Reactant Feeding Strategy Analysis of Sodium Borohydride Hydrolysis Reaction Systems for Instantaneous Hydrogen Generation

Abstract

In this study, the operational procedure of an experiment and simulation for a hydrogen-on-demand system using sodium borohydride hydrolysis is proposed. For an isothermal operating condition of a packed-bed reactor, the dynamic response between the input NaBH4 feed (FNaBH4,0(S)) and the output hydrogen flowrate (FH2(S)) of the reactor can be analytically derived and is a first-order transfer function. The time constant of this transfer function is a function of the reciprocal of the product of the reaction rate constant and the catalyst weight into the liquid volume of the reactor. The kinetic parameters of Co-B/IR-200 catalysts are regressed from the experimental NaBH4 hydrolysis reaction. The result shows a 30 °C operating temperature increase (from 40 °C till 70 °C) can shorten the dynamic response time of the hydrogen generation rate by around two-thirds. From theoretical derivation, a feeding strategy which supplies the combination of impulse function and step function of the NaBH4 feed flowrate can produce a hydrogen-on-demand system. However, for real applications, a combined pulse and step function of the NaBH4 feed flowrate is used due to limitations in pump capacity. Hence, a systematic feeding procedure can then be constructed to achieve the US Department of Energy’s fuel cell start-up time target of less than 5 s. to produce hydrogen. Finally, the experiment was set-up to validate the simulation result.