Sodium tripolyphosphate: properties and applications
Sodium tripolyphosphate (STPP, pentasodium triphosphate, Na₅P₃O₁₀) is an inorganic compound of the condensed phosphate class and one of the most important products of the phosphorus industry. Its molecular mass is 367.86. It appears as a white crystalline powder or granules with no odour. Its relative density is 2.49, and its melting point is 662 °C. Sodium tripolyphosphate is readily soluble in water: at 25 °C, solubility is 14.5 g per 100 g of water; at 80 °C — 23.25 g per 100 g. Aqueous solutions have a weakly alkaline reaction (1% solution — pH 9.7). The material is a low-hygroscopic product, which simplifies its storage and transportation.
Classification and Grades
In industry and trade, sodium tripolyphosphate is produced in two main forms: anhydrous and as a crystallohydrate (hexahydrate) Na₅P₃O₁₀·6H₂O. The anhydrous product, in turn, exists in two crystalline modifications: high-temperature (type I) and low-temperature (type II). Type I is characterised by a higher hydration rate and is widely used in synthetic detergent production. Type II, known as "slow-hydrolysing", is more stable and is used in compositions requiring a long shelf life. The ratio of phases I and II in the commercial product is controlled by the calcination temperature and can vary depending on the intended application.
Depending on purity and intended use, three main grades are distinguished: technical (industrial) sodium tripolyphosphate, used in detergents and water treatment; food-grade sodium tripolyphosphate, complying with sanitary standards; and high-purity sodium tripolyphosphate for special applications.
Regulatory Framework
In Russia and CIS countries, requirements for sodium tripolyphosphate are regulated by GOST 13493-86 "Sodium tripolyphosphate. Specifications". The standard applies to powdered sodium tripolyphosphate, which is a product of the processing of thermal orthophosphoric acid, and establishes requirements for the product manufactured for national economy needs and export. The standard normalises the mass fraction of total phosphorus pentoxide (P₂O₅), the mass fraction of sodium tripolyphosphate (Na₅P₃O₁₀), the mass fraction of iron (Fe) and the degree of whiteness. For food-grade sodium tripolyphosphate, additional requirements of sanitary norms and rules, as well as Codex Alimentarius standards, apply.
Production Technology
Industrial production of sodium tripolyphosphate is based on the neutralisation of orthophosphoric acid with alkaline reagents, followed by thermal treatment (calcination) of the resulting mixture of sodium orthophosphates. A typical commercial process involves reacting phosphoric acid and soda ash (sodium carbonate) in an aqueous solution until a sodium-to-phosphorus molar ratio of 5:3 is achieved, corresponding to the composition of "ortho liquor". The resulting solution is dried and calcined at temperatures sufficient to form anhydrous sodium tripolyphosphate. Drying and heating can be carried out sequentially in a rotary dryer or in a one-step operation by means of spray drying. STPP prepared in a rotary dryer consists of bulky masses which are crushed and screened to yield a granular material. Spray drying provides granular STPP directly.
The crystalline modification of the product (the ratio of phases I and II) is controlled by the calcination temperature: at temperatures around 450 °C, phase II predominantly forms; at 600 °C, phase I forms. A typical commercial product with a phase I/phase II ratio of 25:75 is manufactured in a rotary dryer at calcination temperatures of about 515-530 °C.
Applications
Sodium tripolyphosphate is a multifunctional product and finds application in a wide range of industries.
Synthetic detergents. This is the largest consumption area for sodium tripolyphosphate — it accounted for about 49.62% of the market in 2025. Sodium tripolyphosphate functions as the main component (builder) of synthetic detergents, providing water softening, maintaining pH at around 8.4, emulsifying fats and dispersing soils. It prevents the redeposition of soils on fabrics and enhances the action of surfactants.
Water treatment. Sodium tripolyphosphate is widely used for water softening, binding calcium, magnesium and iron ions, and preventing scale and deposits in boilers, heat exchangers and cooling systems. Thanks to its high complexing ability, it effectively eliminates water hardness, making it indispensable in industrial water treatment and circulating water supply systems.
Food industry. Food-grade sodium tripolyphosphate is used as a moisture-retaining agent, emulsifier, stabiliser and pH regulator. It is widely used in the production of meat and fish products to improve juiciness and texture, in the dairy industry, in processed cheese production, and in beverages and sauces. Food-grade sodium tripolyphosphate complies with safety requirements and is approved for use as a food additive in many countries, including Russia and China.
Ceramic and glass industry. Sodium tripolyphosphate is used in ceramic production as a deflocculant, reducing the viscosity of slips and improving the casting properties of ceramic masses. In the glass industry, it is used for fining glass melt and improving the quality of finished products.
Textile and leather industry. In the textile industry, sodium tripolyphosphate is used for water softening in dyeing and finishing fabrics, as well as a pigment dispersant. In the leather industry, it is used for degreasing and treating hides.
Oil and gas industry. Sodium tripolyphosphate is used in drilling fluids as a dispersant and for regulating rheological properties, as well as for treating oilfield equipment.
Other applications. Sodium tripolyphosphate is used in synthetic rubber production, in the pulp and paper industry, as a catalyst in organic synthesis, and for stabilising hydrogen peroxide solutions.
Global Market
Estimates of the global sodium tripolyphosphate market vary depending on the methodology. According to Mordor Intelligence, the market was valued at USD 1.25 billion in 2025, projected to reach USD 1.31 billion in 2026 and USD 1.64 billion by 2031 at a CAGR of 4.64%. According to Research and Markets, the market in 2026 is estimated at USD 2.4-2.7 billion with a projected growth of 4.5-5.5% per year through 2031. According to another report, the market was valued at USD 2.1 billion in 2025 and is projected to reach USD 3.6 billion by 2032 at a CAGR of 5.4%.
The Asia-Pacific region dominates the global market: in 2025, its share was 52.82%, and the region is forecast to post the fastest regional CAGR at 5.12% through 2031. China remains the largest producer and consumer, controlling over 60% of global capacity. Europe and North America show more moderate growth rates due to regulatory restrictions on phosphate content in household detergents.
Key market growth drivers are rising demand for synthetic detergents, the development of water treatment systems, the expansion of the food processing sector, and growth in ceramic and glass production. Main trends include tightening environmental regulations on phosphates in domestic wastewater, which is driving the transition to phosphate-free detergents in Europe and North America, while growth continues in developing countries.
Safety and Storage
Sodium tripolyphosphate belongs to substances with low toxicity. When working with it, personal protective equipment must be used: respirators, protective goggles and protective clothing. Storage is carried out in dry, well-ventilated areas, in hermetically sealed containers, away from moisture and heat sources. The product is low-hygroscopic; however, during prolonged storage in a humid environment, it may cake. Sodium tripolyphosphate is non-flammable and non-explosive.
Conclusion
Sodium tripolyphosphate remains one of the key products of the global phosphorus industry, providing for the production of synthetic detergents, water treatment, the food industry and ceramic production. Growing demand for detergents in developing countries, the expansion of water treatment systems and increased production of processed foods create sustained demand for this multifunctional product. China, the USA and European countries remain the leading players in the global sodium tripolyphosphate market, and the transition to phosphate-free detergents in developed countries is offset by growing consumption in the Asia-Pacific region.