Reclamation of alkanolamine solutions

• US 5,108,551 A
• Filed: 12/17/1990
• Issued: 04/28/1992
• Est. Priority Date: 12/17/1990
• Status: Expired due to Fees

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Yan, Tsoung Y.
• Primary Examiner(s): Lewis, Michael
• Assistant Examiner(s): DI MAURO, PETER T
• Application Number:
  US07/628,975
• Time in Patent Office: 498 Days
• Field of Search: 208/236, 564/487, 564/497, 564/488, 564/489, 201/2.5, 203/28, 203/29, 203/6, 203/96, 210/766, 423/228, 423/229
• US Class Current: 203/6
• CPC Class Codes: C07C 213/10 Separation; Purification; Stabilisation; Use of additives

Abstract

The present invention provides a method for purifying alkanolamine solutions which have lost at least a portion of their acid gas sorption capacity due to degradation of the alkanolamine into heat stable salts. Particularly, it has been found that the alkanolamine solution may be rejuvenated by charging the solution to the feed zone of a distillation column reactor at temperatures above about 160° C. and pressure of less than about 2000 mm Hg.

Claims

1. A method for rejuvenating a spent alkanolamine solution which has lost at least a portion of its theoretical acid gas sorption capacity comprising the steps of:

(a) flowing said spent alkanolamine solution to a distillation column reactor into a feed zone, wherein said feed zone is maintained at temperature above about 160°

C. and wherein said distillation column reactor is maintained at pressure below about 2000 mm Hg;

(b) charging acid gas selected from the group consisting of H₂ S and CO₂ to said distillation column reactor;

(c) controlling residence time of said spent alkanolamine solution in said distillation column reactor to at least partially convert said spent alkanolamine solution to a distillable product mixture having a greater affinity for acid gas sorption than said spent alkanolamine solution;

(d) fractionating said distillable product mixture within said distillation column reactor;

(e) withdrawing a rejuvenated alkanolamine solution from said distillation column reactor at a point above said feed zone; and

(f) withdrawing a stream containing rejected residue including heat stable salts from said distillation column reactor at a point below said feed zone.

2. The method of claim 1 further comprising introducing steam to said distillation column reactor at a point below said feed zone.

3. The method of claim 2 wherein said steam is introduced to said alkanolamine solution and charged to said distillation column reactor in volume ratios of steam:

spent alkanolamine charge of from about 0.01 to about 10.

4. The method of claim 1 further comprising controlling pressure within said distillation column reactor at less than about 760 mm Hg.

5. The method of claim 4 wherein pressure within said distillation column reactor is less than about 150 mm Hg.

6. The method of claim 1 wherein the mass flowrate of DEA withdrawn in said rejuvenated alkanolamine solution exceeds the mass flowrate of DEA charged to said distillation column reactor.

9. The method of claim 6 wherein said steam is introduced to said alkanolamine solution and charged to said distillation column reactor in volume ratios of steam:

spent alkanolamine charge of from about 0.01 to about 10.

7. A method for restoring acid gas sorption capacity to a spent alkanolamine solution comprising the steps of:

(a) flowing said spent alkanolamine solution to a distillation column reactor into a feed zone;

(b) charging acid gas selected from the group consisting of H₂ S and CO₂ to said distillation column reactor;

(c) heating said spent alkanolamine solution within said feed zone to a temperature above about 160°

C. for a period of time at least sufficient to convert alkanolamine degradation products contained in said spent alkanolamine solution to their corresponding precursor alkanolamines;

(d) withdrawing alkanolamine from said feed zone and flowing said alkanolamine upwardly through said distillation column reactor to cool said withdrawn alkanolamine solution to a temperature below said feed zone temperature;

(e) withdrawing a rejuvenated alkanolamine solution from said distillation column reactor at a point above said feed zone; and

(f) withdrawing a stream containing rejected residue including heat stable salts from said distillation column reactor at a point below said feed zone.

8. The method of claim 7 further comprising introducing steam to said distillation column reactor at a point below said feed zone.

10. The method of claim 7 further comprising controlling pressure within said distillation column reactor at less than about 150 mm Hg.

11. The method of claim 10 wherein pressure within said distillation column reactor is less than about 30 mm Hg.

12. The method of claim 7 wherein the mass flowrate of DEA withdrawn in said rejuvenated alkanolamine solution exceeds the mass flowrate of DEA charged to said distillation column reactor.

13. A method for restoring acid gas sorption capacity to a spent alkanolamine solution comprising the steps of:

(a) flowing said spent alkanolamine solution to a distillation column reactor into a feed zone;

(b) charging acid gas selected from the group consisting of H₂ S and CO₂ to said distillation column reactor;

(c) heating said spent alkanolamine solution within said feed zone to a temperature above about 160°

C. at pressure of less than 2000 mm Hg for a period of time at least sufficient to convert alkanolamine degradation products contained in said spent alkanolamine solution to their corresponding precursor alkanolamines;

(d) introducing stripping steam to said distillation column reactor at a point below said feed zone and flowing said stripping steam upwardly through said distillation column reactor;

(e) withdrawing alkanolamine from said feed zone, flowing said alkanolamine upwardly through said distillation column reactor, and cooling said withdrawn alkanolamine solution to a temperature below said feed zone temperature wherein the rates of alkanolamine withdrawal and the temperature gradient across the length of said distillation column reactor avoid substantial thermal degradation of said alkanolamine;

(f) withdrawing a rejuvenated alkanolamine solution from said distillation column reactor at a point above said feed zone, said withdrawn rejuvenated alkanolamine solution characterized by an AACI exceeding that of said spent alkanolamine solution; and

(g) withdrawing a stream containing heat stable salts from said distillation column reactor at a point below said feed zone.

14. The method of claim 13 wherein said steam is introduced to said alkanolamine solution and charged to said distillation column reactor in volume ratios of steam:

spent alkanolamine charge of from about 0.01 to about 10.

15. The method of claim 13 further comprising controlling pressure within said distillation column reactor at less than about 760 mm Hg.

16. The method of claim 15 wherein pressure within said distillation column reactor is less than about 150 mm Hg.

17. The method of claim 13 wherein the mass flowrate of DEA withdrawn in said rejuvenated alkanolamine solution exceeds the mass flowrate of DEA charged to said distillation column reactor.