Study On Precipitation Of Supported Metallocene Catalyst Microparticles By Rapid Expansion Of Supercritical Solutions

Metallocene catalysts have a great deal of advantages, such as high activity, narrow molecular weight distribution, and the outstanding catalytic capacity of copolymerization. Except these advantages, there are still several problems, such as the difficulty in controlling polymer morphology with soluble homogeneous catalysts, the inability to be used in continuous slurry and fluidized-bed gas-phase processes, significant reactor fouling, and the very large amount of MAO needed to achieve higher metallocene catalytic activity, are needed to be solved if metallocene catalysts would be used widely in industry. Although immobilizing metallocene complexes on an inorganic support can solve these problems to a certain extent, the surface properties of supports strongly influence the behavior of its supporting catalysts, and immobilization often depresses catalyst activities at some extent. Moreover, the supports influence the processing properties of polymer for their containment in polymer as additional ash. Recently, metallocenes with organic or polymer materials as the supports, although rarely reported, are of great interests in industry and academic research, because polymer-supported metallocenes can offer the following advantages: easy preparation and low cost; preserving fairly high activity and the features such as single-site, narrow comonomer and molecular-weight distribution, and high ability to incorporate comonomers with unsupported metallocenes; lower inorganic residues in polymer products in comparison with inorganic supports such as Si02, A^Os, MgCb; capacity of controlling the morphology of the polymer to reduce the possibility of reactor fouling, and the adaptation to slurry and gas phase polymerization process.The solubility of solids in supercritical solutions is a very sensitive function of temperature and pressure. Because supercritical fluids are highly compressible, small changes in pressure can result in large changes in density and the solve power; the rapid expansion of supercritical solution thus gives rise to very large supersaturation ratios. The speed at which pressure perturbations propagate within the fluid allows precipitation from an essentially uniform medium and clearly distinguishes this process from conventional crystallization, where temperature gradients give rise to a wide distribution of nucleation rates within the solvent. The uniform conditions within the nucleating environments should result in the production of particles that are more even in morphology and narrower in size distribution than those produced by conventional crystallization technique. So the RESS technique is recommended to prepare the polymer-support metallocenes particles with good morphology and narrow size distribution. At the same time, detail knowledge of rapid expansion of the supercritical solution is of interest to chemistry as well as to thermodynamics, pharmaceutics and so on. And this technique associates with a wide range of applications such as bimodal resin, polymer alloy and biocompatibility of artificial organs in medicine. Therefore, the study of the RESS is of important theoretical meaning and has an evident application background.The thesis investigated systematically the preparation of polystyrene-supportedmetallocenes catalyst [Cp2TiCl2] particles by RESS. And the metallocenes microparticles by RESS were characterized through ethylene slurry polymerization. It could be divided into four main sections: (1) the thermodynamic behavior of binary system Cp2TiCl2/SCF-C3H8 and PS/SCF-C3H8, (2) nucleation behavior of solute in supercritical solution, (3) preparation of polymer-supported Cp2TiCl2 through coprecipitation, (4) polymerization characteristic of metallocenes microparticles prepared by RESS. In the first section, the author mainly discussed the binary phase behavior and the dissolution of solid solute in supercritical solution. In the second section, a systematic investigation of effects of process conditions on the characteristics of solid products was performed and discu...