Pressure swing adsorption process

• US 6,497,750 B2
• Filed: 02/26/2001
• Issued: 12/24/2002
• Est. Priority Date: 02/26/2001
• Status: Expired due to Term

• Current Assignee: Engelhard Corporation (BASF SE)
• Original Assignee: Engelhard Corporation (BASF SE)
• Inventors: Kuznicki, Steven M., Dolan, William B., Butwell, Kenneth F.
• Primary Examiner(s): Spitzer, Robert H.
• Application Number:
  US09/793,039
• Publication Number:
  US 20020162452A1
• Time in Patent Office: 666 Days
• Field of Search: 95/96--06, 951/14, 951/15, 951/30, 951/43, 959/01, 959/02
• US Class Current: 95/96
• CPC Class Codes: B01D 2253/308 Pore size
• CPC Class Codes: B01D 2256/10 Nitrogen
• CPC Class Codes: B01D 2256/24 Hydrocarbons
• CPC Class Codes: B01D 2257/7022 Aliphatic hydrocarbons
• CPC Class Codes: B01D 2259/41 using plural beds of the same adsorbent in series
• CPC Class Codes: B01D 53/02 by adsorption, e.g. preparative gas chromatography solid sorbent compositions B01J20/00, preparation of inorganic compounds or elements C01
• CPC Class Codes: B01D 53/04 with stationary adsorbents B01D53/025 takes precedence
• CPC Class Codes: B01D 53/047 Pressure swing adsorption
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• CPC Class Codes: Y10S 95/901 Activated carbon
• CPC Class Codes: Y10S 95/902 Molecular sieve

Abstract

A pressure swing adsorption process for the separation of nitrogen from a mixture of same with methane, utilizing two separate PSA stages, one containing a nitrogen selective adsorbent and the second containing a methane-selective adsorbent. In the process, the first PSA unit containing a nitrogen selective adsorbent forms a product methane stream and a waste stream rich in nitrogen which is passed to a second PSA unit containing a methane selective adsorbent which forms a product nitrogen stream and a waste stream rich in methane. The waste stream rich in methane can be treated to remove heavy hydrocarbons therefrom before the methane is recycled to feed.

Claims

1. A pressure swing adsorption (PSA) process for the separation of nitrogen from a mixture of the same with methane which comprises:

(a) passing a feed stream comprising said mixture to a first PSA unit containing a nitrogen selective adsorbent so as to preferentially adsorb nitrogen and produce a product stream containing at least 90 mol % methane and a purge stream;

(b) recovering said product stream;

(c) passing said purge stream to a second PSA unit containing a methane selective adsorbent so as to produce a product stream rich in nitrogen and a purge stream rich in methane;

(d) recovering said nitrogen-rich product stream; and

(e) treating said purge stream rich in methane so as to remove heavy hydrocarbons from said purge stream rich in methane.

2. The process of claim 1, wherein said purge stream rich in methane is treated by cooling so as to liquefy the heavy hydrocarbons and, subsequently separating said heavy hydrocarbons from methane.

3. The process of claim 1, wherein said purge stream rich in methane after treatment in step (e) is recycled to said feed stream.

4. The process of claim 1, wherein said heavy hydrocarbons removed from said purge stream rich in methane include C₃+ hydrocarbons.

5. The process of claim 1, wherein said heavy hydrocarbons comprise C₃+ hydrocarbons, said purge stream rich in methane containing at least about 1 mol % of said C₃+ hydrocarbons.

6. The process of claim 5, wherein said purge stream rich in methane after treatment in step (e) is recycled to said feed stream.

7. The process of claim 1, wherein the nitrogen selective adsorbent of step (a) is a CTS-1 zeolite characterized as having a pore size of approximately 3-4 Angstrom units and a composition in terms of mol ratios of oxide as follows:

8. The process of claim 7, wherein the methane selective adsorbent of step (c) is selected from the group consisting of a high aluminum X having a silicon-to-aluminum ratio of about 1, zeolite 13X, carbon or silica gel.

9. The process of claim 1, wherein the nitrogen selective adsorbent of step (a) is barium exchanged ETS-4 wherein barium represents at least 30% of the exchangeable cations.

10. The process of claim 1, wherein the methane selective adsorbent of step (c) is selected from the group consisting of a high aluminum X having a silicon-to-aluminum ratio of about 1, zeolite 13X, carbon or silica gel.

11. The process of claim 1, wherein a co-current depressurization step is introduced into said first PSA unit to generate a fuel stream.

12. The process of claim 1, wherein said first PSA unit operates under the conditions of rate selectivity.

13. The process of claim 12, wherein said second PSA unit operates under the conditions of equilibrium selectivity.

14. The process of claim 1, wherein subsequent to step (c) periodically heating said nitrogen selective adsorbent to drive off accumulated methane therefrom.

15. The process of claim 14, wherein the nitrogen selective adsorbent of step (a) is a CTS-1 zeolite characterized as having a pore size of approximately 3-4 Angstrom units and a composition in terms of mol ratios of oxide as follows:

16. The process of claim 14, wherein the nitrogen selective adsorbent of step (a) is barium exchanged ETS-4 wherein barium represents at least 30% of the exchangeable cations.

17. The process of claim 14, wherein the nitrogen-selective adsorbent is periodically heated with the nitrogen rich product stream of said second PSA unit.

18. The process of claim 14, wherein said nitrogen-selective adsorbent is periodically heated with said purge stream from said first PSA unit.

19. The process of claim 14, wherein said nitrogen selective adsorbent is periodically heated with said methane product stream.

20. The process of claim 19, wherein the nitrogen selective adsorbent of step (a) is a CTS-1 zeolite characterized as having a pore size of approximately 3-4 Angstrom units and a composition in terms of mol ratios of oxide as follows: