Pressure swing adsorption process
First Claim
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.
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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.
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Citations
20 Claims
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1. A pressure swing adsorption (PSA) process for the separation of nitrogen from a mixture of the same with methane which comprises:
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(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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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.
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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.
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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.
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11. The process of claim 1, wherein a co-current depressurization step is introduced into said first PSA unit to generate a fuel stream.
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12. The process of claim 1, wherein said first PSA unit operates under the conditions of rate selectivity.
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13. The process of claim 12, wherein said second PSA unit operates under the conditions of equilibrium selectivity.
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14. The process of claim 1, wherein subsequent to step (c) periodically heating said nitrogen selective adsorbent to drive off accumulated methane therefrom.
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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:
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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.
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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.
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18. The process of claim 14, wherein said nitrogen-selective adsorbent is periodically heated with said purge stream from said first PSA unit.
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19. The process of claim 14, wherein said nitrogen selective adsorbent is periodically heated with said methane product stream.
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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:
Specification