Catalysis
Hideki Kurokawa; Shou Kikuchi; Hiroshi Miura
Abstract
MAO-free supported catalysts for ethylene polymerization were prepared by sequentially treating montmorillonites (MMTs) with R₃Al and then with zirconocene. MMTs possessing different physicochemical properties—such as surface area, acidity, and crystallinity—were employed for catalyst preparation. ...
Read More
MAO-free supported catalysts for ethylene polymerization were prepared by sequentially treating montmorillonites (MMTs) with R₃Al and then with zirconocene. MMTs possessing different physicochemical properties—such as surface area, acidity, and crystallinity—were employed for catalyst preparation. Three zirconocenes, Cp₂ZrCl₂, (1,3-Me₂Cp)₂ZrCl₂, and Me₂Si(Cp)₂ZrCl₂, were used. Acid treatment of raw MMT (Na⁺-montmorillonite) increased the surface area while decreasing both the Al content and crystallinity. The maximum surface area (316 m² g⁻¹) was obtained when the residual Al content was 18%. The effects of triethylaluminum (TEA) and triisobutylaluminum (TIBA) on catalyst performance were investigated. Although treatment of surface OH groups was necessary to obtain the zirconocene-supported catalysts with high activity, no significant difference in catalytic activity was observed between TEA- and TIBA-treated MMTs. In contrast, the type of R₃Al used as a scavenger during polymerization strongly influenced catalytic activity: catalysts employing TEA exhibited much lower activity than those using TIBA. Since TEA is a stronger Lewis acid than TIBA, it likely coordinates more strongly to the active sites, thereby acting as an inhibitor. Therefore, TIBA was employed in all subsequent experiments. The catalytic activity, based on catalyst weight, increased with both surface area and the amount of supported zirconocene, reaching a maximum when the residual Al content was 54%. A linear correlation between the activity (per catalyst weight) and the amount of supported zirconocene was observed for two zirconocenes, Cp₂ZrCl₂ and (1,3-Me₂Cp)₂ZrCl₂, indicating that the supported zirconocenes functioned uniformly as active species for ethylene polymerization. However, 5–7 μmol g⁻¹-cat of zirconocene formed inactive species in both catalysts. Unusual behavior was observed for the supported Me₂Si(Cp)₂ZrCl₂ catalysts: at higher residual Al content, the correlation was similar to that of the other two catalysts, whereas at lower residual Al content, most of the supported zirconocene formed inactive species, and only a small fraction acted as active sites. We speculate that Me₂Si(Cp)₂ZrCl₂ is difficult to activate, and that only the species formed by reaction of strong acid sites with R₃Al can specifically activate this complex.
Catalysis
Odilia Pérez-Camacho; Eduardo Cardozo-Villalba
Abstract
In this work, the interaction between a polystearylmethacrylate (Mn = 8,900 g mol-1, Xn = 26, Ð = 1.1) and modified methylaluminoxane 12 (MMAO-12) co-catalyst is studied using different spectroscopic methods. The effect of this oxygen-donor additive was measured by the changes in the bulk ...
Read More
In this work, the interaction between a polystearylmethacrylate (Mn = 8,900 g mol-1, Xn = 26, Ð = 1.1) and modified methylaluminoxane 12 (MMAO-12) co-catalyst is studied using different spectroscopic methods. The effect of this oxygen-donor additive was measured by the changes in the bulk density of the raw polyethylene, which resulted increased respect to those obtained in blank reactions. A decrease in the activity was also observed as a penalty for the improvement of the bulk density, enhancing the possibility of reducing fouling. The coordination of the carbonyl oxygen groups of polystearylmethacrylate to aluminum (III) centers is confirmed by 1H-NMR and FTIR studies, and by a simple semi-empirical computational calculation. A method for obtaining a tri-component co-catalyst mixture is described using the methyl-bridging capacity of trimethylaluminum and its Lewis acidity to get the polystearylmethacrylate and MMAO-12 linked together. This robust adduct introduces a hierarchy over the PE chain growing, leading to higher bulk densities for PE beads (0.43 g cm-3) concerning blank reactions (0.26 g cm-3).
Catalysis
Takao Tayano; Takehiro Sagae; Takashi Atsumi; Hideshi Uchino; Masahide Murata; Tsutomu Sato
Abstract
Spray dry granulation of clay minerals was studied to obtain clay mineral base support material for metallocene supported olefin polymerization catalysts. The morphology of the granules was strongly influenced by the nature of the clay mineral itself. Because of swelling characteristics of montmorillonite, ...
Read More
Spray dry granulation of clay minerals was studied to obtain clay mineral base support material for metallocene supported olefin polymerization catalysts. The morphology of the granules was strongly influenced by the nature of the clay mineral itself. Because of swelling characteristics of montmorillonite, its water dispersion was highly viscous even in the low slurry concentration (< 4 wt %). Therefore, it was very difficult to control the granule characteristics such as size, shape, and inside structure by the spray dry with the clay mineral slurry. Then we examined some methods in order to change the clay mineral surface properties for getting less viscous dispersion. It was found that the milling of montmorillonite increased the amount of surface OH groups. This surface characteristic change should promote the interaction between the edges and basal planes of the primary particles of milled montmorillonite, resulting in the lowering the slurry viscosity. The milling is effective for overcoming difficulty in use of high concentration montmorillonite slurry in spray dry granulation which is indispensable for producing granules in the wide range of size (10–50 μm). The spray-dried montmorillonite granules are useful as a "Support-Activator" for an olefin polymerization catalyst combined with metallocenes.
