Preparation, Characterisation And Catalytic Activity Of Magnesium/Titanium/Attapulgite Catalysts For PET Polycondensation

Polyethylene terephthalate(PET) is widely used in many fields because of the excellent property. At present, PET is also one of the fastest-growing synthetic materials which applied widely in China. Catalyst plays an important role in the production of PET. The traditional industrial application and research of catalysts mainly focus on antimony based catalyst.Antimony based catalyst has high technical maturity, but it is a kind of heavy metal which is harmful to environment and human health. Therefore, the development of new heavy-metal-free PET polycondensation catalyst with high activity and low environmental impact has been one of the biggest researching hotspots in polyester industry with broad development prospect.In this paper, three kinds of catalysts were prepared by different adding orders: A) titanium compound precipitated preferentially, then magnesium compound precipitated; B) magnesium compound precipitated preferentially, then titanium compound precipitated; C) magnesium and titanium compounds precipitated simultaneously, and used attapulgite as a carrier. The morphology, element analyze and thermostability of the composite catalysts(Mg/Ti/ATP) were characterized by field emission scanning electron microscopy(FESEM), Energy Dispersive Spectrometer(EDS), wide angle X-ray diffraction(XRD) and thermogravimetric analysis(TGA).The results showed that the morphology of Mg/Ti/ATP composite catalysts prepared by different precipitation order were different. Catalytic activities of the prepared catalysts were evaluated by TGA and DSC. The reaction kinetics of PET polycondensation was studied through "FWO(Flynn-Wall-Ozawa) method" and "isoconversional method" to calculate the activation energy Ea for PET polycondensation. At the same conversion rate, the results showed that the Mg/Ti/ATP composite catalyst which titanium compound precipitated preferentially was the best, and the activation energy Ea of the catalyst E was the lowest among this kind of composite catalyst, mass ratio of catalyst E was Ti/Mg/ATP =2.4:1.2:1.The catalytic activity of the composite catalysts was further verified by the polymerization experiment. The intrinsic viscosity, thermal properties, crystallinity and other properties of the prepared PET were analyzed. The results showed that the intrinsic viscosity of PET chip obtained by Mg/Ti/ATP catalysts was above 0.65dl/g, which could meet the practical production requirements of PET. At similar polycondensation time, the PET chip achieved a higher viscosity by using catalyst E, implying a higher catalytic activity for catalyst E.