Catalyst transition process

Abstract

A process for transitioning between two different catalysts during the production of polypropylene homo- or copolymers in a continuous multistage polymerisation reaction, the process comprising the steps of: a) polymerising propylene and optionally comonomers in a multi stage polymerisation reactor system comprising a prepolymerisation reactor, a subsequent slurry reactor and thereafter a gas phase reactor in the presence of a first catalyst; b) discontinuing the feed of the first catalyst to the prepolymerisation reactor; c) subsequently introducing, propylene, optionally comonomers, and a second catalyst into the prepolymerisation reactor, and further introducing an aluminium alkyl into the polymerisation reactor simultaneously with the introduction of the second catalyst; d) polymerising propylene and optionally comonomers in the multistage polymerisation reactor system in the presence of the second catalyst; wherein the first catalyst is a Ziegler-Natta catalyst and the second catalyst is a single site catalyst; and wherein the amount of aluminium alkyl fed in step c) is 0.5 to 10.0 g per ton of total propylene fed into the prepolymerisation reactor and the slurry reactor in steps c) and d).

Dependencies are inferred from the claim text.