(70c) The Production of Hydrogen from Partial Oxidation of Biomass in Subcritical and Supercritical Water - a Thermodynamic Equilibrium Analysis

Hydrogen energy has become increasingly important in recent years because its combustion produces nothing but water vapor and because it is the most desirable feed for fuel cells. It has been demonstrated that high yield of hydrogen gas can be produced from the gasification of biomass materials in supercritical water. However, investigations so far have been mostly experimental, and theoretical studies are scarce. Supercritical water possesses many unique features including high temperature (> 647.4 K), high pressure (> 22 MPa), low hydrogen-bond concentration in addition to other typical characteristics of supercritical fluids, making it a promising, and sometimes ideal, media for the reactions of organics. Despite numerous successful experimental demonstrations, effects of the major operating parameters, e.g. reaction temperature, pressure, water density, feed composition, on the process remain unclear. The present study attempts to investigate the optimum operating conditions of the partial oxidation of biomass materials in supercritical water by means of thermodynamic equilibrium modeling to access the influence of the major parameters. A thermodynamic equilibrium model based on equilibrium equations and equations of state has been proposed, and implemented through an extremely efficient computational scheme that is capable of generating a solution in merely fractions of a millisecond using a notebook computer.