Patent ID: 6022933
Filing Date: 2000-02-08
Classification: C08F,Y10S

Abstract:
A process for preparing high density polyethylene in the gas phase comprising contacting a mixture comprising ethylene and one or more alpha-olefins with the supported reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound or a hydrocarbyl boron compound in a fluidized bed reactor having a recycle gas line, under polymerization conditions, with the following provisos:(i) the atomic ratio of aluminum to chromium is in the range of about 0.1:1 to 2.9:1;(ii) the amount of catalyst is in the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of the high density polyethylene;(iii) the partial pressure of ethylene is in the range of about 200 to about 400 psia;(iv) oxygen and/or another catalyst poison is introduced into the reactor in the range of about 0.005 to about 0.5 part by volume of catalyst poison per million parts by volume of ethylene;(v) the molar ratio of alpha-olefin to ethylene is about 0.0001:1 to about 0.1:1;(vi) hydrogen is introduced into the reactor in the range of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene;(vii) the polymerization is carried out at a temperature in the range of about 80 to about 110 degrees C.; and(viii) a relatively low boiling inert hydrocarbon is introduced into the recycle gas line in an amount sufficient to raise the dew point of the recycle gas, which is comprised of alpha-olefins and other reactor gases, and the recycle gas is partially condensed and recycled to the reactor where it promotes cooling by evaporation.