Highly Efficient and Reversible Absorption of SO₂ from Flue Gas Using Diamino Polycarboxylate Protic Ionic Liquid Aqueous Solutions

Abstract

Ionic liquid (IL) aqueous solutions (aq) have emerged as promising candidates for SO2 absorption. In this work, a new series of diamino polycarboxylate protic ionic liquids (DPPILs) aq with low viscosities and high stabilities were developed and used for SO2 capture. All of the prepared absorbents could efficiently absorb low-concentration SO2 in simulated flue gas. Among them, DPPILs aq based on citric acid (CA) presented the most excellent SO2 desorption performance; nearly all absorbed SO2 could be easily desorbed under mild conditions. Particularly, N,N-dimethylethylenediamine citrate [DMEDA]­[CA] showed the highest available absorption capacity toward 0.2 vol % SO2 (up to 0.51 molSO2 /molILs and 0.058 gSO2 /gabs in 50 wt % aq at 20 °C), which also presented satisfactory SO2/CO2 selectivity, reusability, and SO2 removal efficiency. Fourier transform infrared and nuclear magnetic resonance spectroscopic analyses revealed that the protonation of [DMEDA]+ and [CA]− promoted SO2 absorption. Overall, the studied DPPILs aq with excellent physical properties, SO2 absorption–desorption performance, and stability may have a great perspective in industrial SO2 removal.

Ether-Linked Diamine Carboxylate Ionic Liquid Aqueous Solution for Efficient Absorption of SO2

“…We have previously reported a class of novel diamine polycarboxylate protic ionic liquids (DPPILs) aq, which can be utilized for the removal of SO 2 , in which 50 wt %N,N-dimethylethylenediamine citrate [DMEDA][CA] aq achieved a high SO 2 removal efficiency. 25 According to previous studies, PILs synthesized from weak acids with pK a values >1.8 have been found to efficiently absorb low concentrations of SO 2 from flue gas. 26 Moreover, considering that SO 2 desorption is a high-temperature process (occurring at 100−120 °C for organic amine scrubbing), 27 the thermostabilities and volatilities of PILs should be further optimized to meet the condition.…”

“…28 Moreover, appropriate modification of the molecular structure of PILs is necessary for improved thermal stability. Multisite PILs with specific molecular structures exhibit outstanding SO 2 absorption−desorption performance 25 and excellent stability during absorption−desorption cycles, 28,29 which are suitable for SO 2 absorption. Ether-functionalized ILs have attracted immense attention due to superior physical and chemical properties like high biodegradability, 30 high thermal stability, 31 and low viscosity.…”

Molecular Insights into SO2 Absorption by [EMIM][Cl]-Based Deep Eutectic Solvents

“…The basic functions and physical interactions of ILs, especially hydrogen bonding, are revealed by molecular simulation. Zhang et al 11 developed a series of diamino polycarboxylate cationic liquids (DPPILs-aq) with low viscosity and high stability and applied them to SO 2 capture. The results show that the prepared absorbents can effectively absorb low-concentration SO 2 in simulated flue gas, and almost all the absorbed SO 2 can be easily desorbed under mild conditions.…”

Sorbents for the Capture of CO2 and Other Acid Gases: A Review

“…Ionic liquids have been studied widely as an emerging class of acid gas sorbent. ,,, These materials consist of [cation]­[anion] pairs and are typically liquids at temperatures less than 100 °C. A large number of possible such cation–anion pairs creates a substantial material design space and enables tunability of the sorbents for specific properties. , This permits both physical ,, and chemical , interactions for the reversible capture and release of CO 2 , − SO x , ,− NO x , − and H 2 S. , There has been some success in handling mixtures, − although often the presence of contaminants reduces performance, , and requires sorbent recovery . This is a problem for these high cost materials, partially offset by the negligible vapor pressure of ionic liquids, , which eliminates losses to the gas phase.…”