Sodium tripolyphosphate

Chemical properties

white or colourless crystals, granules or powder

The Uses of Sodium tripolyphosphate

Sodium tripolyphosphate is used in water softening, heavy-duty fabric washing, automatic dish washing, drilling fluid cleaning and liquid cattle feed supplements. It is also used as a peptizing, emulsifying, dispersing agent and as a hydrogen peroxide solution stabilizer. It acts as a preservative for seafood, meats, poultry, and animal feeds. It finds application as a polyanion crosslinker in polysaccharide based drug delivery. Further, it is used as a sealant for leaking farm ponds and a calcium and magnesium chelating agent. In addition to this, it is used in ceramics, leather tanning, flame retardants, paper pulping, paper coatings, textile processing, ore flotation, anticorrosion pigments and rubber production.

Flammability and Explosibility

Non flammable

Preparation

Food-grade Sodium tripolyphosphate is produced industrially by reacting thermal (or highly purified wet) phosphoric acid with soda ash, spray drying or crystallizing the resulting orthophosphate, then igniting the powder to permit polymerization (Kijkowska, Kowalski, Pawlowska-Kozinska, Wzorek, & Gorzada, 2008).

Purification Methods

Purify it by repeated precipitation from aqueous solution by slow addition of MeOH and dried in air. Also a solution of anhydrous sodium tripolyphosphate (840g) in water (3.8L) is filtered, MeOH (1.4L) is added with vigorous stirring to precipitate Na5P3O10.6H2O. The precipitate is collected on a filter, air dried by suction, then left to dry in air overnight. It is crystallised twice more in this way, using a 13% aqueous solution (w/w), and leaching the crystals with 200mL portions of water [Watters et al. J Am Chem Soc 78 4855 1956]. Similarly, EtOH can be added to precipitate the salt from a filtered 12-15% aqueous solution, the final solution containing ca 25% EtOH (v/v). Air drying should be at a relative humidity of 40-60%. Heat and vacuum drying should be avoided. [Quimby J Phys Chem 58 603 1954, Klement in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 547 1963.]