(A) study on hydrogen production from the gasification of glucose and valine over activated charcoal supported Ni catalysts in supercritical water

Abstract

In this work, supercritical water gasification (SCWG) method was studied using a continuous-flow reactor made of Hastelloy C-276 tubing as a means of hydrogen production from wet biomass without drying procedure. Glucose and valine was used as model compounds for carbohydrates (including cellulose and hemicellulose) and nitrogenous organic compounds (including protein), respectively. Dilute molasses-fermented waste as a whole biomass was also gasified using the SCWG system. Effect of major reaction parameters such as temperature, pressure, feed concentration, residence time, and catalyst on the gasification efficiencies and product distribution was investigated. Activated charcoal supported nickel (Ni/AC) and activated charcoal supported nickel-yttrium (Ni-Y/AC) catalysts were made and tested in the SCWG of the reactants. Other materials including Ni-Fe/AC, Ni-Co/AC, and AC were also prepared and tested as catalyst candidates. Activity and stability of the catalysts were discussed on the basis of product analysis and catalyst characterization. Product analysis was performed for the yields of $H_2$, CO, $CO_2$, $CH_4$, and light hydrocarbons in gaseous products and for the concentrations of reactant, COD, TOC, nitrogen-containing compounds (in case of valine gasification). Catalyst characterization was carried out for both fresh and spent catalysts by elemental analysis, $N_2$-adsorption, CO chemisorption, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) analysis methods. In SCWG of glucose without catalyst, gasification of glucose solution (0.3-1.2 M) in supercritical water was investigated at temperatures over 480-750℃ and pressure over 23-28 MPa with a reactor residence time of 10-50 s. The yield of hydrogen among gaseous products increased very sharply with increasing temperature above 660℃. On the other hand, the yield of carbon monoxide decreased with temperature most probably due to the role of water-gas shift reaction....