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

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.