Sodium Tripolyphosphate STPP 94%

Sodium tripolyphosphate stpp, with the synonyms of pentasodium triphosphate, tripolyphosphate, is a type of amorphous water-soluble linear polyphosphate. For convenience, we usually call its abbreviation, STPP or stpp chemical. Sodium tripolyphosphate is a colourless salt, which exists both in the form of anhydrous and hexahydrate. With some special chemical properties, stpp can be widely used in detergents, water treatment, food processing industry and many other industrial fields.

Types: Anhydrous and hexahydrate. A condensed phosphate with a chain structure.

Anhydrous

This type can be divided into high temperature（Ⅱ） type and low temperature（Ⅰ） type.
Appearance: white crystal or crystalline powder.
The relative molecular mass is 367.86, the relative density is 2.49 and the melting point is 662℃. It is easily soluble in water, the solubility is 14.5g/100g at 25℃, 23.25g/100g at 80℃. The aqueous solution is weakly alkaline, and the PH of 1% aqueous solution is 9.7. STPP powder will gradually hydrolyze in aqueous solution to produce pyrophosphate or orthophosphate. STPP chemical has complexing effect on alkaline earth metals and heavy metal ions, and can soft water. It also has iron exchange capability, which can make the suspension become solution, as well as strong dispersibility. TypeⅠ has a higher hydrolysis rate than typeⅡ, so typeⅡ is also called slow hydrolysis type. TypeⅡ will transform to typeⅠat the temperature of 417℃.

Hexahydrate

Chemical formula: Na5P3O10·6H2O
Appearance: White prismatic crystals of triclinic orthorhombic system.
The relative density is 1.786, melting point is 53℃. It is soluble in water and can be weathered. This type of stpp chemical can be decomposed during recrystallization. Even if sealed, it can still be decomposed into sodium diphosphate at room temperature. When heated to 100℃, it will decompose into sodium diphosphate and original sodium phosphate. Therefore, the hexahydrate sodium tripolyphosphate can’t be stored and must be used immediately.

Thermal phosphoric acid process

This is a method of neutralization of thermal phosphoric acid and soda ash.
The main production processes of using thermal phosphoric acid to produce stpp powder include preparation, neutralization of phosphoric acid, dry polycondensation of sodium phosphate and recovery, discharge of tail gas.

• Neutralization operation. Acid first and then alkali, or alkali first and then acid. But no matter using which method, the feeding speed should be uniform and appropriate to prevent the overflow of slurry. 
• Alkali addition method. One is to add pre-prepared lye. Generally, add water carbon steel alkali dissolving tank, make the temperature is raised to 40℃ to 50℃ and stir. Then put a certain amount of soda ash to prepare a soda lye with 50% alkali content and put it into the neutralization tank for phosphoric acid using. The other is the neutralization of solid soda ash. Phosphoric acid is measured from the high tank and put into the stainless steel neutralization tank, start the mixer and add solid soda ash to H3PO4 for neutralization.
• Control the neutralization degree. After all the materials are put in, boil for 30 minutes to make the neutralization reaction complete. Control the end point of the reaction PH value to 6.5-7, the relative density of the neutralization liquid slurry is 1.5-1.6. Then add appropriate amount of NH4NO3 to prepare a qualified sodium orthophosphate neutralization solution for polymerization. The neutralized mixed sodium orthophosphate salt solution is dried and obtain powdery sodium phosphate. Then enter the rotary polymerization furnace for calcination polymerization. The sodium tripolyphosphate produced by polymerization is cooled to become the finished stpp powder chemical.

Wet phosphoric acid process

This is a method of neutralization of wet process phosphoric acid and soda ash. Wet-process phosphoric acid must undergo purification treatments such as, defluorination and desulfurization. Because the impurities won’t only reduce the stpp content, but also play a counter-catalytic effect on the dehydration polycondensation process. When necessary, use Na2S or P2S5 to remove arsenic and heavy metal ions. The drying polymerization stage of this method can be one-step method or two-step method.