2024 AIChE Annual Meeting
(388b) Understanding the Free Energy Landscape for Catalytic Conversion of Polyethylene Waste to Liquid Fuels Via Hydrogenolysis
Author
Lee, E. - Presenter, University of Chicago
Catalytic polymer hydrogenolysis of waste plastic is a promising method for the selective chemical upcycling of polymers. In this process, metal catalysts and hydrogen gas convert long-chain polymers into lightweight hydrocarbons as liquid fuels with low energy input. Studies have shown that polyethylene, the most common plastic, can be broken down and converted into liquid fuels using transition metal catalysts and excess hydrogen gas. However, controlling the reaction specificity and efficiency for waste-to-fuel conversion presents considerable challenges, and little is known about the molecular mechanism of polymer deconstruction at the polymer-metal interface. Here, I will elucidate the hydrogenolysis process of hydrocarbons on metal catalysts by using dodecane and ethane on ruthenium (001) surface as prototypical catalytic systems. We employ ab initio molecular dynamics with enhanced sampling to simulate the evolution of the polymer deconstruction process and the free energetics under varying reaction conditions, including explicit gas pressure and temperature. Using this computational framework, we solve the electronic structure and include thermal effects to directly sample the molecular conformations and electronic analysis of multiple hydrocarbon states during the catalytic conversion. We find several competing reaction pathways for cleaving carbon-carbon bonds, depending on the concentration and the mobility of adsorbed hydrogen species and hydrocarbon chains, which have often been neglected in density functional theory studies of catalytic surface reactions. The detailed view of the mechanisms presented here provides insights into the selective cleavage of carbon-carbon bonds for polymer waste deconstruction.