纳米多级孔Silicalite-1分子筛负载Ziegler-Natta催化剂对聚丙烯性能的影响

Support Effect of Nanosized Hierarchical Silicalite-1 Zeolite on the Properties of Ziegler-Natta Catalyzed Polypropylene

分子筛无机多孔材料具有特殊的孔道结构、较大的比表面积、极佳的稳定性和独特的择形选择性,是一种优异的绿色无机载体材料.本文采用具有MFI拓扑结构的纳米尺寸多级孔分子筛Silicalite-1(S-1)作为无机载体负载Ziegler-Natta催化剂.通过X射线衍射(XRD)、扫描电子显微镜及氮气吸附-脱附等表征手段研究了纳米S-1载体的理化性质,并研究了S-1载体性质对Ziegler-Natta催化剂在合成聚丙烯反应中催化性能的影响.结果表明,在丙烯聚合反应中,纳米片状无机载体S-1较大的比表面积和多级孔特性有利于提高Ziegler-Natta催化剂负载量及改善传质限制;此外,S-1载体还可以起到模板导向作用,使所得聚丙烯呈现复型效应;在相同压力和反应温度下进行的丙烯聚合反应中,由于丙烯单体受多级孔S-1载体孔道结构和尺寸的择形作用及无机载体的复型效应影响,聚合产物的结晶度和全同立构指数较高,有利于提高聚丙烯产物的熔点.

Due to the characteristics of special pore structure,large specific surface area,excellent stability and unique shape selectivity,zeolites inorganic porous material has become excellent green inorganic supports.Herein,nanosized hierarchical silicalite-1(S-1)zeolite with MFI topology was used as the inorganic support for Ziegler-Natta catalyst.The physicochemical properties of nanosized S-1 support were characterized in detail by X-ray diffraction(XRD),scanning electron microscopy,nitrogen adsorption-desorption,and other characterization methods.The effects of S-1 support on properties of polypropylene were also studied.In propylene polymerization,the larger specific surface area and hierarchical characteristics of the nanozied inorganic support S-1 are beneficial to increase the loading of Ziegler-Natta and improve the diffusion of reactants and products.Besides,the S-1 support can serve as a morphology-directed template,thus exhibiting a replica effect on the polypropylene product.Likewise,the crystallinity and isotactic index of the polymer products are improved in the propylene polymerization reaction at the same pressure and reaction temperature,due to the shape-selective effect and the replica effect of the hierarchical S-1 inorganic support.Consequentially,the S-1 support is conducive to improving the melting point of polypropylene products.