Hydrophilic membrane contactor for improving selective removal of SO2 by NaOH solution

Abstract

Removal of SO2 from ship exhaust gas requires a specifically designed device due to the limitations of narrow space and inconvenient replacement of absorbent. Therefore, the scrubber should be high-efficient and the absorbent for SO2 removal should be efficiently utilized. In this work, a hydrophilic membrane (HIM) contactor was employed to selectively remove SO2 using NaOH solution from simulated ship exhaust gas. Mass transfer analysis demonstrated that the wetted membrane layer contributes to lower mass transfer of CO2 by limiting the diffusion of OH−, but it can improve the mass transfer of SO2 in the membrane phase. Experimental data showed that a SO2/CO2 selectivity factor of ~114 and a SO2 absorption flux over 0.2 mol·m−2·h−1 can be stably obtained using the HIM contactor and 0.4 mol·L−1 NaOH. These values were higher than those obtained in a hydrophobic membrane (HOM) contactor under the same conditions. The performance of selective removal of SO2 under various parameters were also investigated, including NaOH concentration, inlet SO2 concentration and packing density of membrane module.