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 SO32− ions into SO42−. (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.