Al/SO42-modification for CrOx/VOx/SiO2 bimetallic catalysts for ethylene polymerization
A series of bimetallic CrOx/VOx/SiO2 catalysts modified by Al/SO42-were prepared via solution impregnation and high temperature calcination,whose activity for ethylene polymerization were observed.The results show that the activity of modified catalysts with relatively lower mass fraction of Al to S is improved by 20%-40% than that of the unmodified catalysts.The activities are stable for both the modified and unmodified catalysts.The molecular weight(Mw)of the products get higher generally,and whose molecular weight distribution is wider after Al/SO42-modification.Bimodal polyethylene(PE)is synthesized by both modified and unmodified catalysts.The relative content of ultrahigh Mw PE fractions is increased,and the contents of middle-to-high Mw PE fractions decrease obviously for the PE produced by the modified catalyst,which offer an important method for one-pot synthesis of bimodal PE with high efficiency,as well as the regulation of Mw of PE products.
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