Sodium tripolyphosphate

Minerals. Supplementation of macrominerals to mminants is sometimes necessary. Calcium and phosphoms are the minerals most often supplemented in mminant diets. One or both may be deficient, and the level of one affects the utilization of the other. Limestone, 36% calcium, is commonly used as a source of supplemental calcium. Dolomite, 22% calcium oyster sheUs, 35% calcium and gypsum, 29% calcium, are sources of calcium. Bone meal, 29% calcium, 14% phosphoms dicalcium phosphate, 25—28% calcium, 18—21% phosphoms and defluorinated rock phosphate, 32% calcium, 18% phosphoms, are sources of both calcium and phosphoms. Diammonium phosphate, 25% phosphoms phosphoric acid, 32% phosphoms sodium phosphate, 22% phosphoms and sodium tripolyphosphate, 31% phosphoms, are additional sources of phosphoms (5). 

Tripolyphosphates. The most commercially important tripolyphosphate salt is sodium tripolyphosphate (STP), Na P O Q. Three distinct crystalline forms are known two are anhydrous (STP-I and STP-II) the other is the hexahydrate [15091 -98-2] Na P O Q 6H20. Sodium tripolyphosphate anhydrous Form I is the high temperature, thermodynamically stable phase sodium tripolyphosphate anhydrous Form II is the lower temperature form which can be readily converted to STP-I by heating to above 417 8° C, the transition temperature. However, the reverse reaction is extremely slow below 417°C. Both anhydrous forms of sodium tripolyphosphate are therefore stable enough to coexist at room temperature. 

Sodium tripolyphosphate is produced by calcination of an intimate mixture of orthophosphate salts containing the correct overall Na/P mole ratio of 1.67. The proportions of the two anhydrous STP phases are controlled by the calcination conditions. Commercial STP typically contain a few percent of tetrasodium pyrophosphate and some trimetaphosphate. A small amount of unconverted orthophosphates and long-chain polyphosphates also may be present. 

The hydration rate of sodium tripolyphosphate to its stable hexahydrate, Na P O Q 6H20, directly affects detergent processing and product properties. The proportion of STP-I (fast-hydrating form) and STP-II (slow-hydrating form) in commercial sodium tripolyphosphate is controUed by the time—temperature profile during calcination. In most processes, a final product temperature of near 450°C results in a product containing about 30%... 

The pH of a 1% solution of pure sodium tripolyphosphate is 9.9 and that of commercial samples may vary between 9.5 and 10.1. The pH of a given sample of solid STP drops slowly with age because of water adsorption and partial reversion to orthophosphate and pyrophosphate. The pH of solutions varies with concentration because the sodium ion is bound in the complex form NaP O o higher concentrations maximum pH is reached at between 1—2% solution. 

Anhydrous sodium tripolyphosphate is slow to hydrate in contact with the atmosphere under normal ambient conditions and generally remains free-flowing. If the relative humidity is below a critical relative humidity, which is different for both anhydrous forms of STP and dependent on temperature, hydration does not take place. For prolonged storage at room temperature, relative humidities above ca 60% in the air result in water absorption. For shorter periods, high levels of humidity can be tolerated. However, even at higher humidities, the amount of water absorbed is small. The heats evolved from vapor hydration of STP-I and -II have been estimated at 343 and 334 kj /mol (82.0 and 79.9 kcal/mol), respectively (25). 

The only tme metaphosphate (ring stmcture) of significant commercial interest is sodium trimetaphosphate (STMP), Na P O. Because of the strain inherent in the small ring stmcture, STMP is more reactive toward nucleophiles than chain phosphates. In the presence of NaOH, for example, STMP forms sodium tripolyphosphate. 

Sequestration forms the basis for detergent and water-treatment appHcations of polyphosphates. Sequestration of hardness ions by sodium tripolyphosphate used in detergent formulations prevents the precipitation of surfactants by the hardness ions. Sodium polyphosphate glass (SHMP) may be added to water system to prevent the formation of calcium or magnesium scales by reducing the activity of the hardness ions. However, if the ratio of cation to polyphosphate is too high at a given pH, insoluble precipitates such as may result instead of the soluble polyphosphate complexes. The... 

Fig. 13. Combined dryer—calciner processes for sodium tripolyphosphate (a) cocurrent rotary dryer—calciner (b) countercurrent rotary dryer—calciner and...

The largest use of calcium hypochlorite is for water treatment. It is also used for I I and household disinfectants, cleaners, and mildewcides. Most of the household uses have been limited to in-tank toilet bowl cleaners. In areas where chlorine cannot be shipped or is otherwise unavailable, calcium hypochlorite is used to bleach textiles in commercial laundries and textile mills. It is usually first converted to sodium hypochlorite by mixing it with an aqueous solution of sodium carbonate and removing the precipitated calcium carbonate. Or, it can be dissolved in the presence of sufficient sodium tripolyphosphate to prevent the precipitation of calcium salts. However, calcium hypochlorite is not usually used to bleach laundry and textiles because of problems with insoluble inorganic calcium salts and precipitation of soaps and anionic detergents as their calcium salts. 

Starch sodium phosphate monoesters [11120-02-8] are prepared by heating mixtures of 10% moisture starch and sodium monohydrogen and dihydrogen phosphates or sodium tripolyphosphate. Starch phosphate monoesters are used primarily in foods, such as pudding starches and with oH-in-water emulsions. 

A soluble sodium tripolyphosphate is produced as are iasoluble lanthanide and thorium hydroxides (hydrated oxides). 

STPP = sodium tripolyphosphate NTA = nitnlotriacetic acid EDTA = ethylenediaminetetraacetic acid EDTPO = ethylenediaminetetra(methylenephosphonic acid) (see Table 1). 

Phospha.tes, Pentasodium triphosphate [7758-29-4] sodium tripolyphosphate, STPP, Na P O Q, is the most widely used and most effective builder in heavy-duty fabric washing compositions (see also Phosphoric acid and phosphates). It is a strong sequestrant for calcium and magnesium, with a p c of ca 6, and provides exceUent suspending action for soils. Because of its high sequestration power, it also finds extensive appHcation in automatic-dishwashing detergents. Sodium tripolyphosphate forms stable hydrates and thus aids in the manufacture of crisp spray-dried laundry powders. 

Tetrasodium pyrophosphate [7722-88-5] Na4P20y, is another important primary builder and detergent. In sequestration, it is not quite as effective as sodium tripolyphosphate and its usage in heavy-duty laundry powders has declined in recent years. Functionally, tetrasodium pyrophosphate is both a builder for surfactants (ie, water softener) and alkaH. 

Where hardness is present in excess of the sequestering capacity of sodium tripolyphosphate and pyrophosphate, both can function as precipitant builders. 

The sodium soaps of fatty acid form calcium soaps of such low solubdity that they act as their own budders. Initial soap additions precipitate the calcium ion and the soap added thereafter functions in soft water. At high temperatures, the calcium soaps are relatively soluble compared to calcium tripolyphosphate. Thus sodium tripolyphosphate (STEP) can budd (revert) soaps in a hot water wash. However, at low temperatures the relative affinity of STEP for calcium decreases so that STEP cannot budd soaps in a cold water wash. 

The efforts of the detergent industry toward solution of its part of the eutrophication problem are, at this point, less complete than its response to the biodegradabihty problem. Soda ash, Na2C02, sodium siUcate, and, to a lesser extent, sodium citrate formed the basis of the early formulations marketed in the areas where phosphates were harmed. Technically, these substances are considerably less effective than sodium tripolyphosphate. As a precipitant builder, soda ash can lead to undesirable deposits of calcium carbonate on textiles and on washing machines. 

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