Method of polymerizing olefins in slurry reactors

摘要

A process for polymerizing ethylene in at least two cascaded slurry polymerization steps is disclosed. The process comprises polymerizing ethylene in the presence of a polymerization catalyst, hydrogen and optionally one or more alpha-olefin comonomers in a diluent in a first polymerization reactor to produce a first slurry comprising a first ethylene polymer and fluid phase comprising said diluent; withdrawing a first stream of said slurry from said first polymerization reactor; directing said slurry stream into a second polymerization reactor; polymerizing ethylene in the presence of the first ethylene polymer, the polymerization catalyst, hydrogen and optionally one or more alpha-olefin comonomers in a diluent in a second polymerization reactor to produce a second slurry comprising an ethylene polymer mixture and a fluid phase comprising said diluent; withdrawing from said second polymerization reactor a second slurry stream having a solids concentration which is higher than the average solids concentration of the second slurry within the second polymerization reactor; withdrawing from said second polymerization reactor a third slurry stream having a solids concentration which is lower than the average solids concentration of the second slurry within the second polymerization reactor; and directing at least a part of said second slurry stream into one of said first and second polymerization reactor. The process reaches the target operation conditions and recovers from disturbances quickly with reduced production of off-spec material.