Kinetic Study of Sodium Borohydride Hydrolysis Using Langmuir-Hinshelwood Model

Abstract

Hydrogen is an energy carrier that can be used in internal combustion engines or fuel cells and producing virtually no greenhouse gas when combusted with oxygen. The only significant emission is water vapour. The three main techniques for storing hydrogen are (a) as a compressed gas, (b) cryogenic liquid hydrogen and (c) solid-state hydrogen storage.

Compression of hydrogen at high pressure (150-200 bar) is the most common method of storing hydrogen. Liquid hydrogen is stored in cryogenic tanks at ambient pressure. Liquid hydrogen cannot be stored in open systems, due to low critical temperature of hydrogen. In solid state hydrogen storage method the hydrides have high hydrogen content and the stored hydrogen in them can be released by several pathways. NaBH4 is considered best among all the chemical hydrides present for the generation of hydrogen.

In this work the rate and amount of hydrogen generation is studied at the different temperatures by taking four different concentrations of sodium borohydride. After the selection of all the chemicals, the kinetic parameters and affect on the hydrogen generation by changing concentration and temperature is determined. Increase in the hydrogen generation with temperature is observed.

Langmuir- Hinshelwood model is used for the estimation of kinetic parameters of sodium borohydride hydrolysis in the presence of cobalt chloride as a catalyst. This model is considered as a combination of zero and first order kinetic model, with adsorption coefficient K. Heat of adsorption (ΔHadsorption) was found to be -45 kJ/mol for the system. The Langmuir adsorption coefficients are calculated for four different temperatures.