Upcycling Waste Polyethylene into Nylon Precursors and Platform Chemicals via A Hybrid Pyrolysis-Biomanufacturing Approach

聚乙烯（PE）是最常用的塑料之一，主要用于塑料袋、容器、瓶子和玩具。目前，PE的年产量超过1亿吨，占塑料市场总量的34%。不幸的是，大多数PE产品是一次性的，被丢弃在垃圾填埋场，废弃PE占塑料废物流的50%以上。预计每年12%的PE产量增长率，加上缺乏有效的回收方案，使PE成为一个主要的环境问题。为了回收或升级利用废弃PE，人们探索了机械破坏、热化学处理和生化转化等方法，但这些方法最终都会导致产品质量低、转化为增值产品的效率低、加工成本高。现有的PE回收或升级回收方法都不可能单独为循环塑料经济做出贡献。本项目的目的是探索一种两步混合氧化催化热解-生化方法，将废弃PE升级为具有更高价值的化工产品。这一概念利用了热化学（氧化催化热解）和生物化学（生物制造）方法对塑料升级回收的好处。该技术将减少废塑料的处理，减轻其对环境的负面影响。由于UML是马萨诸塞州的少数民族服务机构（MSI）之一，项目团队将从该州服务不足的社区中招募未被充分代表的群体的学生来进行研究。UML的生物制造中心和自闭症研究与教育中心也将分别计划针对当地高中和学习障碍学生从事STEM职业的外展活动。提出了一种新的混合工艺，将废聚乙烯（PE）升级为一系列增值产品。该混合工艺的第一步包括一个氧化热解反应器，将PE在多孔载体上的氧化还原金属氧化物或混合氧化物催化剂上分解成C5-C20烷烃、醇、醛和羧酸。与催化剂表面反应途径相关的基本化学动力学，以及孔隙中物质扩散的影响，将被量化。氧化热解之后是生物制造步骤，使用工程酵母脂解耶氏酵母生产增值平台化学品，如长链二酸（LCDAs）作为尼龙前体，三乙酸内酯（TAL）和间苯三酚（PG），用于广泛的工业应用。研究小组将确定导致各种产品高产的代谢途径，并将利用反应工程原理克服生物反应器的传质限制。该项目的成功将为一个新的范例铺平道路，使未来制造广泛的战略平台化学品，特别是来自ω -氧化，β -氧化和相关代谢途径的分子，不仅可以使废弃PE，还可以使其他类似的废弃聚烯烃（如聚丙烯（PP）和聚苯乙烯（PS））更加节能，经济和强大的增值。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Polyethylene (PE) is one of the most commonly produced plastics, primarily used for plastic bags, containers, bottles, and toys. Currently, over 100 million tons of PE are produced annually, accounting for 34% of the total plastics market. Unfortunately, most PE products are single-use and discarded in landfills, and waste PE contributes to over 50% of the plastics waste stream. The projected 12% annual PE production rate growth combined with the lack of effective recycling options make PE a major environmental concern. To recycle or upcycle waste PE, mechanical disruption, thermochemical treatment, and biochemical conversion processes have been explored, but these methods all ultimately result in low product qualities, inefficient conversion rates to value-added products, and high processing costs. None of the existing PE recycling or upcycling methods alone will likely contribute to a circular plastics economy. The objective of this project is to explore a two-step hybrid oxidative catalytic pyrolysis–biochemical approach to upcycle waste PE into chemical products with significantly higher values. This concept takes advantage of the benefits of both thermochemical (oxidative catalytic pyrolysis) and biochemical (biomanufacturing) methods for plastics upcycling. The proposed technology will lead to reduced waste plastics disposal, mitigating its negative environmental impacts. As UML being one of the Minority Serving Institutions (MSI) in Massachusetts, the project team will recruit students from underrepresented groups from underserved communities of the state to conduct research. Outreach events targeting local high schools and learning-disabled students pursing STEM careers will also be planned via UML’s Biomanufacturing Center and Center for Autism Research and Education, respectively. A novel hybrid process is proposed to upcycle waste polyethylene (PE) into a series of value-added products. The first step of the proposed hybrid process consists of an oxidative pyrolysis reactor to decompose PE over redox metal oxide or mixed oxide catalysts on porous supports into C5–C20 alkanes, alcohols, aldehydes, and carboxylic acids. The fundamental chemical kinetics associated with reaction pathways on the catalyst surfaces, as well as the effects of species diffusion in the pores, will be quantified. Oxidative pyrolysis will be followed by a biomanufacturing step using an engineered yeast Yarrowia lipolytica to produce value-added platform chemicals such as long-chain diacids (LCDAs) as nylon precursors and triacetic acid lactone (TAL) and phloroglucinol (PG) for a wide spectrum of industrial applications. The research team will identify metabolic pathways leading to high yields of various products and will use reaction engineering principles to overcome mass transfer limitations in bioreactors. The success of this project will pave the way to a new paradigm, enabling future manufacturing of a wide range of strategic platform chemicals, particularly the molecules derived from the omega-oxidation, beta-oxidation, and related metabolic pathways, leading to more energy efficient, economical, and robust valorization of not only waste PE but also other similar waste polyolefins, such as polypropylene (PP) and polystyrene (PS).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.