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

•Established the NaBH4 self-hydrolysis kinetics by model-based isoconversional method.•Apparent reaction order decreases with temperature irrespective of extent of conversion.•Apparent activation energy increases with extent of conversion.•Experimental results are in good agreement with the model predictions.

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 first-order 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.