Polymerizaton process

1. Process for the transition between an ethylene co-polymerization process carried out in a polymerization reactor in the presence of a catalyst and of ethylene E and an olefin co-monomer A to produce an ethylene copolymer PEA into an ethylene co-polymerization process carried out in the same polymerization reactor in the presence of a catalyst and of ethylene E and an olefin co-monomer B to produce an ethylene copolymer PEB wherein

co-monomer A and co-monomer B are different;

co-monomer A and co-monomer B are both present in the reactor during at least part of the transition from PEA to PEB; and

the transition is performed continuously

wherein the transition is the period between the steady state production of the copolymer PEA and the steady state production of the copolymer PEB, and

wherein the polymerisation production rate (“R”), defined as the amount of polymer produced by unit of time (e.g. tonnes/hour), must fulfill the following equation

0.55 ×R PEA <R T <1.45 ×R PEA

wherein R PEA is the steady production rate of the copolymer PEA just before the start of the transition, and R T is the production rate of the polymer during the transition, wherein the mass of polymer present in the reactor during the transition is at least 90% of the mass of polymer just before the start of the transition.

2. Process according to claim 1 wherein the polymerisation production rate must fulfill the following equation

0.80 ×R PEA <R T <1.20 ×R PEA .

3. Process according to claim 1 wherein no deinventorying of the reaction system contents is operated during the transition.

4. Process according to claim 1 wherein the ethylene partial pressure (pC 2 = ) must fulfill the following equation

0.55 ×pC 2 = PEA <pC 2 = T <1.45 ×pC 2 = PEA

wherein pC 2 = PEA is the ethylene partial pressure just before the start of the transition, and pC 2 = T is the ethylene partial pressure during the transition.

5. Process according to claim 4 wherein the ethylene partial pressure must fulfill the following equation

0.80 ×pC 2 = PEA <pC 2 = T <1.20 ×pC 2 = PEA.

6. Process according to claim 1 wherein the transition is operated in the absence of injection of a catalyst killer.

7. Process according to claim 1 wherein a polymerisation catalyst activity A, defined as the amount of polymer produced by unit of time and by amount of catalyst (e.g. g/hour/g cata), must fulfill the following equation

0.55 ×A PEA <A T <1.45 ×A PEA

wherein A PEA is the activity of the catalyst system used for the production the copolymer PEA just before the start of the transition (i.e. in steady state operations), and A T is the catalyst activity of the catalyst system used during the transition.

8. Process according to claim 7 wherein a polymerisation catalyst activity must fulfill the following equation

0.80 ×A PEA <A T <1.20 ×A PEA.

9. Process according to claim 1 wherein the transition from PEA to PEB comprises a period during which both fresh co-monomer A and fresh co-monomer B are fed simultaneously in the reactor.

10. Process according to claim 1 wherein the transition is operated between catalysts belonging to the same catalyst family.

11. Process according to claim 1 wherein the same catalyst is used for the production of both the copolymer PEA and the copolymer PEB.

12. Process according to claim 1 wherein the reactor is a gas phase fluidised bed reactor.

13. Process according to claim 1 wherein the comonomer olefins are selected from olefins having 3 to 12 carbon atoms.

14. Process according to claim 1 wherein the mass of polymer present in the reactor during the transition is at least 95% of the mass of polymer just before the start of the transition.

15. Process according to claim 13 wherein the comonomer olefins are selected from the group consisting of propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.

16. Process according to claim 13 wherein the comonomer olefins are selected from the group consisting of 1-butene, 1-hexene and 1-octene.