Patent ID: 6649709
Filing Date: 2003-11-18
Classification: C08F

Abstract:
A continuous vapor-phase fluidized-bed process for the preparation of ethylene homopolymers and copolymers having a density of from 0.87 to 0.97 g/cm3 in which ethylene or mixtures of ethylene and C3-C8 &agr;-monoolefins are (co)polymerized in the presence of a supported chromium catalyst prepared from chromium (VI) oxide, chromium salts, chromium (III) acetylacetonate, chromium hexacarbonyl, bis(cyclopentadienyl) chromium or bis(arene) chromium (0), which has been activated in an oxidizing atmosphere containing oxygen at a temperature of 400Â° to 1100Â° C., wherein the support is a porous oxide selected from the group consisting of SiO2, Al2O3, MgO, ZrO2, Ba2O3, CaO, ZnO and mixtures thereof, in the polymerization zone of a vapor-phase fluidized-bed reactor under pressures ranging from 1 to 100 bar and at temperatures ranging from 30Â° to 125Â° C. in the vapor phase in an agitated bed of bulk material comprising particulate polymer, the resultant heat of polymerization is removed by cooling the recirculated reactor gas and the resulting (co)polymer is removed from the vapor-phase fluidized-bed reactor, wherein, for the preparation of a (co)polymer of a specified density d, (co)polymerization is carried out at a temperature which is in a range restricted by an upper envelope defined by equation I TH=171+6&it;dâ€²0.84-dâ€²(I)and a lower envelope defined by equation II TL=173+7.3&it;dâ€²0.837-dâ€²,(II)in which the variables have the following meanings:TH is the highest reaction temperature in Â° C.; TL is the lowest reaction temperature in Â° C.; dâ€² is the numerical value of the density d of the (co)polymer to be synthesized.