A comparative thermodynamic analysis and experimental studies on hydrogen synthesis by supercritical water gasification of glucose

A thermodynamic equilibrium analysis of hydrogen (H-2) production from supercritical water gasification (SCWG) of glucose was explored based on Gibbs free energy minimization using Soave-Redlich-Kwong equation of state with Boston Mathias alpha function (SRK-BM) property method. The effects of experimental conditions [i.e., glucose concentration (0.1-1.2 M), temperature (773-1073 K), and pressure (22-35 MPa)] on the equilibrium gas product yields and gasification performance were investigated. The temperature of about 923 K, pressure of 23-28 MPa, and glucose concentration being 0.1-0.2 M are justified to provide H-2 yield in the order of its stoichiometric value (12 mol) with negligible amounts of CO and CH4. The simulated product yields, gasification efficiency (GE), cold gas efficiency (CGE(P)), cold gas efficiency of H-2 (CGE(H2)), and calculated heat duty in this study were compared with their respective experimental data taken from the literature. The aforementioned operating conditions correspond to minimum heat duty of 60-107 MW and significant values of CGE(P), CGE(H2), and GE of 121.1-118.4, 118.4-105.4, and 158.3-151.6 %, respectively. The dissimilarity between the experimental product distributions reported in the literature is related to the reactor material and residence time as well as catalyst type. The current study provided thermodynamic parameters for optimizing the operational condition of glucose SCWG, which may be extended to other biomass supercritical water gasification systems.