(478d) Metal-Containing Ionic Liquid As An Effective Catalyst for the Degradation of Poly(ethylene terephthalate) in Ethylene Glycol

The vast emissions of poly(ethylene terephthalate) (PET) wastes have caused serious environmental pollution and resource waste. Its effectively recycling has become a global problem which must be urgently solved.

Chemical recycling is an attractive process because PET can be degraded into monomers which can be used as raw materials to produce virgin plastic products. Glycolysis, as an important chemical recycling method, has received extensive concern due to its advantages of less volatile solvents, high conversion of PET, giving monomers and easily continuous production. But there are some drawbacks, such as high temperature, high pressure, low reaction rate and difficult separation between catalyst and product. Many researchers devoted to developing new catalysts to overcome the drawbacks above. Ionic liquids have been reported that could effectively catalyze the degradation of PET to give BHET monomers with high purity and make the reaction condition mild. But the conversion of PET and the selectivity of monomer bis(2-hydroxyethyl terephthalate)(BHET) are both low, and the reaction rate is slow. Therefore, the development of new catalysts is still critical.

It has been found that synergetic effect of catalysts can speed up a chemical reaction or make reaction condition mild.^[1,2] Yamamoto et al. found that combinations of organic and inorganic molecules bearing acidic groups could result in higher catalytic activity than individual catalysts for acid-catalyzed reactions.^[2] Wang et al. and Zhou et al. found that the synergetic effect of cation and anion of ionic liquid catalyst could make the degradation condition of PET milder.^[3,4] Therefore, we infer that a new catalyst containing two active components maybe has highly catalytic activity.

In this study, a metal-containing ionic liquid catalyst including two active components was synthesized and used for the PET degradation in ethylene glycol. The results showed that the synthesized catalyst has better low-temperature catalytic activity. The conversion of PET and the selectivity of BHET are 100 % and 78.7 % respectively at 175 °C for 1.25 h. The high catalytic activity is mainly attributed to the synergetic effect of two components. Moreover, this catalyst has the advantages of mild reaction condition, fast reaction rate, products being easily separated from catalyst and being of high purity.

[1]      P. R. Schreiner. Science, 2010, 327, 965.

[2]      H. Yamamoto and K. Futatsugi. Angew. Chem. Int. Ed., 2005, 44, 1924.

[3]      H. Wang, R. Y. Yan, Z. X. Li, X. P. Zhang and S. J. Zhang. Catal. Commun., 2010, 11, 763.

[4]      X. Y. Zhou, X. M. Lu, Q. Wang, M. L. Zhu and Z. X. Li. Pure Appl. Chem., 2012, 84, 789.