Home page » Useful information » Basics of Di-ammonium Phosphate Production
Basics of Di-ammonium Phosphate Production
Di-ammonium phosphate (DAP) is a salt of orthophosphoric acid.
It has the formula (NH4)2HPO4. When heated to 70°C, it decomposes actively, releasing ammonia (NH3). It is highly soluble in water.
Ammonium phosphates are mainly obtained by the reaction of ammonia and phosphoric acid. Di-ammonium phosphate and the closely related monoammonium phosphate (MAP) (NH4H2PO4) are concentrated nitrogen-phosphorus fertilizers.
Table 1: Properties of Ammonium Phosphates
| Property |
Di-ammonium
NH4H2PO4 |
Monoammonium
(NH4)2HPO4 |
| Melting point, °C |
192 (decomp.) |
– |
| Density, g/cm3 |
1.803 |
1.619 |
| nD 20 |
1.479 |
1.53 |
| Cp, J/(mol K) |
142.0 |
182.13 |
| ∆Hf, kJ/mol |
-1445.0 |
-1565.7 |
| Solubility in 100 g water (25°C), g |
40.0 |
69.5 |
| pH of 0.1 M solution |
4.4 |
8.0 |
| Nitrogen content, % |
12.2 |
21.2 |
| P2O5 content, % |
61.8 |
53.8 |
The most common nitrogen-phosphorus fertilizer is ammophos. It is very effective and combines excellently with other fertilizers. This property of ammophos makes it possible to create nutrient blends based on it with practically any required combination of nutrients.
Ammophos, as its main component, contains monoammonium phosphate and a small amount (up to 10 percent) of di-ammonium phosphate.
The fertilizer Diammophos consists predominantly of di-ammonium phosphate.
Depending on the purity of the orthophosphoric acid used, the final product may contain impurities: ammonium sulfate, metal phosphates (Al, Fe, Mg, etc.).
In the production of DAP and MAP, thermal or defluorinated extraction orthophosphoric acid is used.
Di-ammonium phosphate is divided into food grade (feed grade) and fertilizer grade. The fertilizer grade is produced in the form of granules of various colors. For example, in Europe, DAP is used in black, because local bird species peck at granules of other colors and get poisoned. In Russia, white granules are mainly used.
Monoammonium phosphate is likewise divided into feed grade and technical grade.
Food-grade DAP is used as feed for farm animals. It is also used to feed nutritional yeast, in cosmetics, and in pharmaceuticals.
Fertilizer-grade DAP is a concentrated, granulated, high-quality fertilizer. This complex nitrogen-phosphorus mineral fertilizer contains no nitrates.
Di-ammonium phosphate increases soil pH, but over the long term it begins to lower it. This happens due to the conversion of ammonium to nitrogen.
In addition, di-ammonium phosphate is used as a flame retardant for treating wood, woven materials, paper products, etc. It has a strong fire-protective effect. Read more about flame retardants here.
In nature, phosphates occur as phosphorites and apatites. In them, phosphorus is present in an insoluble form. To make the phosphorus easier for plants to absorb, these natural phosphates are converted into artificial phosphates.
Superphosphate (including double superphosphate) and precipitate are the main phosphorus-based fertilizers.
Ammonium phosphates — ammophos and diammophos — are produced by combining orthophosphoric acid and ammonia. Both thermal and extraction-grade acid are used for such production, with extraction acid being cheaper.
Nitroammophos is obtained by the joint processing of nitric and orthophosphoric acids.
Ammonium phosphates are now manufactured using several process technologies. The main difference between them lies in the acid-neutralization conditions and in the crystallization process of the final product.
The process itself is affected by impurities in the orthophosphoric acid, the concentration of the acid itself (must not exceed 77%), process temperature, pressure in the working vessels, and other factors.
Ammonium phosphates made from thermal acid are purer than those made from extraction acid. They are used in food production, pharmaceuticals, and elsewhere.
The pulp formed during production is a complex multi-salt system. In addition to phosphates, it contains: ammonium sulfate, and phosphates of Ca, Mg, Al, Fe. It also contains ammonium fluorides in the form of ammonium fluorosilicate and complex compounds.
Calcium and magnesium phosphates can be fully absorbed by plants. Fe and Al phosphates can dissolve in citric acid and be absorbed by plants up to 50%. Complex compounds are insoluble, and their presence significantly reduces the amount of absorbable P2O5 in the final fertilizer.
Complex compounds mainly form at low pH. To prevent their formation, the production process is carried out at pH>3.
Basic Flow Diagram for Producing Ammonium Phosphates
The production scheme incorporates a closed water-recirculation cycle to reduce emissions of ammonia and fluorine into the environment. Flue gas cleaning systems are also used for the same purposes.
It should be noted that using defluorinated acid (achieved by precipitating sodium fluorosilicate) in the production of Di-ammonium phosphate improves the quality of the final product while also simplifying flue gas cleaning.
In general, to produce food-grade di-ammonium phosphate with a content of 52% P2O5 and 19% N, per 1 t (P2O5+N) produced, 0.764 t of P2O5 is consumed in the form of concentrated phosphoric acid, and 0.353 t of ammonia, with a P2O5 utilization rate of 96%.
To buy Di-ammonium phosphate and other chemical materials, call us right now at (495)133-02-40, (495)407-17-86!
Or send a request to order@chimko.com
