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

Abstract

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·lbed−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·lbed−1·h−1. The maximum CH4 productivity achieved in the semi-pilot scale reactor was 17.6 ± 0.6 mmol·lbed−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.