(662e) Additive-Induced Catalyst Poisoning in Polyolefin Hydrocracking

Functional additives are major impediment to the valorization of plastics waste. For instance, catalytic processes that convert discarded polyolefins into value-added products can enable a range of upcycling opportunities; however, widespread implementation of these technologies is often limited by the fact that plastic waste formulations tend to poison catalysts. Detailed and quantitative analysis of additive effects on catalytic properties (e.g., site chemistry) or process outcomes (e.g., yield, selectivity) is required to guide the design of efficient conversion strategies. In this work, we examine the role of base additive formulation and antioxidant chemistry/concentration on the hydrocracking of high-density polyethylene (HDPE) with a platinum on tungstated zirconium catalyst. We demonstrate a significant reduction (at least 2-fold) in activity between pure polymer and base (additive-containing) resin that is attributable to antioxidants and slip agents. Furthermore, we show that at similar loadings, different antioxidant chemistries have different impacts on catalyst activity and product selectivity. For example, at 0.5 wt% butylated hydroxytoluene (BHT) slows hydrocracking, whereas tri-BHT isocyanurate completely poisons the catalyst. By using infrared spectroscopic studies of antioxidant-treated catalysts, we connect these hydrocracking results to fundamental changes of both functionalities (i.e., metal and acid sites) on the catalyst, which drive varying product selectivities. Overall, this work provides an assessment of one of the key challenges in the deconstruction of ‘real’ plastics waste and presents an experimental strategy for assessing the performance of potential valorization routes.