Process

1. A process for separating hydrogen from a gaseous feed stream in a polymerization process, comprising the steps:

i. polymerizing an olefin monomer and optionally at least one olefin comonomer, in the presence of a solvent, optionally in the presence of hydrogen, to form a polymerization reaction mixture comprising a polyolefin polymer, unreacted monomer(s), solvent and hydrogen;

ii. separating said polyolefin polymer from said unreacted monomer(s), solvent and hydrogen;

iii. feeding said unreacted monomer(s), solvent and hydrogen to a separator to form said gaseous feed stream;

iv. contacting said gaseous feed stream with a single hydrogen separating membrane to form a hydrogen-rich gaseous stream and a hydrogen-lean gaseous stream, wherein a separation efficiency of step iv. is at least 75%.

2. The process as claimed in claim 1 , wherein said polymerization process is a solution polymerization process.

3. The process as claimed in claim 1 , further comprising

v. recycling the hydrogen-lean gaseous stream from step iv to step i.

4. The process as claimed in claim 1 , wherein said polyolefin is polyethylene.

5. The process as claimed in claim 4 , wherein said polyethylene is a polyethylene homopolymer or a polyethylene copolymer of ethylene and at least one alpha-olefin comonomer.

6. The process as claimed in claim 5 , wherein the at least one alpha-olefin comonomer comprises a C3-C8 alpha-olefin comonomer.

7. The process as claimed in claim 1 , wherein step i. is carried out in the presence of a polymerization catalyst.

8. The process as claimed in claim 1 , wherein the separation efficiency of step iv. is at least 80%.

9. The process as claimed in claim 1 , wherein said membrane is a polymeric or inorganic membrane.

10. An apparatus arranged to perform the process as defined in claim 1 comprising:

a) at least one reactor configured to receive an olefin monomer and optionally at least one olefin comonomer, solvent and optionally hydrogen via at least one first inlet to produce a polymerization reaction mixture comprising a polyolefin polymer, unreacted monomer(s), solvent and hydrogen;

b) a first separator in fluid communication with said reactor configured to receive said polymerization reaction mixture via at least one second inlet to separate said polyolefin polymer from said unreacted monomer(s), solvent and hydrogen;

c) a second separator in fluid communication with said first separator configured to receive said unreacted monomer(s), solvent and hydrogen via at least one third inlet to produce a gaseous feed stream; and

d) a single membrane contactor in fluid communication with said second separator configured to receive said gaseous feed stream via at least one fourth inlet to produce a hydrogen-rich gaseous stream and a hydrogen-lean gaseous stream, wherein a separation efficiency is at least 75%.

11. A process for controlling molecular weight of a polyolefin polymer comprising the steps:

i. polymerizing an olefin monomer and optionally at least one olefin comonomer in the presence of a solvent, optionally in the presence of hydrogen, to form a polymerization reaction mixture comprising a polyolefin polymer, unreacted monomer(s), solvent and hydrogen;

ii. separating said polyolefin polymer from said unreacted monomer(s), solvent and hydrogen;

iii. feeding said unreacted monomer(s), solvent and hydrogen to a separator to form said gaseous feed stream;

iv. contacting said gaseous feed stream with a single hydrogen separating membrane to form a hydrogen-rich gaseous stream and a hydrogen-lean gaseous stream, wherein a separation efficiency of step iv. is at least 75%; and

v. recycling the hydrogen-lean gaseous stream from step iv to step i.

12. The process as claimed in claim 7 , wherein the polymerization catalyst is a metallocene catalyst.

13. The process as claimed in claim 1 , wherein the separation efficiency of step iv. is at least 90%.