Catalysis
Liang Zhu; Xuelian He; Ruihua Cheng; Zhen Liu; Ning Zhao; Boping Liu
Abstract
SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg ...
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SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg molar ratios, which showed significant effects on the active centers and pore structures of the catalysts. The formation amount of β-MgCl2 carrier increased to a maximum with increasing the Ti/Mg molar ratio from 1.50 to 2.25, and then decreased with the further increasing of Ti/Mg molar to 2.50. When the Ti/Mg molar ratio reached 2.25, the catalyst showed the best performance of polymerization, which could be attributed to the most active centers, high surface area and loose surface structure, mainly owing to the high conversion of Mg(OEt)2 to β-MgCl2. The polymers obtained showed medium and high molecular weight (Mw) with medium molecular weight distribution (MWD). In contrast to the conventional Mg(OEt)2-based ZN catalysts, the sphericity of particles was easy to control in this bi-supported catalyst. Furthermore, the prepared catalysts exhibited rather high activity, good copolymerization ability and hydrogen response.
Catalysis
Goond Hongmanee; Patchanee Chammingkwan; Toshiaki Taniike; Minoru Terano
Abstract
Mg(OEt)2 with spherical morphology is one of the most important precursors for the preparation of industrial Ziegler-Natta catalysts. In the present article, morphology evolution of Mg(OEt)2 particles is studied in the course of the synthesis. The morphology of Mg(OEt)2 particles is observed throughout ...
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Mg(OEt)2 with spherical morphology is one of the most important precursors for the preparation of industrial Ziegler-Natta catalysts. In the present article, morphology evolution of Mg(OEt)2 particles is studied in the course of the synthesis. The morphology of Mg(OEt)2 particles is observed throughout the process by SEM. The results show that Mg(OEt)2 particles are formed through i) seed generation on Mg surfaces, ii) seed growth and isolation as independent particles, and iii) further growth and shaping into smoother and more spherical particles. The size of Mg sources greatly affects the rates of these processes to different extents. A larger size of Mg leads to slower seed formation and growth, and detachment of clustered seeds, making the final particles larger and less spherical, respectively. The crystal growth of Mg(OEt)2 is also affected by the size of Mg sources, which in turn differentiates the pore size distribution to affect the catalyst composition and performance.
