remains a challenge.This project aims to develop catalysts for the chemical recycling of PPC back to its starting epoxide. Using PCHC as a case study, this project will investigate the mechanism behind the catalysed decomposition of polycarbonates and how changing the shape and structure of the polycarbonate affect its rate of decomposition. This information will be used to inform future catalyst and polymer designs. In addition, the chemical recycling of other types of oxygenated polymers, specifically poly(esters-alt-ethers), will be explored.The ultimate goal is to develop effective methods of chemically recycling polymers to enable a sustainable circular plastic economy. This project falls within the EPSCR 'Manufacturing the Future' research area.

尽管在过去的一个世纪里，塑料的使用量呈指数级增长，但很少有人注意到如何处理在使用寿命结束时留下的大量塑料。我们迫切需要一个解决日益增长的塑料垃圾的办法。大多数塑料来自石化产品，虽然机械回收很发达，但它通常与高能源成本和材料降解有关。化学回收有可能创造一个循环塑料经济，因为原始的起始材料可以在温和的条件下回收，允许它们重新组合成新的塑料，避免需要新的原材料。塑料是由被称为聚合物的长链状分子构成的。它们依次由一系列单体构成。单体连接的顺序、连接方式以及单体的单独结构决定了聚合物的性质以及它们用于何种塑料。化学回收将塑料中的聚合物分解为可重复使用的初始单体。化学品回收面临许多挑战。许多商业塑料由于其化学成分而与化学回收不相容，因此需要可以化学回收的替代塑料来取代它们。含有氧连接剂的聚合物，如聚碳酸酯，特别有前途，因为它们更容易被分解。聚碳酸酯可由二氧化碳与环氧化物化合而成。环氧化物是含有一个氧原子的三元环。改变所使用的环氧化物会影响所得聚碳酸酯的性能。虽然先前的研究表明，各种聚碳酸酯可以分解以回收起始环氧化物，但对这些起始环氧化物的选择性是一个主要问题，因为通常会形成环状碳酸盐产物。催化剂是克服这一挑战的关键工具，因为它们可以帮助促进环氧化物的形成，并加快分解反应。虽然已经成功地证明了几种不同的聚碳酸酯催化分解为其起始环氧化物，但为了使聚碳酸酯在工业规模上被采用，它们的性能必须与目前的商业聚合物具有竞争力。聚碳酸环己烯（PCHC）和聚碳酸丙烯（PPC）是两种最有潜力取代现有商用聚合物的聚碳酸酯。不幸的是，由于选择性问题，这些聚碳酸酯的化学回收被证明更加困难。Williams小组最近的工作开发了一种新的高效催化剂，可以将PCHC化学回收为环氧化物，但化学回收PPC仍然是一个挑战。该项目旨在开发用于PPC化学回收的催化剂，以返回其起始环氧化物。本项目将以PCHC为例，研究聚碳酸酯催化分解的机理，以及改变聚碳酸酯的形状和结构如何影响其分解速度。这些信息将用于未来催化剂和聚合物的设计。此外，化学回收其他类型的含氧聚合物，特别是聚（酯-alt-醚），将探讨。最终目标是开发化学回收聚合物的有效方法，以实现可持续的循环塑料经济。该项目属于EPSCR“制造未来”研究领域。