Selecting carrier material for efficient biomethanation of industrial biogas-CO2 in a trickle-bed reactor

• Published in: Journal of CO2 utilization 2021-09, Vol.51, p.101611, Article 101611
• Main Authors: Jensen, Mads Borgbjerg, Poulsen, Súsanna, Jensen, Bjarke, Feilberg, Anders, Kofoed, Michael Vedel Wegener
• Format: Article
• Language: English
• Subjects: Biogas upgrading; Biomethanation; Carrier material; Gas-liquid mass transfer; Trickle-bed reactor
• ISSN: 2212-9820; 2212-9839
• DOI: 10.1016/j.jcou.2021.101611

[Display omitted] •Continuous biomethanation of raw biogas in an ex situ trickle-bed reactor.•Mass transfer properties of six carrier types were characterized abiotically.•Clay-based carriers facilitated the highest KLa values in an abiotic model system.•Clay carriers supported CH4 rates of 6.1 L · L−1 · d−1 at > 99 % H2 conversion.•Metabolic water accumulation in the packed bed decreased H2 conversion. Biogas upgrading via biomethanation of renewable H2 and the CO2 in biogas poses a potential key technology in the decarbonized energy system. This study uses a methanogenic trickle-bed reactor for upgrading raw biogas from an industrial anaerobic digester to natural gas-grade biomethane through ex situ biomethanation. The carrier material comprises a critical design parameter for trickle-bed reactors by supporting the catalytic methanogenic biofilm and thereby the interfacial area for H2 mass transfer. The present study applied an abiotic mass transfer-based screening of six different carrier types to identify a candidate material that can facilitate efficient H2 mass transfer in a biomethanation trickle-bed reactor. The screening included gas-liquid mass transfer experiments in an air-water system in addition to characterizations of the carriers’ surface area, dynamic liquid hold-up volumes, and external porosities. The abiotic experiments showed that the gas-liquid mass transfer coefficient is highly influenced by material type and cannot be predicted solely from differences in the carriers’ surface area. The abiotic characterizations led to the selection of crushed clay particles, whose application in biomethanation-based upgrading of raw biogas from an industrial anaerobic digester was examined. The clay particles facilitated an apparent volumetric mass transfer coefficient for H2 of 10 min−1, enabling CH4 production rates up to 6.1 L · L−1 · d−1 and more than 99 % H2 conversion over 30 days of continuous operation, where after accumulation of metabolic water in the packed bed impaired H2 mass transfer. Apart from the adverse effect of water accumulation, there was no indication that the maximum H2 mass transfer rate was reached, demonstrating the selected carrier material’s industrial potential for biomethanation-based biogas upgrading.