Highly efficient and reversible absorption of SO2 by hydroxyl ammonium ionic liquids at low partial pressure

BLACKGROUND The control of sulfur dioxide (SO2) emissions is vital for the treatment of flue gases of combustion. The wet flue gas desulfurization process using limestone-gypsum is now used widely, due to its high efficiency and reliability. However, it has the disadvantages of high cost and production of hazardous by-products. Ionic liquids are new green organic solvents that can absorb acidic gases selectively. Hydroxyl ammonium ionic liquids with different anions were synthesized by neutralization and used to separate SO2 from simulated flue gas at low partial pressure of SO2. RESULTS The absorption capacities of SO2 using ionic liquids were 1.02 mol/mol, 1.19 mol/mol, and 3.34 mol/mol for [TEOA][AC], [TEOA][LA] and [TEOA][CA], respectively, at the SO2 partial pressure of 4 kPa. Viscosity of ionic liquid affected the absorption process. A longer time was required to attain absorption equilibrium in the case of [TEOA][CA]. Low temperatures favoured absorption because the process was exothermic. Water in flue gas accumulated in the ionic liquids, causing a reduction in absorption of SO2. A mixture containing different ionic liquids could decrease the viscosity and achieve optimal absorption capacities. The ionic liquids could be recycled and regenerated by desorption at high temperature. A reduction of approximate to 2% in absorption capacities was found after four cycles of regeneration. Analysis of the absorption mechanism indicated that nitrogen atoms in the cationic part of ionic liquid molecules were the predominant site for combined chemical and physical absorption processes. CONCLUSION Hydroxyl ammonium ionic liquids exhibited excellent potential for absorption of SO2 at low partial pressure by combined chemical and physical absorption processes. (c) 2019 Society of Chemical Industry