PROCESS FOR PURIFYING ABSORBENTS COMPRISING POLYETHYLENE GLYCOL DIMETHYL ETHERS

• US 20140027285A1
• Filed: 04/10/2012
• Published: 01/30/2014
• Est. Priority Date: 04/11/2011
• Status: Abandoned Application

• Current Assignee: Electrosep Technologies Inc.
• Original Assignee: Electrosep Technologies Inc.
• Inventors: Parisi, Paul
• Application Number:
  US14/111,297
• Publication Number:
  US 20140027285A1
• Time in Patent Office: Days
• US Class Current: 204/541
• CPC Class Codes: B01D 2252/2026 Polyethylene glycol, ethers or esters thereof, e.g. Selexol
• CPC Class Codes: B01D 2257/302 Sulfur oxides
• CPC Class Codes: B01D 2257/304 Hydrogen sulfide
• CPC Class Codes: B01D 2257/306 Organic sulfur compounds, e.g. mercaptans
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 53/1425 Regeneration of liquid absorbents
• CPC Class Codes: B01D 53/1456 Removing acid components
• CPC Class Codes: B01D 61/422 Electrodialysis
• CPC Class Codes: B01J 20/3441 Regeneration or reactivation by electric current, ultrasound or irradiation, e.g. electromagnetic radiation such as X-rays, UV, light, microwaves
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

A process for purifying polyethylene glycol dimethyl ethers (PGDE) based absorbent (known as Selexol®) having acidic contaminants and salts thereof, this process being particularly useful in an acid gas removal loop process (known as Selexol® process). A base, such as ammonium hydroxide (NH₃OH), is added to the absorbent to partly of fully convert the acid into simple salts. The salts are removed in an electrodialysis cell. The base can be added directly to the absorbent either from a fresh chemical feed or as base contained in the re-generator'"'"'s generator'"'"'s reflux stream. Alternatively the base can be added directly into the electrodialysis unit. The solution is diluted before electrodialysis. The absorbent can be simultaneously diluted and neutralized using reflux from the regeneration section that contains dissolved ammonia. The purified solution can be used again to remove carbon dioxide, hydrogen suphide, sulfur dioxide, mercaptans and other acid gases from a gas stream.

Claims

1. A process for removing contaminants containing acids and salts thereof from an absorbent comprising polyethylene glycol dimethyl ethers, hereinafter named PGDE, the process comprising the steps of:

contacting the absorbent with a base for partly or fully converting the contaminants into their corresponding salts containing anions and cations;

adding a fluid to the absorbent for diluting the PGDE;

introducing the absorbent into an electrodialysis cell;

electrodialyzing the absorbent for removing the salts from the absorbent; and

recovering the absorbent depleted of acidic contaminants;

the absorbent being contacted with the base before being introduced into the electrodialysis cell, or directly inside the electrodialysis cell.

2. The process of claim 1, wherein the absorbent is contacted with the base before being introduced into the electrodialysis cell, the electrodialysis cell comprising:

a cathode and an anode operatively connected to an electric power supply, and at least one repeat unit located between the anode and the cathode, each repeat unit comprising two ion exchange membranes delimiting a feed compartment between the two ion exchange membranes and a waste compartment adjacent to the feed compartment;

the process further comprising the steps of;

introducing the absorbent comprising the base into the feed compartment of the electrodialysis cell;

applying a current potential transversely across the compartments of the electrodialysis cell, said current potential being effective to cause at least a part of the anions and cations present in the feed compartment to exit the feed compartment through the membranes; and

discharging the absorbent from the feed compartment, the absorbent being depleted of anions and cations.

3. The process of claim 1, wherein the absorbent is contacted with the base inside the electrodialysis cell, the electrodialysis cell comprising:

a cathode and an anode operatively connected to an electric power supply, and at least one repeat unit located between the cathode and the anode, each unit comprising three ion exchange membranes delimiting a feed compartment;

a base-source compartment between the feed compartment and the cathode compartment, and a waste compartment between the feed compartment and the anode compartment;

the process further comprising the steps of;

introducing the absorbent into the feed compartment;

introducing the base into the base-source compartment;

passing a current potential transversely across the compartments, said current being effective to dissociate the base in the base compartment into corresponding anions and cations, the anions of the base then passing into the feed compartment for contacting the absorbent and the cations of the base then passing into the waste compartment; and

discharging the absorbent from the feed compartment, the absorbent being depleted of anions and cations.

4. The process of claim 2, further comprising the steps of:

discharging a feed stream from the feed compartment and recycling at least a portion of the feed stream to the feed compartment; and

/or

discharging a waste stream from the waste compartment and recycling a least a portion of the waste stream to the waste compartment.

5. The process of claim 2 to wherein the electrodialysis cell comprises from about 10 to about 400 repeat units ion exchange membranes.

6. The process of claim 1, wherein the base comprises sodium hydroxide, potassium hydroxide, ammonium hydroxide, carbonate or bicarbonate thereof, or mixture thereof.

7. The process of claim 1, wherein the base is ammonium hydroxide.

8. The process of claim 1, in which the absorbent is diluted by addition of water and/or a reflux to the absorbent before being fed to the electrolysis zone.

9. The process of claim 8, wherein the reflux is a basic reflux allowing partial neutralization of the acidic contaminants of the absorbent.

10. A loop process for recovering acid gas from an acid gas stream, the loop process comprising the steps of:

i) passing an acid gas stream to an absorption zone wherein the acid gas stream is contacted with an absorbent of acid gases comprising polyethylene glycol dimethyl ethers PGDE;

ii) withdrawing from the absorption zone a product gas stream depleted of acid gases relatively to the gas stream;

iii) withdrawing from the absorption zone a rich solvent stream comprising the absorbent and absorbed contaminants having acids and salt thereof;

iv) passing the rich solvent stream to a regeneration zone wherein absorbed acid gases are desorbed from the rich solvent stream to provide a first tail gas stream comprising acid gases, and a lean solvent stream is formed, said lean solvent stream comprising PGDE absorbent and remaining contaminants having acids and salt thereof;

v) passing the lean solvent stream withdrawn from the regeneration zone to the absorption zone of step (i) for further treatment in the loop process;

vi) partially withdrawing via a bleed stream an amount of the lean solvent stream before the absorption zone;

vii) injecting a fluid to the bleed stream for diluting the PGDE;

viii) contacting the absorbent of the bleed stream with a base for partly or fully converting the contaminants into their corresponding salts containing anions and cations;

ix) introducing the absorbent into an electrodialysis cell;

x) electrodialyzing the absorbent for removing the salts from the absorbent; and

xi) recovering the absorbent depleted of acidic contaminants or slats thereof;

the absorbent being contacted with the base before being introduced into the electrodialysis cell, or directly inside the electrodialysis cell.

11. The loop process of claim 10, wherein the absorbent is contacted with the base before being introduced into the electrodialysis cell, the electrodialysis cell comprising:

a cathode and an anode operatively connected to an electric power supply, and at least one repeat unit located between the anode and the cathode, each repeat unit comprising two ion exchange membranes delimiting a feed compartment between the two ion exchange membranes and a waste compartment adjacent to the feed compartment;

the loop process further comprising the steps of;

introducing the absorbent previously contacted with the base into the feed compartment of the electrodialysis cell;

applying a current potential transversely across the compartments of the electrodialysis cell, said current potential being effective to cause at least a part of the anions and cations present in the feed compartment to exit the feed compartment through the membranes; and

discharging the absorbent from the feed compartment, the absorbent being depleted of anions and cations.

12. The loop process of claim 10, wherein the absorbent is contacted with the base inside the electrodialysis cell, the electrodialysis cell comprising:

a cathode and an anode operatively connected to an electric power supply, and at least one repeat unit located between the cathode and the anode, each unit comprising three ion exchange membranes delimiting a feed compartment;

a base-source compartment between the feed compartment and the cathode compartment, and a waste compartment between the feed compartment and the anode compartment;

the loop process further comprising the steps of;

introducing the absorbent into the feed compartment;

introducing the base into the base-source compartment;

passing a current potential transversely across the compartments, said current being effective to dissociate the base in the base compartment into corresponding anions and cations, the anions of the base then passing into the feed compartment for contacting the absorbent and the cations of the base then passing into the waste compartment; and

discharging the absorbent from the feed compartment, the absorbent being depleted of anions and cations.

13. The loop process of claim 11, further comprising the steps of:

discharging a feed stream from the feed compartment and recycling at least a portion of the feed stream to the feed compartment, and/or

discharging a waste stream from the waste compartment and recycling a least a portion of the waste stream to the waste compartment.

14. The loop process of claim 11, wherein the electrodialysis cell comprises from about 10 to about 400 repeat units ion exchange membranes.

15. The loop process of claim 10, wherein the base comprises sodium hydroxide, potassium hydroxide, ammonium hydroxide, carbonate or bicarbonate thereof, or mixture thereof.

16. The loop process of claim 10, wherein the base is ammonium hydroxide.

17. The loop process of claim 10, in which the absorbent is diluted by addition of water and/or a reflux to the absorbent.

18. The loop process of claim 17, wherein the base is ammonium hydroxide and the reflux is obtained from the ammonium hydroxide presents in the loop that evaporates from the regeneration zone with the tail gas stream, the tail gas stream being partly condensed to form a stream containing ammonium hydroxide which is reinjected in the regeneration zone, a portion of the stream containing ammonium hydroxide being withdrawn before the regeneration zone to be injected to the lean stream containing the absorbent as the reflux.