Degassing process
View Patent ↗An improved process for the polymerization of olefin monomer selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) mixtures of (a), (b) or (c) with one or more alpha-olefins in a fluidized bed gas phase reactor, said process comprising passing a gaseous mixture of said olefin monomers(s) through the fluidized bed under effective polymerization conditions to provide a polymer product containing unreacted monomer(s) and a gaseous effluent stream comprising unreacted monomer(s), removing the polymer product to a degassing vessel, recycling a first portion of the gaseous effluent stream to the fluidized bed and passing a second portion of the gaseous effluent stream to counter currently contact the polymer product in said degassing vessel to produce a polymer product having a reduced amount of unreacted monomer(s), characterized in that the improvements to the process comprise: (i) removing heavy hydrocarbons from the second portion of the effluent stream and returning said hydrocarbons to the first portion of the effluent stream for recycle to the fluidized bed, (ii) removing substantially all of the monomer(s) from the second portion of the effluent stream and returning said monomers(s) to the first portion of the effluent stream for recycle to the fluidized bed, and (iii) recycling the second effluent stream after passage through the degassing vessel to the gaseous effluent stream.
1. A process for the polymerization of olefin monomer(s) selected from the group consisting of (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) mixtures of (a), (b) or (c) with one or more alpha-olefins in a fluidized bed gas phase reactor, said process comprising passing a gaseous mixture of said olefin monomer(s) through the fluidized bed under effective polymerization conditions to provide a polymer product containing unreacted monomer(s) and a gaseous effluent stream containing unreacted monomer(s), removing the polymer product to a degassing vessel, splitting the gaseous effluent stream into first and second portions, recycling the first portion of the gaseous effluent stream to the fluidized bed, removing heavy hydrocarbons from the second portion of the effluent stream and returning said heavy hydrocarbons to the gaseous effluent stream for recycle to the fluidized bed, removing unreacted monomer(s) from the second portion of the effluent stream so that the amount of unreacted monomer(s) in the second portion of the effluent stream is <10% and returning said unreacted monomer(s) to the gaseous effluent stream for recycle to the fluidized bed, thereafter passing the second portion of the gaseous effluent stream to counter currently contact the polymer product in said degassing vessel to produce a polymer product having a reduced amount of unreacted monomer(s) and recycling the second portion of the effluent stream after passage through the degassing vessel to the gaseous effluent stream.
2. The process according to claim 1 wherein the heavy hydrocarbons are removed from the second portion of the effluent stream by a membrane.
3. The process according to claim 1 wherein the unreacted monomer(s) are removed from the second portion of the effluent stream by a membrane.
4. The process according to claim 1 wherein the gaseous effluent stream is split into the first and the second portions downstream of a recycle compressor.
5. The process according to claim 1 wherein the unreacted monomer(s) removed from the second portion of the gaseous effluent stream are returned to the gaseous effluent stream upstream of a recycle compressor.
6. The process according to claim 1 wherein the predominant unreacted monomer in the gaseous effluent stream is ethylene.
7. The process according to claim 1 comprising the copolymerization of ethylene and one or more alpha-olefins.
8. The process according to claim 7 wherein the alpha-olefin is hex-1-ene.
9. The process according to claim 1 wherein the second portion of the gaseous effluent stream is between 5-10% of the total gaseous effluent stream leaving the reactor.
10. The process according to claim 1 wherein the amount of unreacted monomer(s) in the second portion of the effluent stream is <5%.