Polymerization process

1. A polymerization process, comprising

polymerizing an olefin monomer and a comonomer in the presence of a polymerization catalyst in a polymerization step conducted in a polymerization reactor in a solvent to produce a solution comprising a polymer of the olefin monomer and the comonomer;

withdrawing an exhaust stream of the solution from the polymerization reactor in a withdrawing step;

separating the exhaust stream to a first primary stream and a primary concentrated solution stream in a first primary separation step, wherein the first primary stream comprises hydrocarbons and polymer;

separating the first primary stream to a second primary stream and a third primary stream in a second primary separation step, wherein the second primary stream comprises dissolved polymer and the third primary stream comprises majority of the hydrocarbons;

cooling the third primary stream to a temperature of −80 to 20° C. in a primary cooling step to obtain a cooled third primary stream;

separating the cooled third primary stream to a fourth primary stream and a fifth primary stream in a third primary separation step, wherein the fourth primary stream comprises hydrocarbons in vapour phase and the fifth primary stream comprises liquid hydrocarbons; and

returning the fourth primary stream and the fifth primary stream independently in a primary returning step to a location upstream of the polymerization reactor.

2. The polymerization process according to claim 1 , wherein the third primary stream is cooled in the cooling step to a temperature of −80 to 10° C.

3. The polymerization process according to claim 1 , wherein the fourth primary stream and the fifth primary stream are fed in the returning step independently to a feed tank, to a location between an outlet of the feed tank and a feed pump, or to a location between a deep cooler and the polymerization reactor.

4. The polymerization process according to claim 1 , wherein at least a part of the second primary stream is returned to the second primary separation step.

5. The polymerization process according to claim 1 , wherein heat from the third primary stream is recovered in the cooling step and steam is generated using the heat.

6. The polymerization process according to claim 1 , wherein the second primary separation step is conducted using a packed column.

7. The polymerization process according to claim 1 , wherein the cooling step is conducted using a deep cooler or a condenser.

8. The polymerization process according to claim 1 , wherein the comonomer used in the polymerization step is selected from the group consisting of alpha-olefins different from the olefin monomer; polyenes having from 3 to 10 carbon atoms, cyclic olefins having from 6 to 20 carbon atoms and cyclic polyenes having from 6 to 20 carbon atoms.

9. The polymerization process according to claim 1 , comprising

separating the primary concentrated solution stream to a first secondary stream and a secondary concentrated solution stream in a first secondary separation step, wherein the first secondary stream comprises hydrocarbons and polymer;

separating the first secondary stream to a second secondary stream and a third secondary stream in a second secondary separation step, wherein the second secondary stream comprises dissolved polymer and the third secondary stream comprises majority of the hydrocarbons;

cooling the third secondary stream to a temperature of −80 to 20° C. in a secondary cooling step to obtain a cooled third secondary stream;

separating the cooled third secondary stream to a fourth secondary stream and a fifth secondary stream in a third secondary separation step, wherein the fourth secondary stream comprises vapoured hydrocarbons and the fifth secondary stream comprises liquid hydrocarbons; and

returning the fourth secondary stream and the fifth secondary stream independently in a secondary returning step to a location upstream of the polymerization reactor.

10. The polymerization process according to claim 9 , comprising combining the fourth secondary stream with the fourth primary stream and combining the fifth secondary stream with the fifth primary stream before returning them to a location upstream of the polymerization reactor.

11. The polymerization process according to claim 1 , wherein the third primary stream is cooled in the cooling step to a temperature of −80 to 0° C.

12. The polymerization process according to claim 1 , wherein the third primary stream is cooled in the cooling step to a temperature of −80 to −10° C.

13. The polymerization process according to claim 1 , wherein the third primary stream is cooled in the cooling step to a temperature of −80 to −20° C.