Background and overview[1-2]
Hexafluorophosphate series is a very important class of inorganic fluoride salts. Among them, ammonium hexafluorophosphate is an important type of hexafluorophosphate. It can be used to prepare other hexafluorophosphates and is also a preventive agent. Important substances in dental caries. Ammonium hexafluorophosphate is colorless square crystals or rectangular flake or thick plate crystals. It does not corrode glass at room temperature and does not melt or decompose under strong heat. Relative density 2.180. Easily soluble in water, soluble in methanol, ethanol and acetone.
Preparation[1]
A preparation method of ammonium hexafluorophosphate, the preparation method includes the following steps:
Step S1: Pour frozen salt water into the jacket of the reaction kettle, add solid ammonium bifluoride and anhydrous hydrogen fluoride to the reaction kettle in sequence, stir, adjust the vacuum, and add dropwise into the reaction kettle. Phosphorus oxychloride, continue stirring to obtain the first-level reaction liquid. It should be noted that when adding the phosphorus oxychloride dropwise, the dropping operation needs to be carried out slowly;
Step S2, empty the frozen brine in the jacket, add hot water, and adjust the degree of vacuum. It should be noted that the hot water is used to mix the hydrochloric acid solution and the first-level reaction solution. The hydrogen fluoride solution is volatilized (acid discharged), and a certain amount of methanol is added to the reaction kettle to dissolve the primary reactant to obtain a secondary reaction liquid. It should be noted that the methanol can dissolve the hexafluorophosphoric acid Ammonium and other impurities dissolve;
Cabot Carbon Black
Step S3, add ammonia water dropwise in the reaction kettle, and obtain a third-level reaction liquid after sufficient reaction. It should be noted that the ammonia water can react with the iron ions in the second-level reaction liquid. React with ferrous ions to form ferric hydroxide and ferrous hydroxide precipitates, perform solid-liquid separation of the third-level reaction liquid, and adjust the pH to neutral with ammonia water to obtain the precipitation and the fourth-level reaction liquid;
Step S4, transfer the fourth-stage reaction liquid to a concentration kettle for concentration under reduced pressure to obtain methanol gas and ammonium hexafluorophosphate mother liquor. It should be noted that the methanol gas is condensed under the action of the condenser A methanol solution is formed, and the methanol solution continues to participate in the operation in step S2 for recycling the methanol solution;
Step S5: After a crystal film appears on the liquid surface of the ammonium hexafluorophosphate mother liquor, the ammonium hexafluorophosphate mother liquor is transferred to a crystallization kettle, cooled for crystallization, and centrifuged to obtain the finished ammonium hexafluorophosphate and filtrate.
It should be noted that in step S5, the filtrate is transferred to the concentration kettle for concentration under reduced pressure to obtain a concentrated filtrate. When a crystal film appears on the liquid surface of the concentrated filtrate, repeat the process. Describe the operation in step S5.
Specifically, the overall reaction equation of this method is:
NH4HF2+4HF+POCl3→NH4PF6+3HCl↑+H2O
