Phase-stabilized ethylene alpha olefin copolymerization process

1. Process for copolymerizing ethylene and at least one C3 to C8 alpha olefin to obtain an ethylene-C3 to C8 alpha olefin copolymer, the process comprising

a) copolymerizing ethylene and at least one C3 to C8 alpha olefin in a solvent in a solution polymerization reactor ( 1 ) to obtain an intermediate polymer solution,

b) discharging an effluent stream from the intermediate polymer solution into a heat exchanger ( 2 ),

c) setting a temperature of the effluent stream in the heat exchanger ( 2 ) to obtain a heated effluent stream,

d) feeding the heated effluent stream to a first flash separation ( 3 ),

e) separating at least a part of the ethylene-C3 to C8 alpha olefin copolymer in the first flash separation ( 3 ),

wherein the process further comprises the steps of:

feeding an inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. to the solution polymerization reactor ( 1 );

and/or

accumulating an inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. during the polymerization reaction;

and/or

feeding an inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. to the discharged effluent stream of step b), wherein the intermediate polymer solution in the solution polymerization reactor ( 1 ) comprises between 0.05 and 30 wt % inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C., based on a total weight of the intermediate polymer solution.

2. Process according to claim 1 , whereby the inert hydrocarbon fulfilling 90° C.<T(BP)<130° C. is a paraffinic hydrocarbon having 7 or 8 carbon atoms, an olefin having 7 or 8 carbon atoms, or mixtures thereof.

3. Process according to claim 1 , whereby the inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. comprises iso-octene, 4-methyl-3-heptene, 3-ethyl-2-hexene, 3-methyl-3-heptene, 2,3-dimethyl-2-hexene, 3-methyl-2-heptene, 3,4-dimethyl-trans-3-hexene, 2-methyl-2-heptene, or mixtures thereof.

4. Process according to claim 1 , wherein copolymerization of ethylene and the at least one C3 to C8 alpha olefin in solution in step a) takes place at a temperature of at least 140° C.

5. Process according to claim 1 , wherein in step c) the temperature of the effluent stream is set to a temperature within 200 to 280° C.

6. Process according to claim 1 , wherein the pressure in the solution polymerization reactor ( 1 ) and/or in the heat exchanger ( 2 ) is from 80 to 150 bar.

7. Process according to claim 1 , wherein the ethylene-C3 to C8 alpha olefin copolymer separated in step e) is directed into a second flash separation downstream of the first flash separation ( 3 ).

8. Process according to claim 1 , wherein accumulating the inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. during the polymerization reaction is done by

recovering the inert hydrocarbon from the first flash separation ( 3 ) and/or from a second flash separation downstream of the first flash separation ( 3 ), and

recycling the recovered inert hydrocarbon back to the solution polymerisation reactor ( 1 ).

9. Process according to claim 1 , wherein the obtained ethylene-C3 to C8 alpha olefin copolymer has a weight average molecular weight (Mw) of between 50,000 and 180,000 g/mol, determined according to ISO 16014-4:2012.

10. Process according to claim 1 , wherein the obtained ethylene-C3 to C8 alpha olefin copolymer has a melt flow rate MFR2 (2.16 kg, 190° C.) of equal or below 100 g/10 min, determined according to ISO 1133-1.

11. Process according to claim 1 , wherein the at least one C3 to C8 alpha olefin is selected from the group of propene, 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene, or combinations thereof.

12. Process according to claim 1 , wherein the catalyst used in the solution polymerization is a metallocene catalyst or a Ziegler-Natta catalyst.

13. A method for maintaining an intermediate polymer solution in a solution polymerization reactor ( 1 ) in a single phase or for maintaining an effluent stream originating from the solution polymerization reactor in a single phase, comprising:

feeding an inert hydrocarbon to the solution polymerization reactor ( 1 );

wherein the intermediate polymer solution is obtained by copolymerizing ethylene and at least one C3 to C8 alpha olefin copolymer in the solution polymerization reactor ( 1 ); and

wherein the intermediate polymer solution comprises between 0.05 and 30 wt. % of the inert hydrocarbon, based on a total weight of the intermediate polymer solution; and

wherein the inert hydrocarbon has a boiling point T(BP) that fullfills an inequality 90° C.<T(BP)<130° C.

14. A method for maintaining a heated effluent stream heated in a heat exchanger ( 2 ) in a single phase, comprising:

copolymerizing ethylene and at least one C3 to C8 alpha olefin in a solvent in a solution polymerization reactor ( 1 ) to obtain an intermediate polymer solution;

discharging an effluent stream from the intermediate polymer solution into a heat exchanger ( 2 );

feeding an inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C. to the effluent stream discharged from the solution polymerization reactor ( 1 ) into the heat exchanger ( 2 ); and

setting a temperature of the effluent stream in the heat exchanger ( 2 ) to obtain the heated effluent stream;

wherein the intermediate polymer solution comprises between 0.05 and 30 wt. % of the inert hydrocarbon having a boiling point T(BP) fulfilling 90° C.<T(BP)<130° C., based on a total weight of the intermediate polymer solution.