Separation of sodium metaborate from sodium borohydride using nanofiltration membranes for hydrogen storage application

To assist in the practical implementation of irreversible (reactive) hydrogen storage for automotive applications, the separation of the reactants and products is beneficial. This separation could be effective on board where the build-up of reaction products might prove detrimental to operation, or in electrochemical regeneration of the reactant. Three commercial nanofiltration (NF) membranes (FilmTec (TM) NF-270, FilmTec (TM) NF-70 and GE Osmonics thin film (TF), NF-DL) were tested at different operating conditions for the separation of sodium metaborate tetrahydrate (NaBO2 center dot 4H(2)O) from sodium borohydride (NaBH4) for hydrogen storage applications. FilmTec (TM) NF-270 and GE Osmonics TF, NF-DL membranes successfully separated NaBO2 center dot 4H(2)O from NaBH4. The separation performance and chemical stability of the FilmTec (TM) NF-270 membrane were higher than for other tested membranes. The rejection of NaBO2 center dot 4H(2)O by the FilmTec (TM) NF-270 membrane and flux rate were 76% and 17.33 L m(2)/h, respectively, at 350 psig and pH 12.4 for a feed that contained 90 g/L NaBH4 and 62 g/L NaBO2 center dot 4H(2)O. The other two membranes failed to reject NaBO2 center dot 4H(2)O at the above operating conditions. However, NaBO2 center dot 4H(2)O rejection by the GE Osmonics TF, NF-DL membrane was 40% when the feed contained 60 and 30 g/L of NaBH4 and NaBO2 center dot 4H(2)O, respectively. This separation could be potentially applied to increase the concentration of NaBH4 in NaOH stabilized solutions and in the recycling of NaBO2 center dot 4H(2)O. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.