Processo de faso gasosa para a produção de uma combinação de polietileno

摘要

A gas phase process for the production of a polyethylene blend comprising contacting ethylene and at least one alpha-olefin comonomer having 3 to 8 carbon atoms with a magnesium/titanium based catalyst system including an activator and a cocatalyst in each of two fluidized bed reactors connected in series, under polymerization conditions, with the provisos that: (a) the mixture of ethylene copolymer matrix and active catalyst formed in the first reactor in the series is transferred to the second reactor in the series; (b) other than the active catalyst referred to in proviso (a) and the cocatalyst referred to in proviso (e), no additional catalyst is introduced into the second reactor; (c) in the first reactor in which a low melt index copolymer is made: (1) the alpha-olefin is present in a ratio of about 0.01 to about 0.4 mole of alpha-olefin per mole of ethylene; (2) optionally, hydrogen is present in a ratio of about 0.001 to about 0.3 moles of hydrogen per mole of ethylene; and (3) the ethylene partial pressure is at least about 40 pounds per square inch; and (d) in the second reactor in which a high melt index copolymer is made: (1) the alpha-olefin is present in a ratio of about 0.01 to about 0.6 mole of alpha-olefin per mole of ethylene; (2) hydrogen is present in a ratio of about 1 to about 2.5 moles of hydrogen per mole of ethylene; and (3) diethyl zinc is added in an amount of about 2 to about 40 moles of diethyl zinc per mole of titanium; and (e) additional hydrocarbyl aluminum cocatalyst is introduced into the second reactor in an amount sufficient to restore the level of activity of the catalyst transferred from the first reactor to about the initial level of activity in the first reactor.