Preparation of Regular Polyethylene Hollow Spheres with Supported Z-N Catalysts
Author(s): Mei-zhou Qi, Zhi-sheng Fu, Zhi-qiang Fan, Department of Polymer Science and Engineering, Ministry of Education Key Laboratory of Macromolecular Synthesis and Functionalization, Zhejiang Univeristy
Pages: 783-790
Year: 2016 Issue: 6
Journal: Acta Polymerica Sinica
Keyword: Ziegler-Natta catalyst; Polyethylene; Hollow sphere; Preparation;
Abstract: Polyethylene hollow spheres with diameters of 0. 4- 3 mm were synthesized by a two-step slurry polymerization in a single reactor with a spherical Mg Cl2-supported Ziegler-Natta catalyst activated by triisobutylaluminum( TIBA),in which the first step was prepolymerization with propylene under 0. 1 MPa and the second step was ethylene copolymerization with small amount of propylene under 0. 6 MPa at 65 ℃. The hollow spheres have rather smooth outer and inner surfaces and relatively uniform thickness of the shell layer.Under optimized conditions,the catalyst efficiency of the polymerization reached about 7. 49 kg/g Ti·h·MPa( or 6. 5 kg PE/g Cat.). The effects of amount of propylene comonomer,cocatalyst concentration( Al/Ti molar ratio) and type of cocatalyst on the particle morphology and polymerization kinetics were investigated. With increasing the Al/Ti molar ratio and the amount of added propylene,the catalytic activity was sharply increased and the particle morphology was further improved,meanwhile the kinetic curve changed from decay type to build-up type. When TEA or TEA/TIBA mixtures were used as the cocatalyst,the inner surface of the central void became rather irregular,though the whole particle was still spherical. The effects of cocatalyst on particle morphology were explained according to a diffusion controlled morphogenesis model based on the morphology of prepolymer particles.
Pages: 783-790
Year: 2016 Issue: 6
Journal: Acta Polymerica Sinica
Keyword: Ziegler-Natta catalyst; Polyethylene; Hollow sphere; Preparation;
Abstract: Polyethylene hollow spheres with diameters of 0. 4- 3 mm were synthesized by a two-step slurry polymerization in a single reactor with a spherical Mg Cl2-supported Ziegler-Natta catalyst activated by triisobutylaluminum( TIBA),in which the first step was prepolymerization with propylene under 0. 1 MPa and the second step was ethylene copolymerization with small amount of propylene under 0. 6 MPa at 65 ℃. The hollow spheres have rather smooth outer and inner surfaces and relatively uniform thickness of the shell layer.Under optimized conditions,the catalyst efficiency of the polymerization reached about 7. 49 kg/g Ti·h·MPa( or 6. 5 kg PE/g Cat.). The effects of amount of propylene comonomer,cocatalyst concentration( Al/Ti molar ratio) and type of cocatalyst on the particle morphology and polymerization kinetics were investigated. With increasing the Al/Ti molar ratio and the amount of added propylene,the catalytic activity was sharply increased and the particle morphology was further improved,meanwhile the kinetic curve changed from decay type to build-up type. When TEA or TEA/TIBA mixtures were used as the cocatalyst,the inner surface of the central void became rather irregular,though the whole particle was still spherical. The effects of cocatalyst on particle morphology were explained according to a diffusion controlled morphogenesis model based on the morphology of prepolymer particles.
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