(173b) Waste Plastic Upcycling: Microkinetic Modelling of Hdpe Pyrolysis

Plastic pollution is currently a matter of grave environmental concern. Polyethylene (PE) is one of the most widely used plastics due to its applications in packaging and cost-effectiveness. Although mechanical recycling of PE is possible, it becomes infeasible after a few cycles beyond which chemical upcycling to higher value products is a preferred option. Pyrolysis, which is heating of the sample in an inert atmosphere, is a promising way to upcycle PE and thereby produce fuels and chemicals. PE pyrolysis is known to yield gaseous and liquid products, and the product composition strongly depends on reactor operating conditions. Kinetic models developed against experimental data are useful for predicting the reaction characteristics. Global kinetic models available for PE are known to capture overall conversion. Nevertheless, for gaining insights into the reaction mechanism, a microkinetic model is necessary. During pyrolysis, a large number of species of different chain lengths form, and it is computationally very intensive to track every species in a truly mechanistic model. Therefore, it is often more realistic to work with a lumped mechanistic model that tracks ‘classes’ of species having similar properties, such as dead species, end radicals, mid radicals, etc. Each lumped species class has a molecular weight distribution, and their moments and thereby their properties are calculated by solving population balance equations using method of moments. Physically significant kinetic parameters obtained from theoretical calculations and experiments reported in literature are used in the model. Such mechanistic models for pyrolysis of several polymers have been published by the Broadbelt group. A microkinetic model for HDPE pyrolysis validated using experimental data in literature and its features will be discussed.