SO2 sorption by activated carbon supported ionic liquids under simulated atmospheric conditions

• Investigated supported ionic liquid sorbents at low SO2 concentration and humidity.
• High performance of some ionic liquids in pure SO2 is lost in presence of humid air.
• [C2mim][Ac] loaded activated carbon effectively removes SO2 from humid air.
• Increasing [C2mim][Ac] loading on activated carbon will increase SO2 sorption.
• SO2 sorption of [C2mim][Ac] sorbent is inversely proportional to temperature.

This work evaluates the ability of ionic liquid loaded activated carbon sorbents to remove SO2 under simulated atmospheric conditions of 15 ppm SO2 in air, temperature of 25 °C and relative humidity of 50%. Amongst the nine ionic liquid (1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium lactate, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hydrogen sulfate, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate and 1-butyl-3-methylimidazolium hydrogensulfate) sorbents studied, the 1-ethyl-3-methylimidazolium acetate loaded activated carbon exhibited the highest SO2 sorption capacity performance. The attained results clearly indicate that some ionic liquids such as 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with high absorptivity in pure SO2 would perform poorly under practical conditions. As a result of the superior performance of the 1-ethyl-3-methylimidazolium acetate loaded activated carbon, further tests and characterizations were performed on the sorbent. The performance of 1-ethyl-3-methylimidazolium acetate sorbent increased along with ionic liquid loading onto the activated carbon. The 1-ethyl-3-methylimidazolium acetate sorbent breakthrough time was greater than pure activated carbon and 10 wt% potassium hydroxide loaded activated carbon standard. The SO2 sorption rate of 1-ethyl-3-methylimidazolium acetate loaded activated carbon was inversely proportional to test bed temperature. FTIR–ATR, NMR and thermal analysis of SO2 sorbed 1-ethyl-3-methylimidazolium acetate loaded activated carbon indicated the presence of both physisorbed and chemisorbed SO2.