Magnesium chloride‐supported, high‐mileage catalysts for olefin polymerization. V. BET, porosimetry, and x‐ray diffraction studies

Abstract

AbstractThe physical state of the material obtained during the various stages of preparation of a typical MgCl2‐supported, high‐mileage propylene polymerization catalyst was studied by BET, mercury porosimetry, and x‐ray diffraction techniques. The starting MgCl2 and the substance after HCl treatment have negligible BET surface areas. Mercury porosimetry showed that they have large pores with radii > 200 nm which are probably crevices between MgCl2 crystallites. The most pronounced physical changes occur during dry porcelain ball milling in the presence of ethyl benzoate. After 60 h or more of ball milling the material had a 5.1–7.3 m2 g−1 BET surface area, twice the pore surface area, and a smaller pore radius than before ball milling and a large reduction in crystallite sizes to almost ultimate dimensions. The crystallites were probably held together by complexation with ethyl benzoate in the form of large agglomerates. Subsequent reactions with p‐cresol and triethyl aluminum had minor effects in further reduction of the MgCl2 crystallite size but efficiently brokeup the agglomerates. The final refluxing with TiCl4 increased the BET surface area to 110–150 m2 g−1 but may have increased the crystallite size somewhat due to cocrystallization of TiCl3 and AlCl3 with MgCl2. There may have been only 8–10 crystallites in each catalyst particle. The surface structure of the catalyst resembled those of the classical Ziegler‐Natta γ‐TiCl3·0.33 AlCl3 catalyst.