Selective removal of SO₂ from coal-fired flue gas by alkaline solvents using a membrane contactor

The presence of SO₂ in coal-fired flue gas has adverse effects on the amine solutions used for CO₂ capture. In addition, SO₂ emissions in the atmosphere are also a primary source of pollution. In this study, the SO₂ removal efficiency of three aqueous alkaline absorbents NaOH, Na₂SO₃, and CaO was studied using a membrane contactor. The morphology of the used membrane was examined using SEM and contact angle characterization techniques. Gas removal efficiency was studied within a feed gas flow rate of 0.5–5 m³/h, absorbent flow rate of 5–100 mL/min, and absorbent concentration of 0–0.01 mol/L. The gathered results showed that aqueous CaO has superior gas removal performance. It achieved a SO₂ removal efficiency of 99.99 % at a concentration of 0.0025 mol/L, while the aqueous NaOH and Na₂SO₃ absorbents achieved 99.99 % removal efficiency at concentrations of 0.001 mol/L. Through comprehensive experimental work, the optimum operating parameters needed to achieve maximum SO₂ removal efficiency were also determined. Furthermore, the durability of the membrane was tested in a four week continuous gas removal test and SEM images were recorded weekly to observe module morphology. The obtained results indicated that the membrane was quite durable and did not deteriorate noticeably.