Impact of AlCl3 and FeCl2 Addition on Catalytic Behaviors of TiCl4/MgCl2/THF Catalysts for Ethylene Polymerization and Ethylene/1-Hexene Copolymerization

The present research focuses on elucidating of the impact of Lewis acids including AlCl3 and FeCl2 addition on catalytic behaviors during ethylene polymerization and ethylene/1-hexene copolymerization over the TiCl4/MgCl2/THF catalyst (Cat. A). In this study, the Cat. A with the absence and presence of Lewis acids was synthesized via the chemical route. Then, all catalyst samples were characterized and tested in the slurry polymerization. For ethylene polymerization, using the Cat. A with the presence of AlCl3 apparently gave the highest activity among other catalysts. In addition, the activity of catalysts tended to increase with the presence of the Lewis acids. This can be attributed to an enhancement of active center distribution by the addition of Lewis acids leading to larger amounts of the isolated Ti species. Moreover, with the presence of Lewis acids, the effect of hydrogen on the decreased activity was also less pronounced. Considering ethylene/1-hexene copolymerization, it revealed that the catalyst with the presence of mixed Lewis acids (AlCl3 + FeCl2) exhibited the highest activity. It is suggested that the presence of mixed Lewis acids possibly caused a change in acidity of active sites, which is suitable for copolymerization. However, activities of all catalysts in ethylene/1-hexene copolymerization were lower than those in ethylene polymerization. The effect of hydrogen on the decreased activity for both polymerization and copolymerization system was found to be similar with the presence of Lewis acids. Based on this study, it is quite promising to enhance the catalytic activity by addition of proper Lewis acids, especially when the pressure of hydrogen increases. The characteristics of polymers obtained upon the presence of Lewis acids will be discussed further in more detail.