Process for converting cyclic urea to corresponding diamine in a gas treating system

• US 4,282,194 A
• Filed: 02/19/1980
• Issued: 08/04/1981
• Est. Priority Date: 02/19/1980
• Status: Expired due to Term

• Current Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation)
• Original Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation)
• Inventors: Say, Geoffrey R., Iyengar, Jagannathan N., Hays, James R. Sr., Hacker, Barbara A.
• Primary Examiner(s): Thomas, Earl C.
• Application Number:
  US06/122,589
• Time in Patent Office: 532 Days
• Field of Search: 423/223, 423/228, 423/229, 423/232, 423/233, 423/234, 423/243, 423/236, 260/239.3 R, 544/314, 548/317
• US Class Current: 423/223
• CPC Class Codes: B01D 53/1425 Regeneration of liquid absorbents
• CPC Class Codes: B01D 53/1456 Removing acid components
• CPC Class Codes: B01D 53/1493 Selection of liquid materials for use as absorbents
• CPC Class Codes: B01D 53/526 Mixtures of hydrogen sulfide and carbon dioxide
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

Acidic gases such as carbon dioxide are removed from a normally gaseous mixture including the acidic component by contacting the gaseous mixture in an absorption zone with an acid absorbing scrubbing solution comprising a basic alkali metal compound and an activator for the compound, during which process at least a portion of the activator is converted to a cyclic urea. The solution is then transferred to the desorption zone to remove at least a portion of the absorbed acidic component. At least a portion of the partially desorbed scrubbing solution containing the cyclic urea is transferred from the desorption zone to a thermal conversion zone maintained at an elevated temperature wherein at least a portion of the cyclic urea is converted back to the activator. A portion of the scrubbing solution from the thermal conversion zone, relatively rich in the acidic component is vaporized and returned to the desorption zone, and another portion, relatively lean in the acidic component, is returned from the thermal conversion zone to the absorption zone.

Claims

1. A method for removing carbon dioxide from a gaseous mixture including carbon dioxide which comprises:

(a) contacting the gaseous mixture in an absorption zone with an acid-absorbing scrubbing solution comprising;

(i) a basic alkali metal compound selected from the class consisting of alkali metal bicarbonates, carbonates, hydroxides, borates, phosphates and their mixtures; and

(ii) an activator for said basic alkali metal compound having the formula ##STR7## where R is a secondary or tertiary alkyl group and n is the integer 2, 3 or 4, whereby at least some of the acidic component is absorbed by the scrubbing solution and whereby at least some of said activator is converted to a cyclic urea having the formula ##STR8## (b) passing at least a portion of the scrubbing solution containing the absorbed carbon dioxide and the cyclic urea from the absorption zone to a desorption zone wherein the carbon dioxide loading of the scrubbing solution is reduced to below about 20%; and

(c) passing at least a portion of the scrubbing solution from the desorption zone to a thermal conversion zone maintained at a temperature within the range of 120°

C. to 200°

C. to convert at least a portion of the cyclic urea back to the activator, the thermal conversion zone communicating with both the absorption zone and the desorption zone whereby a portion of the scrubbing solution in the thermal conversion zone relatively rich in carbon dioxide is vaporized and returned to the desorption zone, and another portion of the scrubbing solution in the thermal conversion zone relatively lean in carbon dioxide is returned to the absorption zone.

2. The method of claim 1 wherein the temperature in the thermal conversion zone is maintained within the range of about 140°

to about 190°

C.

3. The method of claim 2 wherein the portion of the scrubbing solution returned from the thermal conversion zone to the absorption zone is cooled prior to entering the absorption zone.

4. The method of claim 3 wherein a portion of the scrubbing solution passing from the desorption zone is returned to the absorption zone.

5. The method of claim 4 wherein the portion of the scrubbing solution returned from the desorption zone to the absorption zone is returned at a location below that at which the portion of the scrubbing solution from the thermal conversion zone is returned to the absorption zone.

6. The process of claim 5 wherein the scrubbing solution further comprises a cosolvent.

7. The process of claim 6 wherein the cosolvent has 4 to 8 carbon atoms.

8. The process of claim 7 wherein the activator is N-cyclohexyl-1,3-propanediamine.

9. The process of claim 7 wherein the activator is N-cyclohexyl-1,2-ethanediamine.

10. The process of claim 7 wherein the activator is N-cyclohexyl-1,4-butanediamine.

11. A method for removing an acidic component from a gaseous mixture including the acidic component which comprises:

(a) contacting the gaseous mixture in an absorption zone with a scrubbing solution comprising;

(i) a basic alkali metal compound selected from the class consisting of alkali metal bicarbonates, carbonates, hydroxides, borates, phosphates and their mixtures; and

(ii) an activator for said basic alkali metal compound having the formula;

##STR9## where R is a secondary or tertiary alkyl group and n is the integer 2, 3 or 4; and

(iii) a cosolvent having 4 to 8 carbon atoms, whereby at least some of the acidic component is absorbed by the scrubbing solution and whereby at least some of said activator is converted to a cyclic urea;

(b) passing the scrubbing solution containing the absorbed acidic component and the cyclic urea from the absorption zone to a desorption zone wherein at least a portion of the absorbed acidic component is desorbed;

(c) returning a portion of the partially desorbed scrubbing solution from the desorption zone to the absorption zone; and

(d) passing a portion of the partially desorbed scrubbing solution from the desorption zone to a thermal conversion zone maintained at a temperature within the range of about 140 to about 190°

C. to convert at least a portion of the cyclic urea back to the activator, the thermal conversion zone communicating with both the absorption zone and the desorption zone, whereby a portion of the scrubbing solution in the thermal conversion zone relatively rich in the acidic component is vaporized in the thermal conversion zone and returned to the desorption zone, and a portion of the scrubbing solution in the thermal conversion zone relatively lean in the acidic component is returned after cooling, to the absorption zone at a location above that at which the scrubbing solution from the desorption zone is returned to the absorption zone.