Thermochemical recycling of hydrolyzed NaBH4. Part I: In-situ and ex-situ evaluations

This paper presents a combined application of in-situ and ex-situ evaluations of products obtained by thermochemical recycling process of NaBH4 from NaBO2-Mg-H2 ternary system. In-situ yield evaluation according to on-line pressure measurements of hydrogen gas, although already applied by some authors, is presented here with an innovative analysis which offers a thorough comprehension of the NaBH4 regeneration process making feasible the qualitative and quantitative estimations of product and by-product. On the basis of in-situ observations, NaBH4 formation in presence of NaBO2-Mg-H2 ternary system initiates slowly from 400 °C and accelerates above 550 °C to the melting point of Mg at 650 °C. MgH2 is significantly produced between 370 °C and 450 °C in both heating and cooling. The amounts of these products produced at the different temperatures are clearly detectable by hydrogen pressure drops. Additionally, ex-situ evaluations by titration of NaBH4 have also been performed in order to confirm the correct interpretation of the experimental data.