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.