(201a) Modeling Reactor Systems for Waste Plastic Pyrolysis

About 400 million tonnes of plastic waste is generated every year, with most of it being landfilled, incinerated, or mismanaged as litter.¹ Chemical recycling presents a major opportunity to recover and reuse this plastic waste to manufacture new energy and chemical products. In this study, a first-principles kinetic modeling system in Aspen Plus was utilized to model the pyrolysis of a variety of waste plastic feedstocks in a multiphasic reactor. The kinetic model utilizes the method of moments to track the free radical mechanism for polymer decomposition. It accounts for the detailed random scission, β-scission, cyclic scission, depolymerization, H-abstraction, hydrogen shift, debranching, combination, and disproportionation reactions. The reactor was modeled as a screw extruder with vents for the escaping product gas. To model the vapor-liquid phase evolution, the PC-SAFT property model was used to calculate the state of the polymer system, including explicitly tracked low molecular weight oligomers in the system. Additional reactor dynamics and secondary reactions such as char formation can also be included in the model to accurately represent the operation of a real system. The final model can be utilized as a starting point for design and optimization of a waste plastic chemical recycling system in the circular economy paradigm.

[1] United Nations Environment Program. Visual feature: Beat plastic pollution. Retrieved March 20, 2023, from https://www.unep.org/interactives/beat-plastic-pollution/