Sodium Hexametaphosphate

Description

Brief overview

Sodium hexametaphosphate (SHMP), is basically a hexamer of the chemical formula (NaPO3)6. It is also called Graham’s salt or hexasodium metaphosphate. It is white and granular in appearance and hydrolyses in aqueous solution, during acidic conditions. It is soluble in water, while insoluble in organic solvents. It is a sequestrant that binds with calcium ions.

Manufacturing Process

Sodium dihydrogen phosphate: The soda solution was first subject to neutralization reaction with phosphate acid at 80~100 ℃ for 2h; the resulting sodium dihydrogen phosphate solution was concentrated by evaporation, cooled and crystallized to obtain sodium dihydrogen phosphate dihydrate and heated to 110~230 ℃ to remove two crystal water; further be subject to heating to remove the structural water; further being heated to 620 ℃ for dehydration to result in the molten sodium metaphosphate and further polymerized into sodium hexametaphosphate, and discharged; apply chilling shock for 650 ℃ to 60~80 ℃ for flaking, and crush to obtain the hexametaphosphate products. Its reaction formula is as below:

Na₂CO₃ + 2H₃PO₄ + H₂O → 2NaH₂O₄•2H₂O + CO₂ ↑

NaH₂PO₄•2H₂O [△] → Na₂H₂PO₄ + 2H₂O

2NaH₂PO₄ [△] → Na₂H₂P₂O₇ + H₂O

Na₂H₂P₂O₇ → 2NaPO₃ + H₂O

6NaPO₃ [△] → (NaPO₃)₆

Phosphorus pentoxide method: put the yellow phosphorus into a steam of dry air for combustion and oxidation, the cooling obtained phosphorus pentoxide is mixed together with soda in certain ratio (Na2O: P2O5 = 1~1.1). Put the mixed powder in a graphite crucible and heated indirectly to have it dehydrated and agglomerated, the resulting sodium hexametaphosphate is subject to flaking upon chilling shock and pulverized to obtain industrial hexametaphosphate products. The reaction formula is as below:

P₄ + 5O₂ → 2P₂O₅

P₂O₅ + Na₂CO₃ → 2NaPO₃ + CO₂ ↑

6NaPO₃ [△] → (NaPO₃)₆