Green SO₂ conversion from flue gas by pH variation

Emissions reduction or conversion by clean technologies has always been a mission for environmental protection and sustainable development. A green, electrochemically driven conversion of SO₂ to NaHSO₄ from flue gas by pH variation was conducted. Experiments were carried out to investigate some factors affecting the conversion process, such as O₂ function in flue gas, selected initial pH (pH₀) of solution, and CO₂ effects of high concentration. Experimental results revealed that (i) O₂ was essential for SO₂ absorption, since the pH of solution was decreased more effectively than that of flue gas without O₂. The lowest pH of absorption solution with pouring O₂ was about 3.2, which was benefit to formatting HSO₃ ⁻ but hindering absorption of CO₂. Meanwhile, O₂ from flue gas accelerated the adsorption of SO₂ for its oxidability to change HSO₃ ⁻ and SO₃ ²⁻ ions into SO₄ ²⁻. (ii) At the conditions of different pH₀, the minimum absorption efficiency of SO₂ was 89.3 %, corresponding to pH₀ 5.0 and 7.0, while maximum value was 100.1 % corresponding to pH₀ 6.0, which meant pH₀ 6.0 was more appropriate for SO₂ conversion by electrochemistry under the experimental pH₀ range. (iii) The absorption efficiency of CO₂ was at a very low level under conditions of pH₀ 5.0, 6.0, and 7.0, whose value of minimum and maximum was 0.07 and 0.19 %. The result showed that high concentration of CO₂ from flue gas had little affection on desulfurization under the experimental pH₀ range, which enable to infer that byproduct of NaHSO₄ is pure enough.