Effects of Temperature and Cocatalyst Concentration on the Number of Active Sites in a TiCl4/Mg(OEt)2 Catalyst for Ethylene Polymerization

Abstract

The slurry polymerization of ethylene was studied by employing a (TiCl4/Mg(OEt)2/TEA) catalyst system in hexane. The effects of triethylaluminum concentration and temperature on polymer yield and polymer viscosity average molecular weight, Mv, were investigated. The maximum polymer yield was obtained at an Al/Ti molar ratio of 124. The highest yield and Mv were achieved at 60 °C. The concentration of active sites of the obtained catalyst system for ethylene polymerization was evaluated as a function of Al/Ti molar ratio and polymerization temperature. Increasing Al/Ti molar ratio from 62 to 124 raised the active site concentration of catalyst, [C*], from 0.0003 to 0.0017, whereas a further increase in Al/Ti molar ratio from 124 to 231 reduced [C*] from 0.0017 to 0.0013. Similarly, increasing the temperature from 40 °C to 60 °C increased the [C*] from 0.0002 to 0.0017, but when temperature was increased above the optimum value, [C*] decreased.

Keywords

• active site concentration
• triethylaluminum
• ziegler-natta catalyst
• ethylene polymerization
• molecular weight