Preparation of Diacid Comprising Ionic Liquid Catalyst and Its Application in Catalytic Degradation of PET

Five kinds of diacid comprising ionic liquid catalyst [HO 3 S–(CH 2 ) 4 -mim]Cl–MCl x ] were prepared, and their chemical structure, thermal stability and acidity were tested and analyzed. The performance evaluation of catalysts was carried out, and the process parameters were optimized. The cycling stability of the catalysts was investigated. Then, the catalytic degradation of polyethylene terephthalate (PET) was studied, and used mineral water bottles as an example. The chemical structure and molecular weight of the degradation product terephthalic acid bis(2-hydroxyethyl) ester (BHET) were analyzed. The results showed that among the catalysts synthesized, [HO 3 S–(CH 2 ) 4 -mim]Cl–FeCl 3 had the great catalytic performance and good thermal stability. According to the thermal gravimeter analysis, the decomposition temperature of the diacid ionic liquid catalyst ranges from 400 to 560 °C, while the degradation reaction temperatures in this paper are all below 250 °C, so that it has good thermal stability. At 190 °C, the PET alcoholysis rate reached 98.7% and the BHET yield reached 95.5% for 6 h, and the highest catalytic activity could still be maintained after 6 cycles, which indicate that the catalyst has excellent performance for degrading PET, and will have a great application prospect. Graphic Abstract