Alkali-decomposition (depolymerization) of poly(ethylene terephthalate) (PET) was studied in a mixed solvent of an alcohol (ethanol or methanol) and ether (dioxane, tetrahydrofuran, or dimethoxyethane). The time for complete decomposition (>96%) of solid PET with NaOH in methanol at 60°C was 40 min when dioxane (10 vol%) was added as co-solvent in the reaction mixture, whereas 7 h without dioxane. Disodium terephthalate, a product, precipitated quantitatively in the media and was separated easily. From the filtrate, ethylene glycol (EG) was recovered by distillation while, for practical use, the major portion of the filtrate was recycled repeatedly as the reaction medium.
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The reaction system is composed of liquid-solid bi-phases. The depolymerization takes place rapidly on the solid surface before dissolution of the polymer.
Two types of PET pellets, Mw=30000 and 33000, behaved similarly under the conditions examined.
Chemical stability of DMI in acids and alkalis is reported much higher than that of DMSO, DMF, and NMP. M. Fieser, “Fieser and Fieser’s Reagents for Organic Synthesis,” Vol. 11, John Wiley & Sons, New York, N.Y., 1984, p 202.
In the kinetic treatment of this solid-to-liquid depolymerization, the concentration of PET must be constant because the surface of PET pellets can be considered equivalent to the PET concentration; see also ref 19.
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Hu, LC., Oku, A., Yamada, E. et al. Alkali-Decomposition of Poly(ethylene terephthalate) in Mixed Media of Nonaqueous Alcohol and Ether. Study on Recycling of Poly(ethylene terephthalate). Polym J 29, 708–712 (1997). https://doi.org/10.1295/polymj.29.708
- Poly(ethylene terephthalate) (PET)
- Plastic Recycling
- Alkali Decomposition
- Mixed Solvent System
- Terephthalic Acid
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