Alleviating mass transfer limitations in industrial external-loop syngas-to-ethanol fermentation
Lars Puiman (TU Delft - BT/Bioprocess Engineering)
Britt Abrahamson (University of Washington)
Rob G.J.M.van der van der Lans (TU Delft - BT/Bioprocess Engineering)
C. Haringa (TU Delft - BT/Bioprocess Engineering)
Henk Noorman (TU Delft - BT/Bioprocess Engineering, DSM)
Cristian Picioreanu (King Abdullah University of Science and Technology)
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Abstract
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.
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