Study On Support Prepared By Solution Phase Inversion For Catalysts Of Ethylene Polymerization

As the bimodal polyethylene balanced materials’performance and processing properties, researchers in the world payed a lot of attention on it. Our research group has proposed a tailor-designed hybrid catalyst for production of broad/bimodal polyethylene. Those are two different catalysts supported on the polymer-coated particle’s core part and shell part separately. We achieved our aim finally. The aim of this article is to investigate the synthesis mechanism of the polymer shell and optimize the process conditions for preparing inorganic/organic composite microspheres with more stable structure. These composite microspheres are used as the support of polyolefin catalysts. What the article investigates is following:(1) Poly(styrene-co-acrylic acid)-tetrahydrofuran-Hexane ternary thermodynamic phase diagram was obtained based on the results of thermodynamic theoretical calculations and the titration cloudpoint experiments, which are the basic methods in polymer-solvent-non-solvent system’s thermodynamic principles. Accordingly, the dissolution-adsorption-solidification model for the formation polymer membrane was also provided. Firstly, we estimated the PSA solubility parameter by the group contribution method and then determined the solubility parameter of solvents and non-solvent. Consequently, the reasonable solvent sand non-solvents were determined. Then, the dissolution-adsorption between poly(styrene-co-acrylic acid)/THF solution and silica particles were studied by thermogravmetric analysis. The results indicated that the amount of PSA adsorbed on silica increased with the addition of non-solvent. After that, turbidity titration experiments based on linearization cloudpoint theory were carried out to figure out the phase transformation binodal line in PSA-THF-Hexane system. The influences of temperature, polymer, non-solvent and solvent on binodal line were carefully studied. Later, glasstransition temperature inhibition curves of PSA from the effect of THF were obtained by using the Kelley-Bueche equation to analyze the DSC results. These curves were used to determine the glass boundary line and the gel boundary line in the ternary phase diagram. Finally complete the PSA-THF-Hexane ternary thermodynamic phase diagram was deduced.(2) Silica/poly [styrene-co-(acrylic acid) composite microspheres were prepared based on solution phase inversion principles. The effects of solvent, non-solvent and mass ratio between PSA and silica on the morphorlogy of composite microspheres were investigated. Finally, we provided an optimized process condition for better inorganic/organic composite microspheres and achieved the aim of pilot-production.Complete polymer membrane coating on the surface of silica can be obtained when the amount of nonsolvent was over the gel line of the ternary phase diagram. Further, the surface of the composite microspheres became sticker with the increasing amout of non-solvent. Interestingly, self-nucleation of PSA was effectively inhibited when a small amout of solvent was added in the non-solvent, leading to higher utilization of PSA. In addition, we found that the mass ratio of PSA and silica should be at least0.5in order to successfully synthesize complete polymer-coated silica particles. Obvious holes and cracks on the surface of polymer-coated silica particles were observed when the addition of PSA was not enough. As a result, More PSA should be added to obtain a dense polymer shell of the composite microspheres. For the preparation in10L reactor, we found that the self-nucleation of PSA was effectively inhibited because the phase separation took longer time due to better dispersion of the nonsolvent(3) Iron acetylacetonate/bis(imino)pyridyl ligands homogeneous catalyst was supported on the silica/poly[styrene-co-(acrylic acid) composite microspheres and thens slurry ethylene polymerization was carried out to evaluate these supported catalysts. The result showed that the supported catalysts produced not only polyethylene with high mass molecular weight and high crystallinity (72%) but also a-olefins. Compared with the polyethylene produced by the catalyst supported on silica, the polyethylene produced by the iron acetylacetonate/bis(imino)pyridyl ligands homogeneous catalyst supported on the composite microspheres has higher molecular weight. The effects of pressure, Al/Fe and temperature on ethylene polymerization were also carefully studied. The results indicated that the catalyst activity increased when pressure increased. The polymerizationactivity achieved highest when Al/Fe ratio is750. The amount of polyethylene increased with more Al/Fe ratio. The kinetic curves showed different characteristics in presence of different cocatalyst. More a-olefins were produced when alkylaluminum was used as cocatalyst due to more β-H elimination reaction. Further, catalytic activity increased at lower temperature, especially the activity for production of α-olefins. We concluded that the produced polyethylene had much higher molecular weight when the iron catalyst system was supported on the poly[styrene-co-(acrylic acid)].(4) Iron acetylacetonate/bis(imino)pyridyl ligands homogeneous catalyst and Cp2ZrCl2were supported on the poly[styrene-co-(acrylic acid) and silica in the composite microspheres, respectively. Thus, a kind of metallocene/late-transition metal hybrid catalyst was obtained. This hybrid catalyst was employed for ethylene slurry polymerization to produce bimodal polyethylene. The active site from iron acetylacetonate/bis(imino)pyridyl ligands catalyst was firstly activated to produce a-olefin and polyethylene with low molecular weight. Later, the outer part of the particles was broken and Cp2ZrCl2immobilized on the SiO2started to produce polyethylene with high molecular weight. Finally, bimodal polyethylene was obtained.