Integration of two trickle-bed reactors in series for enhanced biomethane production from syngas

Biomethanation using trickle-bed reactors offers a viable solution for converting syngas from gasification or pyrolysis to methane. Under the power-to-methane concept, extraneous hydrogen is added to increase methane yield. However, optimizing the bioconversion to meet high methane purity remains a challenge. This study addresses this gap by evaluating a novel reactor configuration consisting of two thermophilic trickle-bed reactors in series. The first reactor in the series was fed with a syngas mixture (CO:CO₂:H₂:N₂ = 1:1:1:1) and enriched to convert carbon monoxide completely. The second reactor was enriched to convert carbon dioxide and externally added hydrogen to methane. This approach was compared with a single reactor configuration, where extraneous hydrogen was added in the first reactor. The series configuration achieved 100% carbon monoxide conversion, 95% methane purity, and a methane production rate of 4.60 Nm 3 · m -3 · d -1 . Based on reactor size optimization a methane production rate of 6.13 Nm 3 · m -3 · d -1 was calculated. The single reactor configuration achieved a methane production rate of 4.64 Nm 3 · m -3 · d -1 with conversion and purity on par with the series configuration. The two reactors in series offer a more flexible configuration for use with real syngas and operation under a variable hydrogen supply in the context of power-to-methane. • The outlet from the first reactor is only methane and carbon dioxide. • In the absence of external hydrogen syngas can be cleaned and sold as biogas. • Two-reactor setup boosts methane purity to 95% from syngas. • Series configuration ensures 100% carbon monoxide conversion. • Methane yield rises to 6.13 Nm³·m⁻³·d⁻¹ using two thermophilic reactors. • Series design offers flexibility for variable hydrogen supply scenarios.