Semi-permeable membrane separation process for the production of very high purity nitrogen

• US 5,693,121 A
• Filed: 11/09/1995
• Issued: 12/02/1997
• Est. Priority Date: 11/17/1994
• Status: Expired due to Fees

• Current Assignee: Enerfex Incorporated
• Original Assignee: Enerfex Incorporated
• Inventors: Callahan, Richard A., Khandavalli, Kishore V.
• Primary Examiner(s): SPITZER, ROBERT H
• Application Number:
  US08/552,466
• Time in Patent Office: 754 Days
• Field of Search: 95/39, 95/45, 95/51, 95/54, 95/55
• US Class Current: 95/39
• CPC Class Codes: B01D 53/22 by diffusion manufacturing semi-permeable membranes B01D67/00; form, structure or properties of semi-permeable membranes B01D69/00; material for semi-permeable membranes B01D71/00
• CPC Class Codes: B01D 53/226 in serial connexion
• CPC Class Codes: C01B 21/0438 by making use of membranes
• CPC Class Codes: C01B 2210/0051 Carbon dioxide

Abstract

A semi-permeable gas membrane process is described for the separation of very high purity nitrogen from a process feed gas mixture that is predominantly nitrogen, and one or more other permeable gases, which process comprises providing a feed gas mixture under pressure to a membrane separator unit comprising a semi-permeable separation membrane with respect to which the largest fraction of the other permeable gases is at least 20 times more permeable than nitrogen, to provide a very high purity raffinate nitrogen gas product.

Claims

1. A semi-permeable gas membrane process for the separation of very high purity nitrogen of ≧

99.5 vol. % from a process feed gas mixture that is predominantly nitrogen, and one or more other permeable gases, obtained from ammonia production, from stoichiometric combustion, or from combustion gas after treatment by a chemical or catalytic process, such that the O₂ content is ≦

5 vol. %, which semi-permeable gas membrane process comprises providing said feed gas mixture under pressure to a membrane separator unit comprising a semi-permeable separation membrane with respect to which the largest fraction of the other permeable gases is a least 20 times more permeable than nitrogen, to provide a very high purity raffinate nitrogen gas product of ≧

99.5 vol. % nitrogen.

2. A semi-permeable gas membrane process as in claim 1, which further comprises a pretreatment step wherein the process feed gas mixture is cooled, compressed, and dried.

3. A semi-permeable gas membrane process as in claim 1, wherein the gases obtained from either the stoichiometric combustion or the combustion gas after treatment by a chemical or catalytic process comprises products of fossil fuel combustion.

4. A semi-permeable gas membrane process as in claim 3, wherein the process feed gas mixture contains 79 vol. % or more of nitrogen.

5. A semi-permeable gas membrane process as in claim 1, wherein the gases obtained from either the stoichiometric combustion or the combustion gas after treatment by a chemical or catalytic process comprises vent gas from a limekiln.

6. A semi-permeable gas membrane process as in claim 1, wherein the largest fraction of the other permeable gases is carbon dioxide, and said semi-permeable separation membrane has a selective permeability for carbon dioxide over nitrogen of at least 20 times.

7. A semi-permeable gas membrane process as in claim 6, which further comprises a membrane requirement per standard cubic foot of non-permeate raffinate nitrogen gas product at 99.9995 vol. % purity which in the case of carbon dioxide from nitrogen separation is less than 4/10ths that of an air separation membrane requirement per standard cubic foot at 99.5 vol. % nitrogen product purity.

8. A semi-permeable gas membrane process as in claim 6, wherein said semi-permeable separation membrane is made from at least one polymeric material selected from the group consisting of polyimide, cellulose acetate, polysulfone, polycarbonate, and polyphenylene oxide.

9. A semi-permeable gas membrane process as in claim 1, wherein said feed gas mixture is a compressed feed gas stream of predominantly nitrogen, and contains carbon dioxide in a concentration of from 10% to 30 vol. %.

10. A semi-permeable gas membrane process as in claim 1, wherein there is provided a compressed non-permeate raffinate product stream which is nitrogen in a concentration of from 99.9 vol. % to 99.9995 vol. %.

11. A semi-permeable gas membrane process as in claim 1, which further comprises a permeate waste stream which is predominantly nitrogen and has a carbon dioxide concentration of from 27.0 vol. % to 30.0 vol. %.

12. A semi-permeable gas membrane process as in claim 1, which further comprises a feed gas mixture:

non-permeate raffinate gas product ratio of not more than 1.8;

1 to provide a product to feed recovery of at least 56% at 99.9995 vol. % nitrogen product purity.

13. A semi-permeable gas membrane process as in claim 1, carried out at a production efficiency of at least 2 standard cubic feet of nitrogen per minute per compression horsepower at 99.9995 vol. % nitrogen product purity.

14. A semi-permeable gas membrane process as in claim 1 which further comprises a membrane requirement per standard cubic foot of non-permeate nitrogen product at 99.5 vol. % purity which is less than 3/10ths that of an air separation membrane process at 99.5 vol. % nitrogen product purity.

15. A semi-permeable gas membrane process as in claim 1, wherein said semi-permeable separation membrane is made from at least one polymeric material selected from the group consisting of polyimide, cellulose acetate, polysulfone, polycarbonate, and polyphenylene oxide.

16. A semi-permeable gas membrane process as in claim 1, wherein the largest fraction of the other permeable gases is hydrogen, and said semi-permeable separation membrane has a selective permeability for hydrogen over nitrogen of at least 50 times.

17. A semi-permeable gas membrane process for the separation of ultra high purity nitrogen of >

99.9 vol. % from a process feed gas mixture that is predominantly nitrogen, and one or more other permeable gases, obtained from ammonia production, from stoichiometric combustion, or from combustion gas after treatment by a chemical or catalytic process, such that the O₂ content is ≦

5 vol. %, which semi-permeable gas membrane process comprises providing said feed gas mixture under pressure to a first membrane separator unit comprising a first semi-permeable separation membrane with respect to which the largest fraction of the other permeable gases is a least 20 times more permeable than nitrogen, to provide a very high purity intermediate raffinate nitrogen gas product, and further providing said intermediate gas product to a second membrane separator unit comprising a second semi-permeable separation membrane having sub-atmospheric pressure on the permeate side of the second separation membrane, in order to provide an ultra high purity raffinate nitrogen gas product of >

99.9 vol. % nitrogen.

18. A semi-permeable gas membrane process as in claim 17, wherein said sub-atmospheric pressure on the permeate side of the second separation membrane is provided by use of a vacuum pump.

19. A semi-permeable gas membrane process as in claim 17, wherein said second semi-permeable separation membrane is made from at least one polymeric material selected from the group consisting of polyimide, cellulose acetate, polysulfone, polycarbonate, and polyphenylene oxide.

20. A semi-permeable gas membrane process as in claim 17, wherein the permeate gas stream from the secondary membrane stage is recycled to the feed of the first membrane separator unit.