03/12/2025
By Danielle Fretwell
Candidate Name: Mihriye Doga Tekbas
Degree: Doctoral
Defense Date: Monday, March 24, 2025
Time: 11 a.m. – 1 p.m.
Location: Ball Hall, Room 302
Committee:
Advisor: Hsi-Wu Wong, Associate Professor, Department of Chemical Engineering, University of Massachusetts Lowell
Committee Members*
1. Wei Fan, Professor, Department of Chemical Engineering, University of Massachusetts Amherst
2. Dongming Xie, Associate Professor, Department of Chemical Engineering, University of Massachusetts Lowell
3. Grace Chen, Associate Professor, Department of Plastics Engineering, University of Massachusetts Lowell
Brief Abstract:
The production of alternative fuels and renewable chemicals from waste biomass and plastics is projected to grow in the coming decades due to increasing energy demand and the environmental impact of fossil fuels. Pyrolysis, a thermochemical decomposition process conducted in the absence of oxygen, presents a promising and cost-effective pathway to convert organic waste materials into liquid oil, syngas, and char. However, large-scale implementation of pyrolysis faces key challenges, including non-selective product distributions and limited understanding of the reaction engineering principles at the molecular level. Addressing the detailed, mechanistic interplay between mass transfer and chemical kinetics in the pyrolysis of waste macromolecules is crucial to overcoming these barriers.
This dissertation aims to shed light on these couplings, using high-density polyethylene (HDPE) and cellulose as model plastic and biomass waste compounds, respectively. Three distinct macromolecular pyrolysis systems are investigated. First, the competition between the evaporation of HDPE-derived pyrolysis products and their further decomposition is explored under varying reaction pressures. Our results reveal that reaction pressure significantly influences this competition, and the dimensionless Damköhler (Da) number effectively characterizes whether the process is limited by chemical kinetics or mass transfer. This work establishes a quantitative framework for controlling product distributions by tuning reaction pressure. Second, the presence of a second macromolecule, such as molten plastics or lignin, during cellulose fast pyrolysis is studied. It is revealed that the presence of the secondary molten phase affects cellulose-derived pyrolysis products by inhibiting the escape (evaporation or thermal injection) of large molecules, leading to their further decomposition. Additionally, functional groups within the secondary molten phase induce noncovalent interactions, which either catalyze or inhibit specific reaction pathways during cellulose pyrolysis. Third and the final section of this dissertation examines the use of zeolite catalysts to selectively tune HDPE pyrolysis. A novel aluminosilicate zeolite (ZEO-1), characterized by intersecting three-dimensional pores of varying sizes, high surface area, and exceptional thermal stability (up to 1000°C), is tested. Results indicate that system pressure and zeolite framework can be leveraged to optimize product selectivity, offering a tunable approach to enhancing the yields of valuable hydrocarbon products.
This dissertation provides a fundamental understanding of the reaction engineering principles governing macromolecule pyrolysis, contributing to the future scale-up and commercialization of pyrolysis technologies. Additionally, it supports advancements in sustainability and circular economy strategies by presenting pathways to optimize pyrolysis for improved utilization of biomass and plastic waste.