Maximization of the amount of active titanium fixed on the surface of the supported ziegler-natta catalyst

Abstract

Slurry polymerization of propylene polymerization was investigated to maximize the amount of active titanium fixed on the surface of supported Ziegler-Natta catalyst composed of magnesium chloride/2-ethylhexanol/titanium tetrachloride/internal electron donor where diethyl phthalate and triethylaluminum were employed as internal electron donor and cocatalyst, respectively. The novel characterized techniques, Electron Spin Resonance (ESR) and CO2 Temperature Programmed Desorption (CO2 TPD), were found to be useful for the characterization of the supported Ziegler-Natta catalyst. From the ESR experimental results, the correlation between the intensity of ESR signal and the catalytic activity was discovered to be linearity and it can be assigned that the ESR signal intensity reflects to the performance of catalysts. The catalysts were also characterized for the amount of CO2 desorbed from the catalysts by Temperature Programmed Desorption method. The total desorbed CO2 molecules were related to the catalytic activity linearly and it can be mentioned that the total amount of CO2 desorbed from the catalyst surface reflects to the active site concentration and then the performance of catalysts. From the CO2 TPD result of the catalyst prepared without internal electron donor, the TPD curve contained two maxima while the CO2 TPD curves of the catalysts prepared with different DEP/MgCl2 mole ratios were appeared in four maxima. Thus, it can be concluded that internal electron donor can increase the multiplicity of active site in the supported catalyst. This study also showed that the maxima at the temperature of 450-500 ํC is assigned to the desorption of CO2 from the aspecific active site. Besides, triethylaluminum used as the cocatalyst can promote the vacant sites in the active center of the supported Ziegler-Natta catalyst.