氢气对钒系聚乙烯催化剂性能的影响

Effects of Hydrogen on the Properties of Vanadium-Based Catalyst for Ethylene Polymerization

用复合载体负载钒化合物,同时加入邻苯二甲酸二丁酯,制得钒系聚乙烯催化剂,并通过淤浆聚合得到聚乙烯。用GPC和13C NMR等方法研究H2对催化剂聚合活性及聚乙烯性能的影响。实验结果表明,催化剂的活性中心分两类:一类受H2影响较大,一类受H2影响很小;H2是有效的链转移剂。随加氢量的增大,聚合活性逐渐降低,当H2分压为0.08 MPa时,聚合活性衰减趋于平稳。聚合物的表观密度随加氢量的增大呈先升高后降低的趋势。不加氢时聚合物粒径分布相对较分散,而加氢后聚合物粒径分布较集中。随加氢量的增大,聚合物的熔体流动速率增大、相对分子质量减小、相对分子质量分布也逐渐变宽、聚合物的甲基支化度逐渐增大,有利于提高聚合物的加工性能。

A vanadium-based catalyst was prepared by immobilization of a vanadium compound onto a novel composite support and addition of dibutyl phthalate, and then was used in the slurry polymerization of ethylene with triisobutylaluminium as the co-catalyst. The effects of hydrogen on the properties of both the catalyst and the polyethylene products were investigated by means of GPC and ~3C NMR. The results showed that： there were two kinds of active centers in the catalyst： one was affected evidently by hydrogen and another was affected a little; and hydrogen was an effective chain transferer. The catalyst activities decreased gradually with increasing the hydrogen amount, and at the partial pressure of hydrogen of 0.08 MPa, the activities tend to smooth and steady. With increasing the partial pressure of hydrogen, the bulk density of the polymer increased firstly and then decreased, the molecular weight distribution widened, and the particle size distribution became relatively concentrated. Besides, the degree of methyl branching of the polyethylene produced with the catalyst system increased with the addition of hydrogen, which was beneficial to processing the polymer products.