Patent ID: 8796402

Claim:
A process for start-up of a gas phase fluidised bed polymerisation reaction, said reaction comprising polymerisation of one or more monomers using a catalyst in a reactor, and said process comprising: a) providing a start-up bed of particles in the reactor in the presence of the one or more monomers but in the absence of the catalyst, b) introducing catalyst to the reactor to initiate reaction and start-up polymer production, said introduction being designated as time T 0 , c) at a time T i , T i being between 1 and 6 hours after T 0 , the value of X i is less than a threshold value, wherein: X i = Cumulative ⁢ ⁢ production ⁢ ⁢ in ⁢ ⁢ the ⁢ ⁢ time ⁢ ⁢ period ⁢ ⁢ T 0 ⁢ ⁢ to ⁢ ⁢ T i ( Cumulative ⁢ ⁢ catalyst ⁢ ⁢ injection ⁢ ⁢ the ⁢ ⁢ time ⁢ ⁢ period ⁢ ⁢ T 0 ⁢ ⁢ to ⁢ T i * P i ⁢ C 2 = ) , P i C 2 =being the ethylene partial pressure in the reactor at the time T i , d) subsequently stopping the injection of catalyst, e) taking a corrective action to address the low value of X i .