Polymerisation process

1. A process for the polymerisation of monomer in a reactor, which process comprises withdrawing an effluent from the reactor which is a slurry of polymer solids in a liquid medium and contacting a first stream comprising vapour derived from the effluent withdrawn from the reactor with a feed stream to the reactor, said first stream comprising the majority of the vaporised components of the liquid medium in the effluent withdrawn from the reactor, wherein the first stream is brought into contact with the feedstream to the reactor at a pressure of 0.5 MPa or above and/or wherein the first stream is separated from the polymer withdrawn from the reactor at a pressure of 0.5 MPa or above.

2. A process as claimed in claim 1 wherein the feed stream is in a liquid form.

3. A process according to claim 1 which comprises first and second reactors connected in series and the feed stream is a feed stream to the second reactor.

4. A process according to claim 3 wherein the feed stream comprises effluent derived from the first reactor.

5. A process according to claim 1 wherein the first stream comprises diluent and monomer, and may also comprise comonomers, hydrogen and impurities.

6. A process according to claim 1 wherein the first stream is derived from the effluent by flashing all or a portion of the liquid medium to form a vapour, and separating this from the polymer solids.

7. A process according to claim 1 wherein a portion of the first stream is condensed prior to contact with the feedstream.

8. A process according to claim 1 wherein the majority of the first stream is in vapour form when brought into contact with the feed stream.

9. A process according to claim 8 wherein at least 80% by weight of the first stream is in vapour form when brought into contact with the feed stream.

10. A process according to claim 1 wherein the first stream is passed from its source to the contacting step without any compression and/or wherein the first stream is passed from its source to the contacting step without passing through any filters and/or wherein the first stream is passed directly from its source to the contacting step with the feed stream.

11. A process according to claim 1 wherein the first stream comprises entrained solids which are preferentially entrained into the feed stream.

12. A process according to claim 1 which is a process for the production of bimodal polymer products.

13. A process according to claim 1 wherein the contacting takes place in a contactor which is configured in association with a fractionator.

14. A process according to claim 13 wherein the vapour, or at least a portion thereof, recovered from the contactor or the contactor/fractionator combination is passed to one or more steps which include removal of inert components and/or include removal of heavy components prior to recycle.

15. A process according to claim 1 wherein the process has a monomer efficiency in excess of 99.5% and/or has an hydrogen efficiency of 80% or less.

16. A process for the polymerisation of monomer in at least two reactors operated in series, which process comprises contacting a first stream comprising vapour derived from the effluent withdrawn from the second reactor with a feed stream to the second reactor to produce a second stream comprising vapour which is passed to further processing and a third stream which is passed to the second reactor.

17. A process as claimed in claim 16 wherein the feed stream is in a liquid form.

18. A process as claimed in claim 16 wherein the feed stream comprises effluent derived from the first reactor.

19. A process according to claim 16 wherein the first stream comprises diluent and monomer, and may also comprise comonomers, hydrogen and impurities.

20. A process according to claim 16 wherein the first stream is brought into contact with the feedstream to the second reactor at a pressure of 0.5 MPa or above and/or wherein the first stream is separated from the polymer withdrawn from the second reactor at a pressure of 0.5 MPa or above.

21. A process according to claim 16 wherein the effluent withdrawn from the second reactor is a slurry of polymer solids in a liquid medium comprising diluent, and wherein the first stream is derived from the effluent by flashing all or a portion of the liquid medium to form a vapour, and separating this from the polymer solids.

22. A process according to claim 21 wherein the first stream is a majority of the separated stream.

23. A process according to claim 16 wherein a portion of the first stream is condensed prior to contact with the feedstream.

24. A process according to claim 16 wherein the majority of the first stream is in vapour form when brought into contact with the feed stream.

25. A process according to claim 24 wherein at least 80% by weight of the first stream is in vapour form when brought into contact with the feed stream.

26. A process according to claim 16 wherein the first stream is passed from its source to the contacting step without any compression and/or wherein the first stream is passed from its source to the contacting step without passing through any filters and/or wherein the first stream is passed directly from its source to the contacting step with the feed stream.

27. A process according to claim 16 wherein the third stream comprises a slurry of polymer solids in a liquid medium.

28. A process according to claim 16 wherein the first stream comprises entrained solids which are preferentially entrained into the third stream.

29. A process according to claim 16 which is a process for the production of bimodal polymer products.

30. A process according to claim 16 wherein the contacting takes place in a contactor which is configured in association with a fractionator.

31. A process according to claim 30 wherein the vapour, or at least a portion thereof, recovered from the contactor or the contactor/fractionator combination is passed to one or more steps which include removal of inert components and/or include removal of heavy components prior to recycle.

32. A process according to claim 16 wherein the process has a monomer efficiency in excess of 99.5% and/or has an hydrogen efficiency of 80% or less.

33. A process for the polymerisation of monomer in a reactor, which process comprises withdrawing an effluent from the reactor which is a slurry of polymer solids in a liquid medium and contacting a first stream comprising vapour derived from the effluent withdrawn from the reactor with a feed stream to the reactor, said first stream comprising the majority of the vaporised components of the liquid medium in the effluent withdrawn from the reactor and wherein

a) a portion of the first stream is condensed prior to contact with the feedstream, and/or

b) the first stream comprises entrained solids which are preferentially entrained into the feed stream.

34. A process as claimed in claim 33 wherein the feed stream is in a liquid form.

35. A process according to claim 33 which comprises first and second reactors connected in series and the feed stream is a feed stream to the second reactor.

36. A process according to claim 33 wherein the first stream comprises diluent and monomer, and may also comprise comonomers, hydrogen and impurities.

37. A process according to claim 33 wherein the first stream is brought into contact with the feedstream to the reactor at a pressure of 0.5 MPa or above and/or wherein the first stream is separated from the polymer withdrawn from the reactor at a pressure of 0.5 MPa or above.

38. A process according to claim 33 wherein the first stream is derived from the effluent by flashing all or a portion of the liquid medium to form a vapour, and separating this from the polymer solids.

39. A process according to claim 33 wherein the majority of the first stream is in vapour form when brought into contact with the feed stream.

40. A process according to claim 33 wherein the first stream is passed from its source to the contacting step without any compression and/or wherein the first stream is passed from its source to the contacting step without passing through any filters and/or wherein the first stream is passed directly from its source to the contacting step with the feed stream.

41. A process according to claim 33 which is a process for the production of bimodal polymer products.

42. A process according to claim 33 wherein the contacting takes place in a contactor which is configured in association with a fractionator.

43. A process according to claim 33 wherein the process has a monomer efficiency in excess of 99.5% and/or has an hydrogen efficiency of 80% or less.

44. A process according to claim 35 wherein the feed stream comprises effluent derived from the first reactor.

45. A process according to claim 39 wherein at least 80% by weight of the first stream is in vapour form when brought into contact with the feed stream.

46. A process according to claim 42 wherein the vapour, or at least a portion thereof, recovered from the contactor or the contactor/fractionator combination is passed to one or more steps which include removal of inert components and/or include removal of heavy components prior to recycle.

47. A process for the polymerisation of monomer in a reactor, which process comprises withdrawing an effluent from the reactor which is a slurry of polymer solids in a liquid medium and contacting a first stream comprising vapour derived from the effluent withdrawn from the reactor with a feed stream to the reactor, said first stream comprising the majority of the vaporised components of the liquid medium in the effluent withdrawn from the reactor, wherein the contacting takes place in a contactor which is configured in association with a fractionator.

48. A process as claimed in claim 47 wherein the feed stream is in a liquid form.

49. A process according to claim 47 which comprises first and second reactors connected in series and the feed stream is a feed stream to the second reactor.

50. A process according to claim 47 wherein the first stream comprises diluent and monomer, and may also comprise comonomers, hydrogen and impurities.

51. A process according to claim 47 wherein the first stream is brought into contact with the feedstream to the reactor at a pressure of 0.5 MPa or above and/or wherein the first stream is separated from the polymer withdrawn from the reactor at a pressure of 0.5 MPa or above.

52. A process according to claim 47 wherein the first stream is derived from the effluent by flashing all or a portion of the liquid medium to form a vapour, and separating this from the polymer solids.

53. A process according to claim 47 wherein a portion of the first stream is condensed prior to contact with the feedstream.

54. A process according to claim 47 wherein the majority of the first stream is in vapour form when brought into contact with the feed stream.

55. A process according to claim 47 wherein the first stream is passed from its source to the contacting step without any compression and/or wherein the first stream is passed from its source to the contacting step without passing through any filters and/or wherein the first stream is passed directly from its source to the contacting step with the feed stream.

56. A process according to claim 47 wherein the first stream comprises entrained solids which are preferentially entrained into the feed stream.

57. A process according to claim 47 which is a process for the production of bimodal polymer products.

58. A process according to claim 47 wherein the process has a monomer efficiency in excess of 99.5% and/or has an hydrogen efficiency of 80% or less.

59. A process according to claim 49 wherein the feed stream comprises effluent derived from the first reactor.

60. A process according to claim 54 wherein at least 80% by weight of the first stream is in vapour form when brought into contact with the feed stream.

61. A process according to claim 47 wherein the vapour, or at least a portion thereof, recovered from the contactor or the contactor/fractionator combination is passed to one or more steps which include removal of inert components and/or include removal of heavy components prior to recycle.