Improvements to the Phillips Catalyst

The modified catalyst formulation was then tested in an ethylene polymerization experiment carried out at 225-235 F in isobutane at a total pressure of 500 psig. A control catalyst prepared under. similar conditions without the titanium compoimd was also examined in a similar polymerization experiment. The results showed that the Melt Index of the polyethylene prepared with the titanium-containing catalyst was 3.5, while the control catalyst produced polyethylene with a Melt Index of only 0.48. Hence, the Melt Index data showed that the molecular weight of the 

In another investigation of chromium and titanium-based catalysts, Hoff and coworkers showed that the Melt Index of polyethylene produced with titanium-containing chromium catalysts was very dependent on catalyst preparation variables [7]. 

A series of catalysts were prepared in which the CrO - (2 wt%) impregnated silica was fluidized in a quartz tube with nitrogen, heated to 170°C, and then liquid titanium tetraisopropoxide was added to the fluidized bed. After ten minutes, carbon monoxide was added to the fluidizing stream and the entire contents of the quartz tube was heated to 700°C and maintained 

Additional characterization of the Phillips catalyst was reported by McDaniel and Welch in 1983 in a series of three papers [12-14] that 

Finally in a rather surprising finding, McDaniel showed that the type of compound(s) used in the first thermal activation step greatly affected the molecular weight of the polyethylene produced with a particular catalyst. Catalysts prepared with a support that was thermally treated at 870°C with carbonyl sulfide, then impregnated with dicumene chromium (0) to provide a material with 0.5 wt% Cr, and then activated in oxygen between 315 and 650°C, produced polyethylene with a very low molecular weight. 

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