Study On The Preparation Of Adjustable UHMWPE With Compose-Carrier Supported Catalysts

In recent years, great advance in the research of UHMWPE have been made. Although the commercialized catalyst possesses high activity, the catalytic kinetics displays an attenuation characteristic and the reaction temperature could not be easily controlled. Despite abundant researches made on the catalyst for preparation of UHMWPE with a viscosity average molecular weight above 300×10⁴g/mol, the scarcity of researches on preparation of VHMWPE with a viscosity average molecular weight less than 150×10⁴g/mol under trace hydrogen condition and its molecular weight control is obvious. A composite carrier supported catalyst with stable kinetics characteristics was prepared. The preparation of UHMWPE, the control of molecular weight and the preparation of VHMWPE under trace hydrogen was also investigated, which shows great significance in the commercialization of VHMWPE preparation.During preparation, the effects of composite carrier composition on morphology, activity and kinetic characteristics of catalyst was investigated via adjusting the silicon to MgCl₂ ratio in composite carrier. The performance and kinetic characteristics of the catalyst in polymerization of UHMWPE were investigated. The effects of polymerization temperature and pressure on the solubility of ethylene in hexane and the effects of stir and solid polymer weight on mass transfer coefficient were also investigated. Hydrogen sensitivity of this catalyst was characterized. The polymerization characteristics of VHMWPE preparation under trace hydrogen. The relationship between polymerization and VHMWPE performance were also clarified.With the increase of silica gel in composite carrier, the morphology of catalyst and the stability of kinetics were improved, which facilitate the reaction control while impair the catalyst activity. The prolongation of reaction time or addition of catalyst amount will increase mass transport limitation on catalyst activity. The polymerization temperature and pressure contribute more to the catalyst activity than other factors in UHMWPE preparation. The viscosity average molecular weight of polyethylene is relatively sensitive to reaction temperature while much more sensitive to hydrogen content. The existence of trace hydrogen in polymerization atmosphere can cause noticeable decrease in the viscosity molecular weight of polyethylene. As the hydrogen content increases, the influence of polymerization temperature and co-catalyst on molecular weight is undermined, while that of pressure enhanced and the optimum Al to Ti ratio of max activity increases.