A Membrane Cascade Absorption Process for Synergistic Removal of SO₂ and CO₂ from Flue Gas

A cascaded hollow fiber membrane contactor (HFMC) process for the simultaneous removal and separation of SO2 and CO2 from flue gas was proposed in this study. SO2 and CO2 were separated in stage I, where SO2 and CO2 showed a strong interaction affect. SO2 had an obvious inhibition on CO2, while CO2 showed little of a promotion effect on SO2. The removal rate of SO2 was as high as 100%, which of CO2 was 15.6%. The total CO2 removal rate could reach 92.55% with 2 mol/L MDEA-MEA aqueous solution with a ratio of 1:0.75 after being absorbed in stage II. Chemical precipitation and thermal desorption were applied in the regeneration of effluent, respectively, by which 66.2% MDEA and 80.5% MDEA-MEA were regenerated. Meanwhile, mixed inorganic calcium salt and pure CO2 could be obtained as byproducts. After 90 days' being soaked in 0.5 mol/L MDEA solution and 2.5 mol/L MDEA-MEA solution, the contact angle of the hollow fiber membrane was still greater than 90°, the structure of functional group was not obviously changed, and the surface morphology was changed slightly. All of these results indicated that this membrane cascade process integrated with chemical precipitation and thermal desorption regeneration could efficiently remove the acidic gas from flue gas, realize the recycling of absorbent, and utilize the SO2 and CO2 as chemical resources. It also provided a new pathway for efficient control and resource utilization of air pollution.