Preparation of metal-based ionic liquid catalysts and their application to degrade waste polyester fiber

Abstract

Four types of metal-based ionic liquid catalysts [DA-2PS][FeCl₄]₂, [DA-2PS][MnCl₃]₂, [DA-2PS][AlCl₄]₂, and [DA-2PS][SnCl₅]₂ were prepared. Their structure and thermal properties were characterized and analyzed by FTIR, ¹H NMR, and TGA. The type of acid was analyzed using pyridine infrared spectroscopy. Waste polyester fiber (PET) was used as the sample for glycolysis, and the performance of the four metal-based ionic liquid catalysts in degrading PET was investigated. By optimizing the process parameters, the best reaction conditions were obtained, and the chemical structure and purity of the degradation product bis(hydroxyethyl) terephthalate (BHET) were analyzed. The results showed that the four metal-based ionic liquid catalysts were successfully synthesized and exhibited good thermal stability, among which [DA-2PS][FeCl₄]₂ demonstrated the best catalytic performance. Under the conditions of a temperature of 190 °C, a mass ratio of ethylene glycol to PET of 9 : 1, a reaction time of 7 h, and a catalyst amount of 2.5% of the total mass of the reactants, the PET conversion reached 96.5%, and the BHET yield was 89.1%. Furthermore, the catalyst maintained high catalytic activity even after six cycles of use, indicating that the synthesized metal-based ionic liquid catalysts exhibit excellent catalytic degradation performance for PET, providing a theoretical basis for the chemical recycling of waste polyester fiber.