Comparative studies of low concentration SO2 and NO2 sorption by activated carbon supported [C2mim][Ac] and KOH sorbents

This work evaluated the ability of 1-ethyl-3-methylimidazolium acetate ionic liquid and potassium hydroxide loaded activated carbon sorbents to remove SO2 and NO2 under simulated atmospheric conditions containing ≤10 ppm of gas contaminants in air at 25 °C and relative humidity of 50%. The studies indicate the 1-ethyl-3-methylimidazolium acetate loaded activated carbon, [C2mim][Ac] sorbent, has superior sorption performance for SO2, with breakthrough times greater than pure activated carbon, pelletized KOH activated carbon and granulated KOH loaded activated carbon. The pelletized KOH loaded activated carbon had lowest performance indicating pelletized sorbents are not ideal for use in high flow rate applications such as fuel cells. The SO2 concentration significantly impacted the breakthrough times of the [C2mim][Ac] sorbent, low SO2 concentration resulted in the longest break through times but lowest sorption capacities. The granulated KOH activated carbon and pure activated carbon had highest NO2 break through times compared to [C2mim][Ac] sorbents. The simultaneous SO2 and NO2 sorption studies indicated that the [C2mim][Ac] sorbent had greater selectivity for SO2 than NO2 compared to the KOH sorbents, as evidenced by high breakthrough times for SO2 compared to NO2. Theoretical studies using DFT-B3LYP were performed to elucidate the favored binding interactions of the [C2mim][Ac] with acidic gas contaminants. Theory indicates acidic gas contaminants preferentially interact strongly with the oxygen atoms of the acetate anion compared to the imidazole cation. The computational work also confirmed experiments showing high selectivity of the 1-ethyl-3-methylimidazolium acetate ionic liquid sorbent for SO2 compared to NO2.