Semester

Summer

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Dr. Yuxin Wang

Committee Co-Chair

Dr. Jianli (John) Hu

Committee Member

Dr. Jianli (John) Hu

Committee Member

Dr. Debangsu Bhattacharrya

Committee Member

Dr. Oishi Sanyal

Committee Member

Dr. Cosmin Dumitrescu

Committee Member

Dr. V'yacheslav Akkerman

Abstract

Single-use plastics (Low Density Polyethylene, LDPE; Polystyrene, PS; Polypropylene, PP) are increasingly used in the modern world, with their usage growing every year. An effective method to manage the resulting waste is urgently needed, as landfilling and incineration have proven harmful to the environment in the long term. Mechanical recycling may not maintain the desirable characteristics of the single-use plastics through several cycles. Pyrolysis emerges as a promising approach to address plastic waste. Given that single-use plastic waste often comes in a mixture, combining plastic in the feedstock is a viable solution to effectively convert these polymers altogether to gain market value. The emergence of microwave heating technology enhances plastic pyrolysis by significantly improving heating efficiency. Contributed to penetrative and selective heating capabilities of electromagnetic waves. This advancement can potentially enhance the catalytic pyrolysis process to yield more valuable products. These hypotheses were tested in detail.

The depolymerization of LDPE, PS, and their mixture was investigated under conventional thermal and microwave conditions. PS and LDPE were studied for co-pyrolysis performance in a thermal reactor. In both catalytic (using HZSM-5 as catalysts) and non-catalytic cases, PS had higher degradation temperature than LDPE. When the plastics were mixed, the reaction temperature decreased. Compared to individual PS or LDPE depolymerization, the mixture demonstrated a different depolymerization mechanism. Additionally, the PS-LDPE 1:1 blend yielded higher amounts of BTX (benzene, toluene, xylene) compared to PS and LDPE alone. The reaction mechanism was supported by the in-situ FTIR, which showed prolonged BTX production during the mixed plastic catalytic degradation. The interaction between the radicals released from PS and LDPE cracking was hypothesized to enhance BTX aromatics production in the presence of HZSM-5 catalysts.

The catalytic co-pyrolysis of PS and LDPE were tested in the presence of electromagnetic waves. The mixed plastics exhibited synergistic effects, leading to increased BTX production under microwave conditions. Individually, PS and LDPE were observed to possess a separate pyrolysis mechanism. However, when pyrolyzed together in a mixture, their intermediates interacted with each other. With the presence of HZSM-5 catalyst, the product distribution favored BTX production due to the synergy mechanism. The microwave-assisted pyrolysis of mixed plastic was compared between microwave heating and conventional heating methods. Overall, microwave heating offers more efficient heating. Ultimately, resulting in higher conversion rates and better yield towards BTX products.

A kinetic study was conducted on microwave heating and conventional thermal heating to determine the activation energy (Ea) of PS, LDPE and their mixture during catalytic pyrolysis. It was found that when the plastics were mixed, the Ea decreased under both heating methods. This phenomenon was attributed to the interaction between the intermediates of each plastic, in which one component facilitated the degradation of the other. Compared to thermal heating, microwave heating reduced the Ea of all plastic types, which was attributed to local heating through hotspot formations. The reaction mechanism of mixed plastic was elucidated with more pathways towards BTX production, which was corroborated with the reactor performance results.

Download

Share

COinS