Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Berruti, Franco

Abstract

In this study, the use of pyrolytic cracking for managing non-recyclable plastic waste by conversion into value-added liquid and gaseous products was investigated. A single-stage reactor and a novel, two-stage reactor set-up were used for experiments involving polyethylene and polypropylene. Parameters including feedstock composition, feed rate, temperature and residence time were studied. The two-stage approach was investigated to overcome existing transportation limitations involved in the typical plastic waste lifecycle. Bulky plastic collected in towns and cities must be transported to industrial facilities typically located elsewhere for reprocessing. Both HDPE and LDPE showed promising results for olefin recovery with ethylene gas yields of 26.6% and 34.1% of the original polymer, respectively. A maximum hydrogen yield over all the experiments of 46.2% which was obtained using LDPE. The economic feasibility of scaling up the processes was analyzed. It was found that the two-stage set up increased the gas yields of both hydrogen and ethylene and rendered the process to be economically viable with a payback period of 3 years.

Summary for Lay Audience

The persistence and dispersion of plastic waste has been proven to be a very visible and damaging environmental issue. Enhanced by the COVID-19 global pandemic, the world’s plastic use and consumption is drastically increasing. New technologies need to be developed to address concerns of waste accumulation.

In this study, a thermochemical technology called pyrolysis was used to convert plastic waste into value added products. Pyrolysis involves the thermal decomposition of polymers in the absence of oxygen at elevated temperatures. The aim of this process is to deconstruct the polymer materials back into their “building block” monomer components, so that new plastic can be remade of the same quality as the virgin material. In this study, an analysis was performed on plastic feedstock demonstrating the ability to convert an overall percentage of 34.1% into the gaseous monomer form.

Other products from pyrolysis include oil and other gaseous components. The oil collected showed promise to be used as a fuel, and the other gas components can be recycled back to the process for use in powering the plant. An economic evaluation was done to demonstrate the economic feasibility of this system.

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