Thermodynamic analysis of methane reforming with CO2, CO2+H2O and CO2+O2 for hydrogen and synthesis gas production

Dry reforming of methane for the production of hydrogen and syngas has attracted much attention from both industrial and environmental aspects. The major problem encountered in the application of this process is the rapid deactivation of the catalyst, which is mainly due to coke accumulation and sintering of the catalyst. As an alternative to reduce the coke formation, the combination of CO2 reforming with steam reforming and oxidative reforming has been proposed in literature. The understanding of the thermodynamic behavior of these systems is important to determine the most favorable reaction conditions. In this context, the main objective of this work is performing a thermodynamic evaluation of methane reforming with CO2, CO2+H2O, CO2+O2 and CO2+air. These evaluation were carried out by Gibbs energy minimization and entropy maximization to determine the equilibrium compositions and equilibrium temperatures, respectively. Both cases were treated as optimization problems (using nonlinear programming formulation), satisfying the restrictions imposed by atom balance and non-negativity of number of moles. The GAMS®23.1 software and the CONOPT solver were used in the resolution of the proposed problems. All calculations performed presented a low computational time (less than 1 second). The calculated results were compared with previously published experimental and simulated data with a good agreement between them for all systems. The H2 and syngas production were favored at high temperature and low pressure conditions. The addition of H2O and O2 proved to be an effective way to reduce the coke formation in the systems. The CO2 reforming presented endothermic behavior, but the addition of O2 and air reduced this trend and in some conditions, autothermal behavior was observed.