Patent ID: 6572678
Filing Date: 2003-06-03
Classification: B01D,C07C,C10L

Abstract:
A process for removing nitrogen from a gas stream comprising methane and at least about 4% nitrogen, the process comprising the steps of:(a) providing a first membrane unit containing a first membrane having a first feed side and a first permeate side, the first membrane being characterized by having the capability to exhibit a first nitrogen/methane selectivity in the range about 2-5 at a first temperature higher than about âˆ’25Â° C.; (b) providing a second membrane unit containing a second membrane having a second feed side and a second permeate side, the second membrane being characterized by having the capability to exhibit a second nitrogen/methane selectivity in the range about 2-5 at a second temperature higher than about âˆ’25Â° C., the second membrane unit being connected in series with the first membrane unit such that gas leaving the first feed side can enter the second membrane unit on the second feed side; (c) passing the gas stream at a feed temperature above about âˆ’25Â° C. into the first membrane unit and across the first feed side; (d) withdrawing from the first feed side a first residue stream enriched in methane compared with the gas stream; (e) withdrawing from the first permeate side a first permeate stream depleted in methane compared with the gas stream; (f) passing the first residue stream into the second membrane unit and across the second feed side; (g) withdrawing from the second feed side as a product stream a second residue stream enriched in methane compared with the first residue stream, and containing no more than about 6% nitrogen; (h) withdrawing from the second permeate side a second permeate stream depleted in methane compared with the first residue stream.