Glycolysis of Poly(ethylene terephthalate) over Mg-Al Mixed Oxides Catalysts Derived from Hydrotalcites

Poly(ethylene terephthalate) (PET) was depolymerized by ethylene glycol (EG) in the presence of Mg-Al hydrotalcites and their corresponding mixed oxides as solid base catalysts. Mg-Al hydrotalcites with different Mg/Al molar ratios were prepared; it was confirmed by powder X-ray diffraction (XRD) that the materials had hydrotalcite structure. Compared with their corresponding precursors, Mg-Al mixed oxides obtained by the calcination of hydrotalcites exhibited higher catalytic activity for the glycolysis of PET. Furthermore, Mg-Al mixed oxides calcinated at 500 degrees C with Mg/Al molar ratio of 3 offered the highest catalytic activity for the glycolysis of PET. The experimental results showed that the basicity of catalyst played an important role on the glycolysis activity. The solid catalyst could be easily separated and reused after calcinations again. The influences of experimental parameters on the yield of bis(hydroxyethyl terephthalate)(BHET) were investigated. The evolution of the glycolysis of PET was described by infrared spectroscopy (IR), viscosity-average molecular weight, and scanning electron microscope (SEM).