(A) study on the effect of ethyl benzoate in the precipitated MgCl2-supported TiCl4 catalyst for gas-phase propylene polymerization

Abstract

The effect of ethyl benzoate[EB] as internal Lewis base in the recrystallized $MgCl_2$ supported $TiCl_4$ catalysts was investigated. The titanium content in the catalyst increased with the [EB]/[Mg] molar ratio. The surface area of the catalyst was increased by adding small amount of EB but not affected further with excess EB. It is believed from X-ray diffractions and FTIR spectra that excessive amount of EB induced the formation of a $TiCl_4$-EB complex during the activation step. For the gas phase polymerization of propylene, there existed two different temperature regions of positive and negative activation energies, i.e., 1.0 to 6.5 kcal/mol at low temperature (below $50\,^\circ\!C$) and -6.0 to -4.0 kcal/mol at high temperature (above $50\,^\circ\!C$) respectively. The number of active sites measured by CO inhibition method decreased with EB and also the amount of cocatalyst $Al(C_2H_5)_3$. required to reach the mnaximum polymerization rate decreased. Investigations were made concerning the effect on the number average molecular weight of plymerization parameters.