Crystallization of ammonium phosphate
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This post was last edited by lij1887 on 2010-2-17 at 20:16. There is currently a device for treating ammonia exhaust gases, using phosphoric acid to absorb those gases; it is desired to recover the resulting ammonium phosphate in a simple manner. Apart from evaporation crystallization, can ammonium phosphate also be crystallized through cryogenic methods? What are the operation control points for the two?
What type of chemical manufacturing company is yours? What production facilities do you have, and what are your main manufacturing processes? I am an operator at the small ligand production facility, and I’m not very familiar with the specific manufacturing process in your company. So it’s hard to give an opinion.
It is best to use the cyclic absorption method to maintain the pH of the absorption solution above 4.2; this ensures that the solution is a system dominated by MAP. In such a system, crystallization can take place either by cooling the solution depending on the concentration of MAP in it, or by concentrating the solution first and then cooling it to induce crystallization! Note: It is very difficult to crystallize MAP from its phosphate solution!
It is recommended to check out books on phosphoric acid in Building 1#. High-purity phosphoric acid must be used.
Could you specify the conditions more clearly: lol
Reply to the original poster: Sorry, I haven’t checked that post recently. Since you use phosphoric acid to absorb ammonia-containing exhaust gases, in order to increase the ammonia absorption rate, an excess of phosphoric acid is necessary. If absorption occurs only once, the presence of an excessive amount of phosphoric acid in the absorption solution makes it impossible to crystallize ammonium phosphate; only through cyclic absorption, by raising the pH of the absorption solution to above 4.2, can ammonium phosphate be crystallized!
I use two-stage phosphoric acid absorption; will crystallization occur automatically once the liquid from the first stage becomes saturated? Can it be extracted at room temperature? Also, what is a suitable concentration for phosphoric acid?
Do not absorb ammonia to a crystalline concentration in one step, as this will not result in high ammonia recovery efficiency. Considering our production process for monoammonium phosphate (thermal method), 60%–70% H3PO4 can be used for phosphoric acid; after it is neutralized to a pH of around 4.2, it is placed in a crystallizer to cool and crystallize.
To what temperature must it be cooled for crystals to precipitate?
Back to Floor 7: I was on a business trip out of town a few days ago and had no internet access; I just saw the post you sent me. In fact, the crystallization of monoammonium phosphate depends on its concentration in the solution. Under normal circumstances, a cooling temperature of 40–50°C is sufficient in industrial installations, at which point the concentration should be above 45%. This post was last edited by qiwu9981 on 2008-10-13 10:42.]
Error correction: “This is” in the above text should be changed to “At this time”; apologies! Additionally, if you need more help, you can send an email to arniezhang@163.com
After neutralization to around pH 4.2, what are the components of the crystallized phosphates?
Returning to the 12th floor, when the pH is adjusted to 4.2, the product is primarily an ammonium phosphate solution (with a very small amount of diammonium phosphate); of course, this is related to the phosphate concentration in the system.
Then the utilization rate of phosphoric acid isn’t very low; triammonium is unstable. Under what conditions can more diammonium be produced to improve the utilization rate of phosphoric acid?
Back to floor 14: Monoammonium phosphate sells well in the market, while the market for diammonium phosphate is smaller. If diammonium is to be produced, the pH can be raised to around 8.2.
I think it mainly depends on the concentration of phosphoric acid used for absorption? What is the impurity content? For ordinary wet-process phosphoric acid produced in standard ways, it’s simply not possible to apply crystallization methods; such treatment is required instead.
The experts have already discussed it in great detail, so I don’t have much to add.