Thermodynamic analysis of CO2 methanation for power-to-gas applications: Impact of in-situ water removal on performances and heat release

Abstract

This study presents a comprehensive thermodynamic analysis of CO₂ methanation, aimed at identifying optimal operating conditions for a reaction governed by a complex network. Simulations were performed in Aspen Plus® using Gibbs free energy minimization. Key variables were systematically investigated, including temperature (200–500 °C), pressure (1, 5, 10 and 30 atm), and H_2/CO₂ molar ratio (2:1, 4:1, 6:1). A special attention is given to selective water removal, analyzed across a full range (0–100 %) to simulate sorption-enhanced and membrane reactor systems. For these scenarios, the H_2/CO₂ ratio was fixed at 4:1 to reflect typical conditions. Given the exothermic nature of CO₂ hydrogenation, a thermal analysis was also performed to estimate heat release and assess the feasibility of thermoneutral operation. This was evaluated over an extended temperature range (200–700 °C) and the same pressures and feed ratios, providing insights into energy efficiency and operational stability.

Results show that water removal strongly shifts the thermodynamic equilibrium, significantly increasing CO₂ conversion and CH₄ selectivity up to a critical point, beyond which coke formation becomes favorable. The location of this optimum is highly sensitive to temperature and pressure, highlighting the need for strict operational control. Corresponding variations in the reaction heat profile further emphasize these dependencies. Overall, this work offers a detailed thermodynamic perspective on a kinetically complex system, identifies favorable operating windows and highlights process limitations. These findings complement existing literature and provide valuable guidance for the design and optimization of CO₂ methanation technologies.