Abstract
Interests in large scale use of biomass for energy and in hydrogen production are motivated largely by global environmental issues. Generation of hydrogen and syngas from biomass using supercritical water gasification (SCWG) is an environmentally benign method to produce energy. In the present work the Gibbs energy minimization, at constant pressure (P) and temperature (T), and entropy maximization at constant P and enthalpy (H), were utilized to calculate the equilibrium compositions and equilibrium temperatures for SCWG of glucose and cellulose. The effect of pressure, temperature and initial composition of reactants were evaluated. The problems were formulated as non-linear programs. The formulation used ensures finding the global optimal solution with no need initial estimate. The model predictions were compared with experimental and simulated data found in literature with a good agreement between them. In both SCWG processes, hydrogen production was favored in high temperatures and low molar compositions of glucose or cellulose in the feed. The effect of pressure was found to be irrelevant. Syngas with a H2/CO molar ratio close to 2 (ideal for Fischer-Tropsch synthesis applications) are obtained with an addition of CO2 as a co-reactant. The calculated final temperatures were close to the initial temperature of the reaction in both systems thus, indicating low energy requirements for maintain these reactions, and in the reaction conditions analyzed here these systems can be considered safe. Both systems showed potential for application in hydrogen and syngas production.
