CFD Study for CO2–KOH Reactive Absorption in a Bubble Column Reactor

Abstract

Carbon dioxide capture through reactive absorption is a promising approach for mitigating industrial CO₂ emissions. This study investigates transient CO₂ absorption into aqueous KOH in a semi-batch bubble column using an integrated Computational Fluid Dynamics (CFD) framework that combines a Eulerian multiphase formulation, interfacial-force closures, Higbie penetration theory for liquid-side mass transfer, and a reaction enhancement factor. The framework was quantitatively validated against the experimental normalized CO₂ breakthrough response, showing close agreement with an R² of 0.986 and an RMSE of 0.003. The validated framework was subsequently used to interpret the spatial coupling among hydrodynamics, interfacial transport, and reactive absorption. Under the investigated bubbly-flow condition, the model predicted an average gas holdup of 0.089, an interfacial area of 177.8 m⁻¹, and a spatially averaged interphase mass-transfer coefficient of 0.0065 m/s. The simulation further predicted an aqueous KHCO₃ concentration of 0.0395 mol/L during absorption. Following product recovery by evaporation at 110 °C, X-ray diffraction identified K₂CO₃ as the dominant crystalline phase with minor KHCO₃ reflections, consistent with partial carbonate–bicarbonate transformation during recovery, while scanning electron microscopy revealed well-faceted prismatic particles with an average size of 3.42 ± 1.89 µm. The solid-phase characterization provides complementary post-recovery evidence rather than direct validation of the CFD-predicted internal fields. Overall, the study demonstrates the value of an experimentally constrained, engineering-scale CFD framework for mechanistically interpreting the coupling between bubble-column hydrodynamics, mass transfer, and reaction during transient CO₂–KOH absorption.