(473b) Techno-Economic Analysis and Life Cycle Assessment of Modular Microwave-Assisted PET Depolymerization

Plastic waste is a pressing global issue due to the massive greenhouse gas emissions associated with its production and the lack of proper end-of-life management.¹ Polyethylene terephthalate (PET) is the most common polymer used for the production of plastics with wide applications in the packaging and textile industry.² Currently, only less than 20% of waste PET is recycled in the US, while the rest ends up in landfill or incineration facilities, which causes increasing land and air pollution. Moreover, mechanical recycling inevitably causes product quality degradation, which reduces the value of recycled products.³ Consequently, chemical recycling and upcycling of PET, such as glycolysis and methanolysis, have become increasingly popular.^{4, 5} PET glycolysis utilizes ethylene glycol (EG) to break the polymer chain into bis(2-hydroxyethyl) terephthalate (BHET), an essential intermediate in the industrial PET resin synthesis.^{6, 7}

In this work, we evaluated the economic and environmental impacts of a microwave (MW) assisted PET glycolysis process. Unlike most PET glycolysis studies using homogeneous catalysts,^8-10 the proposed process utilizes the heterogeneous ZnO catalyst that is more efficient and easier to separate. First, the flowsheet model of the MW-assisted PET glycolysis process is built using Aspen Plus based on reaction conditions and yields. The traditional BHET production from petroleum-based dimethyl terephthalate (DMT) is also simulated. Next, techno-economic analysis (TEA) is conducted using the discounted cash flow method to calculate the minimum selling prices for both routes. A "cradle-to-gate" life cycle assessment (LCA) is performed to compare the environmental impacts of MW-assisted PET depolymerization with traditional BHET production from DMT, including the global warming potential, ecotoxicity, and fuel depletion.¹¹ Our preliminary TEA and LCA demonstrate the economic and environmental benefits of using waste plastics as feedstock.

PET waste is geographically distributed. Thus, building a centralized treatment facility for post-consumer waste PET could suffer from insufficient or disrupted supply and high transportation cost.^{12, 13} Hence, we simulated the modular MW-assisted PET depolymerization plant at small scales so that they could be built close to plastic waste source and have faster response to supply uncertainties.^{14, 15} Sievers et al. proposed a fixed capital cost evaluation method for modular plants with a backbone facility and several expandable production line modules.¹⁴ This method is applied to our modular MW-assisted waste PET depolymerization process for TEA. High PET conversion and BHET selectivity of this process also enable easy separation of the product, leading to reduced production cost even at a much smaller plant capacity than the centralized BHET production facility using traditional petrochemical feedstock.

Reference

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