Alleviating mass transfer limitations in industrial external-loop syngas-to-ethanol fermentation

• Published in: Chemical engineering science 2022-09, Vol.259, p.117770, Article 117770
• Main Authors: Puiman, Lars, Abrahamson, Britt, Lans, Rob G.J.M. van der, Haringa, Cees, Noorman, Henk J., Picioreanu, Cristian
• Format: Article
• Language: English
• Subjects: Airlift bioreactor; CFD; Ethanol; Industrial; Mass transfer; Syngas fermentation
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2022.117770

[Display omitted] •Detailed analysis on gas transfer rate in industrial syngas fermentation.•CFD reveals mass transfer limitation topography in external-loop gas-lift reactors.•Bubbles smaller than 2 mm are key to reach required mass transfer capacities.•The produced ethanol minimizes bubble size and increases gas hold-up.•Transport limitations in air–water systems can be alleviated in syngas fermentation. Mass transfer limitations in syngas fermentation processes are mostly attributed to poor solubility of CO and H2 in water. Despite these assumed limitations, a syngas fermentation process has recently been commercialized. Using large-sale external-loop gas-lift reactors (EL-GLR), CO-rich off-gases are converted into ethanol, with high mass transfer performance (7–8.5 g.L-1.h−1). However, when applying established mass transfer correlations, a much poorer performance is predicted (0.3–2.7 g.L-1.h−1). We developed a CFD model, validated on pilot-scale data, to provide detailed insights on hydrodynamics and mass transfer in a large-scale EL-GLR. As produced ethanol could increase gas hold-up (+30%) and decrease the bubble diameter (≤2 mm) compared to air–water mixtures, we found with our model that a high volumetric mass transfer coefficient (650–750 h−1) and mass transfer capacity (7.5–8 g.L-1.h−1) for CO are feasible. Thus, the typical mass transfer limitations encountered in air–water systems can be alleviated in the syngas-to-ethanol fermentation process.