Production of urea and melamine

Patent metadata

Field	Value
Publication number	US-12338201-B2
Application number	US-202318553330-A
Country	US
Kind code	B2
Filing date	Jul 6, 2023
Priority date	Jul 7, 2022
Publication date	Jun 24, 2025
Grant date	Jun 24, 2025

Abstract

The disclosure pertains to a process for the production of urea and melamine, wherein off-has from a high pressure melamine plant is combined with a urea liquid obtained from flashing of a urea synthesis solution. Also disclosed is a system for the combined production, and the modification of an existing plant or system.

First claim

The invention claimed is:

1. A process for the production of urea and melamine, wherein the production of urea comprises subjecting ammonia and carbon dioxide to a urea-forming reaction in a high-pressure urea synthesis section so as to obtain a high pressure urea synthesis solution, subjecting the urea synthesis solution to flashing, resulting in a flash vapour comprising ammonia and carbon dioxide, and a flashed urea liquid; subjecting the flashed urea liquid to treatment so as to obtain a urea product solution and a carbamate recovery vapour, said treatment comprising one or more ammonia and carbon dioxide liberating steps, thereby removing ammonia and carbon dioxide vapour from the flashed urea liquid, wherein the production of melamine comprises subjecting urea to a non-catalytic, high pressure melamine forming reaction, so as to obtain melamine and a melamine off-gas vapour comprising ammonia and carbon dioxide; and wherein the combined process comprises contacting at least part of the melamine off-gas with the flashed urea liquid before or during at least one of said ammonia and carbon dioxide liberating steps.

2. The process according to claim 1 , wherein the flashing is conducted at medium pressure, and comprising subjecting the flashed urea liquid to treatment in a medium pressure treatment section, so as to obtain a medium pressure urea product solution, and a medium pressure carbamate recovery vapour.

3. The process according to claim 1 , wherein at least part of the high pressure urea synthesis solution is obtained from subjecting an effluent from the urea-forming reaction to high pressure stripping.

4. The process according to claim 3 , wherein the high pressure stripping is by applying carbon dioxide as a stripping medium.

5. The process according to claim 1 , wherein the flash vapour and the carbamate recovery vapour are subjected to condensation so as to form a carbamate solution, and subjecting said carbamate solution to recirculation to the high pressure synthesis section.

6. The process according to claim 5 , wherein a carbamate liquid obtained from melamine synthesis is combined with at least one carbamate solution.

7. The process according to claim 1 , comprising subjecting the urea product solution to recovery of still present ammonia and carbon dioxide at low pressure, obtaining a low pressure carbamate solution and a low pressure urea product stream.

8. The process according to claim 1 , wherein obtaining a medium pressure urea product stream comprises medium pressure stripping.

9. The process according to claim 8 , wherein the medium pressure stripping is by applying carbon dioxide as a stripping medium.

10. The process according to claim 1 , wherein at least part of the produced urea is the urea that is subjected to the melamine forming reaction.

11. The process according to claim 1 , comprising contacting the melamine off-gas vapour in a counter-current manner with the flashed urea liquid.

12. The process according to claim 1 , wherein the melamine off-gas vapour contacted with the flashed urea liquid has a temperature of 150° to 300° C.

13. The process according to claim 12 , wherein the melamine off-gas vapour contacted with the flashed urea liquid has a temperature of 200° C. to 250° C.

14. A system for the production of urea and melamine, said system comprising a urea production zone; said urea production zone comprising a high pressure urea synthesis section and, downstream thereof and in fluid communication therewith, a urea recovery section adapted to separately obtain a urea solution and a carbamate recovery stream; the system further comprising a melamine production zone; said melamine production zone comprising a high pressure melamine synthesis section, said production zones being connected with each other so as to allow transport of melamine off-gas obtained from the melamine synthesis section to the urea production zone, whereby the urea production zone comprises a medium or low pressure treatment section adapted to receive said melamine off-gas, said treatment section comprising a flashing unit and at least one ammonia and carbon dioxide liberating unit, said flashing unit having an inlet for urea synthesis solution connected to an outlet of the high pressure synthesis section via a pressure reducing device, an outlet for flash vapour and an outlet for flashed liquid, said ammonia and carbon dioxide liberating unit having an inlet for flashed liquid connected to the outlet for flashed liquid from the flashing unit, an outlet for carbamate recovery vapour and an outlet for a urea product stream, said outlets for flash vapour and carbamate recovery vapour each being connected via a condensation and recirculation circuit to the urea synthesis section, wherein an outlet for melamine off-gas vapour from the melamine synthesis section is in fluid communication with an inlet of at least one ammonia and carbon dioxide liberating unit, allowing the melamine off-gas vapour to be contacted with flashed liquid in or upstream of the ammonia and carbon dioxide liberating unit.

15. The system according to claim 14 , wherein the urea production zone comprises an outlet for urea connected to an inlet of the melamine synthesis section.

16. The system according to claim 14 , wherein the flashing unit and the heating unit are connected via a rectifying column.

17. The system according to claim 16 , wherein the rectifying column comprises a packed bed, and wherein an outlet for melamine off-gas vapour from the melamine synthesis section is in fluid communication with an inlet of the rectifying column positioned such to allow the off-gas vapour to flow across the packed bed.

18. The system according to claim 16 , wherein an outlet for melamine off-gas vapour from the melamine synthesis section is in fluid communication with an inlet of the heating unit.

19. The system according to claim 18 , wherein the outlet for melamine off-gas vapour from the melamine synthesis section is in fluid communication with an inlet of the heating unit and is positioned at a lower end thereof.

20. The system according to claim 16 , wherein the flashing unit and the heating unit are connected via a rectifying column and are contained in a single apparatus.

21. The system according to claim 14 , wherein said treatment section comprising a flashing unit and at least one ammonia and carbon dioxide liberating unit is a heating unit.

22. A method for the modification of a pre-existing urea plant comprising a high pressure urea synthesis section and, downstream thereof and in fluid communication therewith, a urea recovery section adapted to separately obtain a urea solution and a carbamate recovery stream, the method comprising connecting the urea plant with a melamine plant comprising a high pressure melamine synthesis section so as to allow recirculation of melamine off-gas from the melamine off-gas treatment section to the urea plant, the method comprising adding a medium or low pressure treatment section adapted to receive said melamine off-gas, said treatment section comprising a flashing unit and at least one ammonia and carbon dioxide liberating unit, said flashing unit having an inlet for urea synthesis solution connected to an outlet of the high pressure synthesis section via a pressure reducing device, an outlet for flash vapour and an outlet for flashed liquid, said ammonia and carbon dioxide liberating unit having an inlet for flashed liquid connected to the outlet for flashed liquid from the flashin

Assignees

• Stamicarbon

Inventors

• Abdelmagid Ahmed
• Geurts Wilhelmus Hubertus

Classifications

• C07D251/62

  Purification of melamine · CPC title

• C07D251/60

  from urea or from carbon dioxide and ammonia · CPC title

• C07C273/16

  Separation; Purification · CPC title

• C07C273/04

  from carbon dioxide and ammonia · CPC title

• C07C273/12 Primary

  combined with the synthesis of melamine · CPC title