1-Hexene Polymerization Using Ziegler-Natta Catalytic System with Response Surface Methodology

The effects of process conditions and their interactions on the catalyst activity in 1-hexene polymerization were studied with design of experiments by response surface methodology (RSM) using a commercial Ziegler-Natta (ZN) catalyst in the form of TiCl4/MgCl2/Di-n-butyl phthalate. The effect of different operational variables on the catalyst activity was examined by performing the primary experiments of 1-hexene polymerization. Among different operational variables, three variables including monomer concentration, polymerization temperature and cocatalyst/catalyst molar ratio (Al/Ti) were considered as the main parameters which affected the catalyst activity in the 1-hexene polymerization. The Box-Behnken model with three main parameters in three level responses for each factor was applied to analyze the parameter relationships. After demonstrating the reproducibility of the experimental results, the statistical analysis of experimental data showed that the monomer concentration and Al/Ti molar ratio affected the catalyst activity significantly. It was found that, at room temperature, by increasing the monomer concentration from 80.0 mmol to 239.9 mmol, the activity of the studied ZN catalyst increased from 75.2 to 265.1 gpoly(1-hexene)/gcat. In addition, by changing the Al/Ti ratio from 45.9 to 136.8, the catalyst activity increased from 145.2 to 265.1 gpoly(1-hexene)/gcat. The maximum activity of catalyst was obtained at the polymerization temperature around 25°C, and by increasing the temperature the activity of studied catalyst decreased. Based on the RSM, the best polymerization condition was obtained at a polymerization temperature of about 35°C, Al/Ti ratio of 136.8, and monomer concentration of 239.9 mmol, which resulted in maximum productivity of the catalyst.