Kinetic modeling frameworks for the chemical recycling of polyolefins

Plastics have become essential to modern life, yet their durability has led to a global waste challenge (> 360 Mt per year). Among this gigantic among of plastic wastes, most of them have been landfilled, incinerated, or even mismanaged. Only a small portion of them have been recycled. However, current mechanical recycling cannot solve the issue that material properties will degrade during the recycling process. Chemical recycling offers new pathways by converting polymers back into valuable molecules selectively, but the underlying reactions are extremely complex due to a wide range of chain lengths in polymers, different features and functional groups among products, and different phases in a reactor scale that stretch traditional kinetic tools past their limits. This dissertation develops a set of kinetic modeling frameworks for the chemical recycling of polyolefins. First, we examine mass-transfer limits using a diffusion–reaction model that describes how processive catalysts perform inside stagnant and stirred polymer melts. The core of the dissertation then advances the mechanistic modeling for polyethylene (PE) and polypropylene (PP) depolymerization. We begin with a length-agnostic microkinetic model (MKM) that includes all surface and bulk species for a model compound, allowing extraction of rate constants and validation of mechanistic hypotheses from experiments. Then, we started with PP pyrolysis mechanism to build a continuous feature x population balance models (PBMs) that resolve the realistic molecular weight distribution (MWD) while keeping track of the evolution of functional motifs such as double bonds or end groups with a feature balance framework (FBM). We show how FBMs can be coupled to PBMs to follow both detailed kinetics and evolving MWDs across multiple species and predict experimental observables and MWDs.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Ge, Jiankai

Contributors dc:contributor

• Peters, Baron G
• Schweizer, Kenneth S
• Mironenko, Alexander V
• Bickel Rogers, Elizabeth

• Chemical recycling
• Kinetics
• Modeling
• Polyolefins

Statement dc:rights

• Copyright 2025 Jiankai Ge

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132535

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132535