Carbon dioxide methanation in a catalytic microchannel reactor

Abstract

The work reported in this dissertation demonstrated the practicality of a catalytic microchannel reactor for CO2 methanation implemented via the Sabatier reaction for potential power-to-gas applications. A combined experimental and computational fluid dynamic (CFD) modelling approach was used to evaluate the microchannel reactor washcoated with an 8.5 wt.% Ru/Al2O3 catalyst. For the experiments, a stoichiometric feed ratio (1:4) of CO2 and H2 was used. The reactor was evaluated for CO2 methanation at different reaction temperatures (250‒400°C), pressures (atmospheric, 5 bar and 10 bar), and gas hourly space velocities (32.6–97.8 NL.gcat-1.h-1). The highest CO2 conversion of 96.8% was achieved for the lowest space velocity (32.6 NL.gcat-1.h-1) and conditions corresponding to 375°C and 10 bar. The CH4 production was however maximised operating the reactor at conditions corresponding to high space velocity (97.8 NL.gcat-1.h-1), high temperature (400°C) and at 5 bar. At this operating point the reactor showed 83.4% CO2 conversion, 83.5% CH4 yield and high CH4 productivity (16.9 NL.gcat-1.h-1). The microchannel reactor demonstrated good long-term performance and no observable catalyst deactivation even after start-stop and continuous cycles, thereby proving its ability to handle dynamic operation required for power-to-gas applications. A CFD model was developed and used to interpret the experimental reactor performance, as well as provide fundamental insight into the reaction-coupled transport phenomena within the reactor. Most importantly, global kinetic rate expressions were developed using model-based parameter estimation. Results from the CFD model corresponded with good agreement to the experimental reactor performance in terms of CO2 conversion and CH4 yield over a wide range of operating parameters. The model also provided velocity and concentration distributions to better understand the transport principles established within the reactor. Overall, the results presented in this dissertation pinpointed the important aspects of realising CO2 methanation at the micro-scale and could provide a platform for future studies using microchannel reactors for power-to-gas applications