Preparation of trisodium pyrophosphate_industrial additives

Background and overview^[1]

Trisodium monohydrogendiphosphate is a moisture retaining agent and one of the five new food additives approved by the Ministry of Health. It is a member of the pyrophosphate family with the best water-retaining properties and has better solubility than alkaline pyrophosphates due to its neutral pH.

Preparation^[1-2]

Report 1,

Using disodium dihydrogen pyrophosphate and sodium hydroxide with a molar ratio of 1:1 as raw materials, according to the chemical reaction formula: Na₂H₂P ₂O₇+NaOH=Na₃HP₂O₇+H₂O, to obtain trisodium pyrophosphate monohydrogen.

First, heat the process water in the reaction kettle to 45°C. Cabot White Carbon Black adds disodium dihydrogen pyrophosphate into the reaction kettle to dissolve it, and then slowly adds 45% sodium hydroxide solution to it. Carry out neutralization reaction (the weight ratio of solid to liquid in the neutralization liquid is 3:7). This reaction process is an exothermic reaction. After the reaction is completed, maintain the temperature of the neutralization liquid at 85°C for high-temperature crystallization, and culture as needed depending on the crystallization situation. Large and small crystals. The temperature of the solution containing crystals should be kept above 70°C.

Then the crystallization liquid is centrifuged and filtered, the thickness of the feed filter cake is controlled at 3.5cm, and the centrifugal speed is controlled at 950-1100 rpm. The dry filter cake is a trisodium pyrophosphate monohydrate product containing 2% moisture on the surface. The filtrate contains less than 5% of the target trisodium pyrophosphate monohydrate, and the balance is water. The filtrate can be returned to the reactor for recycling without contaminating the product.

The surface of trisodium pyrophosphate monohydrate containing 2% moisture can be dried with a round emulsifier disc dryer. The air outlet temperature of the disc dryer should be controlled at 95°C. The moisture content of the obtained trisodium pyrophosphate monohydrate product is controlled below 1.0%.

Report 2,

Add a certain amount of phosphoric acid into the neutralization pot, continuously add ion membrane caustic soda until Na:P is 1.50-1.51, control the slurry concentration at 30-60%, the reaction temperature is 80-120°C, and keep the temperature for 0.5-1h. The solution obtained by the reaction is spray-dried at 140-180°C, and the dried powder is sent to a polymerization furnace for polymerization. The polymerization temperature is controlled at 170-250°C, and the reaction is carried out for 2 hours to obtain the trisodium monohydrogen pyrophosphate product.

The equation of the entire reaction process is:

3NaOH+2H₃PO4→Na₂HPO₄+NaH₂PO₄+3H₂O

Na₂HPO₄+NaH₂PO₄→Na₃ HP₂O₇+H₂O