Recycling Sodium Metaborate to Sodium Borohydride Using Wind-Solar Energy System for Direct Borohydride Fuel Cell

Abstract

One of the major issues with DBFC is availability of Sodium borohydride and economics of converting sodium metaborate, product of reactions in DBFC, to sodium borohydide. Work has been done by L Kong et all [1] to convert Sodium metaborate to sodium borohydride using magnesium hydride. The work presented here discusses various other possibilities to recycle NaBO2 and how it could be coupled with existing wind and solar energy systems to make it economically viable. A little variation form Brown Schlesinger process [2], commonly used to produce sodium borohydide is proposed and with discussion on possible renewable energy system are presented below. a] Steam reforming of methane : Solar energy can be utilized to convert water into steam. Also possibilities of using geothermal energy where available cannot be ruled out. b] Using sea water to get sodium metal: Electrolysis of seawater enables us to have this process on board on offshore wind mills. Also presence of other salts in sea like calcium chloride favor electrolysis. c] Hydrolysis of NaBO2 to make boric acid: This is the deviation from the exiting Brown Schlesinger and thermoeconomics is under investigation. d] Boric acid reacts with methanol to give trimethylborate. e] Sodium metal in presence of hydrogen from steam reforming react to give sodium hydride. f] Sodium hydride and trimethylboate react to give sodium borohydide and sodium methoxide which decomposes into methanol and NaOH. Another method that would be included in this study is using NaBO2 to produce borohallide (BX3) which in presence of LiAlH4 would give B2H6 which with sodium carbonate (from sodium metaborate and methane or carbon dioxide) would give sodium hydroxide. This is under study and hence not much data is available right now. From the cost study it is seen that for the first mentioned process the initial cost associated is high and exact amount is still under debate. Advantage of utilizing renewable source is that the renewable energy can be converted into efficient source of energy for mobile applications.