Continuous gas-phase polymerization process
Continuous gas-phase polymerization process for preparing ethylene and propene homopolymers and copolymers, in which ethylene, propene or mixtures comprising ethylene or propene and C 3 -C 8 -α-monoolefins are polymerized in the polymerization zone of a gas-phase polymerization reactor at from 30 to 125° C. and pressures of from 1 to 100 bar in the gas phase in a bed comprising finely divided polymer in the presence of a catalyst. To remove the heat of polymerization, the reactor gas is circulated and firstly passes through a cyclone after leaving the reactor. To prevent polymer deposits in the circulating gas system, a catalyst poison having a boiling point above the maximum temperature within the circulating gas system is fed into this circulating gas system at a position between the reactor and the cyclone.
1. A continuous gas phase polymerization process for preparing ethylene and propene homopolymers and copolymers, in which ethylene, propene or mixtures comprising ethylene and propene and C 3 -C 8 -α-monoolefins are polymerized in the polymerization zone of a gas-phase polymerization reactor at from 30 to 125° C. and pressures of from 1 to 100 bar in the gas phase in a bed comprising finely divided polymer in the presence of a catalyst, with the reactor gas being circulated to remove the heat of polymerization and the circulated reactor gas being firstly passed through a cyclone after leaving the reactor, wherein a catalyst poison having a boiling point above the maximum temperature within the circulating gas system is fed into this circulating gas system at a position between the reactor and the cyclone to prevent polymer deposits in the circulating gas system.
2. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the polymerization is carried out in a fluidized-bed reactor.
3. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the catalyst poison fed in is a compound or a mixture of compounds containing at least one of the functional groups —NR 2 , —NR—, —OR, —O—, ═O, —OS, —S— and ═S, where R is hydrogen or an alkyl radical having from 1 to 8 carbon atoms.
4. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the catalyst poison has a vapor pressure of less than 10 000 Pa at 20° C.
5. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the catalyst poison has a vapor pressure of less than 2000 Pa at 20° C.
6. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the catalyst poison is fed into the circulating gas system as a solution in a C 3 -C 8 -a-monoolefin.
7. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the catalyst poison is fed together with a surface-active compound into the circulating gas system.
8. A continuous gas-phase polymerization process as claimed in claim 1 , wherein the mixture of fine dust and catalyst poison which has been separated off in the cyclone is added to the polymerization product.
9. A continuous polymerization process as claimed in claim 1 , wherein the polymerization reactor does not have a calming zone.