Oxygen removal from contaminated gases

• US 8,221,524 B2
• Filed: 10/23/2009
• Issued: 07/17/2012
• Est. Priority Date: 10/23/2009
• Status: Expired due to Fees

• Current Assignee: Guild Associates Incorporated
• Original Assignee: Guild Associates Incorporated
• Inventors: Mitariten, Michael J.
• Primary Examiner(s): Greene, Jason M
• Application Number:
  US12/604,803
• Publication Number:
  US 20110094378A1
• Time in Patent Office: 998 Days
• Field of Search: 95/45, 95/51, 95/54, 95/96, 951/30, 951/38, 951/48, 95/50, 959/03, 96/4, 961/21, 961/31, 961/32, 961/43
• US Class Current: 95/54
• CPC Class Codes: B01D 2257/104 Oxygen
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 2258/05 Biogas
• CPC Class Codes: B01D 53/047 Pressure swing adsorption
• CPC Class Codes: B01D 53/229 Integrated processes (Diffusion and at least one other process, e.g. adsorption, absorption)
• CPC Class Codes: C10L 3/101 Removal of contaminants
• CPC Class Codes: C10L 3/104 Carbon dioxide
• CPC Class Codes: C10L 3/105 of nitrogen
• CPC Class Codes: Y02C 20/40 of CO2
• CPC Class Codes: Y02E 50/30 Fuel from waste, e.g. synthetic alcohol or diesel
• CPC Class Codes: Y10S 95/903 Carbon

Abstract

The invention relates to a method for achieving low oxygen levels in a natural gas stream without the use of a catalytic system. In one embodiment, the method comprises: membrane treatment for the removal of the bulk of CO₂ and oxygen in the natural gas feed and the addition of a PSA system using a carbon molecular sieve adsorbent for the adsorption of residual oxygen.

Claims

1. A process for the improved separation of oxygen from a natural gas feed stream which comprises:

a. passing said natural gas feed stream to a first separation unit so as to partially separate oxygen from said feed stream and produce a first product stream enriched with methane and a waste stream having a higher molar concentration of oxygen than said feed stream; and

b. passing said first product stream to a second separation unit containing an oxygen-selective adsorbent comprising a carbon molecular sieve and operated with a pressure swing so as to preferentially adsorb residual said oxygen from said first product stream to produce a low pressure gas stream enriched with oxygen and produce a higher pressure second product stream enriched with methane and having an oxygen content of less than 2,000 ppm.

2. The process of claim 1, wherein the natural gas feed stream comes from landfill gas, coal mine methane, coal bed methane, natural gas wells, or biogas.

3. The process of claim 1, wherein said natural gas is from landfill gas.

4. The process of claim 1, wherein said first separation unit is a membrane unit.

5. The process of claim 4, wherein said first product stream is a non-permeate stream.

6. The process of claim 1, wherein said first separation unit is a pressure swing adsorption unit.

7. The process of claim 1, wherein said low pressure gas stream of said second separation unit is recycled back to said natural gas feed stream.

8. The process of claim 1, wherein the oxygen concentration of said second product stream is about 1000 ppm or less.

9. The process of claim 1, wherein the oxygen concentration of said second product stream is about 100 ppm or less.

10. The process of claim 1, further comprising:

prior to passing said first product to said second separation unit;

a. passing said first product stream to a pressure swing adsorption nitrogen removal unit so as to remove nitrogen from said first product stream to produce a low pressure tail gas enriched with nitrogen and produce a higher pressure nitrogen-depleted product stream; and

b. passing said nitrogen-depleted product stream to said second separation unit.

11. The process of claim 10, wherein the nitrogen removal unit contains a molecular sieve selective for adsorbing nitrogen.

12. The process of claim 11, wherein nitrogen concentration of said second product stream is about 7% or less.

13. The process of claim 11, wherein the nitrogen concentration of said second product stream is about 4% or less.

14. The process of claim 1 comprising passing said first product stream to a pressure swing adsorption unit containing a combination of said carbon molecular sieve adsorbent and a nitrogen selective adsorbent.

15. The process of claim 14, wherein said nitrogen selective adsorbent is ETS-4 or CTS-1.

16. The process of claim 1, wherein said second product stream is directed to a pressure swing adsorption unit containing a nitrogen selective adsorbent.

17. The process of claim 11, wherein said molecular sieve is ETS-4 or CTS-1.

18. The process of claim 1 wherein said first separation unit also removes carbon dioxide.

19. A process for the improved separation of oxygen from a natural gas feed stream, which comprises:

a. passing said natural gas feed stream to a membrane separation unit so as to partially separate oxygen from said feed stream and produce a first product stream enriched with methane and a permeate waste stream having a higher molar concentration of oxygen than said feed stream;

b. passing said first product stream to a pressure swing adsorption unit containing a carbon molecular sieve so as to preferentially adsorb residual oxygen from said first product stream to produce a low pressure gas stream enriched with oxygen and to produce a second product stream enriched with methane and having an oxygen content of 1,000 ppm or less; and

c. recycling said low pressure gas stream back to said feed stream for said membrane separation unit.

20. The process of claim 19, wherein said first separation unit also removes carbon dioxide.

21. The process of claim 19, further comprising:

prior to passing said first product to said second separation unit;

a. passing said first product stream to a pressure swing adsorption nitrogen removal unit so as to remove nitrogen from said first product stream to produce a low pressure tail gas enriched with nitrogen and produce a higher pressure nitrogen-depleted product stream; and

b. passing said nitrogen-depleted product stream to said second separation unit.