CO2 In Ionic Liquids Research Articles

Prediction of Henry's law constant of CO2 in ionic liquids based on SEP and Sσ-profile molecular descriptors

Nowadays, greenhouse gas CO2 emissions have caused serious global warming problems. Unique properties of ionic liquids (ILs), such as negligible vapor pressure, good thermal and chemical stability, high gas dissolution capacity, etc., have made them highly promising in capturing CO2. Although researchers have done a lot of experimental work using ILs to capture CO2, time-consuming and high experimental economic costs have led to a strong interest in establishing predictive models. In this work, 297 experimental data points including 16 cations and 9 anions for 34 ILs are collected and the structures of cations and anions are optimized by quantum chemistry. Then the electrostatic potential surface area (SEP) and charge distribution area (Sσ-profile) descriptors are calculated and used to predict the Henry's law constant (HLC) of CO2 in ILs. Three new models, namely, the multiple linear regression (MLR), support vector machine (SVM), and extreme learning machine (ELM) are finally developed based on the above-calculated descriptors. Results show that the ELM model with AARD = 3.22% for the entire data set is the most valid and powerful one to predict the HLC of CO2.

Accurate prediction of miscibility of CO2 and supercritical CO2 in ionic liquids using machine learning

In this study, the solubility of CO2 and supercritical (SC) CO2 in 20 ionic liquids (ILs) of different chemical families over a wide range of pressure (0.25–100.12 MPa) and temperature (278.15–450.49 K) were predicted, using a robust machine learning method of multi-layer perceptron neural network (MLP-NN). The developed model with the R2 of 0.9987, MSE of 0.6293 and AARD% of 1.8416 showed a great accuracy in predicting experimental values. In another approach for predicting the CO2 solubility, an empirical correlation with several constants was developed. With the R2 of 0.9922, MSE of 3.7874 and AARD% of 3.5078 the empirical correlation showed acceptable results; nevertheless weak compared to the ANN. The significance of this correlation is that it needs no physical property of the ILs or their mixture, and for its estimation, even a simple calculator is sufficient. A comprehensive statistical assessment conducted to assure the robustness and generality of the model. In addition, the applicability of the model and quality of experimental data was fully investigated by Leverage approach.

Measurement and Correlation of CO2 Solubility in 1-Ethyl-3-methylimidazolium ([EMIM]) Cation-Based Ionic Liquids: [EMIM][Ac], [EMIM][Cl], and [EMIM][MeSO4

The solubility of carbon dioxide (CO2) was investigated using three different 1-ethyl-3-methylimidazolium ([EMIM]) cation-based ionic liquids: 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), 1-ethyl-3-methylimidazolium chloride ([EMIM][Cl]), and 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO4]). The CO2 solubility data for the three ionic liquids were produced by measuring the bubble-point and cloud-point pressures of the CO2 + ionic liquid mixtures. The temperature range was from 303.15 to 403.15 K, and the pressure range was from 0.45 to 48.6 MPa. The experimental data provided results showing that the solubility of CO2 in ionic liquids increased with pressure, decreased with temperature, and was also affected by the different anions used in the experiment. The solubility is determined by CO2 mole fraction in ionic liquids, and the order of magnitude of the CO2 solubility was found to be [EMIM][Ac] > [EMIM][MeSO4] > [EMIM][Cl]. For the correlation and calculation of the experimental data, we ...

Modelling the solubility of H2S and CO2 in ionic liquids using PC-SAFT equation of state

The Perturbed Chain Statistical Association Fluid Theory (PC-SAFT) is used to investigate the solubility of carbon dioxide (CO2) and hydrogen sulfide (H2S) in several methylimidazolium bis (trifluoromethylsulfonyl) imide ionic liquids (ILs) or [Cnmim][NTf2] where n=2, 4, 6, and 8. The pure component parameters of the ILs are estimated by fitting to experimental density data and binary solubility data of acid gases in ILs reported in literature. Two strategies are examined to model the ILs. In the first strategy, the ILs are treated as neutral molecules. In the second strategy, the ILs are modelled as two charged ions: imidazolium cation [Cnmim]+ and bis (trifluoromethylsulfonyl) imide anion [NTf2]−. For each strategy, four different self association schemes are examined: non-associating, 2-site, 3-site, and 4-site schemes. The inclusion of self-association of the IL improves the calculated acid gas solubility. The 4-site association scheme with two donors and two acceptors provided the best results for almost all the investigated acid gases-IL binary systems, with an AARD of 2.76%–6.62% for H2S-ILs systems and 1.54%–4.98% for CO2-IL systems. Using these parameters, the solubility of ternary systems of CO2 and H2S in C8mimNTf2 IL is successfully represented, with an AARD of 6.24% for CO2 and 7.99% for H2S, without the need for binary interaction parameters. The high pressure density of ILs and the binary solubility of CO2-ILs at high pressure is also represented with reasonable accuracy. The inclusion of the electrolyte term in the second strategy improves the high pressure density and solubility results as well as the predictive capability of the model by allowing for the examination of the effect of using different cation-anion combinations.

The effect of cyano groups on the solubility of carbon dioxide in ionic liquids containing cyano groups in anion

The solubility of carbon dioxide (CO2) was investigated using three ionic liquids containing different numbers of cyano groups in the anion, 1-hexyl-3-methylimidazolium tricyanomethanide ([c6mim][C(CN)3]), 1-hexyl-3-methylimidazolium dicyanamide ([c6mim][N(CN)2]), and 1-hexyl-3-methylimidazolium thiocyanate ([c6mim][SCN]). The CO2 solubilities were determined by measuring the bubble point pressures of the CO2+ionic liquid mixtures at temperatures ranging from 303.15 to 373.15 K and pressure up to 105MPa. The experimental results showed that the solubilities of CO2 in ionic liquids increased with pressure, decreased with temperature, and increased with the length of the alkyl chains in the cation. Furthermore, a higher CO2 solubility was achieved in the ionic liquid with more cyano groups in the anion. The experimental data were correlated with the Peng-Robinson equation of state (PR-EoS), using the conventional van der Waals one fluid mixing rule and the modified Lydersen-Joback-Reid method. The average absolute deviation values of pressure (AAD-P) were 0.0658 for CO2+[c6mim][SCN], 0.0633 for CO2+[c6mim][N(CN)2], and 0.0761 for CO2+[c6mim][C(CN)3] system.

Descriptive and predictive models for Henry’s law constant of CO2 in ionic liquids: A QSPR study

Associate surplus substances presence in natural gases like carbon dioxide (CO2) causes prominent problems in transporting and storage stages. Unique features of ionic liquids such as low vapor pressure, excellent thermal and chemical stability, high power of dissolution, etc., have made them as green solvents and organic solvents substitution in the separation processes, especially the separation of CO2. Although many experimental works have been done to determine the ability of ionic liquids in separation of CO2, expensive and time-consuming laboratory methods have led to a strong interest in the modeling methods. In this work, quantitative structure–property relationship (QSPR) models for predicting the Henry’s law constant (HLC) for CO2 dissolution in 32 ionic liquids have been developed. Chosen descriptors by genetic algorithm were used to develop two models by MLR and LS-SVM methods. The three-parameter model has been considered as the main model and a detailed physical interpretation has been mentioned for all parameters. Comparison of the predicted values of HLC with the experimental data, internal validation results and statistical parameters show that the proposed QSPR model by MLR and LS-SVM methods are reliable, predictive and stable; however the non-linear model is more powerful than the linear one.

The QSPR models to predict the solubility of CO2 in ionic liquids based on least-squares support vector machines and genetic algorithm-multi linear regression

Global warming is an issue of high concern which is mostly caused by growing concentrations of carbon dioxide in the atmosphere. Many novel technologies offer different solutions to decline carbon dioxide emissions to the environment. Ionic liquids (ILs) are counted to be highly promising media for CO2 capture in the near future. Due to costly nature of ionic liquids and time consuming laboratory research procedures, modeling and prediction of solubility of CO2 based on the structure of ILs are highly required. Some studies on this field demonstrate the relationship between the structure and the CO2 absorption capacity of ILs. One of the modeling approaches for stating this relationship is quantitative structure-property relationship (QSPR). In this work, an efficient approach based on the combination of genetic algorithm-multi linear regression (GA-MLR) and least-squares support vector machines (LS-SVM) was utilized to build a nonlinear QSPR model. The nonlinear model can give very satisfactory prediction results: the square of correlation coefficient (R2) and the root mean square error (RMSE) were 0.962 and 0.015, respectively for the whole dataset. In addition, another QSPR model, multi-linear regression (MLR), was also implemented and R2and RMSE were 0.876 and 0.027, respectively. The results demonstrate that the LS-SVM model drastically enhances the ability of prediction in QSPR studies and is superior to MLR one.

Investigation of the absorption of CO2 in ionic liquid

Due to environmental concerns, current interest is the development of technologies that may be able to remove CO2 efficiently from exhaust gases and thus avoid its dispersion in the atmosphere. The density functional theory (DFT) calculations with the modern continuum solvation model (IEFPCM-SMD) was used to study the mechanism of CO2 absorption in room temperature ionic liquid such as, [EMIM][BF4] (1-ethyl-3- methylimidazolium tetrafluoroborate). We determine the minimum energy structures and to determine the possible binding sites for CO2 absorption process in [EMIM][BF4]; by comparing the relative minimum energy of [EMIM][BF4] in the presence and absence of CO2.Bangladesh J. Sci. Res. 29(1): 41-46, June-2016

Mechanism of CO2 Capture in 1-Alkyl-3-Methylimidazolium Acetate: Is N-Heterocyclic Carbene Involved?

Ionic liquids (ILs) offer a promising alternative absorbent for CO2 capture because of their unique properties, such as negligible vapor pressures, high thermal stabilities, excellent CO2 solubilities and tunability. More importantly, ILs consisting of 1-alkyl-3-alkyl’-imidazolium cations paired with acetate anions can react with CO2 and form carboxylate compounds. N-heterocyclic carbene that can be formed via proton transfer from an imidazolium cation to an acetate anion is often invoked in the mechanistic explanation of these CO2–IL reactions. However, the detection of the carbene species has been elusive experimentally. In this talk, we present our results for classical and ab initio molecular dynamics simulations as well as for density functional theory calculations to gain molecular insight into CO2 capture by 1-ethyl-3-methylimidazolium acetate. Our analysis indicates that N-heterocyclic carbene is not formed and thus not involved in CO2 capture at room temperature. Based on our computational results, a novel concerted mechanism is proposed.

Solubility and selectivity of CO2 in ether-functionalized imidazolium ionic liquids

Ionic liquids are widely recognized new materials in carbon dioxide capture and separation technology. In this work, we synthesized and characterized two kinds of ether-functionalized imidazolium ionic liquids, 1-methoxyethyl-3-methylimidazolium hexafluoroborate ([EOMmim][PF6]) and 1-methoxyethyl-3-methylimidazolium bis(trifluoro-methylsulfony)imide ([EOMmim][Tf2N]). Solubility values of CO2 in these ionic liquids were determined by isometric weight method at the temperatures from 298.15K to 343.15K and the pressure up to 5.185MPa. Furthermore, solubilities of other flue gases, N2 and O2, in these two ionic liquids were also measured at 303.15K. It was shown that little influence had been exerted on CO2 solubility by the introduction of ether groups on the cation, but it decreased N2 and O2 solubility, resulting in the remarkable increase of CO2/N2 and CO2/O2 selectivity. In addition, the solubility data were well correlated by Pitzer model, and the standard state solution Gibbs energy, solution enthalpy and solution entropy of CO2 in the two ionic liquids were reported. Regeneration characteristics of the investigated ionic liquids was also studied by vacuum desorption and atmospheric desorption, respectively.

Prediction of CO2 solubility in ionic liquids with QM and UNIQUAC models

In recent years, ionic liquids shows their abilities in many processes, like enzymatic reactions, electrochemical applications, catalysis processes, or separation processes. In this work, CO2 solubility in Ionic liquids has been calculated based on two thermodynamic models, i.e., the UNIQUAC model and the quantum model, based on COSMO-RS theory of interacting molecular surface charge. To investigate the accuracy of the considered models the predicted solubility of CO2 in ionic liquids was compared with experimental data in a wide range of pressure and temperature. The ionic liquids [bmim][Bf4], [bmim][Tf2N], [emim][Tf2N], [Omim][Pf6], [Omim][Tf2N], [emim][Bf4] and [Hmim][Tf2N] were used here to investigate the capability of the models in predicting CO2 solubility. It was found that the accuracy of COSMO-RS is good, but only for some ILs, whereas UNIQUAC is the most capable method in predicting the gas solubility.

Volumetric and phase behaviour of mixtures of fluoroalkylphosphate-based ionic liquids with high pressure carbon dioxide

The high-pressure solubility of carbon dioxide in ionic liquids based on tris(pentafluoroethyl)trifluorophosphate ([eFAP]) anion, combined with 1-ethyl-3-methylimidazolium ([emim]), 1-butyl-3-methylimidazolium ([bmim]) and 1-hexyl-3-methylimidazolium ([hmim]) cation, was determined experimentally at the temperature of 313.15K and pressures up to 10MPa. Measurements of the volume expansion of the liquid phase upon carbon dioxide dissolution are also reported. The obtained results show that the solubility of CO2 in ionic liquids with the fluoroalkylphosphate anion, as well as the CO2-induced volume expansion of the liquid, are among the highest so far reported for ionic liquids where CO2 dissolves through “physical” mechanisms.

Carbon dioxide in an ionic liquid: Structural and rotational dynamics.

Ionic liquids (ILs), which have widely tunable structural motifs and intermolecular interactions with solutes, have been proposed as possible carbon capture media. To inform the choice of an optimal ionic liquid system, it can be useful to understand the details of dynamics and interactions on fundamental time scales (femtoseconds to picoseconds) of dissolved gases, particularly carbon dioxide (CO2), within the complex solvation structures present in these uniquely organized materials. The rotational and local structural fluctuation dynamics of CO2 in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2) were investigated by using ultrafast infrared spectroscopy to interrogate the CO2 asymmetric stretch. Polarization-selective pump probe measurements yielded the orientational correlation function of the CO2 vibrational transition dipole. It was found that reorientation of the carbon dioxide occurs on 3 time scales: 0.91 ± 0.03, 8.3 ± 0.1, 54 ± 1 ps. The initial two are attributed to restricted wobbling motions originating from a gating of CO2 motions by the IL cations and anions. The final (slowest) decay corresponds to complete orientational randomization. Two-dimensional infrared vibrational echo (2D IR) spectroscopy provided information on structural rearrangements, which cause spectral diffusion, through the time dependence of the 2D line shape. Analysis of the time-dependent 2D IR spectra yields the frequency-frequency correlation function (FFCF). Polarization-selective 2D IR experiments conducted on the CO2 asymmetric stretch in the parallel- and perpendicular-pumped geometries yield significantly different FFCFs due to a phenomenon known as reorientation-induced spectral diffusion (RISD), revealing strong vector interactions with the liquid structures that evolve slowly on the (independently measured) rotation time scales. To separate the RISD contribution to the FFCF from the structural spectral diffusion contribution, the previously developed first order Stark effect RISD model is reformulated to describe the second order (quadratic) Stark effect--the first order Stark effect vanishes because CO2 does not have a permanent dipole moment. Through this analysis, we characterize the structural fluctuations of CO2 in the ionic liquid solvation environment, which separate into magnitude-only and combined magnitude and directional correlations of the liquid's time dependent electric field. This new methodology will enable highly incisive comparisons between CO2 dynamics in a variety of ionic liquid systems.

Kinetics of CO2 capture by ionic liquid—CO2 binding organic liquid dual systems

A dual system, which aims to combine the individual advantages of two different solvents, has been developed for CO2 capture in order to intensify the process by reducing the reboiler duty. The dual system consisted of 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) and 1.8-diazabicyclo 5.4.0 undec-7-ene (DBU) in 1-hexanol medium and the relevant kinetics were determined by using a stopped flow equipment. Based on pseudo-first-order reaction kinetics of CO2, the reaction was modeled by a modified termolecular reaction mechanism and rate constants and the activation energies of the [bmim][Tf2N]–DBU system were obtained. In addition, the absorption capacity and the initial absorption rate of the 10wt% [bmim][Tf2N]-15wt% DBU dual system were measured in a gas-liquid reactor at 303K and 2atm 0.815:1mol ratio of CO2:DBU was achieved with this dual system – which approximately doubles the capacity of commercial alkanolamine solutions – and the initial CO2 absorption rate of the dual system was found to be 3.500×10−5kmol/m2s. Reversibility of dual system was also briefly investigated by using Fourier transform infrared spectrometry.

Measurement of infinite dilution partition coefficients of isomeric benzene derivatives in [bmim][Tf2N]-CO2 biphasic system and correlation with the ePC-SAFT equation of state

Infinite dilution partition coefficients of isomeric benzene derivatives in the [bmim][Tf2N] (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide)-CO2 biphasic system were measured with a supercritical fluid chromatography technique at pressures of 6–15 MPa and at temperatures of 313–353 K. The partition coefficients of o-cresol were always larger than those of m and p-cresol, while those of o-xylene were always smaller than those of m and p-xylene for all temperatures and pressures. The partition coefficients of the solutes in the ionic liquid-CO2 systems were found to be in the order of their vapor pressure in accordance with previous reports. The partition coefficient data were correlated with the ePC-SAFT (electrolytes perturbed-chain statistical associating fluid theory) equations and with the empirical LSER (Linear Solvation Energy Relationship)-δ model. The overall average relative deviation (ARD) of the ePC-SAFT equation using interaction parameters between ionic liquid and solute as fitting parameters was 8.2% and compared well with the LSER-δ model (7.5%). In one approach to improve the prediction capability of the ePC-SAFT equation, literature data of infinite dilution activity coefficients of toluene in the [bmim][Tf2N]-toluene biphasic system at atmospheric pressure were used to determine ePC-SAFT interaction parameters between [bmim][Tf2N] and toluene. Although this approach improved the ePC-SAFT description of the [bmim][Tf2N]–CO2–toluene system, the correlation was qualitative at high pressure and can be attributed to CO2 in the liquid phase that affects [bmim][Tf2N]-toluene interactions.

Numerical simulation of CO2-ionic liquid flow in a stirred tank

Ionic liquids (ILs) are new solvents that represent a breakthrough for absorption and conversion of CO2. However, there has been little research on the hydrodynamics of gas-IL systems in stirred tanks, and this has become a bottleneck for development of IL-based reactors. In the present study, a CO2-IL ([bmim][BF4]) flow in a stirred tank was studied using computational fluid dynamics (CFD). A new drag coefficient model that is specific to a gas-ionic liquid system and a population balance model (PBM) were adopted to describe the bubble behavior, such as gas holdup and bubble size evolution, precisely. The predicted results for the total gas holdup and local Sauter diameter agree well with the experimental data. The influences of the gassing rate, agitation speed, and temperature on local gas holdup, bubble size distribution, and interfacial area for the CO2-[bmim][BF4] system were also investigated. The results of this study provide fundamental information for designing gas-IL systems for stirred tanks.

What Determines CO₂ Solubility in Ionic Liquids? A Molecular Simulation Study.

Molecular dynamics (MD) simulations of 10 different pure and CO2-saturated ionic liquids are performed to identify the factors that determine CO2 solubility. Imidazolium-based cations with varying alkyl chain length and functionalization are paired with anions of different hydrophobicity and size. Simulations are carried out with an empirical force field based on liquid-phase charges. The partial molar volume of CO2 in ionic liquids (ILs) varies from 30 to 40 cm(3)/mol. This indicates that slight ion displacements are necessary to enable CO2 insertions. However, the absorption of CO2 does not affect the overall organization of ions in the ILs as demonstrated by almost equal cation-anion radial distribution functions of pure ILs and ILs saturated with CO2. The solubility of CO2 in ILs is not influenced by direct CO2-ion interactions. Instead, a strong correlation between the ratio of unoccupied space in pure ILs and their ability to absorb CO2 is found. This preformed unoccupied space is regularly dispersed throughout the ILs and needs to be expanded by slight ion displacements to accommodate CO2. The amount of preformed unoccupied space is a good indicator for ion cohesion in ILs. Weak electrostatic cation-anion interaction densities in ILs, i.e., weak ion cohesion, leads to larger average distances between ions and hence to more unoccupied space. Weak ion cohesion facilitates ion displacement to enable an expansion of empty space to accommodate CO2. Moreover, it is demonstrated that the strength of ion cohesion is primarily determined by the ion density, which in turn is given by the ion sizes. Ion cohesion is influenced additionally to a smaller extent by local electrostatic interactions among ion moieties between which CO2 is inserted and which do not depend on the ion density. Overall, the factors that determine the solubility of CO2 in ILs are identified consistently across a large variety of constituting ions through MD simulations.

Ultrafast vibrational spectroscopy (2D-IR) of CO2 in ionic liquids: Carbon capture from carbon dioxide's point of view.

The CO2ν3 asymmetric stretching mode is established as a vibrational chromophore for ultrafast two-dimensional infrared (2D-IR) spectroscopic studies of local structure and dynamics in ionic liquids, which are of interest for carbon capture applications. CO2 is dissolved in a series of 1-butyl-3-methylimidazolium-based ionic liquids ([C4C1im][X], where [X](-) is the anion from the series hexafluorophosphate (PF6 (-)), tetrafluoroborate (BF4 (-)), bis-(trifluoromethyl)sulfonylimide (Tf2N(-)), triflate (TfO(-)), trifluoroacetate (TFA(-)), dicyanamide (DCA(-)), and thiocyanate (SCN(-))). In the ionic liquids studied, the ν3 center frequency is sensitive to the local solvation environment and reports on the timescales for local structural relaxation. Density functional theory calculations predict charge transfer from the anion to the CO2 and from CO2 to the cation. The charge transfer drives geometrical distortion of CO2, which in turn changes the ν3 frequency. The observed structural relaxation timescales vary by up to an order of magnitude between ionic liquids. Shoulders in the 2D-IR spectra arise from anharmonic coupling of the ν2 and ν3 normal modes of CO2. Thermal fluctuations in the ν2 population stochastically modulate the ν3 frequency and generate dynamic cross-peaks. These timescales are attributed to the breakup of ion cages that create a well-defined local environment for CO2. The results suggest that the picosecond dynamics of CO2 are gated by local diffusion of anions and cations.

Measurement of CO2 solubility in cyanide anion based ionic liquids; [c4mim][SCN], [c4mim][N(CN)2], [c4mim][C(CN)3

To investigate the effect of cyanide ions on the solubility of CO2 in ionic liquid, we measured the solubility of CO2 in three ionic liquids which contain three different numbers of cyanide anions, 1-butyl-3-methylimidazolium thiocyanate ([c4mim][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([c4mim][N(CN)2]) and 1-butyl-3-methylimidazolium tricyanomethanide ([c4mim][C(CN)3]). The solubility of CO2 in ionic liquids was determined by measuring bubble-point pressure in high-pressure variable-volume view cell at temperatures from 303.15 to 373.15 K in 10 K intervals. The measured data were correlated with the Peng-Robinson equation of state (PR-EoS) using the van der Waals one fluid mixing rules. The critical properties and acentric factor of ionic liquids were estimated by using the modified Lydersen-Joback-Reid method. As a result, the calculated data were relatively well agreed with the experimental results and, as is commonly known, the solubility of CO2 was observed to increase with increasing pressure and with decreasing temperature. The results also show that the highest solubility was obtained by [c4mim][C(CN)3] among those three experimented ionic liquids while [c4mim][SCN] had the lowest. This implies that the CO2 solubility is affected by the number of cyanide anions contained in ionic liquid. From this result, it is concluded that the cyanide anion enhances the CO2 solubility in ionic liquid and that the ionic liquid which contains more cyanide anions has higher CO2 solubility.

SO2 Solvation in the 1-Ethyl-3-Methylimidazolium Thiocyanate Ionic Liquid by Incorporation into the Extended Cation-Anion Network.

We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO2 adduct, the cations create a “cage” around SO2 with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the pi -system. Despite these similarities between the solvation of SO2 and CO2 in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO2 avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO2 can from O(SO2)–H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO2 acts in this way was termed a linker effect by us, because the SO2 can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation)cdots O(SO2) hydrogen bond and a S(anion)–S(SO2) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO2 solubility in these ionic liquids is so high.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-015-0321-5) contains supplementary material, which is available to authorized users.