Sadashiv Swami, Chemical & Environmental Engineering, University of Toledo, 2805 Bancroft Street, 3048 Nitschke Hall, Toledo, OH 43606, Ponnaiyan Ayyappan, Department of Chemical and Environmental Engineering, University of Toledo, 2801 W. Bancroft street, Toledo, OH 43606, and Martin Abraham, University of Toledo, Dept. of Chemical Engineering, MS 310, 2801 West Bancroft, Toledo, OH 43606.
Research on hydrogen production is given much attention nowadays due to its importance as a future alternate energy source. It reduces the dependence on fossil fuel and the production of carbon-based emissions. Aqueous phase reforming of biomass and bio-derived compounds has been studied as an alternative for steam and auto-thermal reforming. However, direct conversion of biomass to hydrogen in APR is still in its infancy due to technical challenges involved in the process. Therefore, an integrated biological and thermo chemical conversion approach has been adopted. Biomass is first converted to bio-derived compounds such as ethanol which are relatively easier to reform under aqueous phase reforming conditions. APR experiments were carried out at lower temperature (225-275 °C) and moderate pressure 400-900 psi. Hydrogen yields obtained during APR of ethanol were in the range of 20-25%. Different metal and support combinations have been explored to obtain active, stable and inexpensive catalyst. While most of the catalysts were found to be stable when exposed to simulated sample (simulated sample being 5 % pure ethanol in DI water), these catalyst were rapidly deactivated when exposed to the fermentation broth. Impurities in the fermentation broth were suspected to cause catalyst deactivation. These impurities could be sulfur, phosphorus and nitrogen compounds present in cells used for the biological conversion step. An elemental analysis of the fermentation broth showed the concentration of S and P to be approximately 10 ppm. The effects of these impurities were modeled using surrogate compounds such as L-Cysteine (a sulfur-containing amino acid) and adenosine triphosphate (a phosphorus surrogate), both of which are basic ingredients of the cell structure. Catalyst deactivation in case of simulated sample doped with 10 ppm of L-cysteine was found to be of linear type. In order to eliminate the problems of catalyst deactivation, fermentation broth was treated using nano-filtration membranes. Filtered fermentation broth was subsequently used in APR process. It was observed that the catalyst performance was stable for 65 hrs of reaction time.