Steam reforming of oxygenated hydrocarbons for hydrogen production over metal catalysts
With the increase in production of biodiesel, a glut of glycerol has resulted in the world market. Glycerol, once a valuable chemical, has become a recalcitrant byproduct. It is also a potential renewable feedstock for hydrogen production. This study is focused on hydrogen production from glycerol steam reforming. During the initial stage, effect of process variables, such as system pressure (1-5 atm), temperature (327 – 727 oC), and water/glycerol molar ratio of (1:1-9:1) on hydrogen yield was investigated using a thermodynamic analysis. The equilibrium concentrations of different compounds were calculated by the method of Gibbs free energy minimization. The study revealed that the best conditions for producing hydrogen is at temperature > 627 oC, atmospheric pressure, and water/glycerol molar ratio (WGMR) 9:1. As a part of catalysts screening, 14 catalysts were prepared on monoliths and tested for their activity. Effects of those catalysts on hydrogen selectivity and glycerol conversion in temperatures ranging from 600-900 oC were discussed. Ni/Al2O3 and Rh/CeO2/Al2O3 were found to be the best performing catalysts based on hydrogen selectivity and glycerol conversion under the conditions investigated in this study. Also, the effect of WGMR, metal loading, and feed flow rate (FFR) were analyzed for the two best performing catalysts. Subsequently, effect of CeO2, MgO, and TiO2 supported Ni catalysts on hydrogen production from glycerol was studied. Effects of reaction temperature, FFR, and WGMR on hydrogen selectivity and glycerol conversion were also analyzed. Ni/CeO2 was found to be the best performing catalyst when compared to Ni/MgO and Ni/TiO2 under the experimental conditions investigated. The activation energy of glycerol reforming reaction was found to be 103 kJ/mol, and the reaction order with respect to glycerol was 0.23 over Ni/CeO2 catalysts based on the power law.