Polyolefin adsorption on catalyst supports for chemical recycling
Research Poster Engineering 2025 Graduate ExhibitionPresentation by Fawaz Motolani
Exhibition Number 41
Abstract
Catalytic upcycling of polyolefins into value-added products offers a promising pathway to economically incentivize plastic waste recycling. However, scaling these processes remains challenging due to knowledge gaps in reaction mechanisms, including transport limitations, size-dependent adsorption/desorption dynamics, and catalyst deactivation rates, all of which influence product distribution and value. Catalyst deactivation is often attributed to coking that results from the aromatization of adsorbed species. In this study, we investigated the deactivation by examining the material adsorbed to a model hydrogenolysis catalyst, Pt on silica, under low hydrogen pressures to promote coking. Contrary to expectations, FTIR analysis of residual organics on the catalyst revealed no aromatic species, only hydrocarbons. Similar levels of residual organics were found on the silica support without Pt, suggesting that irreversible adsorption occurs on the support surface. To better understand this adsorption behavior, polyethylene and its oligomeric analog, hexatriacontane, were heated at 250 °C with silica. Thermogravimetric analysis (TGA) of the residues, following typical solid extraction methods reported in literatures, revealed a two-step weight loss. The first step corresponded to neat hexatriacontane, while the second indicated higher-temperature interactions, consistent with strong adsorption. These findings demonstrate that even in the absence of functional groups, polyethylene can irreversibly adsorb to silica surfaces. This strong adsorption, often overlooked in catalytic upcycling models, may significantly impact catalyst performance. Our results highlight the need to better understand polymer-support interactions to improve catalyst design and efficiency for catalytic chemical recycling of plastics.
Importance
Plastic waste is a growing global challenge, and finding ways to recycle it into useful products can help address both environmental and economic concerns. This study explores how plastics interact with materials used as catalysts during the recycling process, specifically focusing on how certain behaviors—like sticking to surfaces(adsorption)—might affect the process. We found that even simple plastics such as polyethylene can strongly adhere to surfaces, potentially reducing the efficiency of recycling processes. By uncovering new details about these interactions, our work provides valuable insights that could help scientists design better catalysts, making plastic recycling more efficient and effective. Ultimately, this research supports the development of technologies that can turn discarded plastics into valuable resources, reducing waste and promoting sustainability.