Multiscale 3D CFD Transport and Interfacial Wetting Dynamics in Membrane Contactors for Ionic Liquid-Based Post-Combustion CO2 Capture

Abstract

Post-combustion carbon dioxide capture using membrane contactors offers exceptional interfacial area without direct phase dispersion, yet localized concentration polarization, boundary layer mass transfer resistance, and module design trade-offs present critical scale-up challenges. This study presents an advanced 3D Computational Fluid Dynamics (CFD) investigation of non-dispersive CO2 absorption from a binary gas feed (15 vol% CO2 / 85 vol% N2) into a continuously recirculated 50 vol% aqueous ionic liquid solution ([OMIM][BF4]) across a hydrophobic flat-sheet PTFE membrane module under counter-current flow conditions. By resolving conjugated convective and diffusive species transport equations, the numerical model captures the spatial evolution of species concentration profiles and directional flux behavior. Results reveal a distinct transport dichotomy: convective flux dominates along the axial direction but declines progressively from module inlet to outlet as the ionic liquid nears saturation, diminishing the local concentration driving force. Conversely, radial diffusive flux intensifies across the membrane boundary layer due to localized concentration polarization at the gas-liquid interface within the pore structure. Parametric evaluation of the liquid sweep ratio demonstrates a strong non-linear enhancement in separation efficiency, with CO2 removal increasing from 38% at a sweep ratio of 0.5 to 95% at a ratio of 3.0, albeit at the expense of higher solvent inventory and regeneration duties.  Furthermore, module geometry optimization highlights that extending effective module length enhances residence time and overall capture efficiency, but elevates axial pressure drops and risks exceeding the Liquid Entry Pressure (LEP) threshold, leading to pore wetting. Increasing packing density—scaling fiber count from 5,000 to over 40,000—successfully bypasses pressure-induced wetting limits by increasing mass transfer surface area, achieving over 90% CO2 capture. This multiscale CFD framework directly links microscopic transport mechanisms to module-scale hydrodynamics, providing quantitative design criteria for intensified ionic liquid-based carbon capture processes