Supported titanium–magnesium catalysts with different titanium content: Kinetic peculiarities at ethylene homopolymerization and copolymerization and molecular weight characteristics of polyethylene

Abstract

The effect of Ti content on the activity of titanium-magnesium catalysts (TMC) and molecular weight distribution (MWD) of polyethylene (PE) produced has been studied. It was found that the activity enhances sharply as Ti content decreases from 0.6 to 0.07 wt %, and shows no significant changes in the Ti content range of 0.6-5.0 wt %. The maximum activity (36 kg PE/mmol Ti  h  bar C 2 H 4 ) was observed for TMC with the lowest Ti content. The catalyst with low titanium content ($ 0.1 wt % of Ti) produced PE with narrower MWD (M w /M n ¼ 3.1-3.5) as compared to catalysts with higher titanium content (3-5 wt % of Ti; M w /M n ¼ 4.8-5.0). New data on the effect of hydrogen on MWD of PE have been found. Increasing hydrogen concentration results in broadening the MWD of PE, especially in the case of TMC with high titanium content. The data presented indicate the heterogeneity of active centers of TMC in the reaction of chain transfer with hydrogen. The data on the ethylenehexene-1 copolymerization over TMC with different titanium content are presented. Comonomer reactivity ratios were shown to be independent of the Ti content in TMC. Presumably the difference in activity of these catalysts is mainly caused by the difference in the number of active centers.

A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization

“…11 That type of support, i.e., highly dispersed MgCl 2 , was used to immobilize TiCl 4 and a catalytic system was obtained which was highly active both in ethylene polymerization and copolymerization. 12 In other studies, TiCl 4 was fixed to the magnesium support in the form of magnesium chloride complex with tetrahydrofuran modified with diethyl aluminum chloride. 13 That catalyst not only offered high activity but also it turned out stable in ethylene polymerization, and the polymer product was characterized by good morphology.…”

Ethylene Polymerization over Supported Titanium‐Magnesium Catalysts: Heterogeneity of Active Centers and Effect of Catalyst Composition on the Molecular Mass Distribution of Polymer

“…The activity of TMC-0.07 is about ten times higher then that of TMC-5. It was shown [2] that the reason of higher activity of TMC with low Ti content is the higher number of active centers. Similar Kp values for ethylene polymerization over TMC with different Ti content (0.1 and 0.9 wt.…”

“…Catalysts were synthesized via procedure described elsewhere [2,7] by supporting of titanium tetrachloride on highly dispersed magnesium chloride with average particle size 10 mm and narrow particle size distribution. Two catalysts with Ti content of 0.07 wt.…”

“…Highly active supported TMC with optimal morphology and controlled Ti content have been used in this study. Recently [2] we have presented some data on the activity of these catalysts and effects of Ti content and hydrogen content at polymerization on the MWD of PE produced. Based on these data we have selected TMC with low and high Ti content for the more detailed analysis of the heterogeneity of active centers of TMC by fractionation of PE samples for narrow fractions with following construction of MWD curves.…”

“…Polydispersity values (PD ¼ Mw/Mn) for PE produced with TMC are usually within the range of 4 Ä 8. [1,2] It is supposed that the main reason for MWD broadening (Mw/ Mn > 2) is heterogeneity of the active centers of these catalysts (multisite catalysts). However, the nature of this heterogeneity remains unclear.…”