Journal
CATALYSTS
Volume 11, Issue 12, Pages -Publisher
MDPI
DOI: 10.3390/catal11121535
Keywords
Ziegler-Natta catalyst; bi-supported; ethylene; 1-hexene copolymerization; MCM-41; MgCl2
Categories
Funding
- National Natural Science Foundation of China [U1462114, 51773178]
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In this study, TiCl4/MgCl2/MCM-41 type bi-supported Ziegler-Natta catalysts with different MgCl2/MCM-41 ratios were synthesized and used for ethylene/1-hexene copolymerization. It was found that the bi-supported catalysts exhibited higher activity and stronger comonomer activation effect compared to the TiCl4/MgCl2 catalyst. The introduction of MCM-41 in the support significantly changed the active center distribution of the catalyst, resulting in less production of low molecular weight copolymer fractions with high 1-hexene content.
TiCl4/MgCl2/MCM-41 type bi-supported Ziegler-Natta catalysts with different MgCl2/MCM-41 ratios were synthesized by adsorbing TiCl4 onto MgCl2 crystallites anchored in mesopores of MCM-41 (mesoporous silica with 3.4 nm pore size). Ethylene/1-hexene copolymerization with the catalysts was conducted at different 1-hexene concentrations and ethylene pressures. MgCl2/MCM-41 composite supports and the catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption analysis (BET), and elemental analysis. The copolymers were fractionated by extraction with boiling n-heptane, and comonomer contents of the fractions were determined. Under 4 bar ethylene pressure, the bi-supported catalysts showed higher activity and a stronger comonomer activation effect than the TiCl4/MgCl2 catalyst. In comparison with the TiCl4/MgCl2 catalyst, the bi-supported catalysts produced much less copolymer fraction of low molecular weight and high 1-hexene content, meaning that the active center distribution of the catalyst was significantly changed by introducing MCM-41 in the support. The copolymer produced by the bi-supported catalysts showed similar melting temperature to that produced by TiCl4/MgCl2 under the same polymerization conditions. The space confinement effect of the mesopores of MCM-41 on the size and structure of MgCl2 crystallites is proposed as the main reason for the special active center distribution of the bi-supported catalysts.
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