Patent ID: 7632901

Claim:
A process of polymerizing ethylene in a slurry polymerization reactor, the process comprising: (a) providing a supported chromium catalyst comprising: (i) chromium supported on a silica-titania support, or (ii) titanium surface-modified supported chromium catalyst; (b) providing a trialkylaluminum cocatalyst of formula AlR 3 , where each R group is independently a linear or branched C 4 -C 12 alkyl group; (c) contacting the catalyst and cocatalyst to form a catalyst system wherein the ratio of moles of cocatalyst to moles of chromium in the catalyst is in the range of 3:1 to 8:1 by: (i) cofeeding the catalyst and cocatalyst to a polymerization reactor, wherein the catalyst and cocatalyst are not contacted prior to the step of cofeeding, or (ii) feeding the catalyst and cocatalyst separately to the polymerization reactor, wherein the catalyst and cocatalyst are not contacted prior to the step of feeding, (d) contacting the catalyst system with a monomer feed consisting essentially of liquid phase ethylene, wherein the reactor is operated at a temperature and pressure sufficient to polymerize ethylene in a slurry phase; and (e) recovering a polymer having an ESCR of at least 500 hours according to ASTM D 1693, Condition B.