Date of Award

2022

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

David Shonnard

Committee Member 1

Rebecca Ong

Committee Member 2

Michael Mullins

Committee Member 3

Ezra Bar Ziv

Abstract

Plastic usage has quickly grown in recent years as plastics have become an essential part of everyday life. Unfortunately, recycling rates have not matched the increased growth, with the majority of waste plastic landfilled. The strategy of circular economy has been proposed to reuse the waste plastic to create new polymers, thus avoiding both landfilling and the use of virgin raw materials. Achieving a circular economy for plastics requires the development of new technologies capable of recycling plastic waste under a circular economy perspective. In this dissertation, a novel liquid-fed fast pyrolysis process is introduced towards achieving a circular economy. Recycled pyrolysis wax is used to dissolve waste polyolefin plastic and create a liquid feed to the pyrolysis reactor. The oil product from the pyrolysis reaction is naphtha-like in appearance and could be used as a feedstock for petro-chemical facilities for the production of new polymers. The fundamental pyrolysis reaction kinetics are investigated using a novel two-stage micropyrolysis reactor accessory to a commercial pyroprobe unit. A practical lumped kinetic model was created using generated micropyrolysis data to predict the effect of temperature (550-600 °C) and vapor residence time (VRT; 1-6 seconds) on product distribution. The presented kinetic model shows strong agreement with known degradation mechanisms and was applied for scaling-up the pyrolysis process to a 250 g/hr pilot plant. By testing three different reactor volumes, it was found that VRT had a significant effect on wax, liquid, and gas product distribution. A multiphysics model was developed and predicted reactor temperature, pyrolysis product species, and velocity profiles. The trends for product distribution as a function of VRT were found to be consistent between both the pilot plant and micropyrolysis systems, demonstrating that the pilot system can be tuned to produce the desired pyrolysis product. Finally, the data generated using the pilot plant was used to guide a process simulation for an 84,000 tonne/yr waste plastic pyrolysis facility. A techno-economic analysis and life cycle assessment of the process found favorable economic and environmental results for pyrolysis oil when compared to fossil naphtha.

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