An improved purification of NaBH_4 from storage-induced impurities by ammonia assisted crystallization in diglyme

摘要

It was shown by ATR FTIR, XRD and B-11 MAS NMR methods that increasing contents of sodium polyborate and sodium carbonate impurities were formed in solid sodium borohydride upon its storage and contact with the air. To increase the NaBH4 purity after storage, it was re-crystallized in diglyme using the well-known Brown's procedure. The purification efficiency was further improved by ammonia treatment during NaBH4 dissolution. It was found that the advantages of using the gaseous ammonia consisted in an increased NaBH4 solubility in diglyme and a more efficient reduction in the content of impurities to form a material consisting of uniform highly dispersed particles of the hydride having a regular cubic shape. It was found for the process of catalytic hydrolysis of NaBH4 that the rate of hydrogen generation and its yield increased with the decreasing content of impurities. These results demonstrate the importance of investigations aimed at improving the existing methods of NaBH4 purification and creating new ones. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.