The purpose of the present invention is to overcome the deficiency of existing production method, provide a kind of production method of sodium monofluorophosphate with low energy consumption, easy to get raw material, less impurities in the product introduced in the production process, and low product production cost.
The object of the present invention is achieved by the following technical solutions: with phosphoric acid and alkali (soda ash or caustic soda) as raw materials, the ratio of the two is sodium/phosphorus (Na/P) mol ratio=1: 1 ± 0.005, through neutralization, drying Polymerization, polymer polymeric sodium phosphate and sodium fluoride are mixed and melted to obtain monofluorophosphate sodium product, the ratio of polymeric sodium phosphate to sodium fluoride is: phosphorus/fluorine (P/F) molar ratio=1.000±0.005. There is no need to prepare monosodium metaphosphate, and sodium fluoride is used as the fluorinating agent for continuous production.
Its production method includes the following processes: 1. Polymerized phosphate preparation: feed alkali (soda ash or caustic soda) and phosphoric acid into a horizontal stirred wall scraping reactor, control the reaction temperature to be less than 95°C, and use the heat of reaction to evaporate a part of the water. After the neutralization is completed, the jacket of the reactor is heated up for dehydration and polymerization, and the temperature of the reactant rises to 250°C to 350°C and is kept for 45 to 60 minutes. The obtained polymerized sodium phosphate is in the form of acid pyrophosphate and a small part of metaphosphate Existence, moisture<0.2%.
2. Mixing of sodium fluoride: polymerized sodium phosphate and sodium fluoride are fed into the pulverizer at the same time for crushing and mixing, the molar ratio of polymerized sodium phosphate and sodium fluoride is controlled to be 1-10:10-1, and the pulverized material enters a mixer Homogenize.
3. Melting reaction: After homogenization, the mixture is continuously fed into the upper part of a carbonaceous reactor heated by power frequency, and the material is extruded from the bottom by the gravity of the upper material through the melting reaction. The residence time of the melting reaction is 14 to 18 minutes. The melt in the discharge pipe is solidified and blocked, and the discharge pipe is also equipped with a power frequency heating source. Control the temperature of the material at the outlet to 680°C to 730°C, feed the mixture continuously, and discharge the product continuously.
4. The melt is cooled and formed into flakes, crushed and sieved to obtain the product.
Compared with the prior art, the present invention has the following advantages: 1. The raw materials of phosphoric acid and alkali (soda ash or caustic soda) are easy to get and the cost is low.
2. Compared with sodium metaphosphate as raw material, the energy consumption is low, impurities are not easily introduced in the production process, and the product whiteness is high.
3. Compared with the neutralization method, there is no corrosion problem, and the investment in production equipment is small.
4. Compared with the fluorination method, there is no problem of gas treatment and environmental pollution, and it is a clean production process.
5. The production method of the present invention is easy for continuous production, and the production control is simple.