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.