Effects of reaction heat and active radicals derived from oxygen on supercritical water gasification of methanol for hydrogen production

The role of oxygen in the product characteristics and reaction mechanism during supercritical water gasification of methanol was studied through detailed kinetic simulations. A kinetics model for methanol gasification in supercritical water with oxygen was developed by extending established low-pressure methanol combustion mechanisms and adding submechanisms for high-pressure hydrogen combustion. Experimental chemical oxygen demand removal efficiencies and gas ratios were obtained for comparison with the simulation results and validation of the model. A rapid temperature drop occurred in the adiabatic reactor during the initial stage, adversely affecting the steam reforming reaction. The water gas shift reaction was limited in the second stage by its own exothermic nature. Driven by the heat release and consequent temperature rise, the reactions proceeded to equilibrium more rapidly in the third stage. The addition of oxygen accelerates methanol decomposition and enhances the steam reforming reaction by providing reaction heat and active radicals. Furthermore, an optimal oxidation coefficient exists for maximizing the hydrogen yield. The active radicals derived from oxygen promote methanol decomposition, but also accelerate the consumption of H 2 under high oxidation coefficients. Moreover, an optimal oxidation coefficient ranging from 0 to 0.2 facilitates efficient steam reforming under conditions of lower initial temperatures and higher feed concentrations.