High Purity Phosphotungstic Acid Preparation Method

Heteropoly acid is one of the most active catalysts in acid catalytic reaction and redox reaction. The hydration and esterification of olefin, the etherification of epoxides, the condensation reaction of olefin and aldehyde, alkylation, alkene epoxidation, alkyl alkylation, etc. have good catalytic properties. In heteropoly acid, phosphotungstic acid H₃PW₁₂O₄₀ nH₂O is the most widely used, its purity affects the catalytic system directly. Therefore, it is especially important to prepare high purity phosphotungstic acid.

Traditional methods generally use scheelite as a raw material to prepare phosphotungstic acid, however, scheelite often contains a large number of other impurity ions, such as iron ions, manganese ions, calcium ions, sulfate ions, phosphate ions, etc. It is difficult to remove the phosphotungstic acid on the surface of phosphotungstic acid during the crystallization of phosphotungstic acid. For this reason, some scholars have provided a purification method of phosphotungstic acid crystal. The steps are as follows:

Step one: the crystal of industrial phosphotungstic acid is dissolved in water, and the inorganic acid is added to the solution of phosphotungstic acid containing inorganic acid. The concentration of tungsten trioxide is 50-150g/L, and the volume molar concentration of the inorganic acid is 0.5 ~ 6mol/L.

Step two: in step 1, an organic alcohol extractant with a volume concentration of 5-50% is extracted in the solution of phosphotungstic acid containing inorganic acid, and the volume ratio of the two phase is oil phase = 1:1-10:1, and the organic phase containing tungsten is obtained.

Step three: extract the tungsten loaded organic phase from step two by using the volumetric ratio as the oil phase: water phase = 3:1-10:1 distilled water, and get the stripping solution.

Step four: obtain the high purity phosphotungstic acid crystal by heating the evaporating crystal or spray drying with the stripping solution obtained in step three.

For example, 568g industrial phosphotungstic acid (no molybdenum impurity) is dissolved in water, then added hydrochloric acid, so that the concentration of tungsten trioxide 80g/L and hydrochloric acid in solution is 3mol/L. The secondary octanol of 15% was used as the extractant, the diluent was sulfonated kerosene, and then the four stage countercurrent extraction was carried out, and the loaded organic phase was extracted with distilled water as the reagents, and the five stage countercurrent extraction was carried out. The high purity white phosphotungstic acid 542g is obtained by evaporation crystallization. The yield is 95.4%. This method is simple in process, short in process, low in preparation cost, no pollution to the environment and easy to be produced in large scale.

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