Effect of hydrogen on Ziegler - Natta catalysts prepared by different methods for ethylene polymerization

Abstract

This study focuses on effect of hydrogen on Ziegler-Natta (ZN) catalyst system for ethylene polymerization. The study was divided into four parts. Regarding to the first part, two types of ZN catalysts, TiCl4/MgCl2/THF (ZN-THF) and TiCl4/MgCl2•6EtOH (ZN-EtOH) catalysts, were compared. The results showed that ZN-EtOH had better active center distribution than that of ZN-THF. As a result, ZN-EtOH could retard the effect of hydrogen and showed higher activity than ZN-THF. According to higher hydrogen response of ZN-THF, ZN-THF system was selected to study in the second and the third parts with Lewis acid modification in order to improve the catalytic performance. AlCl3 and FeCl2 were employed in the second part. FeCl2 showed higher efficiency to remove the remaining THF in MgCl2 structure and provided better hydrogen response than AlCl3. For the third part, ZnCl2, mixed ZnCl2 with AlCl3 and mixed ZnCl2 with FeCl2 were studied in ZN-THF system. The results showed that ZnCl2 acted as a poison to catalyst resulting to the reduction of activity. The addition of the second Lewis acid could improve the activity; however, activity was still slightly lower than undoped ZnCl2 catalyst. For the last part, effect of alkoxysilanes as external donor on 2 types of the commercial catalysts, TiCl4/MgCl2•nEtOH and TiCl4/phthalate type/MgCl2, was investigated. Cyclohexylmethyldimethoxysilane could decrease activity more than dimethoxydimethylsilane did and provide higher hydrogen sensitivity as well.