Reaction engineering approach to the synthesis of sodium borohydride

A mathematical model for the synthesis of sodium borohydride (NaBH₄) from finely dispersed solid sodium hydride (NaH) and dissolved trimethyl borate (B(OH)₃) in inert mineral oil was developed. The model is based on a plausible reaction mechanism of dissolved and adsorbed trimethyl borate on the surface of sodium hydride, where the reaction is presumed to take place. The surface reaction between sodium hydride and trimethyl borate leads to the formation of main (NaBH₄) and side products (methoxy borohydrides), which was verified by chemical analysis of sodium borohydride and methanol in the water extract of the oil phase. Extensive kinetic experiments in a laboratory-scale isothermal and isobaric slurry reactor enabled a detailed kinetic analysis of the data, including the derivation of a mathematical model for the formation of sodium borohydride in a semibatch slurry reactor. The kinetic model was verified with experimental information and can be used as an element for process design.