Molecular Level Understanding of Polyethylene Terephthalate (PET) Depolymerization in Base/Alcohol Hybrid Systems

Yu, Hyejin [Argonne National Laboratory (ANL), Argonne, IL (United States)]; Oh, Younghoon [Boston Univ., MA (United States)]; Kim, Yu Lim [Argonne National Laboratory (ANL), Argonne, IL (United States)]; Liu, Cong [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000221455034); Park, Kyobin [Argonne National Laboratory (ANL), Argonne, IL (United States)]; Cha, Hyun Gil [Korea Research Institute of Chemical Technology (KRICT), Ulsan (Korea, Republic of)] (ORCID:0000000212284464); Delferro, Massimiliano [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:000000024443165X); Kang, Donghyeon [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000339600823)

doi:10.1021/acsami.4c20887

DOE OSTI · 2574034

Molecular Level Understanding of Polyethylene Terephthalate (PET) Depolymerization in Base/Alcohol Hybrid Systems

Yu, Hyejin [Argonne National Laboratory (ANL), Argonne, IL (United States)]·Oh, Younghoon [Boston Univ., MA (United States)]·Kim, Yu Lim [Argonne National Laboratory (ANL), Argonne, IL (United States)]·Liu, Cong [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000221455034)·Park, Kyobin [Argonne National Laboratory (ANL), Argonne, IL (United States)]·Cha, Hyun Gil [Korea Research Institute of Chemical Technology (KRICT), Ulsan (Korea, Republic of)] (ORCID:0000000212284464)·Delferro, Massimiliano [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:000000024443165X)·Kang, Donghyeon [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000339600823)

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Abstract

Polyethylene terephthalate (PET) depolymerization in base/alcohol hybrid systems represents a promising low-energy approach for chemically recycling PET waste into valuable monomers. This study investigates the mechanistic pathways of PET depolymerization in NaOH/alcohol solutions, emphasizing the competing roles of hydroxide and alkoxide species. Utilizing a combination of experimental techniques, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations, we explore how factors such as base concentration, alcohol chain length, and pKa values of alcohols influence PET depolymerization efficiency and pathways. Our findings indicate that alkoxide ions (RO⁻) exhibit notably higher reactivity than hydroxide ions (HO⁻), favoring an alcoholysis pathway in the base/alcohol hybrid system. Experimental results across a series of C1 to C5 alcohols show that longer-chain alcohols, particularly 1-butanol, achieve higher PET conversion, although this does not align solely with simple nucleophilicity trends of alkoxides. While DFT calculations reveal comparable activation energies for various alkoxides in PET depolymerization, MD simulations underscore the significant role of alcohol chain length, with longer-chain alcohols forming more stable or frequent interactions with PET. Additionally, the alkoxide concentration, influenced by the alcohol’s pK a , directly impacts PET conversion. These suggest that PET depolymerization is governed by a balance between alkoxide concentration and alkoxide-PET interactions, rather than activation energies or nucleophilicity alone. From a practical perspective, incorporating long-chain alcohols as cosolvents may enhance process efficiency but increases raw material costs by approximately 30%. However, long-chain alcohols present a safer and more sustainable alternative to hazardous cosolvents such as dichloromethane. This work offers a molecular-level understanding of PET depolymerization in base/alcohol systems and provides insights into optimizing these systems for more efficient and sustainable PET recycling processes.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY PET alcohols anions depolymerization hydrolysis methanolysis molecular dynamics polyethylene terephthalate recycling solvent effects solvents

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Yu, Hyejin [Argonne National Laboratory (ANL), Argonne, IL (United States)], Oh, Younghoon [Boston Univ., MA (United States)], Kim, Yu Lim [Argonne National Laboratory (ANL), Argonne, IL (United States)], Liu, Cong [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000221455034), Park, Kyobin [Argonne National Laboratory (ANL), Argonne, IL (United States)], Cha, Hyun Gil [Korea Research Institute of Chemical Technology (KRICT), Ulsan (Korea, Republic of)] (ORCID:0000000212284464), Delferro, Massimiliano [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:000000024443165X), Kang, Donghyeon [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000339600823). 2025-03-27. Molecular Level Understanding of Polyethylene Terephthalate (PET) Depolymerization in Base/Alcohol Hybrid Systems. https://doi.org/10.1021/acsami.4c20887

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