Hydrogen from urea: a novel energy source

This research presents a viability assessment of using urea as an energy vector. Urea is attractive in comparison to the chemicals previously considered for supplying hydrogen since it is non-toxic, non-flammable and stable at room temperature and atmospheric pressure. Urea is cheap to produce and has an existing manufacturing infrastructure, but it also has a huge untapped natural resource, of which this study found that the knowledge to extract was technically attainable. Modelling predicted that when urea is heated with steam, a simple hydrogen-rich synthesis gas is formed, with product concentrations of ca. 60 % H2, 20 % CO2 and 20 % N2. Relatively mild temperatures of 500 °C ≤ T ≤ 700 °C were predicted for optimum steam conversion and H2 yield. Experimental steam reforming in this temperature range using a fixed bed catalytic flow reactor was developed specifically for aqueous urea fuel using a novel drop-feed and passively cooled inlet system. Steady state operation created a hydrogen rich syngas with a composition closely matching that predicted at equilibrium. A nickel catalyst was found to be effective and robust for the process, permitting repeated cycling without observed degradation. Characterisation of the catalyst revealed urea steam reforming to be clean, with no evidence of carbon formation apparent. The experimental study used urea solutions in the steam to urea (S:C) range of 3:1 to 7:1. Preliminary analyses of these mixtures confirmed that the fuel would be unaffected by isomerisation and decomposition prior to reactor input. Further preliminary experimentation of kinetic mechanisms confirmed that thermal urea conversion alone would be at worst 99.9 % within 0.5 seconds at T ≥ 500 °C. Simultaneous thermal analyses explored a greater than previously reported range of evolved species produced by thermolysis of urea and urea solution in the presence of nickel catalyst.