Patent ID: 7388059

Claim:
A method for producing an ethylene polymer, which comprises: continuously copolymerizing ethylene and a C 3 -C 8 α-olefin in a plurality of reaction zones connected in series in the presence of a chromium catalyst having at least a part of the chromium atoms converted to hexavalent chromium supported on an inorganic oxide support by calcination-activating in a non-reducing atmosphere and which comprises the following steps (1) to (4): (1) copolymerizing ethylene and the α-olefin in a slurry state by introducing the chromium catalyst, ethylene, the α-olefin and a reaction solvent into the first reaction zone, (2) withdrawing a part or all of a reaction mixture including the catalyst and the reaction medium from the reaction zone and transferring the withdrawn portion to a next reaction zone, (3) continuing the slurry polymerization by introducing hydrogen, an organoaluminum compound having the formula (2), R 6 R 7 Al(OCR 8 R 9 R 10 ) (2) wherein in the above formula, R 6 and R 7 may be the same or different, and each represents a C 1 -C 18 alkyl group; R 8 , R 9 and R 10 may be the same or different, and each represents a hydrogen atom, a C 1 -C 17 alkyl group or a C 6 -C 17 aryl group, provided that the total carbon number of R 8 , R 9 and R 10 is at most 17, as a co-catalyst separately from a chromium catalyst, and ethylene into the reaction zone, to which the reaction mixture is transferred, and (4) withdrawing the reaction mixture from the reaction zone to obtain an ethylene polymer.