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Polymerization process in a slurry loop reactor having a slurry loop reaction zone with a volume of at least 50 m3 and an internal diameter (D) of 50 cm or greater, a feed inlet for monomers and diluent, a catalyst inlet for polymerisation catalyst, and a discharge conduit for removal of polymer. Mo

Polymerization process in a slurry loop reactor having a slurry loop reaction zone with a volume of at least 50 m3 and an internal diameter (D) of 50 cm or greater, a feed inlet for monomers and diluent, a catalyst inlet for polymerisation catalyst, and a discharge conduit for removal of polymer. Monomer, diluent and catalyst are passed into the reaction zone through their respective inlets where they form a slurry of polymer solids having a polymer solids concentration in the reaction zone of greater than 20 wt %. The space-time yield (STY) is greater than 100 kg/h/m3, and the catalyst inlet is an inlet pipe such that no part of the inlet pipe protrudes beyond the wall of the reaction zone and into the reaction zone by more than 1/10th of the diameter of the reaction zone at the point where the inlet pipe joins the reaction zone.

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1. A process for polymerisation in a slurry loop polymerisation reactor, which reactor comprises: a) a reaction zone in the form of a slurry loop and having a volume of at least 50 m3 and an internal diameter (D) of 50 cm or greater,b) at least one feed inlet for monomers and diluent,c) at least one

1. A process for polymerisation in a slurry loop polymerisation reactor, which reactor comprises: a) a reaction zone in the form of a slurry loop and having a volume of at least 50 m3 and an internal diameter (D) of 50 cm or greater,b) at least one feed inlet for monomers and diluent,c) at least one catalyst inlet for polymerisation catalyst, andd) at least one discharge conduit for removal of polymer,and which process comprises passing monomer, diluent and catalyst into the reaction zone through their respective inlets, and wherein they react to form a slurry of polymer solids having a concentration of polymer solids in the reaction zone of greater than 20 wt %, being the weight of polymer solids relative to the total weight of the slurry (solids and liquid), wherein the process is operated at a space-time yield (STY) greater than 100 kg/h/m3, andwherein the at least one catalyst inlet is in the form of an inlet pipe and no part of the inlet pipe protrudes beyond the wall of the reaction zone and into the reaction zone by more than 1/10th of the diameter of the reaction zone at the point where the inlet pipe joins the reaction zone. 2. A process as claimed in claim 1 wherein the catalyst is introduced through the at least one catalyst inlet as a catalyst stream comprising catalyst in a diluent at a concentration of catalyst of less than 10 wt % relative to the weight of catalyst and diluent. 3. A process as claimed in claim 1 wherein the concentration of catalyst in the catalyst stream is less than 1/10th of the concentration of polymer solids in the reaction zone. 4. A process as claimed in claim 1 wherein the catalyst stream is passed through the catalyst inlet or inlets at a linear velocity of at least 0.25 m/s. 5. A process as claimed in claim 1 wherein the ratio of flow velocity, measured in m/s, of the catalyst slurry to the concentration of catalyst, measured in wt %, in the catalyst slurry is greater than or equal to 0.25. 6. A process as claimed in claim 1 wherein the concentration of polymer solids in the reaction zone is greater than 30 wt %, being the weight of polymer solids relative to the total weight of the slurry (solids and liquid). 7. A process as claimed in claim 1 wherein the flow velocity, measured in m/s, of the catalyst slurry is equal or greater than 10 times the ratio of the concentration of catalyst, measured in wt %, in the catalyst slurry to the concentration of polymer solids, measured in wt %, of the polymer slurry in the reaction zone. 8. A process as claimed in claim 1 wherein the process is operated at a space-time yield (STY) greater than 150 kg/h/m3. 9. A process as claimed in claim 1 wherein the monomer is ethylene, and the ethylene concentration in the reactor is greater than 4 wt %, based on the total weight of the slurry. 10. A process according to claim 1 wherein the catalyst inlet pipe has an internal diameter (d) at its exit of less than 8 cm. 11. A process according to claim 1 wherein the reaction zone has an internal diameter (D) of 60 cm or greater. 12. A process according to claim 1 wherein L/D is less than 0.05, L being the maximum length by which the inlet pipe protrudes into the reaction zone, and D being the diameter of the reaction zone. 13. A process according to claim 1 wherein the inlet pipe does not protrude into the reaction zone at all. 14. A process according to claim 1 wherein the L/d is less than 2, L being the maximum length by which the inlet pipe protrudes into the reaction zone and d being the internal diameter of the catalyst inlet pipe. 15. A process according to claim 1 wherein the reaction zone has a volume of at least 80 m3. 16. A process as claimed in claim 3 wherein the concentration of catalyst in the catalyst stream is less than 1/20th of the concentration of polymer solids in the reaction zone. 17. A process as claimed in claim 3 wherein the concentration of catalyst in the catalyst stream is less than 1/40th of the concentration of polymer solids in the reaction zone. 18. A process as claimed in claim 4 wherein the catalyst stream is passed through the catalyst inlet or inlets at a linear velocity of at least 0.5 m/s. 19. A process as claimed in claim 6 wherein the concentration of polymer solids in the reaction zone is greater than 40 wt %, being the weight of polymer solids relative to the total weight of the slurry (solids and liquid). 20. A process as claimed in claim 8 wherein the process is operated at a space-time yield (STY) in the range 200-400 kg/h/m3. 21. A process as claimed in claim 9 wherein the monomer is ethylene, and the ethylene concentration in the reactor is in the range 4 to 10 wt % based on the total weight of the slurry. 22. A process according to claim 10 wherein the catalyst inlet pipe has an internal diameter (d) at its exit of less than 5 cm. 23. A process according to claim 10 wherein the catalyst inlet pipe has an internal diameter (d) at its exit in the range 1 to 3 cm. 24. A process according to claim 11 wherein the reaction zone has an internal diameter (D) in the range 60 to 90 cm. 25. A process according to claim 12 wherein L/D is less than 0.025. 26. A process according to claim 14 wherein the L/d is in the range 0 to 1. 27. A process according to claim 14 wherein the L/d is 0 (when L=0). 28. A process according to claim 15 wherein the reaction zone has a volume in the range 100-150 m3. 29. A process according to claim 1 wherein monomers, diluent, catalyst and comonomers are passed into the reaction zone.