| Polypropylene with high stereoregularity has been applied in extensive fields. The development of the new type catalyst with spherical morphology for propylene polymerization is very critical for obtaining polypropylene granules with spherical morphology directly from polymerization. However, very few reports on the study of preparation of the spherical catalyst, especially on the preparation of the spherical support for this catalyst are found. And the discussions on the mechanism of the electronic donors (ED) in the supported catalysts haven't yet come to a decisive conclusion. In this paper, we prepared the spherical supports for the spherical catalyst using an improved method at first and then discussed about the conditions for the support preparation and the catalyst preparation systematically; the obtained spherical catalysts were used in propylene polymerization and the properties of the catalysts and the behavior of the propylene polymerizations were also investigated.For the first time, this paper systematically studied on the preparation of the spherical MgQ2 by high-speed dispersing method. We mainly discussed on the particle size and particle size distributions of the spherical MgC^ under different dispersion speeds and different dosages of ethanol. In comparison with the patent, we obtained the spherical MgCl2 under lower dispersing speeds. In our experiments, the particle size and particle size distributions of the spherical MgCl2 were mainly controlled by the dispersion speed and dosages of ethanol made no distinctive effects, however it is considered that dosages of ethanol have influence not only on the chemical component, but also on the crystal structure of the resultant spherical MgCl2, which leads to give the MgC^ supports with more defects so that to be in favor of the Ti loading. In addition, we found it favored to obtain larger spherical MgCl2 after adding some ED (for example: DIBP) during dispersing procedure. When considering the dosages of ethanol and the particle size and particle size distributions, we found more favorable conditions for preparing good spherical MgCl2 used as the supports for the spherical catalysts: EtOH/MgCl2=2.8, the pre-dispersion speed is 500~700rpm and the dispersion speed 800-1 OOOrpm; or without pre-dispersion, adding DIBP with DIBP/MgCl2=0.09 in the first preparation step and dispersion speed is 400~500rpm.When considering the conditions for the catalyst preparation, the temperature, the number of the TiCU loading and the amount and the kinds of EDs made distinctive effect on the Ti loading in the resultant catalysts. Also the temperature played a role on the morphology of the catalysts, however the number of the TiCU loading and the amount and the kinds of EDs didn't. Higher temperature and more times of TiCU loading led to lower Ti content in the resultant catalysts; different kinds of EDs with different structures led to different complex abilities so that had different effect on the Ti loading. When using DIBP as the ED, the resultant catalysts contained lower Ti content than that of using DNBP. And the more the amount of ED is, the higher the Ti content. When preparing spherical catalysts, the morphology of the supports controlled the morphology of the catalysts. It was also considered that the stirring condition was critical in controlling the morphology of the catalysts; we found that stirring by bubbling with Ar made it possible to obtain good morphological catalysts. In the end, we concluded that when making Ti loading at the temperature of 13CTC for at least two times by bubbling with Ar, we could get spherical catalysts with good performance.At last, we investigated the propylene polymerization kinetics using the obtained spherical catalysts. We found the kinetics related to the texures of the catalysts drastically. Because the pre-active centers distributed outside and inside the heterogeneous catalyst, the activation of the pre-active centers inside the catalyst by the cocatalyst was delayed in case of diffusion phenomena controllin... |
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