Molecular Insights into Competitive Adsorption in the Deconstruction of Mixed Polyolefin Waste

Abstract To enable the full potential of polyolefin hydrogenolysis, catalysts must handle mixed plastics waste streams. However, a major barrier is the limited understanding of how different polymers and their degradation products competitively adsorb onto the catalyst surface, which influences overall reactivity and product selectivity. To address this, we employ Replica-Exchange Molecular Dynamics (RE-MD) simulations of competitive adsorption of linear polyethylene (PE), methyl-branched alkane polypropylene (PP), and branched PE on Pt(111). Comparison of surface and bulk polymer densities in mixed polyolefin simulations reveal that linear PE preferentially adsorbs over PP over a range of molecular weights. Hydrogen/deuterium exchange experiments of PE/PP mixtures and analogous model alkane mixtures validate the MD simulations. Through simulations of three-component polymer mixtures we demonstrate that polymer branching densities and branch lengths dominate competitive adsorption, outweighing molecular weight effects. We develop a correlation for quantifying the surface segregation based on the molecular weight, highlighting the need for developing detailed adsorption models. We show that the same trends in preferential adsorption also apply at lower molecular weights within the range of typical hydrogenolysis products, highlighting the impact of preferential adsorption even at later stages of the reaction. Collectively, we provide key insights into the short-time and long-time states of polymer-catalyst interactions in multicomponent polyolefin hydrogenolysis. We emphasize the key role of chain architecture in modeling adsorption of mixed polyolefin melts on catalysts.