Abstract
Porous organic polymers (POPs) have proven to be an efficient support in the olefin polymerization catalyst field. In this paper, nano TiO2 beads were used to modulate the pore structure, bulk density, and surface morphology and flowability of the prepared POPs. With the incorporation of the hydrophilic nano TiO2 beads, the prepared TiO2/POP supports obtained reasonable specific surface area (100–300 m2/g) and higher bulk density (0.26–0.35 g/mL) and flowability than the pure POP supports. The results show that bulk density of the prepared TiO2/POP particles increased when adding an increased amount of TiO2, and when 37.5% TiO2 (weight percent to the total comonomers divinylbenzene (DVB) and 2-hydroxyethyl methacrylate (HEMA)) and 3:1 DVB/HEMA (molar ratio) were added, highly flowable TiO2/POP composites (POP-6 and POP-7) were obtained. With the modulation of the nano TiO2 template during the support synthesis, the prepared POP-7 particles successfully achieved a normal distribution with a narrow particle size distribution (PSD) of 0.717 and average particle size of 24.1 μm, a specific surface area (SSA) of 279 m2/g, and relatively high bulk density of 0.30 g/mL. Furthermore, all the prepared TiO2/POP supports obtained higher ethylene polymerization activity than silica gel-supported commercial metallocene catalyst. The immobilized (n-BuCp)2ZrCl2/MAO@POP-7 catalyst exhibited the highest ethylene polymerization activity of 4794 kg PE/mol Zr.bar.h and productivity of 389 g PE/g cat, more than twice that of the commercial counterpart. Even higher catalyst productivity (3197 g PE/g cat) and bulk density of the produced PE (0.36 g/mL) could be obtained in higher ethylene partial pressure at 80 °C for 2 h, and the prepared TiO2/POP catalyst shows no obvious Zr+ active sites decay during the ethylene polymerization.
Highlights
Polyolefins are undoubtedly one of the most robust fields in polymer production and consumption globally [1,2,3]
The nano TiO2 beads were used as a significant component to modulate the bulk density, surface morphology, and flowability of the produced porous organic polymers (POPs) particles
As the POPs grow larger around the inorganic particles, the nano TiO2 particles could be dispersed in the prepared POP matrix in order to regulate the pore structure, bulk density, and flowability of the TiO2 /POP
Summary
Polyolefins are undoubtedly one of the most robust fields in polymer production and consumption globally [1,2,3]. Heterogeneous catalysis is required in the gas-phase or the slurry process for industrial applications to avoid reactor fouling and to control the polymer morphology or the forming granule reactor by immobilization of the homogeneous catalytic sites into a carrier [16,17,18,19,20]. Inorganic supports, such as silica gel, magnesium chloride, aluminum oxide, zeolite, molecular sieves, etc., have been reported as metallocene catalysts carriers in numerous literatures. Nano TiO2 beads were selected for an effective template agent to modulate the pore structure and particle morphology of the prepared TiO2 /POP composites without needing to remove the metal oxide, and highly free-flowing TiO2 /POP composites with higher bulk density, narrow particle size distribution, and high ethylene catalytic activity were obtained
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