Abstract
Silica generated from agricultural waste is more cost effective and environmentally friendly than silica from traditional commercial processes. In this study, spherical silica particles with a diameter of around 120 nm were fabricated from rice husk ash (RHA), and were used to support two bridged zirconcene complexes ((I) Me2Si(Ind)2ZrCl2 and (II) C2H4(Ind)2ZrCl2) for catalyzing propylene polymerization to produce polypropylene (PP) in a temperature range of 40–70 °C and in a solution methylaluminoxane (MAO) range of 0.1–0.6 wt%. Due to its small particle size, RHA-supported catalyst exhibited much higher activity than micro-sized commercial silica-supported catalyst. At the optimum polymerization temperature of 55 °C and with increasing MAO concentration, polymer yield increased proportionally with the increase of number average molecular weight. Compared to (I), (II) produced more polymer molecules but with much shorter chain length, ascribed to the differences of Zr loading and bridge structure. With increasing polymerization temperature, polymer molecular weight decreased rapidly and resulted in a significant change of PP assembly morphology (shape and size). At 55 °C, (I) produced uniform PP assemblies which had dumbbell-like structure with a smooth middle section and two fibrillar ends, while (II) produced spherical PP particles. The dumbbell middle part width was essentially identical to the Batchelor microscale proposed in turbulent mixing theory.
Highlights
Polypropylene (PP) is a flexible product which can be used in many industries, including packing, automobile, toy making, carpeting, plastic paper, and laboratory equipment manufacturing [1,2,3,4]
Coupled plasma-atomic emission spectrometer (ICP-AES) measurements indicated that MAO-treated rice husk ash (RHA) had an Al content of around 1.2 wt%, the RHA-supported Me2 Si(Ind)2 ZrCl2 that MAO-treated RHA had an Al content of around 1.2 wt%, the RHA-supported Me2Si(Ind)2ZrCl2 and C2 H4 (Ind)2 ZrCl2 catalysts had Zr contents of 0.39 wt% and 0.68 wt% (i.e., [Al]/[Zr] atomic ratios and C2H4(Ind)2ZrCl2 catalysts had Zr contents of 0.39 wt% and 0.68 wt% (i.e., [Al]/[Zr] atomic ratios were 10.3 and 5.9), respectively, suggesting that C2 H4 (Ind)2 ZrCl2 had greater adsorption ability than were 10.3 and 5.9), respectively, suggesting that C2H4(Ind)2ZrCl2 had greater adsorption ability than
Polymerization temperature effect was studied at 0.4 wt% MAO concentration and 400 rpm Polymerization temperature effect was studied at 0.4 wt% MAO concentration and 400 rpm agitation speed
Summary
Polypropylene (PP) is a flexible product which can be used in many industries, including packing, automobile, toy making, carpeting, plastic paper, and laboratory equipment manufacturing [1,2,3,4]. In order to produce morphologically uniform polymer particles with high bulk density and to avoid reactor fouling, industrial metallocene catalysts have to be supported on a MAO-modified solid carrier (so-called drop-in catalysts) [8]. Micro-sized amorphous and porous silica is most commonly used for supporting metallocence/MAO catalysts because of its high surface area/porosity, good mechanical properties, and fine stability under reaction and processing conditions [9,10]. Rice husk is an agricultural waste material abundantly available in occurring silica,countries, especiallycontaining those found agro38%. Pentose, and 2% other silica has been used recently to support zirconcene/MAO ethylene polymerization organic compounds [12,13].
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