Engineered bio- and heterogeneous catalysts for improved polymer circularity

人造塑料的滥用导致了生物圈中不可降解物质的积累。现在人们普遍认识到，这些塑料构成了严重的全球污染威胁，特别是在海洋生态系统中(Science 2010,329,1185-1188)。Science 2015,347,768-771)。因此，迫切需要新的催化战略来有效地解构这些人为污染物，以最大限度地减少和扭转其对环境的影响，并允许以环境可持续的方式回收有价值的原材料。在这个项目中，我们将结合多相催化、生物催化和化学工程生物和间歇反应器技术，开发集成和可扩展的催化工艺，以有效回收两种丰富的塑料-聚对苯二甲酸乙二醇酯(PET)和聚苯乙烯。PET是产量最大的合成聚合物之一(2014年全球产量约为4000万吨)，并以惊人的速度在环境中积累。微生物正开始通过进化其分解代谢途径来适应环境中PET的存在，现在已经表征了几种“PETase”酶，它们能够通过水解聚酯主干来降解PET(Science 2016,351,1196-1199)。不幸的是，PETase的热稳定性差，催化效率低，这阻碍了它们作为生物催化剂用于商业PET降解。这种低效率可能反映了最近出现的PETase对人为污染的反应，因为它们的催化功能并没有通过长期的自然进化而得到磨练。在过去的12个月里，我们的实验室开发了自动化的高通量定向进化工作流，以设计能够在不溶聚合物材料上操作的酶。我们利用这些工作流程设计了一种高效且耐热的PETase，从而朝着商业上可行的塑料垃圾生物降解迈进了一大步。有了这种工程生物催化剂，我们现在准备开发一种可扩展的PET回收工艺，这将在本专业的学生中进行探索。我们将制定优化的塑料前处理条件、工艺操作条件和回收单体积木的下游分离方案。随后将进行更多轮的酶进化，以开发一种定制的生物催化剂，专门用于商业PET回收的最佳条件下操作。CEAS最近的多相催化工作表明，一些纯聚烯烃原料(聚乙烯、聚丙烯和聚苯乙烯)及其混合物可以在较低的温度下成功地快速加氢裂解，产生主要的C3-C9烃(IND)。英语。化学。决议，58(45)，20601；EP专利2437886B1-2019年)。我们的目标是通过仔细优化多相催化剂(沸石上的贵金属和氧化铝上的镍钼)，使用间歇反应器调整时间、温度和氢气压力的操作参数(图1)，并通过动力学模拟实现聚苯乙烯(PS)的低温加氢裂解，乙苯的选择性超过90%。随后，我们将发现并设计生物催化剂，包括脱饱和酶和/或加氧酶与脱水酶相结合，用于乙苯的脱饱和生产苯乙烯作为进一步聚合的单体构建块，从而为循环塑料经济的发展做出重大贡献。该项目采用了一种创新的方法，将生物催化、多相催化和化学工程领域结合在一起，从而与ICAT网络的战略重点完全一致。

The misuse of manmade plastics has resulted in an accumulation of non-degradable materials in the biosphere. It is now widely recognized that these plastics pose a serious global pollution threat, especially in marine ecosystems (Science 2010, 329, 1185-1188. Science 2015, 347, 768-771). Consequently, there is a pressing demand for new catalytic strategies to efficiently deconstruct these anthropogenic contaminants to minimize and reverse their environmental impact and to allow valuable raw materials to be recovered in an environmentally sustainable manner. In this studentship we will develop integrated and scalable catalytic processes for the efficient recycling of two abundant plastics, poly(ethylene terephthalate) (PET) and polystyrene, using a combination of heterogeneous catalysis, biological catalysis and chemical engineering bio- and batch reactor technology. PET is one of the most abundantly produced synthetic polymers (ca. 40 million tonnes produced globally in 2014) and is accumulating in the environment at an alarming rate. Microbes are beginning to adapt to the presence of PET in the environment by evolving catabolic pathways its deconstruction, and several 'PETase' enzymes have now been characterized that are able to degrade PET through hydrolysis of the polyester backbone (Science 2016, 351, 1196-1199.) Unfortunately PETases suffer from poor thermostability and low catalytic efficiency which preclude their use as biocatalysts for commercial PET degradation. This low efficiency likely reflects the recent emergence of PETases in response to anthropogenic contaminants, as their catalytic functions have not been honed through prolonged periods of Natural evolution. Over the past 12 months, our lab has developed automated high-throughput directed evolution workflows to engineer enzymes that are able to operate on insoluble polymeric materials. We have exploited these workflows to engineer a highly efficient and thermostable PETase, thus taking strides towards commercially viable biodegradation of plastic waste. Armed with this engineered biocatalyst, we are now poised to develop a scalable process for PET recycling which will be explored within this studentship. We will develop optimized plastic pre-treatment conditions, process operating conditions and protocols for downstream isolation of recycled monomeric building blocks. Further rounds of enzyme evolution will subsequently be performed to develop a bespoke biocatalyst specialised to operate under the optimal conditions for commercial PET recycling.Recent heterogeneous catalysis work in CEAS has demonstrated that a number of pure polyolefin feedstocks (polyethylene, polypropylene and polystyrene) and blends of these three can be successfully hydrocracked rapidly at much reduced temperatures yielding a predominantly C3 - C9 hydrocarbons (Ind. Eng. Chem. Res., 58 (45), 20601; EP Patent 2437886B1 -2019). We aim through careful optimisation of the heterogeneous catalysts (noble metal on zeolites and NiMo on alumina), adjustment of the operating parameters of time, temperature and H2 pressure using batch reactors (Figure 1), and, through kinetic modelling to achieve low temperature hydrocracking of polystyrene (PS) with over 90% selectivity to ethyl benzene. We will subsequently discover and engineer biocatalysts, including desaturases and/or oxygenases in combination with dehydratases, for the desaturation of ethyl benzene to produce styrene as a monomeric building block for further polymerizations, thus making a significant contribution to the development of a circular plastics economy.The project takes an innovative approach to merge the fields of biocatalysis, heterogeneous catalysis and chemical engineering and thus is perfectly aligned to the strategic priorities of the iCAT network.