Hydrogen generation process development via methanolysis and hydrolysis of sodium borohydride.

摘要

Hydrogen storage is a major challenge for the commercialization of vehicular fuel cells and sodium borohydride is a high hydrogen density compound that can potentially meet the US Department of Energy requirement. In this thesis, the reaction kinetics of hydrogen generation from sodium borohydride and four solvent/reactant systems were studied over a temperature range between -20°C and 60°C. These four solvent/reactant systems were methanol, nearly dry methanol (2:1 water to sodium borohydride mole ratio), wet methanol (10:1 water to sodium borohydride ratio), and water. Kinetic studies indicated that all systems appeared to follow a first order rate law with respect to sodium borohydride concentration only.; The reaction kinetics were similar between methanol and nearly dry methanol solvent systems, but the by-products for the two systems were different at temperatures below 0°C, which indicated that the by-product underwent a second reaction with water at temperatures above 0°C. For a system reacting sodium borohydride with wet methanol, hydrolysis was favoured at all temperatures investigated and had the lowest activation energy. The low activation energy indicated the by-product dissolution in methanol that prevents passivation problem in other hydrolysis of sodium borohydride systems.; In addition to the kinetics of the above mentioned studies, selected catalysts were screened for their catalytic activity towards methanolysis of sodium borohydride to increase the rate of reaction for low temperature operations. The best catalyst tested was cobalt chloride, which is economical and showed no degradation after several cycles.