Abstract
Solid oxide fuel cells have a proven efficiency for the direct conversion of biogas into electricity, and their full potential from European agricultural and waste-water sites still has to be fully evaluated and harnessed. Biogases are methane-rich mixtures whose composition and trace contaminants, especially of sulfur compounds, can vary greatly.
To avoid carbon deposition from the carbon-rich CH4-CO2 mixtures, some amount of steam and/or extra CO2 needs to be added to process the biogas. Ideally this can be recovered from the SOFC exhaust. In a preparatory work, biogas/SOFC integrated systems were studied and compared using Aspen Plus[1]. Best performances are reached with a catalytic methane pre-reformer when a fraction of the anode off-gas is recirculated for mixing with the biogas feed. This work provided the guidelines for the present catalytic study and predicted thermodynamic equilibria of gas mixtures.
Here, the overall performance of a ruthenium exsolution catalyst[2] for the reforming of methane was evaluated for these different biogas compositions at various gas hourly space velocities. Gas chromatography and material balance calculations enabled the full measurement of inlet and outlet gas compositions which, in turn, permitted to calculate precise conversion rates, reforming ratio, and the deviation from thermodynamic equilibrium. Methane conversion reached >95 % for a dry-dominant reforming mixture, which simplifies the overall system. The longer-term stability of the catalyst as well as its tolerance towards different sulfur traces that occur in biogas was then evaluated and analyzed.
[1] Shuai Ma, Gabriele Loreti, Ligang Wang, Andrea L. Facci, Stefano Ubertini, Changqing Dong, François Maréchal, and Jan Van herle, E3S Web of Conferences 2021 238:04002
DOI: 10.1051/e3sconf/202123804002
[2] Muhammad A. Naeem, Paula M. Abdala, Andac Armutlulu, Sung Min Kim, Alexey Fedorov, and Christoph R. Müller, ACS Catalysis 2020 10 (3), 1923-1937
DOI: 10.1021/acscatal.9b04555