Kinetics of sodium borohydride hydrolysis in aqueous-basic solutions

Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kinetics. The estimation of kinetic parameters is performed by gPROMS (general PRocess Modeling System) parameter estimation tool. The reaction kinetics differs from low to highly-concentrated NaOH solutions. In highly-basic (.10 wt% NaOH), aqueous solutions of NaBH4, the rate is independent of NaOH concentration, while for lower-basic (< 10 wt% NaOH) solutions, the dependence is -0.57, confirming the inhibition of hydrolysis kinetics by NaOH

Modeling of self-gydrolysis of concentrated sodium borohydride solution

In spite of the US DOE recommendation of no-go for sodium borohydride for on-board vehicular hydrogen storage, a great deal of interest remains particularly with view to portable applications. In this work we report on experimental and modeling studies of the kinetics of self-hydrolysis of concentrated NaBH4 solutions (10 – 20 wt %) for temperatures varying between 25 – 80 0C, based on 11B NMR study. The models studied were a power law model and a model which describes the change in order of borohydride during the course of reaction. The modeling results show an increase in rate constant and decrease in the order of reaction with respect to borohydride with temperature, while reverse trends are observed with increasing initial borohydride concentration. A theoretical analysis based on solubility product constant for precipitate formation is also carried out under the studied experimental conditions and is in good agreement with the experimental observation

Kinetic modeling of self-hydrolysis of aqueous NaBH4 solutions by model-based isoconversional method

The present work reports the kinetic modeling of self-hydrolysis of non-buffered, nonstabilized NaBH4 solutions by model-based isoconversional method. The overall kinetics is described by a ‘reaction-order’ model in a practical operating window of 10-20 wt% NaBH4 solutions at 25-80 ºC and 0-50% conversions. The apparent activation energy and preexponential factor are interrelated through a kinetic compensation effect (KCE). The apparent reaction order remains constant at a given temperature irrespective of extent of conversion and decreases with increase in temperature. It decreases from first-order to 0.26 with increase in temperature from 25 to 80 ºC.

Kinetic Modeling of Self-Hydrolysis of Aqueous NaBH\u3csub\u3e4\u3c/sub\u3e Solutions by Model-Based Isoconversional Method

The present work reports the kinetic modeling of self-hydrolysis of non-buffered, non-stabilized NaBH4 solutions by model-based isoconversional method. The overall kinetics is described by a „reaction-order‟ model in a practical operating window of 10-20 wt% NaBH4 solutions at 25-80 C and 0-50% conversions. The apparent activation energy and pre-exponential factor are interrelated through a kinetic compensation effect (KCE). The apparent reaction order remains constant at a given temperature irrespective of extent of conversion and decreases with increase in temperature. It decreases from firstorder to 0.26 with increase in temperature from 25 to 80 C. The apparent activation energy is found to increase from 65 +/- 11 to 162 +/- 2 kJ mol-1 with increase in extent of conversion from 0 to 50%. The variation of parameters with extent of conversion is discussed based on changes in solution properties during the progress of hydrolysis reaction