Studying the effects of SiO2 specifications and properties of (SiO2/MgCl2/TEOS/TiCl4/AlEt3) catalyst system on kinetic behavior and hydrogen responsibility of ethylene slurry polymerization

Abstract

A series of silica gels with different physico-chemical properties such as average pore size diameter, pore volume, attrition quality index, and bulk density were prepared, characterized, and subjected to treatment in special thermal program. Catalyst precursors were prepared by reaction of these silica gels with dibutyl magnesium (MgBu2) at 50°C and then addition of tetraethoxy ortho silicate and subsequent impregnation with titanium tetrachloride (TiCl4). Polymerization of ethylene by these catalysts at comparable conditions and also at different Ph2/Pc2 ratio was carried out; the results showed that support properties have significant influence on polymerization behaviors such as activity profile, productivity, and hydrogen responsibility. To quantitative analysis of the results, a new kinetic relation for rate-time profiles was derived, and these kinetic parameters were used to study and calculate of the effects of support specification. It was observed that trends of activity profiles were mainly affected by support properties and as well as PH2/PC2 ratio. Interestingly enough, catalysts with different pore volume diameter show different behavior with variation of PH2/PC2 ratio. Increasing in pore size diameter from 60 to 200 Å give raises catalyst activity by two times. Finally, mentioned variables were attributed to different particle growth and mechanism of fragmentation during polymerization. © 2010 Wiley Periodicals, Inc.