Patent EA-002782-B1 (EA)
Title: Process and apparatus for preparing propylene homopolymers and copolymers
Inventor: HARLIN ALI
IPC: B01J8/26
Filed: 1998-06-24
Abstract: 1. A process for preparing propylene homopolymers and copolymers, which comprises polymerizing propylene optionally with comonomers in the presence of a catalyst at elevated temperature and pressure in at least one slurry reactor and at least one gas phase reactor, wherein the production rate of the slurry reactor is 10 to 70 wt-%, of the total production rate of the slurry and the first gas phase reactor, wherein the polymerization product of at least one slurry reactor, containing unreacted monomers, being directly conducted to a first gas phase reactor essentially without recycling of the unreacted monomers to the slurry reactor. 2. The process according to claim 1, wherein the polymerization product of the slurry reactor comprises polymeric substances selected from the group consisting of polypropylene, propylene copolymers and mixtures of polypropylene and propylene copolymers. 3. The process according to claim 1 or 2, wherein the slurry reactor comprises a loop reactor and wherein the concentration of propylene in the reaction medium is over 60 wt-% and the product forms in a particulate form. 4. The process according to any of claims 1 to 3, wherein the slurry reactor is operated at a temperature in the range of 60 to 80 degree C for preparing random or tercopolymers. 5. The process according to any of claims 1 to 3, wherein the slurry reactor is operated at a temperature in the range of 80 degree C to the critical temperature of the reaction medium. 6. The process according to any of claims 1 to 3, wherein the slurry reactor is operated at a temperature higher than the critical temperature of the reaction medium and below the softening temperature of the polymer. 7. The process according to any of claims 1 to 6, wherein the slurry reactor is operated at a pressure in the range of 35x10<5> to 100x10<5> Pa (35 to 100 bar). 8. The process according to any of the preceding claims, wherein the polymerization product is conducted from the slurry reactor to the first gas phase reactor via a direct pipeline. 9. The process according to any of the preceding claims, wherein the reaction medium of the polymerization product is evaporated before the polymerization product is fed into a first gas phase reactor. 10. The process according to claim 9, wherein the polymerization product is conducted from the slurry reactor to the first gas phase reactor via a jacketed pipe line heated by steam for providing at least a part of the energy needed for evaporation of the reaction medium. 11. The process according to any of the preceding claims, wherein the polymerization product fed to the first gas phase reactor contains copolymers comprising > 0.5 wt-%, preferably 2 to 16 wt-%, of at least one comonomer. 12. The process according to claim 11, wherein the polymerization product fed to the first gas phase reactor contains copolymers comprising 2 to 16 wt-%, of at least one comonomer. 13. The process according to claim 11, wherein the polymerization product is copolymerized in the first gas phase reactor with additional comonomers to increase the comonomer content. 14. The process according to claim 13, wherein the copolymerization is continued in the first gas phase reactor untill the comonomer content is increased up to 20 wt-%. 15. The process according to any of claims 1 to 14, wherein polymerization in the first gas phase reactor is carried out without additional monomer feed. 16. The process according to any one of the preceding claims, wherein a polymerization product is recovered from the gas phase reactor to provide improved properties, such as stiffness, creep properties, or softness. 17. The process according to claim 16, wherein the polymerization product is subjected to copolymerization in the presence of comonomers to provide a third polymer product with improved impact strength properties. 18. The process according to claim 17, wherein the copolymerization is carried out in a second gas phase reactor arranged in series with the first gas phase reactor. 19. The process according to claim 16 or 17, wherein the third polymer product is recovered and subjected to further copolymerization to provide a fourth polymer product having properties of improved stiffness, impact balance or stress whitening or white blush properties. 20. The process according to claim 19, wherein the further copolymerization reaction is carried out in a third gas phase reactor arranged in series with the second gas phase reactor. 21. The process according to claim 19 or 20, wherein the fourth polymer product is subjected to at least one further copolymerization reaction in at least one further reactor. 22. The process according to any of the preceding claims, wherein at least part of the unreacted monomers are recovered from the second and/or third gas phase reactor and recycled back to the previous gas phase reactor(s). 23. The process according to any of the preceding claims, wherein the unreacted monomers recovered from the first gas phase reactor are recycled back to the gas phase reactor. 24. The process according to any of the preceding claims, wherein the unreacted monomers recovered from the first gas phase reactor are recycled back to the slurry reactor. 25. The process according to any of the preceding claims, wherein a part of the unreacted monomers recovered from the first gas phase reactor is recycled back to the slurry reactor. 26. The process according to claim 25, wherein the amount of monomers recycled comprises 1 to 65 wt-% of the amount of monomers in the feed of the slurry reactor. 27. The process according to any of the preceding claims, wherein the production rate of the slurry reactor is 20 to 65 wt-%, in particular 40 to 60 wt-%, of the total production rate of the slurry and the first gas phase reactor. 28. The process according to any of the preceding claims, wherein hydrogen is used in at least one reactor as a molar mass modifier. 29. The process according to any of the preceding claims, wherein the catalyst used is prepolymerized before feeding it into the process. 30. A process for preparing propylene homopolymers and copolymers, which comprises the steps of - subjecting propylene optionally with comonomers to polymerization in the presence of a catalyst at elevated temperature and pressure in at least one slurry reactor to produce a first polymerization product comprising propylene polymer and unreacted monomers, - recovering the polymer and the unreacted monomers, - feeding the polymer to at least one gas phase reactor, - feeding essentially all of the unreacted monomers to said gas phase reactor, - subjecting the polymers and the unreacted monomers to polymerization in said gas phase reactor to produce a second polymerization product containing propylene polymer and gaseous substances, and - recovering the propylene polymer, wherein all unreacted monomers are fed directly to the first gas phase reactor without recycling the unreacted monomers back to the slurry reactor. 31. The process according to claim 30, wherein the propylene polymer is fed to a further gas phase reactor for copolymerization. 32. The process according to claim 30 or claim 31, wherein hydrogen is used as molar mass modifier in at least one of the reactors. 33. The process according to any of claims 30 to 32, wherein the polymerization in gas phase is carried out essentially without additional feed of monomers. 34. The process according to any of claims 30 to 33, wherein the first polymerization product is conducted to a flash tank to reduce the pressure thereof and in order to separate a gaseous product, unreacted monomers are recovered from the gaseous product, and the unreacted monomers are fed into the gas phase reactor. 35. The process according to claim 34, wherein hydrogen and/or inert hydrocarbons are separated from the gaseous product. 36. The process according to claim 35, wherein hydrogen and/or inert hydrocarbons are separated by membranes or stripping. 37. Apparatus for preparing propylene homopolymers and copolymers, which comprises - at least one slurry reactor and at least one gas phase reactor, arranged in series to form a cascade, which comprises  - a conduit interconnecting at least one slurry reactor with at least one gas phase reactor for conducting the polymer and essentially all of the unreacted monomers from the slurry reactor directly to the gas phase reactor. 38. The apparatus according to claim 37, wherein there is no conduit connected to a slurry reactor for recycling of unreacted monomers back to the same reactor. 39. The apparatus according to claim 37 or claim 38, wherein at least one of the gas phase reactors is provided with a conduit interconnecting said gas phase reactor with at least one slurry reactor for recycling any unreacted monomers. 40. The apparatus according to any of claims 37 to 39, wherein the conduit interconnecting the slurry reactor with the gas phase reactor comprises a jacketed pipe line. 41. The apparatus according to claim 40, wherein the conduit is provided with means for heating it with steam. 42. Apparatus for preparing propylene homopolymers and copolymers, which comprises - at least one slurry reactor and at least one gas phase reactor, arranged in series to form a cascade, - a flash tank for separating polymer from reaction medium containing unreacted monomers and volatile compounds, said tank having an inlet for a polymerization product and an outlet for the polymer and an outlet for the reaction medium, - a separation means for separating volatile compounds from the reaction medium, said separation means having an inlet for the reaction medium and an outlet for the reaction medium and an outlet for the volatile compounds, - a first conduit interconnecting at least one slurry reactor with the inlet of the flash tank, - a second conduit interconnecting the outlet of the polymer with at least one gas phase reactor, wherein comprises - a third conduit interconnecting the outlet of