Study On The Regulation And Mechanism Of Hydrogen Sensitivity On Ziegler-Natta Catalyst System

After decades of development,Ziegler-Natta catalyst has been developed from the first generation to the sixth generation.The performance of the catalysts has been continuously improved,and new polyolefin products and new applications have been emerging.Although Ziegler-Natta catalyst and its preparation technology have been developed relatively mature,in the complex heterogeneous catalyst system,the scientific understanding about each component of Ziegler-Natta catalyst system is still very limited,the interactions among various components such as carriers,active species and internal electron donors are still unclear,and the understandings on the microstructure of the catalyst system are limited,which has become a bottleneck for the further optimization and improvement of Ziegler-Natta catalyst.Therefore,using modern methods to study the microstructure of the catalyst system,to further clarify the relationship between the microstructure of the catalyst and the catalytic performance,to adjust the relationship between the structure of the catalyst and the actual application effect,are very important for the research and development of new high performance catalysts.With the increasing demand for high melt flow rate polypropylene products in the market,the hydrogen sensitivity of catalysts has gradually become one of the main hot spots in Ziegler-Natta catalyst research and development.However,there is still a lack of systematic research on the regulation and mechanism of hydrogen sensitivity on Ziegler-Natta catalyst system,which affects the improvement of hydrogen sensitivity of catalysts.The internal electron donor has an important influence on the hydrogen sensitivity of the catalyst,but the mode of action of the internal electron donor in the catalyst and the mechanism of action affecting the hydrogen sensitivity of the catalyst have not been clearly understood.Therefore,it is of great significance to study the influence of internal electron donor on the catalytic performance of the catalyst,especially the relationship between the structure of internal electron donor and the hydrogen sensitivity of the catalyst,as well as the mechanism of action of internal electron donor.Based on the structure and composition innovation of the catalyst,three internal electron donors ID1(fluorene diether),ID2(fluorene diether ester)and ID3(fluorene diol ester)were synthesized in this thesis,and the structure of the target product was proved by 1H-NMR analysis.Four highly efficient propylene polymerization catalysts were prepared by using ID1(fluorene diether),ID2(fluorene diether ester),ID3(fluorene diol ester)and ID4(phthalic acid ester)as internal electron donors.The effects of internal electron donor structure on the polymerization behavior and hydrogen sensitivity of the catalyst were studied,the influence law of internal electron donor structure on the catalytic performance of the catalyst was revealed,and the effective control on the hydrogen sensitivity of the catalyst was realized.The catalyst of the internal electron donor with ether group and ester group structure has the highest hydrogen sensitivity,the internal electron donor with two ether groups has the middle hydrogen sensitivity,and the internal electron donor with two ester groups has the lowest hydrogen sensitivity.The molecular weight distribution curves of the polymer synthesized by the catalysts with low hydrogen sensitivity had a small bulge in the high molecular weight part,which may be related to the type of titanium active center in the catalyst.Through FT-IR,XPS and other characterization methods,the way in which the internal electron donor acts in Ziegler-Natta catalyst was revealed:the internal electron donor interacts with Mg and Ti through oxygen atom.In the case of simultaneous existence of ether oxygen atom and carbonyl oxygen atom,carbonyl oxygen atom preferentially interacts with Mg and Ti,indicating that the binding ability of carbonyl oxygen atom and Mg and Ti is higher than ether oxygen atom.The influence of the crystal structure of magnesium chloride in the catalyst on the hydrogen sensitivity was studied by X-ray Diffraction.The results showed that the hydrogen sensitivity is related to the ratio of the crystal forms ?-magnesium chloride in the catalyst.The higher the ratio of ?-magnesium chloride,the better the hydrogen sensitivity of the catalyst is,which is of great significance to the structural design of high hydrogen sensitivity catalysts.Through molecular simulation calculation,the coordination model of internal electron donor on magnesium chloride surface and titanium tetrachloride was analyzed,the stabilizing effect of electron donor on magnesium chloride crystal plane was analyzed,and the mechanism of hydrogen sensitivity is explored.Density functional theory calculations show that the hydrogen sensitivity of the catalyst is related to the ZIP-bound surface energy on(104)and(011)crystal plane,and the higher the ZIP-bound surface energy on(011)crystal plane,the better the hydrogen sensitivity of the catalyst is.