Hydrogen effects in TiCl4/MgCl2/THF catalysts with second Lewis acid addition on ethylene polymerization behaviors

Abstract

In this study, four Ziegler–Natta (ZN) catalysts with the absence and presence of Lewis acids including TiCl4/MgCl2/THF (None–THF), TiCl4/ZnCl2/MgCl2/THF (Zn–THF), TiCl4/ZnCl2/AlCl3/MgCl2/THF (ZnAl–THF), and TiCl4/ZnCl2/FeCl2/MgCl2/THF (ZnFe–THF) were synthesized, characterized, and used for ethylene polymerization. This research aims to elucidate the hydrogen effects in different Lewis acid-doped ZN catalysts on ethylene polymerization behaviors in terms of catalytic activity and polymer properties. With the absence of hydrogen during polymerization, it was found that ZnCl2 decreased the catalytic, because it acted as a catalyst poison. The catalytic activity was in the order of None–THF > ZnFe–THF > ZnAl–THF > Zn–THF. Thus, the addition of second Lewis acids such as AlCl3 and FeCl2 was able to improve the catalytic activity of Zn–THF catalyst. In addition, ZnFe–THF catalyst exhibited slightly higher activity than ZnAl–THF catalyst. This is because FeCl2 may better participate in MgCl2 structure due to similar atomic radius, leading to more efficiently removal of the remaining THF in the final catalyst. With the presence of hydrogen during polymerization, the decrease in catalytic activity was in the order of ZnFe–THF < ZnAl–THF < Zn–THF < None–THF with increasing H2/C2H4 molar ratio from 0.08 to 0.60. The hydrogen response on molecular weight was also observed for all catalysts in this study.