Carbamimidic acid--nitric acid (1/1) → Urea

The washed urea nitrate filter cake is reacted with ammonia and water to form a solution of urea and ammonium nitrate. Urea is added as needed to adjust the composition of the solution. The reaction is carried out with efficient agitation and cooling to preclude the possibility of localized over-heating which could possibly cause decomposition of some of the nitrate. FIG. 3 is a flowsheet of a preferred embodiment of my process which generally illustrates the principles of my new and novel process for purification of wet-process phosphoric acid with co-production of nitrogen solution. Wet-process phosphoric acid and urea are introduced via lines 1 and 2 to any known process 3 for the formation of urea phosphate slurry (none of the processes are described since they are known to those skilled in the art). Urea phosphate slurry is introduced via line 4 to filtration and washing equipment 5. The filtrate which contains most of the impurities originally present in the wet-process phosphoric acid is withdrawn via line 6. From 0.15 to 0.7 pounds of purified acid product per pound of filter cake are introduced via line 7 to displace mother liquor from the filter cake. Most of the wash acid is retained by the filter cake; the rest is withdrawn with the filtrate. The washed urea phosphate filter cake is withdrawn from the filtration and washing apparatus via line 8 and delivered to reactor 9. One mole of nitric acid per mole of urea phosphate and about 0.9 pounds of recycle purified acid product per pound of urea phosphate are delivered to reactor 9 via lines 10 and 11. The nitric acid was first used to wash the urea nitrate filter cake and it contains phosphoric acid and dissolved urea nitrate. The nitric acid and the urea phosphate react to form a slurry of urea nitrate in purified phosphoric acid. The recycle phosphoric acid is used to fluidize the urea nitrate slurry. The reaction mixture is stirred and its temperature is maintained below 35°C by a cooling device, not shown. After a residence time in reactor 9 from 15 to 60 minutes, the reaction mixture consists of a slurry of urea nitrate in phosphoric acid and it is withdrawn via line 12 and delivered to filtration and washing apparatus 13. The filtrate is purified acid and is withdrawn via line 14; part is delivered to apparatus 5 via line 7 and another part is delivered to reactor 9 via line 11. The rest is withdrawn via line 15 as product. Sixty-five percent nitric acid is introduced to the process via line 16 and is first delivered to washing apparatus 13 to wash the urea nitrate filter cake. The amount of nitric acid introduced is that required for reaction with the urea phosphate in reactor 9 (a mole of nitric acid per mole of urea phosphate), plus that retained by the urea nitrate filter cake. The nitric acid wash is withdrawn from the washing apparatus 13 via line 10 and delivered to reactor 9. The washed urea nitrate filter cake is withdrawn from washing apparatus 13 via line 17 and delivered to reactor 18 where it is reacted with ammonia and water introduced via lines 19 and 20 to form a solution of urea and ammonium nitrate. Urea is added via line 21 to reactor 18 as needed for adjustment of the composition of the solution to that of standard grades. Product nitrogen solution is withdrawn from reactor 18 via line 22. The purified acid product typically contains 51 percent P2O5 and 5 percent dissolved urea nitrate and less than 5 percent of the impurities originally present in the wet-process phosphoric acid. When the wet-process phosphoric acid is black with carbonaceous matter, the purified phosphoric acid is clear amber in color.

1. temperatureits temperature is maintained below 35°C by a cooling device
2. customis withdrawn via line 12
3. filtrationdelivered to filtration
4. washwashing apparatus 13
5. customThe filtrate is purified acid
6. customis withdrawn via line 14
7. customanother part is delivered to reactor
8. customThe rest is withdrawn via line 15 as product
9. additionSixty-five percent nitric acid is introduced to the process via line 16
10. washto washing apparatus 13
11. washto wash the urea nitrate
12. filtrationfilter cake
13. additionThe amount of nitric acid introduced
14. customthat required for reaction with the urea phosphate in reactor 9 (a mole of nitric acid per mole of urea phosphate), plus
15. filtrationfilter cake
16. washThe nitric acid wash
17. customis withdrawn from the washing apparatus 13 via line 10
18. customdelivered to reactor
19. filtrationThe washed urea nitrate filter cake
20. customis withdrawn
21. washfrom washing apparatus 13 via line 17
22. customdelivered to reactor
23. custom18 where it is reacted with ammonia and water
24. additionintroduced via lines 19 and 20

ORD record

ord-76d8cfc16f3d4804ac4bc1f12759f7f7

Source dataset

uspto-grants-1976_07

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US03967948