Ethylene polymerization with methylaluminoxane/(nBuCp)₂ZrCl₂ catalyst supported on silica and silica‐alumina at different Al_MAO/Zr molar ratios

Abstract

Methylaluminoxane (MAO)/(nBuCp) 2 ZrCl 2 metallocene catalytic system was supported on silica and silica-alumina. The Zr loading was varied between 0.2-0.4 wt %, and the MAO amount was calculated to get (Al MAO / Zr) molar ratios between 100 and 200, suitable for the industrial ethylene polymerization of supported metallocene catalysts. Catalytic activity was statistically analyzed through the response surface method. Within the ranges studied, it was found that Zr loading had a negative effect on polymerization activity, which increases with the (Al MAO /Zr) molar ratio. Catalysts supported on silica-alumina are more active than those supported on silica, needing less MAO to reach similar productivity, which constitutes an important advantage from an economical and environmental point of view. Supported catalysts were characterized by ICP-AES, SEM-energy-dispersive X-ray spectrometer, and UV-Vis spectroscopy, whereas polyethylenes were characterized by GPC and DSC. Molecular weight and crystallinity are not influenced by Zr loading or (Al MAO /Zr) ratio, in the range studied. In general, silica-supported MAO/(nBuCp) 2 ZrCl 2 catalysts give polyethylenes with higher molecular weight and polydispersity but lower crystallinity.

Kinetics and Growth of Polyethylene Nanofibrils over Metallocene Catalyst Supported on Flat Silica and Spherical Nano‐Silica Particles

“…It is shown that the catalyst loading per unit surface area of the non‐porous silica nanoparticles is much larger than the typical catalyst loading in conventional (commercial) porous micron‐sized silica supported catalyst as illustrated in Table . According to the literature, the Zr loading on silica by impregnation method is about 1.8 × 10 −7 mol Zr m −2 (0.4 wt%), which is consistent with the Zr loading data as shown in Table .It is also observed that the Zr loading (mol m −2 ) for the flat silica supported catalyst is about three times larger than that for the nano‐silica supported catalyst. The data in Table indicates that although the zirconium loadings (mol per gram of silica) for the nano‐silica and commercial micron‐sized porous silica supported catalysts are quite similar, the Zr loading per unit surface area (mol m −2 ) on the commercially available silica supports is only 3.8–4.8% of that on the nano‐silica support and 1.4–1.7% of that on the flat silica support.…”

Development of a new synthetic method based on in situ strategies for polyethylene/clay composites

“…The catalyst supported on silica (REF) was used as a reference because it is the most common support for metallocene systems 43. The amounts of MAO and metallocene were calculated in order to get supported catalysts with an Al(MAO)/Zr molar ratio of 190, according to previous studies 49. The impregnations were performed at room temperature, in a stirred vessel for 3 h with a volume of impregnating solution thrice the pore volume of the support.…”

Synthesis and structural characterization of a nickel(II) precatalyst bearing a β‐triketimine ligand and study of its ethylene polymerization performance using response surface methods

“…with the minimal number of experimental runs 26. Although there has been use of RSM to evaluate the effects of polymerization controlling factors in Ziegler Natta and metallocene systems,26–29 the work reported herein represents its first application to the field of late transition metal polymerizations.…”