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 (FilmTecTM NF-270, FilmTecTM NF-70 and GE Osmonics thin film (TF), NF-DL) were tested at different operating conditions for the separation of sodium metaborate tetrahydrate ( NaBO 2 · 4 H 2 O ) from sodium borohydride ( NaBH 4 ) for hydrogen storage applications. FilmTecTM NF-270 and GE Osmonics TF, NF-DL membranes successfully separated NaBO 2 · 4 H 2 O from NaBH 4 . The separation performance and chemical stability of the FilmTecTM NF-270 membrane were higher than for other tested membranes. The rejection of NaBO 2 · 4 H 2 O by the FilmTecTM 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 NaBH 4 and 62 g/L NaBO 2 · 4 H 2 O . The other two membranes failed to reject NaBO 2 · 4 H 2 O at the above operating conditions. However, NaBO 2 · 4 H 2 O rejection by the GE Osmonics TF, NF-DL membrane was 40% when the feed contained 60 and 30 g/L of NaBH 4 and NaBO 2 · 4 H 2 O , respectively. This separation could be potentially applied to increase the concentration of NaBH 4 in NaOH stabilized solutions and in the recycling of NaBO 2 · 4 H 2 O .