Solid Phase Method of Ammonium Metatungstate

Ammonium metatungstate is an important tungsten intermediate compound. It is mainly used for the manufacture of tungsten carbide and other tungsten compounds in the petrochemical industry. It is an important precursor for the production of tungsten carbide catalysts. Tungsten carbide is widely used because of its catalytic activity similar to that of platinum metal in catalytic reactions such as alkane dehydrogenation to olefins, olefin isomerization, and hydrogenation reactions.

In recent years, with the rapid development of the petrochemical industry, the use of tungsten carbide and other tungsten-based catalysts has increased rapidly, and the amount of ammonium metatungstate has also grown rapidly. Like APT, AMT's manufacturing method is also not related to the solid phase method and the liquid phase method. The two conversion methods have their own merits. Here, the solid phase method is mainly introduced.

The solid phase method uses ammonium paratungstate (APT) as a raw material, and thermally pyrolyzes APT to lose part of ammonia and crystal water, and converts it into water-soluble ammonium metatungstate. After filtration to remove insoluble impurities, it is crystallized by evaporation or spray-dried. Ammonium metatungstate (AMT) was obtained. The main steps are:

A.Pyrolysis step: The amount of ammonium paratungstate as raw material, quantitative addition of thermal cracking equipment, at a temperature of 240-290 ℃ roasting 2-3 times, each firing time 45-75min, controlling the total roasting heat weight loss rate in 6.0-8.0%, obtained ammonium pyrotungstate thermal cracking products;

B.Pulping conversion step: The obtained ammonium pyraritanate thermal cracking product is dissolved in deionized water and converted at 90-95 ℃ and pH 3.0-4.0. After the conversion is complete, it is aged, cooled, clarified, filtered, and insoluble. Substances, obtained conversion filtrate;

C.Evaporation concentration step: The obtained conversion filtrate is concentrated by evaporation to keep the solution at pH 3.0-4.0. When the solution density is 1.8-2.0 g/cm³, it is stopped, aged, cooled, clarified, filtered to remove insoluble matter, to obtain a concentrate;

D.Spray drying step: The concentrated liquid obtained in step C was transferred into a spray drying apparatus for drying to obtain a hollow spherical ammonium metatungstate product.

Preparation of ammonium metatungstate by solid-phase method has high purity, good solubility, short process flow, high conversion rate, low production cost, low impurity content, and hollow spherical shape. In accordance with the requirements of tungsten carbide and other tungsten catalysts on the precursor morphology, the solid phase method requires very high control parameters for the cracking time and pyrolysis temperature, which requires considerable experience.

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