Scale up study of a thermophilic trickle bed reactor performing syngas biomethanation

Biomethane constitutes an important biofuel for the transition towards a biobased circular economy with a sustainable energy sector. An environmentally friendly pathway for its production is through the gasification of 2nd generation biomass that generates syngas (H₂, CO, and CO₂), followed by syngas biomethanation. A novel design thermophilic trickle bed bioreactor was successfully tested at semi-pilot scale. It was operated continuously performing biomethanation of an artificial syngas mixture (45% H₂, 20% CO, 25% CO₂ and 10% N₂). Its effectiveness was compared to a primitive design lab scale trickle bed reactor with a 28 times lower bed volume under identical operating conditions. At an empty bed residence time of 0.6 h, the novel semi-pilot scale trickle bed reactor converted 100% and 98% of the influent H₂ and CO, respectively and produced CH₄ at a rate of 10.6 ± 0.2 mmol·l_bed⁻¹·h⁻¹, whereas the lab scale reactor converted 89% of the H₂ and 73% of the CO and achieved a CH₄ productivity of 8.5 mmol·l_bed⁻¹·h⁻¹. The maximum CH₄ productivity achieved in the semi-pilot scale reactor was 17.6 ± 0.6 mmol·l_bed⁻¹·h⁻¹ at an empty bed residence time of 0.33 h with a 99.2 ± 0.1% product selectivity. Furthermore, the semi-pilot scale reactor was connected in series with a fluidized bed gasifier fed with wood pellets to assess the biomethanation potential of the system when supplied with real syngas. The obtained results showed no process inhibition in the semi-pilot scale reactor, which accomplished 100% H₂ conversion efficiency and 92.4 ± 0.6% CO conversion efficiency at an empty bed residence time of 0.6 h.