Mixed PET Plastics Waste to Dimethyl Terephthalate & Ethylene Glycol

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Senior Design Reports (CBE)
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Biochemical and Biomolecular Engineering
Chemical Engineering
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Cao, Chelsea
Choi, Hyuck
Kline, Christopher
Zhang, Shannon

Polyethylene terephthalate (PET) plastic is integral to our everyday lives. As the primary plastic used in food and beverage packaging and synthetic textiles (PET Resin Association, 2015), PET is produced in North America at a rate of 3.1 million tons per year. However, as of 2015, only 26.6% of the PET produced is being recycled per year (PET Resin Association, 2015). Thus, the accumulation of PET waste has become a significant environmental concern. To address this problem, this report proposes a methanolysis plant using technology from Eastman Chemical Company (Sharpe et al., 2020) to depolymerize 100,000 metric tons of PET plastic waste annually into dimethyl terephthalate (DMT) and ethylene glycol (EG). The process in this report uses a sodium carbonate catalyst with a methanol reagent at a temperature of 160°C and pressure of 250 psig for one hour, during which the PET polymer undergoes a transesterification reaction to produce DMT and EG. Various separation processes were included in the design to produce products of 99.8 wt% pure DMT and 99.1 wt% pure glycols (97.5 wt% EG). Preprocessing equipment was also included in the design to filter out impurities from the PET waste feedstock before it entered the reactors. Based on a cost of capital of 15% and current prices of feedstock and products, economic analyses predicted a -$198MM net present value (NPV), return of investment (ROI) of –12.18% in year 3, and a negative internal rate of return (IRR). However, based on aggressive growth rate projections of the recycled PET market, it is possible but unlikely to reach a positive NPV of 677MM. Thus, although the process is not currently economically viable, it is likely that future uptake of sustainable plastics would make the process profitable.

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