High Purity Phosphotungstic Acid Preparation

Phosphotungstic acid is an important catalyst in the petrochemical industry. Its traditional synthesis method is ether acid extraction. This traditional method uses a low boiling organic compound, diethyl ether, as a complex extractant. The boiling point of ether is 34.5 °C, which is extremely volatile. Therefore, there are defects in safety and environmental pollution in the process of conventional synthesis of phosphotungstic acid.

In order to overcome the shortcomings of traditional process technology, researchers have proposed a method for preparing high-purity phosphotungstic acid, which has a very low phosphate content and is suitable for use as an acid catalyst. The method has the following steps:

(1)The sodium tungstate solution is contacted with the inorganic acid solution until the active tungstic acid precipitation is formed. The contact temperature is 0-60 ℃ and the molar ratio of H + to WO₄^{2 -} is 1~10.

(2)Contact the activated tungstic acid precipitation with the phosphoric acid solution until the activated tungstic acid precipitation dissolves completely and the phosphotungstic acid solution is obtained.

(3)High purity phosphotungstic acid was obtained by adding inorganic acid precipitator to phosphotungstic acid solution to precipitate, filter and crystallize phosphotungstic acid. The molar concentration of inorganic acid precipitator in the reaction system was 0.1-6 mol/L.

Examples are as follows:

50 grams of sodium tungstate were weighed, the concentration of sodium tungstate was 0.08 mol/L, 1875 ml, 25 grams of concentrated hydrochloric acid was weighed, the concentration of hydrochloric acid was 0.4 mol/L, 560 ml (H + and WO₄^{2 -} molar ratio was 1.5), the hydrochloric acid solution was poured into the glass beaker, at 45 degrees Celsius, the prepared sodium tungstate solution was dripped into the beaker, adding 4.0 after the completion of the dripping. Chlorinated aluminum chloride (molar concentration of 0.01mol/L), aging after 0.5 hours of filtration, washing.

The 41.5g active tungstic acid precipitate was added to 1000ml 0.06mol/L aqueous phosphoric acid solution and stirred for 2 hours at room temperature to obtain a clear and transparent phosphotungstic acid solution. The white phosphotungstic acid with 34.22 grams of high purity was obtained by adding 25 grams of hydrochloric acid with a weight concentration of 36% (molar concentration of 0.24 mol/L) to the solution at 74 ℃. The yield was 78.8%.

Compared with the existing technology, the advantages of the new process are: (1) low content of phosphate in the product, high purity, meet the requirements of acid catalyst; (2) simple process, high yield, conducive to reducing production costs; (3) production process does not use a large number of high concentration of strong acid, corrosion of equipment significantly reduced; (4) do not use flammability. The low boiling point organic extractant has obvious safety improvement in production operation and is suitable for large-scale industrial production.

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