Effect Of Silica Support On The Structure And Performance Of Modified Phillips Catalysts

About 1/4 of the polyethylene(PE)was produced with Phillips catalysts globally.At present,Phillips catsalyst cosumed in china mainly still relies on imports,which are expensive and consume huge.For this reason,it is of great significance to realize the localization of Phillips catalyst.Phillips catalyst is prepared by supporting active components such as Cr on silica gel,and then preparing them through roasting and activation steps.Among them,the supported silica gel is one of the key factors that determine the performance of the catalyst.This article imported 955 silica gel as a carrier to prepare three kinds of catalysts:Cr/SiO₂-955,Cr-Ti/SiO₂-955 and Cr-Ti-Al/SiO₂-955 loaded with Cr,Cr-Ti,and Cr-Ti-Al;Using domestic(GC)silica gel as the carrier,three catalysts,Cr/SiO₂-GC,Cr-Ti/SiO₂-GC and Cr-Ti-Al/SiO₂-GC were prepared,a series of characterization analyses were carried out on the catalysts and the PE products.The result shows:1.The optimal preparation conditions of the catalysts:calcination and activation under N₂atmosphere,activation at 500?for 5 h.2.955 silica gel carrier and Cr/SiO₂-955,Cr-Ti/SiO₂-955,Cr-Ti-Al/SiO₂-955 three catalysts are all mesoporous materials,the specific surface area of the catalyst Cr-Ti-Al/SiO₂-955 is largest,which is 376.876 m²/g,and the smallest pore size is 18.74 nm.The instantaneous catalytic activity of the catalysts increased sequentially,the highest one was Cr-Ti-Al/SiO₂-955catalyst,82 g PE/(g Cat·h).The molecular weight distribution(PDI)of the PE products become wider with the increasing of amount of and the types of active metals on the carrier,the PE product of Cr-Ti-Al/SiO₂-955 have the highest crystallinity of 53.39%.3.The three catalysts prepared with GC silica gel show the similar performance of that of with 955 silica gel.The Cr-Ti-Al/SiO₂-GC catalyst has the largest specific surface area of372.90 m²/g,and the smallest mean pore diameter of 20.16 nm,which is smaller than that of Cr-Ti-Al/SiO₂-955 catalyst;The highest instantaneous activity of Cr-Ti-Al/SiO₂-GC catalyst is92.12g PE/(g Cat·h),higher than that of the Cr-Ti-Al/SiO₂-955 catalyst.The molecular weight distribution of PE produced with catalyst Cr-Ti-Al/SiO₂-GC is 6.14,which was the largest,for the component with molecular weight of 10⁴-10⁵ increased,the PE has the highest crystallinity of 55.48%,higher than that of PE produced with Cr-Ti-Al/SiO₂-955 catalyst.The catalysts prepared using GC silica gel as the carrier showed even better catalytic performance compared with that of 955 silica gel,some more research work should be go on.