Extraction Method Producing Phosphotungstic Acid

Phosphotungstic acid (H3PW12O40·nH2O) has wide application in heteropolyacids, it is also the most typical catalyst. For the hydration and esterification of olefins, the etherification of epoxides, the condensation reaction of olefins and aldehydes, the alkylation of olefins and the epoxidation of olefins and alkylaromatics have good catalytic performance.

The traditional synthesis method is the ether-based extraction method. This traditional method uses a low-boiling organic compound-ether as the complexing agent. The boiling point of the ether is 34.5 ° C., which is extremely volatile. Therefore, the traditional extraction process of phosphotungstic acid has safety and pollution of the environment defects. In order to solve the above technical problems, some scholars provide a process for preparing phosphotungstic acid using sodium tungstate as raw material, which comprises the following steps:

Dissolve sodium tungstate in water, then add phosphorus acid and hydrochloric acid to obtain mixing aqueous containing phosphorus tungstic acid, among which contains tungsten trioxide 100g/L, phosphorus 20g/L, hydrochloric acid 2.5mol/L. Using 15% sec-octanol as extractant and diluent as sulfonated kerosene, and then carrying out four-stage countercurrent extraction with the volume ratio of two phases being O / A (oil phase / water phase) = 1: 1 to obtain the loaded organic phase. The organic phase was loaded with distilled water as the stripping reagent and subjected to five-stage counter-current stripping. The volume ratio of two phases was O / A (oil / water) = 5: 1. Stripping solution of tungsten trioxide concentration 479.4g / L, white crystalline tungstophosphoric acid crystals were evaporated and crystallized. Based on the concentration of tungsten trioxide extracted from the stripping solution, the yield was 95.9%.

The emphasis of the process is to use an alcohol extractant to achieve efficient extraction of phosphotungstic acid by adjusting the concentration of the mineral acid in the phosphotungstic acid solution. Since the extractant used is a neutral extractant, only the phosphotungstic acid molecules are extracted, and impurity cations such as sodium ions and iron ions are not extracted, and impurity anions such as sulfate ions, phosphate ions, chloride ions and the like are not extracted. The effect is very good, so it does not form the entrainment of the aqueous solution. Of particular importance is that the resulting loaded organic phase can be directly stripped with distilled water, and the stripped organic phase can be directly reused without further treatment.

Therefore, compared with the traditional method, the extraction process is simple, the process is short, the preparation cost is low, is also environmental friendly, the industrial production is easy and can realize large-scale.

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