Semester

Fall

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Srinivas Palanki

Committee Member

Jianli Hu

Committee Member

Yuhe Tian

Committee Member

Md Emdadul Haque

Committee Member

Jignesh Solanki

Abstract

Ethylene is one of the most widely produced petrochemicals, with an estimated global output of 180 million metric tons in 2022. Approximately 82 million metric tons of ethylene are used annually for plastic production, primarily for polyethylene (PE), as well as polypropylene (PP) and polyvinyl chloride (PVC). The CO₂ emissions associated with PE production were approximately 14 million metric tons in 2022. Globally, an estimated 70 million metric tons of PE are produced and consumed each year, with the majority (~79%) ending up in landfills or the environment.

This project proposes a novel process in which waste low-density polyethylene (LDPE) is converted into polymer grade ethylene using a microwave-catalyzed reactor, producing 77 tons per hour of ethylene at industrial scale. Laboratory-scale batch experiments were performed under microwave radiation and conventional thermal heating to compare conversion performance and product selectivity. Experimental results demonstrated that the heating method significantly influences product distribution. The microwave-catalyzed reaction exhibited a much higher selectivity toward ethylene, achieving 44.7 wt.%. In contrast, the conventional thermal reaction produced only 24.3 wt.% ethylene, while generating substantially higher amounts of propylene (25.8 wt.%) and aromatics (8.3 wt.%), compared with 9.8 wt.% and 6.4 wt.% respectively in the microwave-catalyzed system. These data were scaled to industrial capacity, and detailed process flowsheets were developed in ASPEN Plus for both the microwave-catalyzed and thermal-catalyzed pathways, as well as for a conventional ethane steam-cracking base case. Reactors were modeled using yield reactors based on experimentally measured product distributions, and distillation columns were sized using rigorous RadFrac simulations. Heat integration and equipment sizing were performed to minimize utility consumption, and capital and operating costs were estimated using ASPEN Economic Analyzer. Techno-economic analysis shows that ethylene production from waste LDPE is more profitable than the conventional ethane steam-cracking process due to its lower reaction temperature, reduced energy demand, and the generation of higher-value by-products. For the same LDPE processing capacity, the microwave-catalyzed process further outperforms the thermal-catalyzed process under comparable reactor-cost conditions. Sensitivity analyses indicate that electricity price and reactor capital cost are the dominant economic factors. When electricity prices remain low and reactor costs are within feasible manufacturing ranges, the microwave-catalyzed process exhibits a higher net present value (NPV) than the thermal alternative. Life-cycle assessment further reveals a substantial reduction in greenhouse-gas emissions compared to the fossil-based ethane steam-cracking route, primarily due to the use of renewable electricity, the lower reaction temperature that reduces utility demand, and the use of plastic waste as the feedstock. The global warming potentials (GWPs) associated with producing 1 kg of ethylene using the conventional ethane steam-cracking process, the microwave-catalyzed LDPE-Catalyzed Process, and the Thermal-Catalyzed LDPE Process are 1.49, 0.35, and 1.45 kg CO₂-eq, respectively. Importantly, if the conventional reactor heating were replaced with renewable electricity, the GWP of both thermal and steam-cracking processes decrease, narrowing the gap between the pathways. Under renewable-electricity scenarios, the overall GWP values for the three models become 1.33 kg CO₂-eq for steam cracking, 0.35 kg CO₂-eq for microwave-catalyzed LDPE conversion, and 0.37 kg CO₂-eq for the thermal-catalyzed LDPE process.

Overall, this work demonstrates the technical feasibility, economic potential, and environmental advantages of microwave-assisted LDPE depolymerization as an emerging pathway for sustainable ethylene production.

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