Process

A process for transitioning from the production of a first polymer to production of a second polymer in a gas phase reactor, wherein production of each polymer comprises:

• a. polymerising a mixture comprising one or more monomers and hydrogen in the gas phase reactor to produce a polymer,
• b. withdrawing from the gas phase reactor a gaseous stream,
• c. passing the gaseous stream to a condenser in which it is partly condensed to produce a liquid phase and a remaining vapour phase,
• d. passing a mixture of liquid phase and remaining vapour from the condenser to a separator in which there is maintained a liquid phase and a vapour phase, a volume of the liquid phase in the separator being a percentage, X, which is between 10 and 80% of a total volume of the separator, and
• e. recycling both liquid and vapour from the separator to the gas phase reactor, a mass rate of liquid returning to the gas phase reactor being L and a mass rate of vapour returning to the gas phase reactor being V, the two defining a ratio V/L,
• wherein a hydrogen concentration in the gas phase reactor is changed between the production of the first polymer and production of the second polymer and the change is effected at least in part by changing the V/L ratio by at least 10% and/or by changing the volume of the liquid phase, X, compared to the values used during production of the first polymer.