Thermodynamic analysis of carbon dioxide reforming of methane in view of solid carbon formation

Abstract

A thermodynamic equilibrium analysis on the multi-reaction system for carbon dioxide reforming of methane in view of carbon formation was performed with Aspen plus based on direct minimization of Gibbs free energy method. The effects of CO2/CH4 ratio (0.5–3), reaction temperature (573–1473K) and pressure (1–25atm) on equilibrium conversions, product compositions and solid carbon were studied. Numerical analysis revealed that the optimal working conditions for syngas production in Fischer–Tropsch synthesis were at temperatures higher than 1173K for CO2/CH4 ratio being 1 at which about 4mol of syngas (H2/CO=1) could be produced from 2mol of reactants with negligible amount of carbon formation. Although temperatures above 973K had suppressed the carbon formation, the moles of water formed increased especially at higher CO2/CH4 ratios (being 2 and 3). The increment could be attributed to RWGS reaction attested by the enhanced number of CO moles, declined H2 moles and gradual increment of CO2 conversion. The simulated reactant conversions and product distribution were compared with experimental results in the literatures to study the differences between the real behavior and thermodynamic equilibrium profile of CO2 reforming of methane. The potential of producing decent yields of ethylene, ethane, methanol and dimethyl ether seemed to depend on active and selective catalysts. Higher pressures suppressed the effect of temperature on reactant conversion, augmented carbon deposition and decreased CO and H2 production due to methane decomposition and CO disproportionation reactions. Analysis of oxidative CO2 reforming of methane with equal amount of CH4 and CO2 revealed reactant conversions and syngas yields above 90% corresponded to the optimal operating temperature and feed ratio of 1073K and CO2:CH4:O2=1:1:0.1, respectively. The H2/CO ratio was maintained at unity while water formation was minimized and solid carbon eliminated.