Potassium pyrophosphate has all the properties of condensed phosphate. The solid at equilibrium in a saturated solution is K4P2O7•3H2O. Anhydrous potassium pyrophosphate has two configurations. The transition temperature from type I to type II is 278°C. Potassium pyrophosphate has similar properties to sodium pyrophosphate, but has greater solubility and can chelate with alkaline earth metals and heavy metal ions; it can form stable complexes with Ca2+ and Mg2+ in hard water to soften hard water and improve washing ability. Remove dirt.
Physical and chemical properties
Potassium pyrophosphate, also known as tetrapotassium pyrophosphate, is produced by melting dipotassium hydrogen phosphate and losing water molecules. It is a white crystalline powder or granule at room temperature. It is highly hygroscopic in the air. Methoxybutanol is extremely hygroscopic. Easily soluble in water, but insoluble in ethanol. The aqueous solution is alkaline and has the effect of inhibiting food spoilage and fermentation. The pH value of 1% aqueous solution is about 10.5. The solubility of potassium pyrophosphate in 100g of water at 25°C is 187g. In acid or It is hydrolyzed into potassium phosphate in an alkaline solution and mixed with water to form a viscous slurry. It is often used in combination with other condensed phosphates, such as potassium pyrophosphate 10%, sodium pyrophosphate 10%, potassium polyphosphate 30%, sodium polyphosphate 30%, sodium metaphosphate 20% to make ham and sausage adhesive. Agents are usually used to prevent the formation of struvite in canned aquatic products, prevent discoloration of canned fruits, increase the expansion of ice cream, extract the amount of coffee raw materials, increase the yield of ham and sausages, enhance the water-holding capacity of fish, improve the taste of noodles and increase the yield. To prevent cheese from aging, etc., in order to make the electroplating layer smooth and firm, the formula of the electroplating solution in industrial production is often very complex. In the past, cyanide was commonly used as a complexing agent to prepare electroplating solutions. However, because CN- is highly toxic, it does great harm to the health of electroplating workers. At the same time, the discharge of sewage and waste gas containing CN- also seriously pollutes the environment. Therefore, cyanide-free electroplating is now mainly used for electroplating, and the complexing agent that replaces cyanide is potassium pyrophosphate.
Synthesis method of potassium pyrophosphate
Neutralization and calcination method
Potassium pyrophosphate is produced using phosphoric acid and potassium hydroxide as raw materials. The reaction formula is as follows:
H3PO4+2KOH→K2HPO4+2H2O
2K2HPO4→K4P2O7+H2O
Potassium hydroxide and phosphoric acid are reacted to form a dipotassium hydrogen phosphate solution, which is spray-dried to obtain a powder, which is then roasted in a rotary kiln at 350°C to obtain the product. If a solution product is required, the powder can be dissolved in deionized water. Food-grade potassium pyrophosphate requires food-grade phosphoric acid as raw material.
Raw material consumption: tons/ton of product
Phosphoric acid (H3PO4 85%) 0.730
Potash (KOH 95%) 0.722
It can also be obtained by melting dipotassium hydrogen phosphate and losing water molecules.
Polyurethane raw materialsMain uses of potassium pyrophosphate
Potassium pyrophosphate is mainly used as a cyanide-free electroplating, industrial and household washing aid, especially as a liquid detergent with broad market prospects. In addition, it is used as a dispersant and buffer for ceramic clays, synthetic rubbers, dyes, soaps and pigments. In the bleaching and dyeing industry, it is used to remove a small amount of ferric ions in water to improve the quality of dyeing and bleaching. In the food industry, it is used as an emulsifier, texture improver, and chelating agent. It is also used as a raw material for alkaline water used in flour products. It is often used in combination with other condensed phosphates. It is usually used to prevent struvite formation in canned aquatic products and prevent discoloration of canned food in fruit shops. Improve the expansion of ice cream, the yield of ham and sausage, the water holding capacity of ground fish; improve the taste of noodles and increase the yield, prevent the aging of cheese, etc.
When hydrogen peroxide is used as an oxidant to bleach leather products, it is often used as a stabilizer, and the effect is remarkable. In the laundry industry, there are two specific conditions under which potassium pyrophosphate must be used. One is a heavy-duty liquid detergent to control foam, and the other is a metal surface cleaning agent. This cleaning agent is alkaline and helps protect the metal surface.
