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Issue 10, 2020
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Degradation of poly(ethylene terephthalate) catalyzed by metal-free choline-based ionic liquids

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Abstract

Glycolysis of poly(ethylene terephthalate) (PET) is a prospective way for degradation of PET to its monomer bis(hydroxyethyl) terephthalate (BHET) which can be polymerized again to form new qualified PET materials, and hence provides possibilities for a permanent loop recycling. However, most of the reported glycolysis catalysts are metal-based, leading to high cost and negative environmental impact. In this study, we developed a series of choline-based ionic liquids (ILs) without metals and applied them in the glycolysis of PET as catalysts. Choline acetate ([Ch][OAc]), which is cheaper, more biologically compatible and environmentally friendly in comparison with conventional imidazolium metal-based ILs, can achieve a comparable or even better performance than them. Under optimum conditions (PET (5.0 g), ethylene glycol (EG) (20.0 g), [Ch][OAc] (5 wt%), 180 °C, 4 h, atmospheric pressure), the yield of BHET reached up to 85.2%. Additionally, the reaction kinetics was studied and proved to be the shrinking-core model. The apparent activation energy is 131.31 kJ mol−1, and the pre-exponential factor is 1.21 × 1013 min−1. Finally, based on the experimental results and density functional theory (DFT) calculations, a possible mechanism was proposed. The promotion of the glycolysis reaction is attributed to the activation of EG by the formation of hydrogen bonds between EG and the IL.

Graphical abstract: Degradation of poly(ethylene terephthalate) catalyzed by metal-free choline-based ionic liquids

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Supplementary files

Article information


Submitted
26 Jan 2020
Accepted
14 Apr 2020
First published
15 Apr 2020

Green Chem., 2020,22, 3122-3131
Article type
Paper

Degradation of poly(ethylene terephthalate) catalyzed by metal-free choline-based ionic liquids

Y. Liu, X. Yao, H. Yao, Q. Zhou, J. Xin, X. Lu and S. Zhang, Green Chem., 2020, 22, 3122
DOI: 10.1039/D0GC00327A

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