Pyrolysis of waste polyethylene into fuel : a two-stage process modeling study

Abstract

Plastic waste is an ever growing problem due to the fact that it does not degrade easily unlike organic materials. Pyrolysis is one effective method to transform waste (biomass, municipal waste, plastic waste among others) into fuel. Researchers, thus far, have been developing tools to understand in depth the mechanisms that drive the thermal or catalytic degradation of polymer waste and to predict the kinetics involved in such processes as well as product distributions. This work aims at developing an efficient pyrolysis prediction system for the process of converting waste high density polyethylene (HDPE) into fuel. The main objectives are concentrated towards the development of a computationally efficient, high fidelity model that describes the thermal degradation of the polymer with high product distribution detail. A combined model with two modeling frameworks has been suggested. It consisted of a Lumped-Empirical model approach whose aim is to depict lumps of products of the first stage (gas, low molecular weight products, waxes, etc.) and a Population-Balance model that tracks the latter products following their mechanistic reactions and depicts their carbon-chain length distribution. A pathway model was developed specifically for this purpose and was based on literature data along with parameter estimation for the kinetic rate constants. The model tracked 181 species showing good fit with literature data. The model has the advantage of being less computationally demanding relative to existing techniques for carbon-chain length tracking of HDPE pyrolysis products.