Mathematical modeling of the simultaneous absorption of carbon dioxide and hydrogen sulfide in a hollow fiber membrane contactor

This work presents a mathematical model for a microporous hollow fiber membrane contactor operated under non-wet or partially wetted conditions, in order to analyze the simultaneous absorption of carbon dioxide and hydrogen sulfide into an aqueous solution of diethanolamine (DEA). The diffusion-reaction processes for both acid gases were modeled based on the assumption that all reactions are reversible in the liquid bulk as well as the wetted parts of the membrane pores. A numerical scheme was developed to solve the simultaneous nonlinear mathematical expressions, and the results from the model were validated with the available experimental data in the literature. The model allows one to predict the gas phase concentration and velocity profile in the axial direction inside the shell, the liquid concentration profile in the axial and radial directions inside the fibers, and also those within the wetted parts of the pores. The results indicate that the membrane contactor can sequestrate both sour gases very effectively. Membrane wetting decreases the removal efficiency of both gases significantly in high wetting fractions. However, it mainly affects the carbon dioxide recovery in low wettings. The effects of various parameters on hydrogen sulfide selectivity were investigated, and it was found that the wetting of the membrane in low fractions increases the selectivity considerably. However, it has the opposite influence in high wetting fractions.