1. Sodium dihydrogen phosphate method:
Neutralize the soda ash solution with phosphoric acid at 80～100℃ for 2h, the resulting sodium dihydrogen phosphate solution is evaporated, concentrated, cooled and crystallized to obtain sodium dihydrogen phosphate dihydrate, heated to 110～230℃ to remove 2 crystals Water, continue to heat to remove structural water, and further heat to 620 ° C to dehydrate, the resulting sodium metaphosphate melt, and polymerize into sodium hexametaphosphate. Then unloaded, quenched from 650°C to 60-80°C, tableted, and pulverized to obtain the finished product of sodium hexametaphosphate.
2. Phosphorus pentoxide method:
The phosphorus pentoxide obtained by burning, oxidizing and cooling yellow phosphorus in a dry air stream is mixed with soda ash in a certain proportion (Na2O:P2O5=1～1.1). The mixed powder is indirectly heated in a graphite crucible to dehydrate and fuse, and the resulting sodium hexametaphosphate melt is quenched, tableted and pulverized to obtain an industrial sodium hexametaphosphate product.
3. Heat the reagent sodium dihydrogen phosphate to 700～900℃ to melt, when the melt is completely transparent and the internal bubbles disappear, then quench to 60～80℃ to obtain a flake glass product, which is sodium hexametaphosphate.
4. The reagent sodium dihydrogen phosphate is heated to 250°C and quenched to obtain the dimer of sodium metaphosphate; heated to 650°C and quenched to obtain sodium hexametaphosphate.
5. Phosphoric anhydride method After heating and melting yellow phosphorus, it is sent to an oxidative combustion furnace, and the oxidative combustion reaction is carried out with oxygen in the dry air to generate an intermediate product, phosphoric anhydride. After mixing phosphoric anhydride and soda ash, after high temperature polymerization reaction, quenching tablet to obtain sheet sodium hexametaphosphate; after crushing, powdery sodium hexametaphosphate can be obtained.
6. Neutralization polymerization method:
The technological process is as follows: phosphoric acid and liquid sodium hydroxide are respectively passed through their respective batch controllers (controlling the input amount of liquid alkali and acid in each batch, automatic batching, and the feeding speed can be adjusted arbitrarily within the range of 0~20L/min), as required The added amount is continuously and accurately added to the neutralization tank for neutralization reaction. After the reaction is completed, the pH value reaches 4 to 4.4, and disodium hydrogen phosphate is generated, which is sent to the high-level tank through the neutralization liquid pump.
A certain amount of disodium hydrogen phosphate is continuously and evenly sent to the dryer for drying to obtain flake disodium hydrogen phosphate with a specified moisture content, and then continuously sent to the high temperature ( 750～850℃) in a polymerization furnace, melt and polymerize disodium hydrogen phosphate; the molten material flows out continuously from the polymerization furnace, and is quenched and pressed into tablets to obtain flaky sodium hexametaphosphate, which is crushed and screened to obtain the product.
