Oxidative reforming of methane for hydrogen and synthesis gas production: Thermodynamic equilibrium analysis

A thermodynamic analysis of methane oxidative reforming was carried out by Gibbs energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods, to determine the equilibrium compositions and equilibrium temperatures, respectively. Both cases were treated as optimization problems (non-linear programming formulation). The GAMS® 23.1 software and the CONOPT2 solver were used in the resolution of the proposed problems. The hydrogen and syngas production were favored at high temperatures and low pressures, and thus the oxygen to methane molar ratio (O2/CH4) was the dominant factor to control the composition of the product formed. For O2/CH4 molar ratios higher than 0.5, the oxidative reforming of methane presented autothermal behavior in the case of either utilizing O2 or air as oxidant agent, but oxidation reaction with air possessed the advantage of avoiding peak temperatures in the system, due to change in the heat capacity of the system caused by the addition of nitrogen. The calculated results were compared with previously published experimental and simulated data with a good agreement between them.