Preparation Of Potassium Borohydride By Double Decomposition Method

Alkali metal borohydride is a kind of hydrogen storage material with high hydrogen storage density that can provide hydrogen circularly. Fuel cells which use borohydride as hydrogen source can be used as portable power source and power supply of vehicles. One of the main limitations of applying borohydride-based fuel cell into industry currently is the expensive prices caused by borohydride production process. Solid sodium borohydride production process exists problems, such as high hydrolysis loss and equipment operational load, during cycling process of mother liquor. For the purpose of improving the production process of sodium borohydride by Schlesinger method, the reactive crystallization process of potassium borohydride by double decomposition method is studied to deal with the mother liquor from sodium borohydride crystallization process, in order to reduce hydrolysis loss, rich product range, reduce polluting emissions and lower production costs.The feasibility of preparation of potassium borohydride through double decomposition method is estimated by use of borohydride-hydroxide-water ternary system phase diagram. Using mother liquor of sodium borohydride crystallization process and precipitate potassium hydroxide as raw materials, potassium borohydride is prepared through double decomposition reaction. The influences of molar ratio of potassium hydroxide and sodium borohydride, reaction temperature, crystallization temperature, stirring rate and solvent evaporation are respectively discussed. The result shows that, feeding the precipitate potassium hydroxide as nearly saturated solution, controlling the molar ratio of 1.10, reaction temperature of 60 °C, crystallization temperature of 10 °C, stirring rate of 500 rpm, without evaporation of the solvent, the product can be gained with alkali content within 8 wt% and yield over 80%.Washing process based on methanol as washing detergent is also studied to improve product purity. The result shows that, using anhydrous methanol as washing detergent, the crude product with alkali content below 8.6 wt% which is washed by 200 mL methanol / 100 g solids one time can be purified into a fine product with purity over 97% and yield over 99%, which is accord with HG/T 3584-2011 chemical industry standard.