Preparation,Characterisation And Catalytic Activity Of Nb₂O₅/AT Catalysts For PET Polycondensation

Heavy metal-free PET polycondensation catalyst is one of research hotspots in polyester industry.The titanium-based catalysts with high catalytic activity are susceptible to hydrolysis which may induce side reactions.The catalytic activity of aluminium-based catalysts is inferior to conventional antimony catalysts,therefore,it need more catalyst dosage in polycondensation.In recent years,the niobium-based catalysts have been proved to be environmentally friendly catalysts and have attracted more and more attractions.In this thesis,attapulgite-supported Nb2O5 catalysts for polycondensation of PET were prepared by direct precipitation and calcined at 130℃.The structure and morphology of the synthesized catalysts were characterized by thermogravimetric analysis(TGA),Fourier Transform infrared spectroscopy(FTIR),wide angle X-ray diffraction(XRD)and scanning electron microscopy(SEM).The catalytic efficiency of the catalysts with different recipes was studied by DSC.The non-isothermal polycondensation kinetics of BHET was studied by Starink methods.In order to verify the catalytic activity of the Nb2O5/AT catalyst,the direct esterification process of terephthalic acid and ethylene glycol were carried out by the preferred catalyst.The crystallization behavior of the resulting PET chips was investigated by DSC,and the spinnability of the chips was studied by the melt-spinning process.The TGA and XRD results showed that Nb2O5 component in Nb2O5/AT catalyst contained crystalliferous water,and was in the amorphous state.The FTIR and SEM results showed that there were plenty of hydroxyl group on the surface of the Nb2O5/AT catalyst,and Nb2O5 was well dispersed on the surface of AT.The catalyst with the mass ratio(Nb2O5:AT)of 50:50 showed the most remarkable catalytic activity among all the receipts.When the condensation conversion was 0.4,the apparent activation energy Ea was 63.3KJ/mol.Compared with Sb2O3 and AlO(OH)/AT catalysts,Nb2O5/AT catalyst had advantages of less dosage and shorter polycondenation time.The intrinsic viscosity of the synthesized PET chip was about 0.68～0.78 dL/g.Owing to the nucleating effect of AT,the obtained PET chips exhibited fast crystallization rate.The result of melt spinning experiments showed that PET chips had good spinnability.