A PROCESS FOR THE PREPARATION OF POLYETHYLENE

摘要

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 bis-hydrocarbylsilyl chromate and hydrocarbylaluminium compounds or a hydrocarbyl boron compound in a fluidized bed reactor having a recycle gas line under polymerization conditions, with the following provision: (i) the atomic ratio of aluminium to chromium is in the range of about 0.1:1 to about 2.9:1; (ii) the catalyst quantity is from 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 within from about 200 to about 400 psia; (iv) oxygen and/or other catalyst poison is introduced into the reactor in the range of about from 0.005 to about 0.5 part by volume per million parts by volume of ethylene; (v) the molar ratio of alpha-olefin to ethylene is about 0.0001:1; (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; (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. 7 claims