Sodium Hexametaphosphate food grade

Outline

Sodium hexametaphosphate is a kind of sodium metaphosphate polymers. It is also known as "polyvinylidene sodium," "sodium multiple metaphosphate", "sodium metaphosphate vitreous body", and "Graham salt". It is a colorless transparent glass-like solid or white powder with greater solubility but low dissolving rate in water. Its aqueous solution exhibits acidic property. Its complex of divalent metal ion is relatively more stable than the complexes of mono-valent metal ion. It can easily be hydrolyzed to orthophosphate in warm water, acid or alkali solution. Hexametaphosphate has a relative strong hygroscopicity with being sticky after absorbing moisture. For certain metal ions (e.g., calcium, magnesium, etc.), it has the ability to form soluble complexes, and thus being able to being used for demineralizing water. It can also from precipitate with lead and silver ions with precipitate being re-dissolved in excess amount of sodium hexametaphosphate solution to form a complex salt. Its barium salt can also form complexes with the sodium hexametaphosphate. It can be used as a kind of highly efficient water softener of power stations, rolling stock boiler water; as detergent additive, as corrosion-controlling or anti-corrosion agents; as cement hardening accelerator; as streptomycin purification agent, and the cleaning agent of textile industry and dyeing industry. It can also be used as a kind of sedative drug, preservative, stabilizer, and fruit juice precipitant in food industry. In the oil industry, it is used for control of drilling pipe rust and adjusting the viscosity of oil drilling mud. It also has applications in fabric dyeing, tanning, paper, color film, soil analysis, radiation chemistry and analytical chemistry and other departments. Our GB2760-1996 provisions that hexametaphosphate is allowable food additives (water retention agent) for being used for canned food, fruit juice drinks, dairy products, soy products; it can also be used as a dye dispersant, and water treatment agent. The above information is edited by the lookchem of Dai Xiongfeng.

Toxicity

Adl 0~70 mg/kg (in terms of phosphorus); LD50:4g/kg (rat, oral). According to the provision of the GB2760-86, it is allowed for being applied to canned food, fruit juice drinks, dairy products, soy milk as quality improver; the maximum usage amount is 1.0 g/kg. When being used as composite phosphate, calculated as the total phosphate, the canned meat products shall not exceed 1.0 g/kg; for condensation of milk, it shall not exceed 0.50 g/kg.

Production method

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 fro 650 ℃ to 60~80 ℃ for flaking, and crush to obtain the hexametaphosphate products. Its reaction formula is as below: Na2CO3 + 2H3PO4 + H2O → 2NaH2PO4?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

Preparation

Sodium hexametaphosphate is prepared by heating monosodium phosphate (NaH2PO4) rapidly to a clear melt, which occurs slightly above 625°C. Rapid chilling of this melt produces a very soluble glass, which is then crushed or milled.

Agricultural Uses

Sodium metaphosphate is the salt of metaphosphoric acid having a molecular formula (NaPO3)n, where n ranges from 3 to 10 (for cyclic molecules) or may be much larger (for polymers). Cyclic molecules have alternate phosphorus and oxygen atoms in the rings and start with trimetaphosphate (NaPO3)3 to at least decametaphosphate. Sodium hexametaphosphate may be a polymer where n is between 10 and 20. Vitreous sodium phosphates have a Na2O:P2O5 ratio near unity and are called Graham's salts. The average number of phosphorus atoms in these vitreous glasses ranges from 25 to infinity.

Industrial uses

Sodium hexametaphosphate (SHMP) or water glass Na6P6O18 is basically the salt of metaphosphoric acid. SHMP is difficult to dissolve. By mixing SHMP for 1-3 h, a solution of 8-10% can be obtained. The pH of this solution is about 5. Because of a weak acid reaction, the SHMP reacts with cations of bivalent metals forming Na2MeP6O18 or Na4MeP6O18. In the presence of oxygen, SHMP slowly decomposes into pyrophosphate and orthophosphate.

Safety Profile

Poison by intravenous route. Moderately toxic by intraperitoneal and subcutaneous routes. Wdly toxic by ingestion. When heated to decomposition it emits toxic fumes of PO, and Na2O. See also PHOSPHATES.

Properties and Applications

TEST ITEMS SPECIFICATION APPEARANCE WHITE POWDER TOTAL PHOSPHATE(P 2 O 5 ) 68.0% min INACTIVE PHOSPHATE (P 2 O 5 ) 7.5% max WATER-INSOLUBLE MATTER 0.05% max Fe CONTENT 0.05% max pH VALUE 1% AQUEOUS SOLUTION 5.8-7.3 As - Pb - F -

TEST ITEMS

SPECIFICATION

APPEARANCE

WHITE POWDER

TOTAL PHOSPHATE(P 2 O 5 )

68.0% min

INACTIVE PHOSPHATE (P 2 O 5 )

7.5% max

WATER-INSOLUBLE MATTER

0.05% max

Fe CONTENT

0.05% max

pH VALUE 1% AQUEOUS SOLUTION

5.8-7.3

As

-

Pb

-

F

-