Process for making ethylene homopolymers

Abstract

A process for making an ethylene homopolymer in the presence of an oxide-supported chromium catalyst is disclosed. A small amount of an α-olefin contacted with the catalyst before polymerizing ethylene or introduced into an ethylene homopolymerization unexpectedly boosts process productivity. When used at part per million levels, the α-olefin improves productivity while maintaining desirable polymer properties. The invention is particularly valuable for making HDPE resins useful for blow molding applications.

1 - 18 . (canceled) 
     
     
         19 . An article made from an ethylene homopolymer made by a process comprising polymerizing ethylene in a reactor in the presence of an oxide-supported chromium catalyst, a diluent, and an alpha olefin to produce an ethylene homopolymer; wherein the alpha olefin is used in an amount effective to increase the productivity of the process compared with the productivity of the process when performed in the absence of the alpha olefin. 
     
     
         20 . The article of  claim 19  comprising a blow molded article. 
     
     
         21 . The article of  claim 19  comprising an extruded sheet. 
     
     
         22 . The article of  claim 19  comprising an injection molded article. 
     
     
         23 . The article of  claim 19  comprising a rotomolded article. 
     
     
         24 . The article of  claim 19  comprising an article for wire and cable applications. 
     
     
         25 . The article of  claim 19  comprising an article for pipe articles. 
     
     
         26 . The article of  claim 19  wherein the reactor is a gas phase process. 
     
     
         27 . The article of  claim 19  wherein the reactor is a slurry-loop reactor. 
     
     
         28 . The article of  claim 19  wherein the oxide-supported chromium catalyst is contacted with the alpha olefin prior to introducing ethylene into the reactor. 
     
     
         29 . The article of  claim 19  wherein the alpha olefin is added to the reactor during the polymerization. 
     
     
         30 . The article of  claim 19  wherein the alpha olefin is selected from the group consisting of propylene, 1-butene, isobutylene, and mixtures thereof. 
     
     
         31 . The article of  claim 19  wherein the alpha olefin is used in an amount within the range of 1 to 500 ppm based on the amount of diluent. 
     
     
         32 . The article of  claim 19  wherein the catalyst further comprises at least one element selected from the group consisting of boron, phosphorus, aluminum, vanadium, titanium, fluorine, and zirconium. 
     
     
         33 . The article of  claim 19  wherein the productivity increase is at least 10%. 
     
     
         34 . The article of  claim 19  wherein the oxide is selected from the group consisting of silicas, silica-aluminas, aluminas, zirconias, titanias, borias, magnesias, aluminum phosphates, and mixtures thereof. 
     
     
         35 . The article of  claim 19  wherein the oxide is a silica. 
     
     
         36 . The article of  claim 19  wherein the ethylene homopolymer has a melt index within the range of MI 20 =5 g/10 min. to MI 2 =10 g/10 min., and a density of at least 0.955 g/cm 3 . 
     
     
         37 . An article made from an ethylene homopolymer made by a process comprising polymerizing ethylene in a slurry-loop reactor in the presence of a silica-supported chromium catalyst, a volatile aliphatic hydrocarbon diluent, and an alpha olefin selected from the group consisting of propylene, 1-butene, and isobutylene, to produce an ethylene homopolymer; wherein the alpha olefin is used in an amount within the range of 1 to 500 ppm based on the amount of diluent. 
     
     
         38 . The article of  claim 33  comprising a blow molded article. 
     
     
         39 . The article of  claim 19  comprising an extruded sheet.