Study On Ethylene Polymerizations Of Metallocene Catalyst Microparticles

Metallocene catalysts have many advantages, such us high activity, narrow molecular weight distribution, and outstanding catalytic capacity of copolymerization. In spite of their numerous advantages, there are several practical problems to be solved in order to use metallocene catalysts widely in industry, such as the difficulty in controlling polymer morphology with soluble homogeneous catalysts, the inability to be used in continuous slurry and fluidized-bed gas-phase processes, significant reactor fouling, and the very large amount of MAO needed to achieve maximum metallocene catalytic activity. For the purpose of keeping the characteristics of homogeneous metallocene catalysts and using metallocene in the presenting industrial apparatus, supporting the catalyst on supporters was the key technology. In the polyolefin industry of using Ziegler-Natta catalyst, in order to improve catalytic activity, various of inorganic compound such as SiC>2, AbOsand MgChare used as supporters. Recently, organic-supported catalysts have been pay more attention by people, because the polymer-supported catalysts offer lower inorganic residues in the polyolefins as compared to these using SiCK, Al^Oj orFirstly, the polystyrene-supported bis(cyclopen-tadienyl) titanium dichloride] microparticles were prepared by RESS process and metallocene [Cp^TiCli] was supported on the polystyrene microparticles through co-precipitation. The obtained catalyst microparticles were employed in the ethylene slurry polymerization in the presence of co-catalyst ?methylaluminoxane.Then, the influence of polymerization temperature, polymerization pressure and [Al]/[Ti] molar ratio on catalytic activities of the obtained catalyst microparticles and molecular weight of polymer were investigated. It was found that the activities increase with increasing polymerization pressure, but the effect of [Al]/[Ti] molar ratio and polymerization temperature is not monotone. There is an maximum activity when the [Al]/[Ti] molar ratio is 2000 or when the polymerization temperature is 60癈. It is also evident that molecular weight increase with increasing polymerization pressure, but decrease with increasing polymerization temperature and [Al]/[Ti] molar ratio.Finally, the morphologies of catalyst microparticle and polymer particle wereanalyzed by SEM. There are five morphological types (spheroid, cobweb, spherical fold, flake and walnut kernel) in the catalyst microparticles and four morphological types (spheroid, stringy, flake and cocoon) in the polymer particles. We have also discussed the mechanism of particle formation.The results showed that the polymer-supported metallocene by RESS process have much higher activities and better morphology than those of inorganic-supported metallocene.