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BACKGROUND Ionic liquids (ILs) have been widely used in the field of SO2 separation for gases. In this study, two kinds of guanidinium‐based dicarboxylic acid ionic liquids including [1,1,3,3‐tetramethylguanidinium][Poly(ethylene glycol) bis(carboxymethyl) ether] ([TMG][PBE]) and [1,1,3,3‐tetramethylguanidinium] [Suberic acid] ([TMG][SUB]) were synthesized, and their absorption and desorption performance of SO2 were investigated. RESULTS The saturated molar ratio of SO2 to [TMG][PBE] and [TMG][SUB] were 8.74 and 5.96 mol SO2 per mole ILs at 25 °C, respectively. [TMG][PBE] saturated with SO2 was easier to desorb and could be recycled at least 5 times without loss of initial performance, while the ability to absorb SO2 by [TMG][SUB] was gradually weakened after desorption. The absorption mechanism is discussed. Results showed that SO2 could interact not only with the amino group on the cation but also with the methylene bonded to the carbonyl carbon on the anion for [TMG][SUB]. As for [TMG][PBE], SO2 could interact with the ether group by S‐O ligand interaction, instead of interacting with the methylene group bonded to the carbonyl carbon on the anion. [TMG][PBE] show good performance for SO2 capture. CONCLUSION The anion of dicarboxylic acid‐based ILs plays an important role in absorption/desorption of SO2 on the basis of the experimental results. © 2016 Society of Chemical Industry

A new series of functionalized ionic liquids (ILs) with 1,1,3,3-tetramethylguanidine ([TMG]+) cations as well as dicarboxylic acid anions {[−OOC–(CH2–CH2) n –COO–], where n = 1, 3, and 5} was synthesized, and their SO2 absorption properties were investigated. A high SO2 absorption capacity of the prepared ILs was achieved. The molar ratios of SO2 to [TMG]­[succinic acid] {([TMG]­[SUC]) (n = 1)}, [TMG]­[suberic acid] {([TMG]­[SUB]) (n = 3)}, and [TMG]­[dodecanedioic acid] {([TMG]­[DOD]) (n = 5)} were 4.76, 5.96, and 5.96, respectively. The evidence of spectroscopic measurements and quantum chemical calculations confirmed that SO2 could interact with the carboxyl and adjacent methylene groups on the anion as well as the amino group on the cation. The SO2 absorption capacity of these ILs was strongly influenced by their asymmetry and space resistance. The high symmetry and large steric hindrance could reduce the SO2 absorption capacity of ILs.

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