Simulation-Based Analysis of a Sabatier Reactor for Conversion of CO2 into Renewable Natural Gas

Abstract

Converting CO2-rich waste streams such as raw biogas, landfill gas and power plant flue gas into synthetic fuels and chemicals will reduce greenhouse gas emissions, and provide revenue at the same time. One option is to convert CO2 into CH4 by hydrogenation via Sabatier reaction. This synthetic methane is renewable if the H2 required for the reaction is generated via water electrolysis using solar and wind energy or hydroelectricity. However, to realize the potential of this approach, a number of technological challenges related to the Sabatier reactor design have to be resolved, including thermal management and catalyst deactivation. The high exothermic nature of the Sabatier reaction can lead to reactor overheating while high temperatures are unfavorable to the exothermic and reversible methanation process, resulting in low CO2 conversions and methane production. In addition, catalyst coking deactivation due to filamentous carbon accumulation caused by methane cracking at high temperature can also lead to low methane production and short operation period. A simulation-based study of a Sabatier reactor was performed in order to optimize the removal of heat, while maximizing CO2 conversion and CH4 production and minimizing deactivation at the same time. The heat exchanger type packed bed reactor with internal cooling by a molten salt was simulated using a transient, pseudo-homogeneous mathematical model. Reactor performance was evaluated in terms of CO2 conversion and CH4 yield. The simulation results showed that feed temperature, feed flow rate and molten salt flow rate are the crucial parameters affecting the reactor performance and catalyst activity. For the optimized operating conditions, the model predicts CO2 conversions and CH4 yields above 90% at high reactor throughputs, with space velocities up to 10,000 h-1. A preliminary techno-economic evaluation is provided and opportunities and challenges are outlined.