Study on regeneration of spent-sodium borohydride

• Main Authors: Hsiao-Ting Yen, 顏孝庭
• Other Authors: Bing-Hung Chen
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/81211792486316191882

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === With increasing awareness in outcomes of severe climate changes and global warming arising from excessive emission of greenhouse gases, such as carbon dioxide from excessive usage of fossil fuels, since the Industrial Revolution, urgent measures in developing alternative and renewable energies have been implemented by mankind. One strategy to amend this situation is development of hydrogen energy, such as hydrogen fuel cell and hydrogen-powered cars. However, the key to realize the hydrogen economics is the successful development of affordable hydrogen storage materials having enough energy-storage density. Among various hydrogen storage materials, chemical hydrides such as sodium borohydride are of the most promising candidates. Sodium borohydride is liquid and relatively stable at room temperature, and evolves hydrogen of high purity that could be consumed directly by subsequent fuel cell devices. Unfortunately, the cost of using sodium borohydrides based on per unit of energy is still quite expensive compared to fossil fuels. That is, cost-down of such materials is of critical importance to its successful applications. In this project, we aim to regenerate sodium borohydride from its spent product, i.e. sodium metaborate, to reduce its cost and to ease any environmental concern on disposal of waste. Our proposal is to convert the sodium metaborate to the intermediate as trimethyl borate and, subsequently, follow the Schlesinger method to regenerate sodium borohydride. Currently, with evidence shown by GC and FT-IR, we have successfully converted sodium metaborate to trimethyl borate. However, presence of water as the byproduct in esterification of boric acid greatly reduces the yield of trimethyl borate. After that, we try to synthesize sodium borohydride via Schlesinger method. By the evidence of NMR analysis, we have successfully regenerated sodium borohydride from trimethyl borate. The corresponding yield is about 60% from the iodimetry analysis data. On the other hand, through NMR and XRD analysis, it has been proved that sodium borohydride can be formed by ball-milling sodium metaborate with magnesium hydride at room temperature. The yields of sodium borohydride can be improved by increasing ball milling duration, and a maximum yield of 76% could be reached at present.