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US 6,572,678 B1Granted
Natural gas separation using nitrogen-selective membranes of modest selectivity
AssigneeMembrane Technology and Research, Inc.
InventorsJohannes Gerard Wijmans, Richard W. Baker, Zhenjie He, Ingo Pinnau
Life of this patent
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Abstract
A process for treating natural gas or other methane-rich gas to remove excess nitrogen and optionally excess carbon dioxide, water vapor or hydrogen sulfide. The invention relies on gas separation by membranes, using nitrogen/methane selective membranes. The membranes are characterized by having the capability to exhibit a nitrogen/methane selectivity between about 2 and 5 at a temperature higher than about −25° C. The gas may be brought to pipeline specification for nitrogen, and acid gases if present, without requiring the use of amine scrubbing or other acid gas removal technique.
Claims43
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 −25° 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 −25° 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 −25° 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.
8 more elements
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 −25° 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 −25° 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 into the first membrane unit, at a feed temperature sufficient to provide a nitrogen/methane selectivity between about 2 and 5 and a transmembrane pressure-normalized nitrogen flux of at least about 1 gpu., 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.
8 more elements
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 −25° 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 −25° 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) providing a third membrane unit containing a third membrane having a third feed side and a third permeate side,
- the third membrane being characterized by having the capability to exhibit a third nitrogen/methane selectivity in the range about 2-5 at a third temperature higher than about −25° C.,
- the third membrane unit being connected in series with the first membrane unit such that gas leaving the first permeate side can enter the third membrane unit on the third feed side;
- (d) passing the gas stream at a first feed temperature into the first membrane unit and across the first feed side;
- (e) withdrawing from the first feed side a first residue stream enriched in methane compared with the gas stream;
- (f) withdrawing from the first permeate side a first permeate stream depleted in methane compared with the gas stream;
- (g) passing the first residue stream into the second membrane unit and across the second feed side;
- (h) 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;
- (i) withdrawing from the second permeate side a second permeate stream depleted in methane compared with the first residue stream;
- (j) passing the first permeate stream into the third membrane unit and across the third feed side;
- (k) withdrawing from the third feed side a third residue stream enriched in methane compared with the first permeate stream;
- (l) withdrawing from the third permeate side a third permeate stream depleted in methane compared with the first permeate stream.
14 more elements
Dependencies are inferred from the claim text.