Extraction of sodium borohydride from alkaline solutions

Sodium borohydride plays a crucial role in hydrogen storage, since it has high capacity for hydrogen. There are two important processes in the production of sodium borohydride, namely Schlesinger Process and Bayer Process. In both processes, in order to have stable sodium borohydride, it should be kept in an alkaline medium (i.e. NaOH solution). Otherwise, it is affected by the moisture in the air and the dehydrated structure is formed. On the other hand, hydrolysis reaction occurs which causes uncontrolled hydrogen gas release in aqueous solutions. To produce pure sodium borohydride, a purification step, extraction, is used to separate it from the alkaline solution.Quantitative analysis of the distributed material in two phases is required for extraction processes. In the first part of this study, three methods for sodium borohydride analysis (iodometric method, spectrophotometric method and voltammetric method) were studied. Calibration curves were produced for each method. It was decided to use the voltammetric method in all extraction studies which was believed to be a fast and reliable method studied in this part of study.In the second part, the effects of sodium borohydride concentration, extraction time, solvent/feed volumetric ratio and temperature on extraction efficiency were investigated.In conclusion, it was observed that 65 - 99 % of sodium borohydride in the feed was extracted to the extract phase within the experimental range studied.