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US 6,565,626 B1Granted
Natural gas separation using nitrogen-selective membranes
AssigneeMembrane Technology and Research, Inc.
InventorsRichard W. Baker, Johannes G. Wijmans, Zhenjie He, Ingo Pinnau
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Abstract
A process for treating natural gas or other methane-rich gas to remove excess nitrogen and carbon dioxide simultaneously. The invention relies on membrane separation using nitrogen/methane and carbon dioxide/methane selective membranes. The gas can typically be brought to pipeline specification for both components, without requiring the use of amine scrubbing or other acid gas removal technique. Where water vapor or hydrogen sulfide is present in the raw gas, these contaminants may also be removed to meet pipeline specification in a single operation.
Claims39
A process for removing nitrogen and carbon dioxide from a gas stream comprising methane, at least about 2% carbon dioxide 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 more permeable to all of nitrogen, carbon dioxide, hydrogen sulfide and water vapor than to methane;
- (b) providing a second membrane unit containing a second membrane having a second feed side and a second permeate side, the second membrane being more permeable to all of nitrogen, carbon dioxide, hydrogen sulfide and water vapor than to methane, 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 first pressure 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 and depleted in nitrogen and carbon dioxide compared with the gas stream;
- (e) withdrawing from the first permeate side, at a second pressure lower than the first pressure, a first permeate stream depleted in methane and enriched in nitrogen and enriched in carbon dioxide 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 and no more than about 3% carbon dioxide;
- (h) withdrawing from the second permeate side, at a third pressure lower than the first pressure, a second permeate stream depleted in methane and enriched in nitrogen and enriched in carbon dioxide compared with the first residue stream.
5 more elements
A process for removing nitrogen and carbon dioxide from a gas stream comprising methane, at least about 2% carbon dioxide 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 more permeable to all of nitrogen, carbon dioxide, hydrogen sulfide and water vapor than to methane;
- (b) providing a second membrane unit containing a second membrane having a second feed side and a second permeate side, the second membrane being more permeable to all of nitrogen, carbon dioxide, hydrogen sulfide and water vapor than to methane, 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 more permeable to all of nitrogen, carbon dioxide, hydrogen sulfide and water vapor than to methane, 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 pressure 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 and depleted in nitrogen and carbon dioxide compared with the gas stream;
- (f) withdrawing from the first permeate side, at a second pressure lower than the first pressure, a first permeate stream depleted in methane and enriched in nitrogen and enriched in carbon dioxide 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 and no more than about 3% carbon dioxide;
- (i) withdrawing from the second permeate side, at a third pressure lower than the first pressure, a second permeate stream depleted in methane and enriched in nitrogen and enriched in carbon dioxide 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, at a fourth pressure lower than the first pressure, a third permeate stream depleted in methane and enriched in nitrogen and enriched in carbon dioxide compared with the first permeate stream.
9 more elements
Dependencies are inferred from the claim text.