用分形方法研究负载型聚烯烃催化剂的表面形貌及其对聚合活性的影响

Research for Morphology of Supported Polyolefin Catalyst and its Effect on Polymerization Activity Using Fractal Theory

以Mg(OEt)2和TiCl4作为钛镁体系聚乙烯催化剂的代表，在不同反应条件下制备了Ti-Mg体系负载型聚乙烯催化剂，并用扫描电镜(SEM)技术对其亚微观结构进行研究，证实其具有分形特征。应用分形理论及其改进的盒子维法对催化剂的亚微观结构进行了详细的分析计算，给出了催化剂表面结构的分维数。结果发现：催化剂分维值Df随着催化剂表面的不规则度及催化剂内部孔隙的增多而增大，而其聚合活性与催化剂表面分维值的关系较为复杂，只有在适宜的催化剂分维值范围内, 才可获得较高的聚合活性。研究证明了分维值可作为比较两个分形无规则度对象的表征参量。

Polyethylene catalysts were prepared by chemical reaction method with Mg(OEt)2 and TiCl4 under different conditions. The submicroscopic-structures of these catalysts were studied with the help of advanced SEM technology. The results after detailed analysis exhibited that the fractal theory can give better description on characterizing catalyst morphology complexity than traditional methods. The fractal dimensions for these catalyst structures were obtained by applying fractal theory. The results showed that the catalyst fractal dimension values were corresponding with its surface irregularity and pore structures and these values increase with the increase of particle complexities. It was also found that, with the increase of the catalyst fractal dimension values the catalyst activity during polymerization process here was of a peak type in value, which meaned an optimal range of fractal dimension valueserists exists. In our experimental conditions the optimum lies in the range of 2.81 to 2.83. It was suggested that the fractal dimension values could be defined as one of the characteristic parameters for describing irregularities.