Metal ions immobilized on polymer ionic liquid as novel efficient and facile recycled catalyst for glycolysis of PET

Abstract

Environmental pollution aroused by accumulation of waste PET has attracted worldwide attention. Metal chloride as Lewis acid catalyst has excellent catalytic performance in enormous organic reaction. However, the high solubility of the metal chloride in ethylene glycol and the residue of metal ions in the product will have an adverse impact on the subsequent process. In this work, polymer ionic liquid containing [NTf2]− which is insoluble in ethylene glycol at room temperature was synthesized and used to immobilize metal ions to catalyze glycolysis of PET. After reaction, the polymer ionic liquid-metal ion catalyst could be recovered at room temperature by simple filtration. PET conversion reached 95.4% and BHET yield reached 77.8% using PIL-Zn2+ as catalyst at 195 °C for 120 min. Ionic liquid was characterized by FT-IR, NMR and ESI-MS. Interaction between ionic liquid and metal ions was characterized by FT-IR. The interaction energy of polymer ionic liquid-metal ion complex is higher than that of ethylene glycol-metal ion complex by DFT calculation (Density functional calculation). The both content of metal ion in polymer ionic liquid-metal ion complex and catalytic performance of as-synthesized catalysts did not obviously decrease after the catalyst was reused for five times. This work mainly provided a way of recovering catalyst and promote development of glycolysis of PET.