Abstract
Poly(ethlyene terephthalate) waste from a local market was depolymerized by ethylene glycol (EG) in the presence of Lewis acidic ionic liquids [Bmim]ZnCl3 and the qualitative analysis showed that bis(hydroxyethyl) terephthalate was the main product. Compared with ionic liquid [Bmim]Cl, the Lewis acidic ionic liquids showed highly catalytic activity in the glycolysis of poly(ethylene terephthalate) PET. Significantly, the conversion of PET and the yield of bis(hydroxyethyl) terephthalate were achieved at 100% and 83.8% with low catalyst ([Bmim]ZnCl3) loading (0.16 wt %). Investigation also showed that the catalytic activity of [Bmim]ZnCl3 was higher than that of [Bmim]MnCl3. Catalyst [Bmim]ZnCl3 can be reused up to five times and 1H-NMR results show that the recovered catalyst is similar to the fresh one. A mechanism of the glycolysis of PET catalyzed by [Bmim]ZnCl3 was proposed.
Highlights
Poly(ethylene terephthalate), commonly known as PET, is used extensively in the manufacture of fibers, photographic films and soft drinks bottled
The components of the ionic liquids were characterized by electrospray ionization mass spectrometry (ESI-MS), and the results were shown in ESI mass spectrum of [Bmim]ZnCl3 showed the peak up to m/e 170.5 with intensity almost 100% and it indicated that the anion of Zn2+-containing ionic liquid was ZnCl3−
When the reaction time was shorted to 2 h, the conversion of PET in the glycolysis arrived at 100% in the presence of 5 wt % [Bmim]ZnCl3, and the bis(hydroxyethyl) terephthalate (BHET) yield rose to 82.6% (Table 1, entry 5), respectively
Summary
Poly(ethylene terephthalate), commonly known as PET, is used extensively in the manufacture of fibers, photographic films and soft drinks bottled. The glycolysis of PET was carried out in the presence of metal acetates [6,7], titanium-phosphate [8], solid superacids [9], metal oxides such as NiO, Fe2O3 or TiO2 [10], etc These catalysts are toxic and/or corrosive and/or resulting in severe pollution. In our previous research [14], the basic ionic liquid, 1-methyl-3-butylimidazolium hydroxyl ([Bmim]OH), was synthesized and used as a catalyst for glycolysis of PET. Lewis acidic ionic liquids were prepared and used to catalyze the glycolysis of PET in ethylene glycol (EG). The components and Lewis acidity of ionic liquids were characterized and the reaction conditions were optimized. Under the optimal reaction conditions, the Lewis acidic ionic liquid showed highly catalytic activity and high selectivity
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