CH4 valorisation reactions: A comparative thermodynamic analysis and their limitations

Abstract

In this study, we report on a first comparative thermodynamic analysis of various CH4 valorisation processes, taking into account the formation of byproducts through a network of side reactions. The analysis is carried out to assess the influence of a wide range of reaction parameters on the performance of each valorisation process in terms of CH4 conversion and desired selectivity metrics. The Gibbs free energy minimization method is used for the equilibrium study of nine CH4 conversion processes, including ten side reactions. The ΔG calculations revealed that the oxidative coupling of methane (OCM) and the methane dehydro-aromatization (MDA) reactions are thermodynamically the most and least feasible reactions, respectively. At P = 1 bar and T = 700 °C, the highest and lowest CH4 conversions were obtained by the dry reforming of methane (DRM) (90%) and oxidative dimerization (18%), respectively. The DRM and steam reforming of methane (SRM) were highly sensitive to changes in operation parameters, while the partial oxidation of methane (POM) and OCM were the least affected. The increasing addition of water in reforming reactions reduced the coke formation to zero at temperatures above 675 °C. From the comparison of the thermodynamic results with the documented experimental data, the carbon deposition was found to decrease both the selectivity and stability of catalysts. Investigations into the thermodynamic and kinetic limitations together with the catalyst design will help in the development of a commercial CH4 valorisation process.