EFRI E3P: Nonthermal Plasma-Assisted Hydrogenolysis of Waste Plastics to Value-added Chemicals and Fuels

由于缺乏商业上可行的回收技术，难以回收的塑料废物在垃圾填埋场和环境中积累，严重恶化了陆地和水生生态系统。该项目将研究一种称为非热等离子体辅助氢解的方法，作为回收塑料废物混合物的潜在方法。非热等离子体辅助氢解为解聚混合塑料（即聚合物）和生成增值小分子（如单体、C2-C3烯烃和液体石蜡）提供了低能途径，这些小分子可作为化学原料和运输燃料。非热等离子体将提供两个关键功能：(i)引导电能来激活聚合物断键过程；（ii）作为电解质将聚合物碎片电化学转化为所需的小分子。该项目整合了来自阿克伦大学和劳伦斯伯克利国家实验室的研究人员的专业知识，其目标是：(1)开发电催化的转型概念，使用聚合物中的氢/碳氢化合物等离子体作为气态电解质；(2)将这一新概念与传统催化相结合，以实现快速和选择性地将聚合物废物转化为所需的化学品。非热等离子体辅助氢解概念的成功演示将为推进气体电解质电催化和等离子体反应工程的科学前沿建立所需的知识基础。建议的技术可以进一步应用于消费产品和集约化畜牧业产生的有机农业废物的升级循环。塑料废物的非热等离子体辅助氢解在关闭塑料碳循环的循环中具有潜在的变革性作用。该项目的目的是研究一种非热等离子体辅助催化方法，用于选择性地将混合塑料（即聚合物）转化为单体和小分子。非热等离子体放电，即介质阻挡放电产生的电电离气态物质，引发C-H和C-C聚合物键的断裂，在气相产生聚合物碎片及其自由基和离子。塑料垃圾中的无机污染物不能汽化，以固体颗粒的形式沉淀。然后，聚合物碎片吸附在催化剂表面，在环境温度和压力下选择性地转化为所需的小分子。离子可以作为电解质，使吸附的物质在电催化剂表面转化，这一过程控制了反应的速率和选择性。常温电催化有几个吸引人的特点：(1)减少对热能的需求；(2)减少副反应（特别是焦油的形成）；(3)提高对所需产物的选择性。通过综合动力学研究、反应性吸附中间体的操作红外光谱研究、催化剂和吸附聚合物碎片结构的原位x射线吸收研究、催化剂表征、催化剂的合理设计以及中试反应器的测试，将实现对非热等离子体辅助催化氢解聚合物废物的机理理解。这项研究的结果将推动非热等离子体辅助氢解作为聚合物废物回收的方法，并产生气相等离子体电催化的机理理解。此外，以等离子体为电解质的气相电催化的革命性概念为进一步的基础研究和实际应用提供了电化学的新范式。最终，该项目将(i)确定适用于非热等离子体辅助塑料废物催化转化的活性、选择性和耐用催化剂；（ii）为非热等离子体气固催化反应器的设计和运行提供技术基础。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。

Difficult to recycle plastic waste accumulates in landfills and the environment since few commercially viable recycling technologies exist, which severely deteriorates terrestrial and aquatic ecosystems. This project will examine a method called nonthermal plasma-assisted hydrogenolysis as a potential approach for recycling mixtures of plastic waste materials. Nonthermal plasma-assisted hydrogenolysis provides a low-energy pathway for depolymerizing mixed plastics (i.e., polymers) and generating value-added small molecules, such as monomers, C2-C3 olefins, and liquid paraffins, which serve as chemical feedstocks and transportation fuels. Nonthermal plasma will provide two key functions: (i) channeling electric energy to activate polymer bond-breaking processes and (ii) serving as an electrolyte for electrochemical conversion of polymer fragments to desired small molecules. This project integrates the expertise of investigators from The University of Akron and Lawrence Berkley National Laboratory with the objective of (i) developing a transformational concept in electrocatalysis, using plasma of hydrogen/hydrocarbon from polymers as gaseous electrolyte and (ii) coupling this novel concept with conventional catalysis to achieve fast and selective conversion of polymer wastes to desired chemicals. Successful demonstration of the nonthermal plasma-assisted hydrogenolysis concept will establish the knowledge base required to advance the scientific frontiers in electrocatalysis with gaseous electrolyte and plasma reaction engineering. The proposed technology could be further applied to upcycle consumer products and organic agricultural wastes generated by intensive animal farming. The nonthermal plasma-assisted hydrogenolysis of plastic wastes has a potentially transformative role in closing the loop of the plastics carbon cycle. The objective of this project is to investigate a non-thermal plasma-assisted catalysis approach for the selective conversion of mixed plastics (i.e., polymers) to monomers and small molecules. Nonthermal plasma discharge, i.e., electrically ionized gaseous species produced by dielectric barrier discharge, initiates the breaking of C-H and C-C polymer bonds which produces polymer fragments as well as their radicals and ionic species in the gas phase. The inorganic contaminants in the plastic waste, which cannot be vaporized, precipitate in the form of solid particles. Then, polymer fragments adsorb on the catalyst surface for the selective conversion to desirable small molecules at ambient temperature and pressure. Ionic species could serve as electrolytes to enable the conversion of adsorbed species on the electrocatalyst surface, a process that controls the rate and selectivity of the reactions. Ambient temperature electrocatalysis provides several attractive features: (i) decreasing the need for thermal energy, (ii) minimizing the side reactions (in particular, the formation of tar), and (iii) enhancing the selectivity toward desired products. The mechanistic understanding of nonthermal plasma-assisted catalytic hydrogenolysis of polymer wastes will be achieved through comprehensive kinetic studies, operando infrared spectroscopic studies of reactive adsorbed intermediates, in situ X-ray absorption studies of the structure of the catalyst and adsorbed polymer fragments, catalyst characterization, rational design of catalysts, and testing of a pilot-scale reactor. The results of this study will advance nonthermal plasma-assisted hydrogenolysis as a method for polymer waste recycling and yield a mechanistic understanding of gas-phase plasma electrocatalysis. Moreover, the transformative concept of gas-phase electrocatalysis with plasma as an electrolyte offers a new paradigm in electrochemistry for further basic research and practical applications. Ultimately, this project will (i) identify active, selective, and durable catalysts suitable for nonthermal plasma-assisted catalytic conversion of plastic wastes and (ii) provide the technical basis for the design and operation of nonthermal plasma gas-solid catalytic reactors.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.