Preparation of functionalised heteropolyacid ionic liquids and their application in catalytic degradation of bottle-grade polyester

Four different acidic and basic ionic liquid intermediates were prepared first, and then combined with designed Fe-molybdenum Keggin-type heteropolyacids to prepare four functionalised heteropolyacid ionic liquid catalysts, functionalised heteropolyacid ionic liquids (FPOM-Ils). The performance of the catalytic degradation of bottle-grade polyester using the four heteropolyacid ionic liquids was investigated by taking waste mineral water bottle fragments as samples. Orthogonal tests were designed to rank reaction conditions in terms of their effects on the catalytic performance, which was most significantly affected by the reaction temperature. The degradation product, bis(hydroxyethyl) terephthalate (BHET), was also analysed for its chemical structure and purity. The results showed that the four heteropolyacid ionic liquid catalysts were successfully prepared, with good thermal stability. Among them, [HO3S-(CH2)3-mim]6[Fe(H2O)FeMo11O39] showed the best catalytic performance, which was achieved at 196 degrees C, a feeding ratio of 8 : 1, a reaction time of 3 h, and a catalyst dosage (as a percentage of reactant mass) of 0.2 wt%. At 196 degrees C, the alcoholysis rate could reach 100% and the yield of BHET was 91.92%. After six times of recycling, the alcoholysis rate was still as high as 94.36% and the yield of BHET was 82.3%, which demonstrated the desirable performance and promising development prospects of the prepared heteropolyacid ionic liquid catalysts in the catalytic degradation of bottle-grade polyester. This research study is related to an environmentally friendly process method for catalytic degradation of bottle-grade PET by using ionic liquid catalysts.