(638g) Modeling and Techno-Economic Optimization of a Microwave-Assisted Catalytic Reactor for Plastics Upcycling

LDPE is the most abundant plastic resin found in the municipal solid waste in the US. Currently in the US, about 88% LDPE goes to landfill, 10% is combusted and only 2% is recycled. There are numerous processes to recycle the plastic waste such as thermal pyrolysis of the polyolefins and catalytic cracking of the polyolefins. However, these processes lead to substantial coke formation, inferior product yield, and high operating temperature. This works focuses on novel microwave (MW)-assisted thermo-catalytic technology for upcycling of waste LDPE, i.e., to selectively produce ethylene along with other value-added products. Most of the products (about 96%) in the MW-assisted process are gaseous compared to conventional thermal pyrolysis that typically yields around 14% gaseous, 67% solid, and remaining liquid products.

A first-principles model of MW-assisted thermo-catalytic laboratory batch reactor is developed. A kinetic model is proposed based on the observed laboratory data. As the yield from the batch reactor is found to be time-varying, a model for the reaction yield for each product is proposed as a function of the remaining mass of the reactants at any instant in the reactor and the reactor operating temperature. Parameters of the yield model are optimally estimated by using the reconciled laboratory data. The laboratory model is scaled up to the commercial scale. Number of batch reactors in parallel is estimated and their operating schedule is developed such that the product flowrate and composition variations with time remain within acceptable tolerance for downstream separation units that produce methane, hydrogen, ethane, ethylene, propane, propylene, n-butane and benzene with purity >99%. An economic model is developed in Aspen Process Economic Analyzer. The economic model leads to net present value (NPV) of about $100.40 MM and $366 MM for conventional and MW-assisted processes, respectively, indicating considerably superior economics of the MW-assisted process.