| MgCl2 is the most popular support for high activity Ziegler-Natta catalyst. A great deal of researches has been carried out in the field of preparing active MgCl2 support, among which the chemical activation has been widely investigated. The chemical activation consists of dissolving MgCl2 with a donor, followed by elimination of coordinate donors. At present, alcohol is one of the most popular chemical reagents for MgCl2 activation. However, the use of alcohol is limited to monohydric alcohol according to most literatures and patents. In our work, the diol was introduced to recrystallize MgCl2, based on which the highly active catalyst was prepared.This paper developed a novel method to prepare active MgCl2 support. The main idea was using diol as precipitant to recrystallize MgCl2 from the solution. The research work focused on three parts as follows: (1) the effect of diol on the properties of catalyst; (2) the influencing factors in the catalyst preparation; (3) the design and study of novel composite catalysts. The main works are as follows:1. Novel structure MgCl2/THF/Bu(OH)2 adduct was synthesized by using 1,4-butanediol to precipitate MgCl2 from THF/ MgCl2 solution. The adduct was treated with TEA to obtain activated MgCl2·nTHF·mAl(OR)3 support. Highly active catalyst for ethylene polymerization was prepared by impregnating TiCl4 on this support. The support was in the crystal form ofδ-MgCl2, and the catalyst presented high surface area (69.70 m2·g-1) and titanium content (5.79 wt%). In ethylene homopolymerization reactions, the catalyst showed high catalytic activity (47.38 kgPE·(gTi)-1·h-1·atm-1). The catalyst exhibited a kinetic curve of decline type. Moreover, the molecular weight distribution of polyethylene produced by this catalyst was broad (MWD=9.02). The MWD was narrow in the presence of hydrogen, and changed slightly with increasing hydrogen concentration.2. The properties of catalyst were influenced by type of diols, diol/Mg molar ratio, dealcoholization agent and Ti/Mg molar ratio. We found that the properties of catalyst, such as crystal form, surface area, particle size, Ti content and polymerization activity, can be controlled by manipulating the preparation conditions. The optimum preparation condition is as follows: using 1,4- butanediol to precipitate MgCl2 and TEA to dealcoholize, the diol/Mg molar ratio is 1, and the Ti/Mg molar ratio is above 2.3. The MgCl2 was recrystallized on the surface of SiO2 by using 1,4-butanediol, and MgCl2/Bu(OH)2/SiO2 complex was prepared. MgCl2/SiO2 composite support was prepared by treating MgCl2/Bu(OH)2/SiO2 complex with TEA, and highly active catalyst for ethylene polymerization was prepared by impregnating TiCl4 on this support. The support had well morphology, high surface area (311.20 m2·g-1), low Ti content (1.38 wt%) and high activity (94.44 kgPE·(gTi)-1·h-1·atm-1). Moreover, the bulk density of polyethylene prepared by this catalyst was improved.4. MgCl2/poly(styrene-co-acrylic acid) (PSA) composite support was prepared by combining MgCl2 with PSA through carboxyls in the PSA, and the novel organic/inorganic composite catalyst was prepared by impregnating TiCl4 on this support. It was found that the catalyst showed layered structure, high surface area (148.71 m-2·g-1) and high activity (41.12 kgPE·(gTi)-1·h-1·atm-1). The introduction of PSA may influence on active centers, and lead to lower molecular weight.
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