Carbon dioxide utilization for methane production: A thermodynamic analysis

• CO2 methanation is thermodynamically favorable (Xe>95%) around 300 °C and 1–30 bar.
• Equilibrium methane selectivities close to 100% are possible under these conditions.
• Coke formation is not favored for stoichiometric or H2-rich feed compositions.
• Hydrogenation of CO2 to CH4 is thermodynamically feasible for CO2-rich natural gases.
• Experimental data over a variety of catalyst systems support the above findings.

Thermodynamic equilibrium analysis of carbon dioxide hydrogenation to methane and side reactions was performed using constrained Gibbs free energy minimization. The applicability for upgrading of CO2-rich natural gas in particular was investigated as a case study. The thermodynamics simulation to obtain equilibrium CO2 conversions and product compositions was performed in the range T=200–550 °C, P=1–30 bar and H2/CO2=1–8 mol/mol. Over the range of practical interest, the carbon dioxide conversion is very high, while the competitive reverse water gas shift is relatively insignificant. Consequently, the equilibrium selectivity to methane is also very high. Below 300 °C, in most cases, complete conversion of CO2 to methane with very high selectivity is thermodynamically feasible. The approach to equilibrium analysis of experimental data suggested that over Ni-based catalysts CO2 methanation could occur via reverse water-gas-shift reaction.