Modeling of CO₂ absorption in a membrane contactor considering solvent evaporation

A comprehensive mathematical model that takes into account momentum, energy, and mass transport was developed. The model is taking into consideration the amount of water evaporated from the liquid solvent at various inlet absorbent temperatures and the accompanied latent heat of vaporization. The model considers the transport of the gas mixture of carbon dioxide and methane through a hollow fiber membrane (HFM) contactor module. The model was based on the non-wetted mode, in which the gas mixture fills the membrane pores in a countercurrent gas-liquid contact. Axial and radial diffusion inside the hollow fiber membrane, through the membrane skin, and within the shell side of the contactor were incorporated to the model. The model was validated for changes in liquid absorbent temperature with the experimental results obtained for carbon dioxide removal from a CO₂/CH₄ gas mixture using lab-made polyvinylidene fluoride (PVDF) hollow fiber membranes fabricated via thermally induced phase separation. The effect of the inlet liquid absorbent temperature on the membrane performance was validated with the experimental data. The amount of water evaporated during the change in absorbent inlet temperature was measured and compared with model predictions. The COMSOL software package was used for solving the model equations. The amount of water vapor increased with increased absorbent inlet temperatures. The CO₂ flux increased with inlet absorbent temperature. The model predictions were in good agreement with experimental data.