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

Biogas upgrading via biomethanation of renewable H-2 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 H-2 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 H-2 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 H-2 of 10 min(-1), enabling CH4 production rates up to 6.1 L . L-1 . d(-1) and more than 99 % H-2 conversion over 30 days of continuous operation, where after accumulation of metabolic water in the packed bed impaired H-2 mass transfer. Apart from the adverse effect of water accumulation, there was no indication that the maximum H-2 mass transfer rate was reached, demonstrating the selected carrier material's industrial potential for biomethanation-based biogas upgrading.

Automated summary

This study explores the use of a methanogenic trickle-bed reactor for upgrading biogas to biomethane using different carrier materials. Among the materials tested, crushed clay particles showed the highest volumetric mass transfer coefficient for H-2, leading to efficient CH4 production rates. However, water accumulation in the packed bed affected H-2 mass transfer, demonstrating the industrial potential of clay particles for biomethanation-based biogas upgrading.