Researcher(s)
- Elisabeth Roberts, Chemical Engineering, University of Delaware
Faculty Mentor(s)
- Dionisios Vlachos, Chemical and Biomolecular Engineering, University of Delaware
Abstract
Plastics play a monumental role in the world around us. Most of the plastic waste generated is not recycled, leading to a growing problem of plastic waste handling. Mechanical recycling, though energy efficient, reduces the quality of the end products. Chemical upcycling offers a useful method to create valuable products from plastic waste. In processes involving heterogeneous catalysts, polymers react chemically on the surface. Hence, the product distribution obtained depends on the conformations the polymer chains adopt on the surface. Understanding this surface adsorption can allow us to design better catalysts and processes to tune the product distributions towards desired chemicals.
Platinum (Pt) catalysts are commonly used for polyethylene (PE) hydrogenolysis, a process that breaks down PE chains into smaller alkanes. Previous studies have shown that the surface morphology of the catalyst affects the adsorption behavior of linear PE chains of different sizes. Most commercial plastics, including PE, have some degree of branching in their structure. Here, we investigate the effect of branching on the adsorption of linear alkane chains on different Pt facets: Pt(111), Pt(557), and Pt(211). We take C24 , C70 , and C142 alkanes as PE surrogates, with methyl (-CH3) and propyl (-CH2CH2CH3) side chains. We use molecular dynamics (MD) simulations with Replica Exchange (RE) as an enhanced sampling technique.
Due to the steric hindrances of the side-chains, we expect branched PE chains to have significantly different adsorption characteristics compared to linear chains. Additionally, we expect branched polymers to pack together differently than linear polymers do, both on the catalyst surface and in the surrounding melt. We thus investigate the surface conformations and selective segregation of linear versus branched chains at the surface in order to gain molecular-level insights into the behavior of these chains with different catalyst facets.