New effective catalysts for glycolysis of polyethylene terephthalate waste: Tropine and tropine-zinc acetate complex

Waste plastic such as polyethylene terephthalate (PET) can be seen everywhere and has become one of the largest sources of household waste. PET is difficult to be degraded naturally and so its glycolysis has been attracted extensive attention. A new catalyzed glycolysis of PET was developed with new catalysts, tropine and tropine-zinc acetate complex. Conversion 100% of waste PET and product yield 82.3% of BHET was obtained in conditions (190℃, EG:PET = 5:1, catalyst:PET = 1:20). The influence of PET particle size on the glycolysis was discussed. It found that smaller particle size could speed up remarkably reaction rate but had little effect on the conversion or yield. Recovery of tropine-zinc acetate complex was tested and the catalytic efficiency was maintained at 70% after five times. In view of the spectrum characteristic and appearance, the complex was most likely to be formed with coordination rather than with hydrogen bond, so it may be called coordination complex of natural alkaloids and metal-salt (CCNAM). Further, the mechanism of catalytic glycolysis was studied and may be attributed to hydrogen bond, coordination bond and electrostatic interactions. It demonstrates that the composite catalyst of tropine and zinc acetate can apparently improve the reaction rate and product selectivity, which may provide a strategy for developing new green catalysts for glycolysis.