Parametric sensitivity in the Sabatier reaction over Ru/Al2O3 – theoretical determination of the minimal requirements for reactor activation

Abstract

The methanation of carbon dioxide is an option for chemical storage of renewable energy together with greenhouse gas reutilization because it offers a product with a high energy density. The reaction CO₂ + 4H₂ ↔ CH₄ + 2H₂O is performed on a Ru/Al₂O₃ catalyst and is strongly exothermal. For this reason, the reactor design must take into account an efficient thermal management system to limit the maximal temperature and guarantee high CO₂ conversion. Additionally, the methanation reactor is subject to parameter sensitivity. This phenomenon can generate instability in the operation of a power to gas plant, due to the variability in the hydrogen production rate. Here we present a parametric study of the thermal properties of the reaction and determine the minimal feed temperature for the normal operation of a reactor. The minimal temperature required is determined by several parameters, such as pressure, space velocity and properties of the cooling system. For adiabatic reactors, the required feed temperature is 210 °C for a space velocity of 3000 h⁻¹ and a pressure of 10 bar. The space velocity strongly affects the positioning of the ignition point, causing a large variability of the feed temperature required. At the same time, the optimal working point of the reactor is at the minimal activation temperature. The properties of cooled reactors are elucidated, showing how the interrelationship between cooling and feed temperature makes the management of this class of reactors more challenging. On the base of the modelling results, we propose a reactor configuration that adjusts the thermodynamic limitations and respects the minimal requirements for reaction ignition, allowing a more stable operation and avoiding the functioning at excessive temperature.