Preparation Of MgCl₂/MMT Composite Supported Iron Based Catalyst For Ethylene Polymerization

Iron based catalyst has the advantages of high activity, copolymerization capability and so on, but the problem of double center inactivation is also detected. Consequently, the study of iron based catalyst loading has become a hot research topic in recent years.Firstly MgCl2 supports and MgCl2/MMT composite supports were respectively prepared by precipitation which is a new recrystallization method. Effects of organic montmorillonite (MMT) dosage, alcohol amount and alcohol type on the morphology and particle size of supports were investigated. The composite supports were activated at 120℃ and then used to load catalyst. Polyethylene/montmorillonite(PE/MMT) nanocomposites were prepared by ethylene polymerization with supported catalysts. Effects of MMT dosage on catalyst loading, activity and polymer properties were studied.The XRD results show that the crystal type of supports has a great change, and the supports are suitable to load catalyst for its poor crystallinity and high disorder degree. It can be concluded that MMT dosage, alcohol consumption and alcohol type can significantly affect the morphology and particle size of the supports through SEM analysis. The addition of MMT can obviously increase particle size of the supports and the suitable dosage of MMT is 5% and 10%, and the optimum amount of alcohol is 12. Butyl alcohol is suitable to prepare supports with small particle size, while ethanol is fit for preparation of large particles. The particle size can be regulated by adjusting the ratio of ethanol, butanol and isooctanol in a certain extent, but n-hexyl alcohol and n-octyl alcohol are not suitable for the preparation of spherical supports.UV spectrophotometry is used to determine the iron content of supported catalysts. The results show that iron content and catalyst load rate decreased significantly with the increase of MMT dosage. The results of polymerization show that the catalytic activity decreases obviously, while the bulk density of PE/MMT nanocomposites increased gradually with the increase of MMT content. And the activity of catalysts improve with the catalyst concentration decrease in polymerization.It can be concluded by XRD that PE/MMT nanocomposites have good crystallinity and the characteristic diffraction peaks of MMT disappear in the composite materials. The results show that MMT is well dispersed in polyethylene matrix.Thermal gravimetric analysis of different PE/MMT nanocomposite is conducted. The results show that the thermal degradation temperature of the polymer is only 360℃ and the thermal stability is poor when MMT dosage is 1.5%. When MMT dosage reach to 5%,10% and 15%, the initial degradation temperature of PE/MMT nanocomposites increased obviously, can up to 410℃.The effects of MMT content on melting temperature and crystalline properties of the nanocomposites are studied by DSC. The results show that the melting temperature increased gradually with increase of MMT dosage, while crystallization temperature shows few change. The crystallinity of composites increased gradually with increase of MMT dosage for the heterogeneous nucleation of MMT.