Urea-ammonium polyphosphate

UREA-AMMONIUM POLYPHOSPHATE. A fertilizer similar fo urea-ammonium othtrophosphate except that about half the phosphorus is in polyphosphate form, which gives improved sequestering action and solubility. It is excellent for use as a liquid fertilizer. 

Fig. 6.6-13 Flow diagram of a TVA pipe reactor-pugmill process producing granular NP fertilizer (urea, ammonium polyphosphate) [6.6.6]...

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. 

Fire-retardant chemicals used by the commercial wood-treating industry are limited almost exclusively to mono- and diammonium phosphate, ammonium sulfate, borax, boric acid, and zinc chloride (4,8). It is believed that some use is also made of the liquid ammonium polyphosphates (9). Some additives such as sodium dichromate as a corrosion inhibitor are also used. Aqueous fire-retardant treatment solutions are usually formulated from two or more of these chemicals to obtain the desired properties and cost advantages For leach-resistant type treatments, the literature shows that some or all of the following are used urea, melamine, dicyandiamide, phosphoric acid, and formaldehyde (10-12) ... 

Camino G, Costa L, Trossarelli L. Study on the mechanism of intumescence in fire retardant polymers. 3. Effect of urea on the ammonium polyphosphate pentaerythritol system. Polym. Degrad. Stab. 1984 7 221-229. 

Cotton Ammonium phosphates are the most effective FRs for cotton as first identified by Gay-Lussac in 1821 and still widely used. All phosphates on heating release phosphoric acid, which catalyses dehydration reactions of cellulose to yield char at the expense of volatiles formation reactions.50 However, ammonium phosphates like mono- or diammonium phosphates are water soluble, hence applicable as nondurable treatments only. Ammonium bromide can be used in combination with ammonium phosphates to provide some vapor-phase FR action. Other examples include borax and boric acid, ammonium sulfamate, and sulfates. These nondurable finishes are useful for disposable fabrics, insulation, wall boards, theatrical scenery, packaging material, paper, etc. Ammonium polyphosphates (APPs) are used in combination with urea to provide semidurable finishes and by curing at 160°C, when some phosphorylation can occur. Semidurable finishes are very useful for materials that may not need frequent washings, e.g., mattresses, drapes, upholstery, carpets, etc. Some commercial examples of semidurable finishes include Flammentin FMB (Thor Specialities), Pyrovatim PBS (Ciba, now marketed by Huntsman), etc.26... 

Organophosphorus and polyphosphate compounds also have been used as fire retardants. In one study, ammonium polyphosphate was used at loading levels of 96 kg/m to achieve a flame-spread index of 15 according to ASTM E 84 (J2). This treatment produced low smoke yields however, this treatment was corrosive to aluminum, slightly corrosive to mild steel, but not corrosive to brass (77). In a patent by Clermont (78), phosphorus pentoxide, dimethylformamide, and urea were used to produce fire-retardant paper or veneer. Other patents (79, 80) describe the reaction of ammonia with partial esters of polyphosphoric acid. All patents demonstrated some leach resistance of the phosphorus. 

TVA developed a process for producing granular ammonium polyphosphate, and in late 1973 the process was put into operation in a demonstration-scale plant with a capacity of 13-17 tph. The plant produced straight ammonium polyphosphate and urea-ammonium phosphate alternately. A flow diagram is shown in Figure 12.16. The process uses the heat of reaction of phosphoric acid (54% P2O5) with gaseous ammonia to evaporate water and dehydrate the ammonium phosphate,... 

In TVA s production of UAP by a melt granulation process, mentioned previously, ammonium polyphosphate melt and molten urea were cogranulated in... 

Ammonium polyphosphate can be obtained by the direct action of ammonia on polyphosphoric acid containing 83% P2O5. If this product is added to water, a fine precipitate of (NH4P03) is obtained. An alternative preparation (used industrially) is to heat orthophosphoric acid with urea which forms urea phosphate which in turn breaks down at a temperature too low to decompose the product. 

Other fertiliser compounds which can satisfactorily provide phosphorus and nitrogen are urea phosphate, CO(NH2)2 H3PO4, ammonium polyphosphate, [(NH4)P03] and phosphazenes such as P3N3(NH2)g (Table 12.4). Red phosphorus is slowly oxidised in damp soil and has been considered as a possible fertiliser [32,33]. 

An early fire-retardant treatment for paper and cotton was to heat them with phosphoric acid and urea at 145-180°C to form insoluble ammonium polyphosphate, (NH4P03) . Ammonium polyphosphate is also used in intumescent paint formulations, where, like the orthophosphate, it releases ammonia and phosphoric acid on heating. The latter facilitates charring which, together with the release of ammonia, retards local combustion. A similar mechanism is believed to account, at least in part, for the fire-retardant action of many other phosphorus compounds. There is now evidence that impregnation of wood with phosphoric acid suppresses the formation of carcinogenic materials during pyrolysis [39]. 

Phosphorus oxynitride (PON) is the name for a family of closely related materials that have been around for over 100 years. They are not well known but are thermally very stable and may be considered as future flame retardants and for intumescent formulations since PON is analogous to ammonium polyphosphate. It can be made from inexpensive starting materials such as ammonium phosphate, melamine phosphate or urea phosphate just by prolonged and intensive heating. 

Heating of ammonium phosphates imder an atmosphere of ammonia or in the presence of urea produces ammonium polyphosphate (21,22). At a high degree of polymerization, the product is a water-insoluble solid. This form of ammonium polyphosphate is used commercially as a flame-retardant additive for plastics and as the latent acid component in intnmescent paints, mastics, and caulks (23,24). The water resistance can be fnrther enhanced by encapsulation with a resin. 

Ammonium diphosphate cannot be made by thermal dehydration of ammonium phosphates because both water and ammonia are split off, and the resulting product is a mixture of short-chain ammonium polyphosphates and short-chain polyphosphoric acids. Ammonium diphosphate usually is prepared from pure diphosphoric acid. The diphosphoric acid is crystallized from a polyphosphoric acid mixture containing 80% PjOs or made by running a solution of sodium diphosphate through an ion exchange column. The resulting diphosphoric acid then is treated with ammonia. Ammonium diphosphate also has been made by heating a mixture of urea and phosphoric acid, but by-products such as cyanuric acid are tedious to remove. The present method is based on the reac-... 

In nitrogenous fertiliser solutions of the NH4NOJ—NHj —HjO type corrosion of steel can be prevented by 500 p.p.m. of sulphur-containing inhibitors, e.g. mercaptobenzothiazole, thiourea and ammonium thiocyanate. However, these inhibitors are not so effective where most of the NHj is replaced by urea. For these solutions phosphate inhibitors such as (NH4>2HP04 and polyphosphates were more effective... 

Crystalline polyammonium catena-polyphosphate, (NH4) H2P 03 + 1, has been prepared by heating urea and monoammonium orthophosphate under ammonia vapor for 16 hours,1 by ammoniation of superphosphoric acid,2 by thermal condensation of urea phosphate,3 and by heating various ammonium phosphates in a current of ammonia.4,5 The procedure given below, in which crude ammonium tetrametaphosphate is reorganized and condensed to a long-chain polymer in a stream of ammonia, is straightforward and permits the use of common laboratory equipment and supplies. 

A cationic starch can be prepared by blending a condensate of formaldehyde plus an inorganic ammonium salt with starch and heating at 80 °C for up to 1 h.1316 A great interest was developed with urea-formaldehyde resins that were made to react with such polyalcohols as starch.1317-1319 It was reported that the reaction of starch with urea-formaldehyde resin required an acidic catalyst592,1320-1325 and the use of such dispersants as polyphosphates.1326 Ammonium metaphosphate catalyzed the reaction without the addition of any other acid catalyst.1327 A product that formed a paste was produced by controlling the proportion of starch to aldehyde (either up to 20% of formaldehyde or up to 30% of acetaldehyde) and urea (up to 15%) at pH 2 1.1328... 

Currently, expandable paints represent the most sophisticated answer. Their formulations are quite complex. They consist of acid based compounds, mainly phosphoric acid derivatives (e.g. ammonium phosphate or polyphosphate), polyhydroxy compounds (such as pentaerythrite, starch, phenolic or urea resin), non-combustible gas-forming compounds (such as chloroparafiins or melamines), and a polymeric matrix (e.g. chlorinated rubber). Such a coating gives good protection but its appearance is generally poor. 

The catalyst or add source can consist of ammonium phosphate or polyphosphate salts, phosphoric add-derived amides or alkyl or halo-alkyl phosphates. Charring agents are based on molecular structures that can form cross-linked networks such as pentaerythritol, sorbitol, melamine, and phenol-formaldehyde resins. Other polymeric systems capable of intumescence are some polyamides and polyurethanes. Blowing agents help form a porous structure in the char and can fadlitate its formation. Common blowing agents are based on urea and urea-formaldehyde resins, melamines, and polyamides that can liberate moisture. 

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