Process for the separation of NH.sub.3 and CO.sub.2 from mixtures of NH.sub . .sub.2 and water

• US 4,251,235 A
• Filed: 04/16/1979
• Issued: 02/17/1981
• Est. Priority Date: 04/29/1978
• Status: Expired due to Term

• Current Assignee: Stamicarbon B.V. (MAIRE)
• Original Assignee: Stamicarbon B.V. (MAIRE)
• Inventors: Biermans, Andreas J.
• Primary Examiner(s): Spitzer, Robert H.
• Application Number:
  US06/030,375
• Time in Patent Office: 673 Days
• Field of Search: 55/48, 55/68, 55/70, 55/89, 423/238
• US Class Current: 95/177
• CPC Class Codes: C01C 1/12 Separation of ammonia from gases and vapours as part of the ammonia synthesis process C01C1/04
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

An improved process for the separate recovery of substantially pure ammonia and substantially pure carbon dioxide from mixtures containing ammonia and carbon dioxide, and possibly water, such as are obtained as by-products in the manufacture of melamine from urea or the synthesis of urea from ammonia and carbon dioxide. The by-product mixture is introduced into a process loop having an ammonia separation zone, a carbon dioxide separation zone and a desorption zone, the zone to which the mixture is initially fed being dependent upon its composition. The separation is effected by maintaining a system pressure differential between the ammonia and carbon dioxide separation zones, or adding diluting water to the carbon dioxide separation zone. The efficiency of the separation is enhanced by introducing an ammonia containing gaseous phase into the bottom of the carbon dioxide separation zone.

Claims

1. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, said process comprising the steps of:

separating an ammonia off-gas substantially free of carbon dioxide and water by rectification in an ammonia separation zone, and removing the resulting residual liquid phase containing ammonia, carbon dioxide and water therefrom and introducing it into a carbon dioxide separation zone;

separating a carbon dioxide off-gas substantially free of ammonia and water by rectification in a carbon dioxide separation zone and removing the resulting residual liquid phase containing ammonia, carbon dioxide and water therefrom and introducing it into a desorption zone; and

separating an off-gas containing ammonia, carbon dioxide and water vapor from a liquid phase of desorption water substantially free of ammonia and carbon dioxide, and introducing at least a portion of said off-gas into said ammonia separation zone;

the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

12. The process of claim 1, 2, 3, 4, 7, 8 or 9 wherein said ammonia containing gaseous phase introduced into said carbon dioxide separation zone is comprised of a portion of said desorption zone off-gas.

13. The process of claim 12 wherein from about 1 to 50% by weight of said off-gas removed from said desorption zone is utilized as said ammonia containing gaseous phase.

14. The process of claim 12 wherein from about 5 to 40% by weight of said off-gas removed from said desorption zone is utilized as said ammonia containing gaseous phase.

2. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is rich with respect to ammonia, said process comprising the steps of:

introducing said mixture into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said ammonia separation zone into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said carbon dioxide separation zone into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide; and

introducing at least a portion of said desorption zone off-gas into said ammonia separation zone;

wherein diluting water is introduced into said carbon dioxide separation zone in an amount of between about 0.2 and 6 times, by weight, the total weight of said residual liquid phase from said ammonia separation zone introduced into said carbon dioxide separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

5. The process of claims 2, 3 or 4 wherein the system pressure in said carbon dioxide separation zone is no greater than twice the system pressure in said ammonia separation zone.

6. The process of claim 5 wherein the system pressure in said carbon dioxide separation zone is substantially the same as the system pressure in said ammonia separation zone.

3. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is lean with respect to ammonia, said process comprising the steps of:

introducing said mixture into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said carbon dioxide separation zone into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide;

introducing at least a portion of said desorption zone off-gas into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water; and

introducing said residual liquid phase from said ammonia separation zone into said carbon dioxide separation zone;

wherein diluting water is introduced into said carbon dioxide separation zone in an amount of between about 0.2 and 6 times, by weight, the combined total weight of said mixture and said residual liquid phase from said mixture and said residual liquid phase from said ammonia separation zone introduced into said carbon dioxide separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

4. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is rich with respect to ammonia and additionally contains a substantial amount of water, said process comprising the steps of:

introducing said mixture into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide;

introducing at least a portion of said desorption zone off-gas into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said ammonia separation zone into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water and a residual liquid phase containing ammonia, carbon dioxide and water; and

introducing said residual liquid phase from said carbon dioxide separation zone into said desorption zone;

wherein diluting water is introduced into said carbon dioxide separation zone in an amount of between about 0.2 and 6 times, by weight, the total weight of said residual liquid phase from said ammonia separation zone introduced into said carbon dioxide separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

7. In an process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is rich with respect to ammonia, said process comprising the steps of:

introducing said mixture into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said ammonia separation zone into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said carbon dioxide separation zone into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide; and

introducing at least a portion of said desorption zone off-gas into said ammonia separation zone;

wherein the system pressure in said carbon dioxide separation zone is greater than twice the system pressure in said ammonia separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

10. The process of claim 7, 8 or 9 wherein the ratio between the respective system pressures in said ammonia separation zone and in said carbon dioxide separation zone is between about 1:

5 and 1;

20.

11. The process of claim 7, 8 or 9 wherein diluting water is introduced into said carbon dioxide separation zone.

8. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is lean with respect to ammonia, said process comprising the steps of:

introducing said mixture into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said carbon dioxide separation zone into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide;

introducing at least a portion of said desorption zone off-gas into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water; and

introducing said residual liquid phase from said ammonia separation zone into said carbon dioxide separation zone;

wherein the system pressure in said carbon dioxide separation one is greater than twice the system pressure in said ammonia separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.

9. In a process for the separate recovery of ammonia substantially free of carbon dioxide and water, and carbon dioxide substantially free of ammonia and water, from a mixture essentially containing ammonia and carbon dioxide, which mixture is rich with respect to ammonia and additionally contains a substantial amount of water, said process comprising the steps of:

introducing said mixture into a desorption zone and separately removing therefrom a desorption zone off-gas containing ammonia, carbon dioxide and water vapor, and a liquid phase of desorption water substantially free of ammonia and carbon dioxide;

introducing at least a portion of said desorption zone off-gas into an ammonia separation zone and separately removing therefrom an ammonia off-gas substantially free of carbon dioxide and water, and a residual liquid phase containing ammonia, carbon dioxide and water;

introducing said residual liquid phase from said ammonia separation zone into a carbon dioxide separation zone and separately removing therefrom a carbon dioxide off-gas substantially free of ammonia and water and a residual liquid phase containing ammonia, carbon dioxide and water; and

introducing said residual liquid phase from said carbon dioxide separation zone into said desorption zone;

wherein the system pressure in said carbon dioxide separation zone is greater than twice the system pressure in said ammonia separation zone, the improvement comprising introducing into the portion of said carbon dioxide separation zone from which said residual liquid phase is removed, an ammonia containing gaseous phase in an amount sufficient to make said residual liquid phase removed therefrom lean with respect to carbon dioxide.