Preparation of Sodium Pyrophosphate

1. Production method of food-grade acid sodium pyrophosphate with low gas evolution rate: phosphoric acid and sodium carbonate are neutralized, the molar ratio of phosphoric acid and sodium carbonate is 2:1, the reaction temperature is controlled at 80°C, aluminum dihydrogen phosphate is added in the neutralization stage, the pH of the neutralized solution is fine-tuned to 4.57 with phosphoric acid or sodium carbonate or water, and the specific gravity is controlled at 1.5, and then the neutralized solution is dried at 140-160°C, crushed, and passed through a 100-mesh sieve. The obtained powder is sent to a polymerization furnace for polymerization at 170-220°C for 1-4 hours, and cooled to obtain food-grade acid sodium pyrophosphate with low gas evolution rate.

The amount of aluminum dihydrogen phosphate added is 0.2-0.3% of the final product food-grade acid sodium pyrophosphate in terms of mass percentage.

2. Production method of high-gassing rate nutritional calcium-type food-grade sodium acid pyrophosphate

Phosphoric acid and ion membrane caustic soda are used as raw materials for neutralization reaction, wherein 81% to 85% of phosphoric acid is 10000L to 11000L, and about 48% of ion membrane caustic soda is 8050L to 8150L. Food-grade calcium salt and food-grade potassium salt are added in the reaction, and the addition amount is: calcium ion 0.2%-0.3%, potassium ion 0.1%-0.2%. The reaction temperature is controlled at 100℃ to 130℃, and the temperature is kept for 2h. The pH of the slurry is controlled to be 4.00 to 4.30, and the specific gravity is 1.40 to 1.50. The neutralized slurry after insulation is filtered and spray-dried. The temperature at the bottom of the drying tower is controlled at 120-140℃. The dried particles are sent to a polymerization furnace for polymerization at 180-200℃ for 1-3 hours, cooled, crushed and screened to obtain a high-gassing rate nutritional calcium-type food-grade sodium acid pyrophosphate product.

The obtained product has a Na2H2P2O7 content of 97.2%, a P2O5 content of 63.3%, a pH value of 4.02, a gas evolution rate (ROR) of 36.4, a calcium content of 2053ppm, and a potassium content of 1237ppm; 81% pass through 100 mesh and 60% pass through 200 mesh.