Sodium Acid Pyrophosphate

Brief Overview 

Sodium acid pyrophosphate is an inorganic compound composed of sodium cation and pyrophosphate anion. It is a white, water-soluble solid that can be used as a buffer and chelating agent and has many applications in the food industry. When crystallized from water, it forms hexahydrate but dehydrates above room temperature. Pyrophosphate is a polyvalent anion with a high affinity for polyvalent cations, for example, calcium ions. Disodium pyrophosphate is produced by heating sodium dihydrogen phosphate:

2NaH₂PO₄ → Na₂H₂P₂O₇ + H₂O

Manufacturing Process

The method of preparing sodium acid pyrophosphate has substantially improved doughnut baking properties which comprises thermally evaporating a monosodium orthophosphate solution containing from 0.50 % to 0.65 % by weight of phosphoric acid together with about 0.10 % to about 0.20 % K₂O and about 0.025 % to about 0.075 % Al₂O₃, basis NaH₂PO₄. To produce substantially dry monosodium orthophosphate, calcining the said monosodium orthophosphate at a temperature of about 225℃ to about 235℃. After sodium acid pyrophosphate has been formed, temper the said pyrophosphate by maintaining it at atmospheric pressure and temperature of about 215℃ to about 245℃. An atmosphere containing 230 mm. to 760 mm. hg of steam, said tempering being carried out for one hour to four hours, and after that adding to the said pyrophosphate a basic sodium phosphate to obtain a product having a pH value of from 4.0 to 4.6.

Food Industry 

Sodium acid pyrophosphate is a popular leavening agent found in baking powders, which is used as a constituent of blanching solutions for preventing the after-cooking darkening of potatoes. Disodium pyrophosphate is used as a constituent of phosphate mixes in meat processing and cheese-emulsifying salts. In addition, it is used as a general buffer and acidifying agent in foodstuffs. In seafood products, it is used as a preservative.

Other Applications 

Sodium acid pyrophosphate is used as a dispersant in oil well drilling muds in petroleum production. In leather treatment, it is used to remove iron stains. It is used in the treatment of kidney stones and skin. It is used in dairy cleaning, electroplating, and metal surface cleaning. Moreover, sodium acid pyrophosphate is also used to stabilize hydrogen peroxide solutions.