| A novel laboratory-scale gas-phase polymerization reactor system with improved temperature control was designed, constructed and used to study the kinetics of polymer-supported bis(n-butylcyclopentadienyl)zirconium dichloride and methyl aluminoxane (MAO) catalysts. The 2 L stainless steel reactor was cooled by flow of proportioned amounts of hot and cold oil coming from a single partitioned heating bath, through drilled bores in the reactor walls. Static mixers in the coolant channels ensured good heat transfer. Control of the bulk gas temperature in the reactor to +/- 0.2°C during polymerization at rates up to 0.04 mol-C2H4/min was achieved with this novel design. An online GC connected via a modified metering-valve with zero volume in the high pressure side was used to analyze the head-space gas composition. A mini-reactor with Pyrex windows built from a Swagelok Tee, interfaced with a video microscope was used to observe the growth of catalyst/polymer particles during polymerization.; Twenty two batches of supported metallocene catalysts, with aluminum and zirconium from 12.9 to 21.2 and 0.12 to 0.35 mass%, respectively and Al:Zr ratio of 168 to 482, were prepared by contacting MAO solution with the carrier, followed by the addition of the metallocene solution and then drying under vacuum to obtain free flowing solid catalysts. Both in-house and commercial organic polymeric porous supports of size range from 5 to 850 mum were used.; The supported catalysts were active for both ethylene homopolymerization and ethylene/1-hexene copolymerization in temperature range 60 to 100°C and ethylene pressure range 0.34 to 2.07 MPa. Except for the 5 mum sized catalysts, all catalysts had in general much higher copolymerization activity [up to 37,000 kg-PE/(mol-Zr)·h] than homopolymerization activity [up to 21,000 kg-PE/(mol-Zr)·h]. However, the highest activity was shown by the 5 mum sized supported catalysts that had both high homo- and co-polymerization activity [up to 189,000 and 78,000 kg-PE/(mol-Zr)·h respectively]. The catalyst activities depended on the polymerization temperature, concentrations of comonomer and scavengers, ethylene pressure, and size of support particles. In the larger-sized lower activity supported catalysts, the catalyst particles fragmented in layers during copolymerization and resulted in formation of concentric shells of polymer while during homopolymerization polymer grew outward from the unfragmented catalyst cores. The shapes of the support particles were replicated during polymerization.; The molar masses of the copolymers (Mw range 50 to 175 kg/mol) were significantly less than that of the homopolymers (Mw range 130 to 265 kg/mol). The short chain branching (SCB) increased with increase in initial concentration of 1-hexene. Both molar masses and SCB depended on polymerization time and radial position in the polymer particle. |
