Patent ID: 8129484

Claim:
A continuous gas-phase polymerization process for making a high strength, high density polyethylene copolymer, comprising: contacting monomers that include ethylene and optionally at least one non-ethylene olefin with fluidized catalyst particles in a gas-phase fluidized-bed reactor in the presence of hydrogen gas at an ethylene partial pressure of 100 psi or more to produce a polyethylene copolymer resin, wherein: (a) the catalyst particles include silica, chromium, and titanium, wherein the silica support is porous and has a surface area of less than 400 square meters per gram; (b) the catalyst particles have been prepared by contacting the silica support with a chromium compound in a vessel; raising the internal temperature of the vessel containing the dried particles and dry air to a final activation temperature of 650° C. or below; maintaining the activation temperature for a period of from 4 to 8 hours to form activated catalyst particles; lowering the internal temperature of the vessel containing the activated catalyst particles; removing air from the vessel using dry nitrogen; and wherein after activation, the supported catalyst particles contain from about 0.1 to about 0.7 weight percent of Cr and from about 1.5 to 9.0 weight percent of titanium, based on the combined weight of the support and the chromium and the titanium; (c) the polyethylene resin is formed at a polymerization temperature of 120° C. or less; (d) the polyethylene resin is formed with a bulk density of 20 lb/ft3 or more; (e) the polyethylene resin has an ESCR Index of 1.0 or more; (f) the polyethylene resin has a density of from 0.945 to 0.965 g/cc; (g) the polyethylene resin has a Molecular Weight Distribution of from 15 to 30.