NSF Award
2132178
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. <br/><br/>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.<br/><br/>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.
