Quantifying synergy for mixed end-scission and random-scission catalysts in polymer upcycling

Abstract

The environmental consequences of plastic waste are driving research into many chemical and catalytic recycling strategies. The isomerizing ethenolysis strategy for polyethylene upcycling combines three catalysts to affect two different actions: non-processive scission at chain ends, and scission at random interior points. We show that population balance equations (PBEs) based on the local density approximation (LDA) accurately describe the end-scission chemistry. We further show that the model can be simplified to a first-order PBE when started from a realistic molecular weight distribution. The simplification enables formulation and solution of a model that includes both end-scission and random-scission modalities. The mixture of catalysts (in theory) can exhibit a quantitative synergy, e.g., with the total number of cuts for the catalyst mixture exceeding that for the sum of its separate component catalyst actions. We develop equations to predict and optimize the synergistic acceleration.