Patent ID: 8349975

Claim:
A method for transitioning from a first process for production of a first polymer to a second process for the production of a second polymer during a polymerisation campaign in a polymerisation apparatus, said polymerisation apparatus comprising a reaction vessel and a degassing vessel, in which the respective first and second processes each comprise: (a) bringing a principal olefin and a comonomer into contact with a catalyst under gas phase polymerisation conditions in the reaction vessel to form the respective first or second polymer, wherein said first and second process utilise the same principal olefin but differ in at least one of (i) the comonomer used and (ii) the reaction temperature at which the polymer is produced, and (b) subsequently contacting the respective first or second polymer with a purge gas in the degassing vessel to remove unreacted monomers, wherein the method for transitioning comprises changing the flow rate of purge gas in the degassing vessel from a first rate, X 1 , used for degassing of the first polymer to a second rate, X 2 , used for degassing of the second polymer, the second rate being defined relative to the flow rate, X i , and temperature, T i , used for an earlier polymer produced during the campaign using the same comonomer as the second process, and the reaction temperature, T 2 in the second process, and wherein a. where T 2 is increased relative to T i , X 2 is at least 1% lower than X i for each 1° C. increase in T 2 compared to T i , b. where T 2 is decreased relative to T i , X 2 is at least 1% higher than X i for each 1° C. decrease in T 2 compared to T i , and c. where T 2 is equal to T i , X 2 is at least equal to X i .