Ammonium phosphate

Ammonium orthophosphates are very important. Known salts include 

The mono-, p = 1.803 g/cc, and di-, p = 1.619 g/cc, ammonium orthophosphates find huge application as fertilisers where they function as sources of both nitrogen and phosphorus (Chapter 12.2). The tri-ammonium salt (NH4)3P04 -3H20 slowly loses ammonia on standing in the atmosphere. 

A dilute aqueous solution of the diammonium salt on boiling slowly evolves ammonia and the pH is gradually reduced from 7.8 to around 5.8. This phenomenon can be used to control the precipitation of alkali-soluble — acid-insoluble dyestuffs on to wool and secure even dyeing. 

Ammonium phosphates will act as fire retardants when wood or fabrics are impregnated with them. On heating they evolve ammonia and phosphoric acid. The former retards combustion of the materials and the latter catalyses the charring of cellulose to carbon. The mono ammonium salt can be used in granular form in some types of fire extinguishers. 

Ammonium dihydrogen phosphate, NH4H2PO4, can be utilised for the removal of NH3 from coke oven gas in the Phospham process . The ammonia is recovered on heating [11]. 

The following ammonium phosphates are used as fertilizers either separately or as mixtures  

Liquid ammonium phosphate fertilizers ammonium polyphosphate (APP) 

Tri-ammonium phosphate is not a commercial product because of its high ammonia vapor pressure. 

Mono- and diammonium phosphate are used as solid fertilizers, whereas ammonium polyphosphate is mainly utilized in solution as a liquid fertilizer, since unlike the orthophosphates, it is very soluble and is more difficult to granulate than the orthophosphates. As a result of its complexing properties, it also keeps impurities (iron, aluminum, magnesium etc.) in solution. 

Ammonium phosphate fertilizers are relatively impure (purity ca. 85%), due to their being prepared with nonpurified wet-process acid. Commercial monoammonium phosphate contains 11 to 13% N and 48 to 53% P2O5 (theoretically 12.2% N, 61.7% P2O5). Commercial diammonium phosphate contains 16 to 18% N and 46 to 48% P2O5 (theoretically 21.2% N, 53.7% P2O,). 

Kubasova [963] has reviewed the chemistry of the ammonium salts of polyphosphoric acids. Much interest in the field derives from the agricultural uses of these substances as fertilizers. Both NH3 and H20 tend to be eliminated simultaneously on heating, but dehydration alone may be achieved in an atmosphere of NH3 [963], e.g. 

Small amounts ( 3.5%) of ammonium salts markedly accelerate [970] the dehydration of Na2HP04 12 H20 to Na2P207. This is attributed to an increase in the concentration of delocalized protons in the structure, as a consequence of the proton donor properties of NH4, and this promotes dehydration. 

Although many ammonium metal phosphates are known, few kinetic studies of their decompositions have been reported and no systematic investigations of the influence of metal ion or structure on the deammi-nation reactions are available. Thermal analyses [971] of compounds of the type MNH4P04 xH20 (where M is a divalent metal) show that, after dehydration, there is a continuous and simultaneous evolution of NH3 and H20 [137], maintained until crystalline M2P207 is formed, e.g. 

Two salts are manufactured by combining ammonia with phosphoric acid diammonium phosphate (DAP) and monoammonium phosphate (MAP). 

DAP is a white, crystalline compound that is completely soluble in water and, hence is 100% available to plants. MAP is a white, crystalline material that is completely soluble in water. In contrast to DAP, the solutions of which are slightly alkaline, MAP gives acid solutions with a pH of about 4.5. As in DAP all of the phosphate is available since it is completely water-soluble. 

The vapor pressure of a saturated solution of MAP is expressed by the following equation238  

MAP is produced by reaction of anhydrous ammonia and phosphoric acid in batch or continuous reactors. It is then crystallized in conventional crystallizers since the partial pressure of ammonia over this acid solution is low. Crystals are centrifuged and dried below 100°C in a rotary dryer, and mother liquor is returned to the reactor238. 

DAP solutions have a high partial pressure of ammonia, and the reaction is normally carried out in a two-stage reactor system with feed acid passing countercurrent to the flow of ammonia gas. Incoming acid reacts in the scrubber with ammonia from the main reactor and may also serve as a scrubber for dryer off-gases238. 

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Another example is the purification of a P-lactam antibiotic, where process-scale reversed-phase separations began to be used around 1983 when suitable, high pressure process-scale equipment became available. A reversed-phase microparticulate (55—105 p.m particle size) C g siUca column, with a mobile phase of aqueous methanol having 0.1 Af ammonium phosphate at pH 5.3, was able to fractionate out impurities not readily removed by hquid—hquid extraction (37). Optimization of the separation resulted in recovery of product at 93% purity and 95% yield. This type of separation differs markedly from protein purification in feed concentration ( i 50 200 g/L for cefonicid vs 1 to 10 g/L for protein), molecular weight of impurities (<5000 compared to 10,000—100,000 for proteins), and throughputs ( i l-2 mg/(g stationary phasemin) compared to 0.01—0.1 mg/(gmin) for proteins). 

Mixed with additives, urea is used in soHd fertilizers of various formulations, eg, urea—ammonium phosphate (UAP), urea—ammonium sulfate (UAS), and urea—phosphate (urea + phosphoric acid). Concentrated solutions of urea and ammonium nitrate (UAN) solutions (80—85 wt%) have a high nitrogen content but low crystallization point, suitable for easy transportation, pipeline distribution, and direct spray appHcation. 

Regulations specify a considerable Hst of additives and treatments which may be permitted under controlled limits and conditions. It is important to note that no wine receives mote than a few of these treatments, and many have none. For example, most grape musts ferment readily without additions, but some extra nitrogen source for the yeasts is occasionally beneficial. If some is requited, ammonium phosphate is the most commonly used. 

Fig. 6. World trends ia types of nitrogenous fertilizers consumed, where (—) represents anhydrous ammonia, ammonium phosphates, cogranulated...

Nitrogen in Multinutrient Fertilizers. Single-nutrient nitrogen materials suppHed over 85% of the fertilizer nitrogen used in the United States during the year ended June 30, 1990. The remaining 15% was suppHed as multinutrient materials (Fig. 3). This included 9% as ammonium phosphate, 2% as cogranulated mixtures, and 3% as fluid mixtures. 

The routes by which mineral phosphates are processed into finished fertilizers are outlined in Eigure 7. World and U.S. trends in the types of products produced are shown in Eigures 8 and 9, respectively. Most notable in both instances is the large, steady increase in the importance of monoammonium and diammonium phosphates as finished phosphate fertilizers at the expense of ordinary superphosphate, and to some extent at the expense of triple superphosphate. In the United States, about 65% of the total phosphate appHed is now in the form of granular ammonium phosphates, and additional amounts of ammonium phosphates are appHed as integral parts of granulated mixtures and fluid fertilizers. 

Fig. 8. World trends in types of phosphate fertilizers consumed, where (—) represents ammonium phosphates and multinutrient compounds (— normal superphosphate ( ), triple superphosphate and (— —), basic slag and raw rock.

Fig. 15. Cutaway view of a TVA-type ammoniator-granulator for production of granular ammonium phosphates or NPK cogranulated mixtures.

Production of nitric phosphates is not expected to expand rapidly ia the near future because the primary phosphate exporters, especially ia North Africa and the United States, have moved to ship upgraded materials, wet-process acid, and ammonium phosphates, ia preference to phosphate rock. The abundant supply of these materials should keep suppHers ia a strong competitive position for at least the short-range future. Moreover, the developiag countries, where nitric phosphates would seem to be appealing for most crops except rice, have already strongly committed to production of urea, a material that blends compatibly with sulfur-based phosphates but not with nitrates. 

Plasticity, and hence granulation efficiency, varies considerably with the nature and proportion of feed materials. Pure salts, such as potassium chloride and ammonium sulfate, lend Httle or no plasticity and thus are difficult to granulate. Superphosphates provide good plasticity. The plasticity of ammonium phosphates depends chiefly on the impurity content of iron and aluminum. The higher the impurity the greater the plasticity. In some cases, binders such as clay are added to provide plasticity. 

Steam granulation is practiced in Europe, AustraUa, and elsewhere, chiefly in small plants in which superphosphate, either ordinary or triple, is a primary ingredient. However, for many of the larger operations, superphosphates have been replaced by ammonium phosphates as the principal P2 s source, and granulation procedures involving chemical reactions are employed in Europe as well as in the United States. 

Some commonly used primary nutrient fertilizers are incidentally also rich sources of calcium. Ordinary superphosphate contains monocalcium phosphate and gypsum in amounts equivalent to all of the calcium originally present in the phosphate rock. Triple superphosphate contains soluble monocalcium phosphate equivalent to essentially all the P2 5 product. Other fertilizers rich in calcium are calcium nitrate [10124-37-5] calcium ammonium nitrate [39368-85-9] and calcium cyanamide [156-62-7]. The popular ammonium phosphate-based fertilizers are essentially devoid of calcium, but, in view of the natural calcium content of soils, this does not appear to be a problem. 

Some of the principal forms in which sulfur is intentionally incorporated in fertilizers are as sulfates of calcium, ammonium, potassium, magnesium, and as elemental sulfur. Ammonium sulfate [7783-20-2] normal superphosphate, and sulfuric acid frequendy are incorporated in ammoniation granulation processes. Ammonium phosphate—sulfate is an excellent sulfur-containing fertilizer, and its production seems likely to grow. Some common grades of this product are 12—48—0—5S, 12—12S, and 8—32—8—6.5S. 

Copper. Some 15 copper compounds (qv) have been used as micronutrient fertilizers. These include copper sulfates, oxides, chlorides, and cupric ammonium phosphate [15928-74-2] and several copper complexes and chelates. Recommended rates of Cu appHcation range from a low of 0.2 to as much as 14 kg/hm. Both soil and foHar appHcations are used. 

Iron. As with copper, some dozen or more materials are used as fertilizer Hon sources. These include ferrous and ferric oxides and sulfides and ferrous ammonium phosphate [10101 -60-7] ferrous ammonium sulfate [10045-89-3] frits, and chelates. In many instances, organic chelates are more effective than inorganic materials. Recommended appHcation rates range widely according to both type of micronutrient used and crop. Quantities of Fe range from as low as 0.5 kg/hm as chelates for vegetables to as much as a few hundred kg/hm as ferrous sulfate for some grains. 

Orthophosphate Hquid mixtures are ineffective as micronuttient carriers because of the formation of metal ammonium phosphates such as ZnNH PO. However, micronutrients are much more soluble in ammonium phosphate solutions in which a substantial proportion of the phosphoms is polyphosphate. The greater solubiHty results from the sequestering action of the polyphosphate. The amounts of Zn, Mn, Cu, and Fe soluble in base solution with 70% of its P as polyphosphate are 10 to 60 times their solubiHties in ammonium orthophosphate solution. When a mixture of several micronutrients is added to the same solution, the solubiHty of the individual metals is lowered significantly. In such mixtures the total micronuttient content should not exceed 3% and the storage time before precipitates appear may be much shorter than when only one micronuttient is present. 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Formulations of ammonium phosphates and ammonium bromide are sold for use on ceUulosic—synthetic fiber blends. Other ammonium phosphate formulations contain wetting and softening agents. A large-volume, ca 9000 t/yr ia 1991, use ia the United States (48) for ammonium phosphate is ia forest fire control, usuaUy by aerial appUcation (see also Ammonium compounds). 

Insoluble Ammonium Polyphosphate. When ammonium phosphates are heated ia the presence of urea (qv), or by themselves under ammonia pressure, relatively water-iasoluble ammonium polyphosphate [68333-79-9] is produced (49). There are several crystal forms and the commercial products, avaUable from Monsanto, Albright WUson, or Hoechst-Celanese, differ ia molecular weight, particle size, solubUity, and surface coating. Insoluble ammonium polyphosphate consists of long chains of repeating 0P(0)(0NH units. 

Effects on Visible Smoke. Smoke is a main impediment to egress from a burning building. Although some examples are known where specific phosphoms flame retardants increased smoke in small-scale tests, other instances are reported where the presence of the retardant reduced smoke. The effect appears to be a complex function of burning conditions and of other ingredients in the formulation (153,156,157). In a carehil Japanese study, ammonium phosphate raised or lowered the smoke from wood depending on pyrolysis temperature (158). Where the phosphoms flame retardant functions by char enhancement, lower smoke levels are likely to be observed. 

Urea—Phosphate Type. Phosphoric acid imparts flame resistance to ceUulose (16,17), but acid degradation accompanies this process. This degradation can be minimized by iacorporation of urea [57-13-6]. Ph osph oryl a ting agents for ceUulose iaclude ammonium phosphate [7783-28-0] urea—phosphoric acid, phosphoms trichloride [7719-12-2] and oxychloride [10025-87-3] monophenyl phosphate [701-64-4] phosphoms pentoxide [1314-56-3] and the chlorides of partiaUy esterified phosphoric acids (see Cellulose esters, inorganic). 

S. cerevisiae is produced by fed-batch processes in which molasses supplemented with sources of nitrogen and phosphoms, such as ammonia, ammonium sulfate, ammonium phosphate, and phosphoric acid, are fed incrementally to meet nutritional requirements of the yeast during growth. Large (150 to 300 m ) total volume aerated fermentors provided with internal coils for cooling water are employed in these processes (5). Substrates and nutrients ate sterilized in a heat exchanger and then fed to a cleaned—sanitized fermentor to minimize contamination problems. 

An aqueous solution of mono ammonium phosphate [10361-65-6] reacts with MgO to form ammonium magnesium phosphate hexahydrate [15490-91-2], NH MgPO 6H20. Several other species of hydrated phosphates are created during this reaction which takes place quickly and produces compounds that have desirable properties as cementing agents. The hexahydrate is the most prevalent. Properties are given in Table 22. 

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