Recovery of olefin monomers

Abstract

In a process for the production of a polyolefin, an olefin monomer is polymerised said polyolefin and residual monomer is recovered. A gas stream comprising the monomer and nitrogen is subjected to a PSA process in which said monomer is adsorbed on a periodically regenerated silica gel or alumina adsorbent to recover a purified gas stream containing said olefin and a nitrogen rich stream containing no less than 99% nitrogen and containing no less than 50% of the nitrogen content of the gas feed to the PSA process.

1 . A process for the production of a polyolefin in which an olefin monomer is polymerised to produce said polyolefin and residual monomer is recovered, said process comprising subjecting a gas stream comprising said monomer and nitrogen to a PSA process in which said monomer is adsorbed on a periodically regenerated solid adsorbent to recover a purified gas stream containing said olefin and a nitrogen rich stream containing no less than 99% nitrogen and containing no less than 50% of the nitrogen content of the gas feed to the PSA process.  
     
     
         2 . A process as claimed in  claim 1 , wherein the adsorbent is silica gel.  
     
     
         3 . A process as claimed in  claim 1 , wherein the adsorbent is alumina having a surface area of no more than 900 m 2 /g.  
     
     
         4 . A process as claimed in  claim 1 , wherein the adsorbent is alumina having a surface area of no more than 800 m 2 /g.  
     
     
         5 . A process as claimed in  claim 1 , wherein the adsorbent is alumina having a surface area of no more than 600 m 2 /g.  
     
     
         6 . A process as claimed in  claim 1 , wherein the adsorbent is alumina having an average pore diameter of at least 1.7 nm.  
     
     
         7 . A process as claimed in  claim 1 , wherein the adsorbent is alumina having an average pore diameter of at least 2.0 nm.  
     
     
         8 . A process as claimed in  claim 1 , wherein the recovery of C 2+  hydrocarbons from the monomer and nitrogen containing gas stream is no less than 99%.  
     
     
         9 . A process as claimed in  claim 1 , wherein at each stage of the PSA process, breakthrough of C 2+  hydrocarbons from the adsorbent is avoided.  
     
     
         10 . A process as claimed in  claim 1 , wherein the ratio of ethylene in the monomer and nitrogen gas stream to the ethylene in the nitrogen rich stream is at least 500.  
     
     
         11 . A process as claimed in  claim 1 , wherein the ratio of ethane in the monomer and nitrogen gas stream to the ethane in the nitrogen rich stream is at least 50.  
     
     
         12 . Apparatus for use in the polymerisation of olefin comprising a polymerisation unit having an inlet for olefin monomer and an outlet for polymer connected to a polymer degassing unit having an inlet for nitrogen purge gas and an outlet for a nitrogen/monomer mixture connected to an olefin recovery unit comprising a compressor feeding said nitrogen/monomer mixture in a compressed state to an inlet of a liquid olefin separator having outlets for liquid olefin and for an olefin depleted nitrogen/olefin mixture, said outlet for liquid olefin being connected to recycle the olefin to the polymerisation unit, and a PSA gas separation unit connected to receive said olefin depleted nitrogen/olefin mixture and to produce therefrom a purified nitrogen stream containing no less than 99% nitrogen and a recovered olefin stream, said PSA unit being connected to return said recovered olefin stream to the inlet of said liquid olefin separator.