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A process is described for increasing the space time yield of polymer production in a fluidized bed reactor employing an exothermic polymerization reaction by cooling the recycle stream to below its dew point and returning the resultant two-phase fluid stream to the reactor to maintain the fluidized

A process is described for increasing the space time yield of polymer production in a fluidized bed reactor employing an exothermic polymerization reaction by cooling the recycle stream to below its dew point and returning the resultant two-phase fluid stream to the reactor to maintain the fluidized bed at a desired temperature above the dew point of the recycle stream.

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1. In a continuous gas fluidized bed polymerization process for the production of polymer from monomer by continuously passing a gaseous stream comprising said monomer through a fluidized bed reactor in the presence of catalyst under reactive conditions, withdrawing polymeric product and a stream co

1. In a continuous gas fluidized bed polymerization process for the production of polymer from monomer by continuously passing a gaseous stream comprising said monomer through a fluidized bed reactor in the presence of catalyst under reactive conditions, withdrawing polymeric product and a stream comprising unreacted monomer gases, cooling said stream comprising unreacted monomer gases and returning said cooled stream to said reactor together with sufficient additional monomer to replace that monomer polymerized and withdrawn as product, the improvement which comprises: cooling part or all of said stream comprising unreacted monomer gases to form a mixture comprising a gas phase and a liquid phase and reintroducing said mixture into said reactor wherein said liquid phase is vaporized. 2. An improved process according to claim 1 wherein said stream comprising unreacted gases is compressed prior to cooling. 3. An improved process according to claim 1 wherein means are provided to maintain said liquid phase entrained in said mixture until such time as said liquid phase is vaporized. 4. An improved process according to claim 1 wherein an inert condensible fluid is present in said mixture to raise the dew point of said mixture. 5. An improved process according to claim 4 wherein said inert condensible fluid is a saturated hydrocarbon. 6. An improved process according to claim 1 wherein said liquid phase of said mixture is less than about 20 percent by weight of the total weight of said mixture. 7. An improved process according to claim 1 wherein said liquid phase of said mixture is less than about 10 percent by weight of the total weight of said mixture. 8. An improved process according to claim 1 wherein the flow rate of said mixture and the ratio of gas to liquid therein are maintained at levels sufficient to maintain said liquid entrained in said gas until vaporized. 9. An improved process according to claim 1 wherein said mixture is divided into at least two separate streams at least one of which is introduced into the reactor at a point below the fluidized bed and one or more of said separate streams is optionally introduced into said fluidized bed, provided that the velocity of all gases introduced below said fluidized bed is at least sufficient to support said bed and to maintain it in a fluidized condition. 10. An improved process according to claim 1 wherein the gas stream flowing upwardly through the fluidized bed is essentially uniform in composition and moving in a manner through said bed such that the entire bed is maintained in a gas fluidized condition and with essentially no dead spaces through which gases do not pass. 11. An improved process according to claim 1 wherein said additional monomer, added to replace monomer polymerized and withdrawn as product, is introduced into said reactor in liquid form, below the fluidized bed and at or near the point of entry of said mixture into said reactor. 12. An improved process according to claim 1 wherein said additional monomer added to replace monomer polymerized and withdrawn as product is introduced into said mixture prior to entry of said mixture into said reactor. 13. An improved process according to claim 1 wherein gas distributor means is provided immediately below the fluidized bed and above the region wherein said mixture is introduced into said reactor. 14. An improved process according to claim 1 wherein the internal pressure within said reactor is from about 100 psi to about 350 psi. 15. An improved process according to claim 1 wherein said monomer is an alpha olefin monomer having from two to four carbon atoms alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 16. An improved process according to claim 15, wherein said monomer is ethylene alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 17. An improved process according to claim 15, wherein said monomer is propylene alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 18. A method for controlling the temperature of a gas fluidized bed during the production of polymer in a fluidized bed reactor by an exothermic polymerization reaction, which comprises continuously introducing into the bed a stream comprising unreacted monomer gas cooled to below the maximum desired temperature within said bed and simultaneously or separately introducing a stream of liquid into said reactor under conditions such that an essentially uniform mixture of said gas and liquid is introduced into said bed at a level below the region of maximum desired temperature within said reactor wherein said liquid is vaporized. 19. A process for producing polymer from monomer by an exothermic polymerization reaction in a gas fluidized bed reactor having an upper polymerization zone containing a bed of growing polymer particles and a lower gas diffusion zone, which comprises: (1) continuously passing a gaseous stream comprising monomer through said polymerization zone with an upward velocity sufficient to maintain said particles in a suspended and gas fluidized condition; (2) introducing a polymerization catalyst into said polymerization zone; (3) withdrawing polymer product from said polymerization zone; (4) continuously withdrawing a stream of unreacted gases comprising monomer from said polymerization zone, compressing and cooling said stream to a temperature below the dew point of said stream to form a mixture comprising a gas phase and a liquid phase; and (5) continuously introducing said mixture into said polymerization zone wherein said liquid phase is vaporized. 20. A process according to claim 19 wherein an inert, condensible fluid is present in said mixture to raise the dew point of said mixture. 21. An improved process according to claim 20 wherein said inert, condensible fluid is a saturated hydrocarbon. 22. A process according to claim 19 wherein the liquid phase of said mixture is less than about 20 percent by weight of the total weight of said mixture. 23. A process according to claim 19 wherein the liquid phase of said mixture is less than about 10 percent by weight of the total weight of said mixture. 24. A process according to claim 19 wherein the flow rate of said mixture and the ratio of gas to liquid in said mixture are maintained at levels sufficient to maintain said liquid entrained in said gas until vaporized. 25. A process according to claim 19 wherein the gas stream flowing upwardly through the fluidized bed is essentially uniform in composition and moving in a manner through said bed such that the entire bed is maintained in a fluidized condition and with essentially no dead spaces through which gases do not pass. 26. A process according to claim 19 wherein additional monomer in liquid or gaseous form is added below the polymerization zone and at or near the point of entry of said mixture into said reactor to replace monomer polymerized and withdrawn as product. 27. A process according to claim 19 wherein additional monomer is added to replace monomer polymerized and withdrawn as product by injection into said mixture prior to entry of said mixture into the reactor. 28. A process according to claim 19 wherein gas distributor means is provided immediately below said polymerization zone. 29. A process according to claim 19 wherein the internal pressure within said reactor is from about 100 psi to about 350 psi. 30. A process according to claim 19 wherein said polymer is produced by reaction of an alpha olefin monomer having from two to four carbon atoms alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 31. An improved process according to claim 30, wherein said monomer is ethylene alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 32. An improved process according to claim 30, wherein said monomer is propylene alone or in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 33. A method for controlling the temperature of a fluidized bed during the production of polymers in a gas fluidized bed reactor by an exothermic polymerization reaction which comprises continuously introducing a stream comprising an essentially uniform gas-liquid mixture containing monomer into said bed wherein said liquid is vaporized. 34. In a continuous gas fluidized bed polymerization process for the production of polymer from monomer by continuously passing a gaseous stream comprising said monomer through a fluidized bed reactor in the presence of catalyst under reactive conditions, withdrawing polymeric product and a stream comprising unreacted monomer gases, cooling said stream comprising unreacted gases and returning said cooled stream to said reactor together with sufficient additional monomer to replace that monomer polymerized and withdrawn as product, the improvement which comprises: cooling part or all of said stream comprising unreacted gases to form a mixture comprising a gas phase and a liquid phase and reintroducing said mixture into said reactor wherein said liquid phase is volatilized; said gaseous stream passing through said fluidized bed reactor at a superficial velocity sufficient to maintain a viable fluidized bed. 35. A process for producing polymer from monomer by an exothermic polymerization reaction in a gas fluidized bed reactor having an upper polymerization zone containing a bed of growing polymer particles and a lower gas diffusion zone, which comprises: (1) continuously passing a gaseous stream comprising monomer through said polymerization zone with an upward velocity sufficient to maintain said particles in a suspended and gas fluidized condition; (2) introducing a polymerization catalyst into said polymerization zone in an inert gas stream at a point 20-40% of the diameter away from the reactor wall and about 5-30% of the height of the bed; (3) withdrawing polymer product from said polymerization zone; (4) continuously withdrawing a stream of unreacted gases comprising monomer from said polymerization zone, compressing and cooling said stream to a temperature below the dew point of said stream to form a mixture comprising a gas phase and a liquid phase; and (5) continuously introducing said mixture into said polymerization zone wherein said liquid phase is vaporized. 36. A process for producing polymer from monomer by an exothermic polymerization reaction in a gas fluidized bed reactor having an upper polymerization zone containing a bed of growing polymer particles and a lower gas diffusion zone, which comprises: (1) continuously passing a gaseous stream comprising monomer through said polymerization zone with an upward velocity sufficient to maintain said particles in a suspended and gas fluidized condition; (2) introducing a polymerization catalyst into said polymerization zone; (3) withdrawing polymer product from said polymerization zone; (4) continuously withdrawing a stream of unreacted gases comprising monomer from said polymerization zone, compressing and cooling said stream to a temperature below the dew point of said stream to form a mixture comprising a gas phase and a liquid phase; (5) continuously introducing said mixture into said polymerization zone wherein said liquid phase is vaporized; and (6) controlling the temperature of said mixture so as to maintain constant temperature in said polymerization zone, as the change in polymerization catalyst feed is varied to control the rate of said polymerization. 37. In a continuous gas fluidized bed polymerization process for the production of polymer from monomer comprising ethylene and/or propylene by continuously passing a gaseous stream comprising said monomer through a fluidized bed reactor in the presence of catalyst under reactive conditions, withdrawing polymeric product and a stream comprising unreacted gases, comprising monomer, cooling said stream comprising unreacted gases and returning said cooled stream to said reactor together with sufficient additional monomer to replace that monomer polymerized and withdrawn as product, the improvement which comprises: cooling part or all of said stream comprising unreacted gases to form a mixture comprising a gas phase and a liquid phase and reintroducing said mixture into said reactor wherein said liquid phase is vaporized. 38. An improved process according to claim 37 wherein said monomer comprises ethylene in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms. 39. An improved process according to claim 37 wherein said monomer comprises propylene in admixture with one or more other alpha olefin monomers having from two to eight carbon atoms.