核壳结构Ziegler-Natta复合催化剂的制备及其乙烯聚合

ETHYLENE POLYMERIZATION WITH CORE-SHELL ZIEGLER-NATTA HYBRID CATALYSTS

采用溶胶-凝胶法,将聚(苯乙烯-co-丙烯酸)(PSA)膜材料和氯化镁的复合物包覆在以硅胶为载体的TiCl3催化剂上,负载TiCl4后制得Ziegler-Natta复合催化剂.采用红外光谱、激光粒度仪和扫描电镜对催化剂进行了表征,结果表明该复合催化剂呈核壳结构.同时,考察了复合催化剂中膜的厚度和反应中的氢气含量对催化剂的聚合活性和聚乙烯性能的影响,实验发现,膜厚约为3μm的核壳结构复合催化剂活性良好,其具有带诱导期的平稳型动力学曲线;膜厚1.5μm的复合催化剂的活性接近于实验所用的以硅胶为载体的TiCl3催化剂,且其具有相似的衰减型动力学曲线.研究同时表明,不同的膜厚能够调节复合催化剂的氢调性能及所得聚乙烯的分子量分布.

Poly （styrene-co-acrylic acid） （PSA ）/MgCl2 complex was coated on TiCl3 catalyst （SLC-S catalyst） supported on SiO2 using sol-gel method,and the Ziegler-Natta hybrid catalysts were prepared.The resulting catalysts were characterized by a series of techniques,namely Fourier transform infrared spectroscopy （FTIR）,laser scattering particle analyzer and scanning electronic microscopy （SEM）.It was found that the hybrid catalysts had a core-shell structure and the thicknesses of membrane of HC-5 （PSA/SLC-S = 5 wt% ） catalyst and HC-20 （PSA/SLC-S = 20 wt% ） catalyst were 1.5 and 3 μm,respectively.Three different kinds of catalysts were used for gas phase ethylene polymerization.The effects of thickness of the membrane in hybrid catalysts on the activity and the profile of the polymerization kinetic curves of the catalysts were investigated.The results indicated that the HC-20 catalyst had a good ethylene polymerization activity and its kinetic curve was stable with an inductive period,while HC-5 catalyst demonstrated a fast decay during polymerization and its activity and kinetic curve both resembled the traditional TiCl3 catalyst.Besides,the properties of the polyethylene made by hybrid catalysts under different hydrogen contents were obtained.It is obvious that the thickness of membranes could affect the hydrogen response of the hybrid catalysts and the molecular weight distribution of the resultant polyethylene.