A polyphosphate is formed by a number of simple phosphate units linked together, and sodium tripolyphosphate contains three such units.
The brief manufacturing processes are as follows (1) :
STPP is commercially produced by the neutralization of phosphoric acid with sodium hydroxide to form the mixture of monosodium phosphate and disodium phosphate.
Then heat the mixture to 500-550 °C. Here is the reaction equation: NaH2PO4 + 2Na2HPO4 → Na5P3O10 + 2H2O
Food grade STPP exists as two forms, and follows the corresponding chemical formula:
STPP Anhydrous: Na5O10P3
STPP Hexahydrate: Na5O10P3 · 6H2O
http://www.chinafooding.com/Sodium_tripolyphosphate-STPP
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