Production of sodium borohydride by using dynamic behaviors of protide at the extreme surface of magnesium particles

An advanced process for the production of sodium borohydride (NaBH4) as a hydrogen storage material was developed, which applied the dynamic hydriding and dehydriding behaviors of protide (H-) in Mg-H system under transitional temperature conditions. An abundant natural resource named borax (Na2B4O7-10H(2)O) and the anhydrous sodium metaborate (NaBO2) recovered from the "spent fuel" as NaBO2-4H(2)O were used as the starting material in the present process. Powder-state Mg played an important role in the transitional hydriding and dehydriding process where the gaseous hydrogen was converted to protide at the extreme surface of Mg to form NaBH4 in exchange with the simultaneous transition of oxygen in NaBO2 to form MgO. In the present process, the protide as the most reactive state among the four states of hydrogen is applied for the synthesis of NaBH4, which can exist in metal-hydrogen complexes, such as NaAlH4 and NaBH4. The NaBH4 yield was reached higher than 90% by a single batch process but was found to be largely dependent on the rate of temperature change and the particle size, i.e., the specific surface area of Mg particles. (c) 2005 Published by Elsevier B.V.