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.