Modeling of a methanation reactor with axial feed distribution for the production of high-purity synthetic natural gas

Methanation of carbon dioxide (CO2), frequently referred to as Sabatier reaction, is a promising strategy for the conversion of H2 produced from renewable energy into a more easily exploitable and storable fuel. It allows the development of a circular carbon economy, reducing CO2 emissions to the atmosphere. Methanation of CO2 is, however, a challenging reaction as its stoichiometry and high exothermicity prevent the complete conversion of H2. Typically, a series of packed bed reactors with several intercooling and water removal steps is required to produce a methane stream with low hydrogen content, ready for natural gas grid injection. This work investigates the use of a polytropic fixed-bed reactor for CO2 methanation over a Ni-based catalyst, focusing on distributed gas feeding strategies (axial staging) to improve CO2 conversion and methane productivity. A detailed mathematical model based on mass and energy balance equations is developed, accounting for Sabatier reaction kinetics and neglecting side reactions. The model accounts for key mass and heat transfer resistances and is validated against literature experimental data. COMSOL Multiphysics® simulations are used to investigate the influence of lateral feed point location and temperature on the simulation results. Additionally, the optimal distribution of reactant flows is examined. Strategic management of lateral feeds enhances methane yields while significantly reducing gas preheating energy consumption. An improvement of 5–32% in the outlet methane molar fraction has been evaluated. By providing practical design guidelines for industrial-scale reactors that efficiently produce synthetic methane from CO2, this work contributes to the development of sustainable energy systems.