Vapor phase batch hydrolysis of NaBH4 at elevated temperature and pressure

Complex chemical hydrides are a means to store hydrogen in the solid state near ambient temperatures and pressures. Hydrolysis of hydrides has the potential to provide high gravimetric and volumetric energy densities if water consumption can be minimized. At low temperatures (110∼140 °C), the product of NaBH4 hydrolysis is NaBO2·2H2O (dihydrate), consuming 2 mol of unutilized water. The objective of this work was to conduct water vapor hydrolysis of NaBH4 at elevated pressure and temperature above 150 °C. It was hypothesized that this would yield a solid borate with decreased water bound in the crystal structure. A series of batch reactions were conducted to verify the hypothesis. Experimental characterization of the sodium metaborate byproducts indicated that the primary product of water vapor hydrolysis was NaBO2·1/3H2O (hemihydrate) under a variety of reaction conditions. For the most cases, the conversion of NaBH4 approached 100%.