Process to reduce polyolefins with extra low impurity content

1. A process for producing polyolefins, comprising the steps of:

polymerizing at least one olefin monomer to obtain a reaction mixture;

separating at least a part of the reaction mixture to obtain a separated portion;

dividing the separated portion of the reaction mixture into a polymer-lean fraction and a polymer-rich fraction, wherein the division is carried out in the liquid or super critical state;

subjecting at least a part of the polymer-lean fraction to a purification step to obtain a purified polymer-lean fraction;

recycling at least a part of the purified polymer-lean fraction back into the polymerizing step of the at least one olefin monomer; wherein

the polymerizing step comprises slurry polymerization;

the polymer-lean fraction is in liquid form or in a super critical state during all of the process steps; and

the subjecting of the at least a part of the polymer-lean fraction to a purification step and the recycling of the at least a part of the purified polymer-lean fraction comprise:

dividing the polymer-lean fraction into a first and a second stream;

recycling the first stream to the polymerizing step of the at least one olefin monomer;

purifying the second stream; and

recycling at least a part of the purified second stream back to the polymerizing step of the at least one olefin monomer.

2. The process according to claim 1 , wherein the subjecting of the at least a part of the polymer-lean fraction to a purification step comprises removing impurities contained in the polymer-lean fraction; and

the reaction mixture comprises at least 50% by mole of hydrocarbons having from 1 to 4 carbon atoms.

3. The process according to claim 1 , wherein the purification step is carried out by conducting at least one distillation step.

4. The process according to claim 1 , wherein the step of dividing the separated portion of the reaction mixture is carried out in a hydrocyclone or a screen.

5. The process according to claim 1 , wherein the step of dividing the polymer-lean fraction is carried out in a hydrocyclone or a screen.

6. The process according to claim 1 , wherein the polymer-lean fraction comprises at least one selected from the group consisting of: olefin oligomers, metal components, unreacted monomer, and byproducts formed during the polymerizing step.

7. The process according to claim 6 , wherein the byproducts comprise at least one selected from the group consisting of ketones, aldehydes, sulphur-containing compounds, and alcohols.

8. The process according to claim 1 , further comprising:

mixing the polymer-rich fraction with fresh olefin monomer to obtain a second mixture; and

dividing the second mixture into a second polymer-rich fraction and a monomer-rich fraction.

9. The process according to claim 8 , further comprising recycling the monomer-rich fraction to the polymerizing step of the at least one olefin monomer.

10. The process according to claim 1 , wherein the dividing of the polymer-lean fraction comprises dividing 10 to 95 wt % of the polymer-lean fraction into the second stream.

11. The process according to claim 1 , wherein the separating at least a part of the reaction mixture is carried out continuously.

12. The process according to claim 1 , wherein the separating at least a part of the reaction mixture is carried out intermittently.

13. The process according to claim 1 , wherein the separating at least a part of the reaction mixture comprises concentrating a polymer in the reaction mixture to obtain another mixture and separating at least a part of the another, mixture to obtain the separated portion.

14. The process according to claim 13 , wherein the concentrating is carried out by a settling leg.

15. The process according to claim 1 , wherein a concentration of a polymer in the reaction mixture is from 30 to 60% by weight.

16. The process according to claim 1 , wherein the polymerizing step is carried out in a stirred tank reactor or loop reactor.