Effects of doping LiCl into MgCl2-supported ziegler-natta catalyst on the molecular weight distribution and isotacticity of polypropylene

Xue Jiang, Hang Wang, Xiuzhi Tian, Yiqi Yang, Zhiqiang Fan

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

A series of MgCl2-supported Ziegler-Natta catalysts was prepared by supporting TiCl4 on LiCl-doped MgCl2, and these catalysts were used to polymerize propylene, using triethylaluminum as a co-catalyst. LiCl and MgCl2 were coprecipitated from ethanol to prepare LiCl-doped MgCl2·nEtOH adducts. The LiCl-doped catalysts were prepared by dipping the adducts into a TiCl4 solution. The crystalline and morphological structures of the adducts and catalysts were characterized by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Two types of mixed crystals-Li2MgCl4 and LiMgCl3-were found in the catalyst that contained 18 mol% LiCl (LMSC18). The molecular weight distribution (MWD) and isotacticity of polypropylene (PP) varied with the dosage of LiCl in the catalyst. PP with a broader MWD was synthesized using LiCl-doped catalysts that contained 11-18 mol% LiCl. Deconvolution of the MWD profiles with multiple Flory "most-probable" functions were applied to analyze the distribution of active centers. There were six types of active centers in LMSC18: A, B, B′, C, D, and E. The combined productivity of (E + D)-type active centers in catalyst LMSC18 was much larger than that of the other catalysts. All the results showed that the properties and distribution of active centers of the catalysts supported on LiCl-doped MgCl2 were markedly changed at a certain range of LiCl dosage.

Original languageEnglish (US)
Pages (from-to)259-266
Number of pages8
JournalIndustrial and Engineering Chemistry Research
Volume50
Issue number1
DOIs
StatePublished - Jan 5 2011

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Magnesium Chloride
Polypropylenes
Molecular weight distribution
Doping (additives)
Catalysts
Deconvolution
Catalyst supports
Propylene
Ethanol
Productivity
Crystalline materials
Transmission electron microscopy
X ray diffraction
Crystals

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering

Cite this

Effects of doping LiCl into MgCl2-supported ziegler-natta catalyst on the molecular weight distribution and isotacticity of polypropylene. / Jiang, Xue; Wang, Hang; Tian, Xiuzhi; Yang, Yiqi; Fan, Zhiqiang.

In: Industrial and Engineering Chemistry Research, Vol. 50, No. 1, 05.01.2011, p. 259-266.

Research output: Contribution to journalArticle

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abstract = "A series of MgCl2-supported Ziegler-Natta catalysts was prepared by supporting TiCl4 on LiCl-doped MgCl2, and these catalysts were used to polymerize propylene, using triethylaluminum as a co-catalyst. LiCl and MgCl2 were coprecipitated from ethanol to prepare LiCl-doped MgCl2·nEtOH adducts. The LiCl-doped catalysts were prepared by dipping the adducts into a TiCl4 solution. The crystalline and morphological structures of the adducts and catalysts were characterized by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Two types of mixed crystals-Li2MgCl4 and LiMgCl3-were found in the catalyst that contained 18 mol{\%} LiCl (LMSC18). The molecular weight distribution (MWD) and isotacticity of polypropylene (PP) varied with the dosage of LiCl in the catalyst. PP with a broader MWD was synthesized using LiCl-doped catalysts that contained 11-18 mol{\%} LiCl. Deconvolution of the MWD profiles with multiple Flory {"}most-probable{"} functions were applied to analyze the distribution of active centers. There were six types of active centers in LMSC18: A, B, B′, C, D, and E. The combined productivity of (E + D)-type active centers in catalyst LMSC18 was much larger than that of the other catalysts. All the results showed that the properties and distribution of active centers of the catalysts supported on LiCl-doped MgCl2 were markedly changed at a certain range of LiCl dosage.",
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