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Reclamation of high-GWP near-azeotropic refrigerant R-410A (50 wt% R-32 (difluoromethane) + 50 wt% R-125 (pentafluoroethane)) can be an effective way to mitigate the greenhouse effect and achieve a circular economy. Efficient ionic liquids (ILs) as extractants needed to be found for the extractive distillation (ED) separation process of R-410A. Given the numerous combinations of cations and anions in ILs, the discovery of an efficient IL via experimental methods proves to be an exceedingly complex task. In this work, the solubilities of R-32, and R-125 in 840 conventional ILs (comprised of 20 cations and 42 anions) were analyzed based on infinite dilution activity coefficient. The absorption mechanisms of R-32 and R-125 in ILs were elucidated by analyzing excess enthalpy (H E ), excess Gibbs free energy (G E )) and surface charge density distribution through COSMO-RS (Conductor-like Screening Model for Real Solvents). Results revealed that H E and G E of the mixture formed by R-125 and most ILs surpassed those of R-32, resulting in higher solubility of R-32 in most ILs compared to R-125. Structural changes of anions and cations had a greater effect on the solubility of R-125 in ILs. It is found for the first time that the existence of a strong hydrogen bond donor region in cations/anions generated intense repulsion with the hydrogen atom in R-125. Furthermore, a large area of weak polarity on the surface of cations/anions was difficult to form an effective charge shield with fluorine atoms in R-125, thus inhibiting the dissolution of R-125. Finally based on the identified interaction sites, combined with melting point and viscosity, some novel functional ILs with high selectivity for R-32 + R-125 were designed and determined for actual separation process. These findings significantly enrich the understanding of the solubility mechanism and provide theoretical guidance for designing new ILs for R-410A reclamation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Metal- and solvent-free carboxylative cyclization of atmospheric CO2 with alkynol can be achieved using a 1-methylhydantoin anion-functionalized ionic liquid. 1H NMR, in situ FT-IR and DFT calculations indicate that the 1-methylhydantoin anion acts as a "pincer ligand" to form chelative interactions with the hydroxyl group, thereby effectively activating the alkynol. [ABSTRACT FROM AUTHOR]

Three imidazole anion-functionalized ionic liquids (IFILs) with tributylethylphosphonium ([P4442]+) cation and imidazolate ([Im]−), 4-methylimidazolate ([4-MeIm]−), or 4-bromimidazolate ([4-BrIm]−) anions were prepared to study the effect of physicochemical properties on CO2 absorption behavior. Density (ρ), viscosity (η), and speed of sound (u) of the studied IFILs were measured, and molecular volume (Vm), standard entropy (S0), lattice energy (UPOT), and isentropic compressibility coefficient (κs) were calculated accordingly. CO2 absorption behavior of [P4442][Im] at T = 313.15–333.15 K and p = 0.2 and 1 bar was investigated as an example. The results show that with the increase of temperature, ρ, η, u, and UPOT decrease, while Vm, S0, and κs increase, due to a decrease in electrostatic interaction correspondingly. The orders of ρ, u, η, Vm, and S0 values are as follows: [P4442][Im] < [P4442][4-MeIm] < [P4442][4-BrIm], while UPOT and κs are in reverse order. Interestingly, CO2 capture capacity of IFILs is approximately linear with η or κs. Due to low η and high κs, CO2 absorption capacity of [P4442][Im] is almost independent of temperature and partial pressure, as high as 0.90 mol CO2/mol IL at 333.15 K and 0.2 bar, indicating that [P4442][Im] has potential applications for CO2 absorption at high temperature and low pressure. [ABSTRACT FROM AUTHOR]

Microstructure of deep eutectic solvents (DESs) based on EmimCl or BmimCl ionic liquid (IL) and triethylene glycol (TEG) was studied by FT‐IR spectra. The influence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) on CO2 absorption behavior and mechanism of DESs was investigated. FT‐IR spectra of pure EmimCl‐TEG and BmimCl‐TEG DESs show that O−H⋅⋅⋅Cl− hydrogen bond interaction formed by IL and TEG gradually strengths with the increase in the molar ratio of IL to TEG, resulting in a corresponding increase in viscosity. Due to the lack of a chemical interaction site, the CO2 absorption capacity of pure DESs at 313.2 K and 1.0 bar is only between 0.15 and 0.56 mol kg−1. Surprisingly, the addition of equimolar DBU to DESs can significantly improve the CO2 absorption capacity, which is up to 2.94 mol kg−1 at the maximum and similar to that of amine‐functionalized DESs. CO2 absorption mechanism characterized by FT‐IR spectra indicates that DBU can form hydrogen bond with O−H of TEG, which leads to deprotonation of O−H of TEG into basic anion under the synergistic effect of O−H⋅⋅⋅Cl− hydrogen bond to achieve efficient CO2 chemisorption via carbonate formation. The obtained results provide a strategy for effectively improving the CO2 capture capacity of EmimCl‐TEG and BmimCl‐TEG DESs. [ABSTRACT FROM AUTHOR]

In order to elucidate the reaction mechanism of ionic liquid-catalyzed CO2 with 2-aminobenzonitrile, [P4442]2[Hy] with two N− sites is designed for the efficient preparation of quinazoline-2,4(1H,3H)-diones. The results show that [Hy]2− can activate 2-aminobenzonitrile by hydrogen bonding with –NH2 in addition to activating CO2, and the key intermediate is revealed. [ABSTRACT FROM AUTHOR]

A new protic ionic liquid, prepared from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with lactic acid, has been synthesized in this paper. Then, the concentration-dependent electric conductivity (κ) of binary solutions of [HDBU][La] with water, ethanol and n-butanol has been measured, respectively, at different temperatures. In addition, the electric conductivities κ have been correlated using Castell–Amis equation with satisfying results. It has been found that with the mole fraction of [HDBU][La] increasing, electric conductivity κ firstly increased because of solvation effects. Afterwards, κ of solutions gradually decreased due to the predomination of strong electrostatic force between ions and enhancement of viscosity of solutions in [HDBU][La]-rich region. Furthermore, the results also indicated that solvents with higher dielectric constant could more easily promote the dissociation of [HDBU][La]. [ABSTRACT FROM AUTHOR]

Abstract The design of acidity and alkalinity is an important characteristic of ionic liquids, and it also affects their application. For this reason, the alkalinity of six hydroxypyridine anion-based protic ionic liquids (PILs) was determined by potentiometric titration, and the effect of the type of cation and the position of nitrogen atom of anion on the alkalinity was discussed. Furthermore, six hydroxypyridine anion-based PILs were used as catalysts for Knoevenagel reaction, and the relationship between the catalytic performance and the alkalinity was investigated. The results indicate that the type of cation has little effect on the alkalinity of the studied PILs, while the position of nitrogen atom of anion has a significant influence on the alkalinity, and the order of the alkalinity is as follows: [2‑Op]− > [4‑Op]− > [3‑Op]−, resulting from the positive cooperative interaction between electronegative nitrogen and oxygen atoms, which is confirmed by DFT calculation. Consequently, the PILs with [2‑Op]− anion showing stronger alkalinity exhibits better catalytic performance for Knoevenagel reaction. Highlights • The alkalinity of six hydroxypyridine anion-based protic ionic liquids (PILs) was determined by potentiometric titration. • The anion has much greater influence on the alkalinity of the studied PILs than the type of the cation. • The position of nitrogen atom of anion is well correlated with the alkalinity and catalytic performance of the studied PILs. • There is a positive cooperative interaction between electronegative nitrogen and oxygen atoms, confirmed by DFT calculation. [ABSTRACT FROM AUTHOR]

In this work, changes in microstructure of two protic ionic liquids (PILs), namely n‐butylammonium acetate (N4Ac) and n‐butylammonium nitrate (N4NO3), are proved by in situ variable‐temperature 1H NMR spectroscopy at the temperature range from 25 to 115 °C, and the influence of the nature of anion is discussed accordingly. The results demonstrate that 1H NMR chemical shifts of alkyl protons of both N4Ac and N4NO3 are almost not changed with the increasing of temperature, due to the absence of hydrogen bond interaction between alkyl protons with anions. Whereas those of +N―H of cation decrease linearly with the temperature increasing, indicating that the hydrogen bond interaction between +N―H and anion weakens gradually. In addition, the strength of hydrogen bond interaction between +N―H and NO3− is stronger than that between +N―H and Ac−, suggesting that anions have a significant influence on microstructure due to the acidity of a Brønsted acid. Consequently, the proton transfer from cation to anion is much easier in N4Ac compared to N4NO3. Further analyses of 1H NMR chemical shifts of +N―H in N4Ac at the temperature range from 100 to 115 °C suggest that the splitting of +N―H peak may be attributed to obvious evidence of the existence of the proton transfer from +N―H to Ac−, which leads to dissociate the contact ion‐pair in N4Ac to form the neutral ion‐pair ‘molecule’. The results will help us to extensively understand the behavior of proton transfer and offer us some valuable information for the design of PILs. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recently, chemical fixation of CO 2 catalyzed by protic ionic liquids (PILs) has been successfully achieved, suggesting that CO 2 absorption behavior plays an important role on CO 2 activation and transformation. For this reason, the influence of the alkalinity and physicochemical properties on CO 2 absorption behavior of four azole-based PILs, namely [DBNH][Pyr], [DBNH][Im], [DBUH][Pyr], and [DBUH][Im] was discussed in this work. The alkalinity of PILs was determined by potentiometric titration, and free space of PILs was evaluated by thermal expansion coefficient and refractive index. Solubility parameter of PILs was obtained from the activation energy for viscous flow. The results show that PILs with [Pyr] − exhibits stronger alkalinity and larger free space, which can help to improve CO 2 capture capacity. Whereas PILs with larger cation size [DBUH] + exerts higher viscosity, resulting in slower absorption rate of CO 2 . Furthermore, the CO 2 absorption capacity is inversely proportional to the solubility parameter of PILs. The absorption mechanism proved by FT-IR and 13 C NMR spectra indicates that [Pyr] − or [Im] − can react with CO 2 to form carbamate. Accordingly, considering the CO 2 capture capacity and absorption rate, [DBNH][Pyr] may be a good candidate for efficient CO 2 capture and activation with low enthalpy of absorption of −38.2 kJ mol −1 . [ABSTRACT FROM AUTHOR]

Six dual functional ionic liquids (DFILs) with metal chelate cation and pyrazolide anion were synthesized by reacting alkanolamine with pyrazole sodium salt, and characterized by 1 H NMR, 13 C NMR, FT-IR, and ESI–MS spectra. Thermal decomposition temperature and viscosity were determined. The behavior of CO 2 absorption for these DFILs was evaluated at T = 353.2 K. Absorption mechanism and the influence of temperature and N 2 on the CO 2 absorption were investigated. The results show that the CO 2 capacity of the DFILs consisting of alkanolamine with pyrazole sodium in a molar ratio of 2:1 is larger than that of the DFILs in a molar ratio of 1:1. The CO 2 absorption mechanism obtained from FT-IR and 13 C NMR spectra indicates that CO 2 could react with a quasi-aza-crown ether cation and pyrazolide anion simultaneously, resulting in improved capacity of CO 2 absorption. According to the saturated CO 2 absorption capacity at 333.2–363.2 K and van’t Hoff’s equation, the enthalpy of CO 2 absorption for three DFILs is derived. Furthermore, the DFILs were carried out for five cycles with no obvious loss in the absorption capacity of CO 2 , indicating that these DFILs may be good candidates for efficient CO 2 capture at relatively high temperature. [ABSTRACT FROM AUTHOR]

Viscosity of the mixture containing ionic liquid (IL) is important for engineering design and application. The modeling of viscosity of the ternary mixtures containing IL is still in its infancy. The aim of this work is to evaluate the predictive ability of the semi-theoretical viscosity equations based on Eyring’s absolute rate theory and excess Gibbs free energy model for the ternary mixtures containing IL in terms of the viscosity of their binary subsystems. Three viscosity equations namely Eyring-UNIQUAC, Eyring-NRTL, and Eyring-Wilson equations are employed and extended to estimate the viscosity of ternary mixtures of IL with two molecular solvents using the interaction parameters obtained from their binary subsystems. The results were compared and discussed. The correlation results of the viscosity for 30 binary subsystems with 444 data points show that the Eyring-Wilson equation has more applicability and precision than those of the Eyring-UNIQUAC and Eyring-NRTL equations. Accordingly, the prediction results of the viscosity for 13 ternary mixtures containing IL with 813 data points indicate that the Eyring-Wilson equation has much better predictive ability than that of the Eyring-UNIQUAC and Eyring-NRTL equations. Moreover, the Eyring-Wilson equation can be used to predict the ternary viscosity at other temperature such as 313.15 K using the interaction parameters obtained from their binary subsystems at 298.15 K. [ABSTRACT FROM AUTHOR]

In order to study micro-structural heterogeneities in the solutions of ionic liquids (ILs), ethanolammonium acetate (EOAA) IL has been synthesized and 1H NMR spectra of its binary solutions, namely EOAA/DMSO and EOAA/n-butanol, have been measured at 298.15 K. Then the concentration-dependent chemical shifts δ (-CH3, EOAA), δ (-CH3, DMSO) and δ (-CH3, n-butanol) have been correlated separately using the local composition (LC) model. The results indicated that self-association of EOAA played the leading role within EOAA-rich region in mixtures. However with the molecular solvents increasing, the interactions between EOAA and solvents gradually predominated. Moreover the comparisons between DMSO and n-butanol have demonstrated that DMSO could break the network of IL more easily, indicating that the influence of DMSO on the properties of EOAA should be more obvious, which was consistent with experimental results of viscosity and conductivity. Furthermore the maximum difference between the local and the bulk appeared at x(EOAA) ≈ 0.5 for both systems, which reflected remarkable nonideality of mixtures at this concentration. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In order to uncover the micro-structural heterogeneities in solutions of ammonium based ionic liquids, triethylamine nitrate (NNO) has been synthesized using acid-base neutralization and the H NMR spectra of two binary mixtures, namely NNO/dimethyl sulfoxide (DMSO) and NNO/acetone at different concentrations, have been measured at 298.15 K. The internal reference method was adopted to obtain the concentration-dependent chemical shifts of -CH in NNO, which have been correlated using the H NMR local composition (LC) model to obtain the local mole fractions. It has been revealed that within NNO rich region, self-association of the ionic liquid was predominant instead of NNO-solvent interactions. However, in the solvent rich region, NNO mainly interacts with solvent molecules, indicating that the self-association network of NNO has been greatly destroyed by solvents. In addition, the different influences of DMSO and acetone have been detected. DMSO molecules more effectively destroy the original network of the ionic liquid, due to its higher dielectric constant. Also, LC behavior in NNO/DMSO systems is more significant than in NNO/acetone, indicating that DMSO can induce more obvious heterogeneities in DMSO/NNO mixtures, which is consistent with physicochemical properties and cellulose solubility of solutions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Densities and viscosities of N4AC+water and N4NO3 +water mixtures were measured. [•] Volumetric and viscosity properties were calculated. [•] Redlich–Kister equation was used to correlate the excess molar volumes and viscosity deviations. [•] Electrical conductivity was fitted according to the empirical Casteel–Amis equation. [•] The interactions and structural effects of N4AC or N4NO3 with water were analyzed. [ABSTRACT FROM AUTHOR]

Thecorrelation model of gas–liquid interfacial tension(surface tension) of nonaqueous mixtures containing ionic liquids(ILs) is still in its infancy. The purpose of this work is to developa modified Hildebrand–Scott equation based on local compositionconcept and the group surface area parameters of UNIFAC model as wellas to evaluate the capability of this model. The surface tension of33 IL–cosolvent binary systems were correlated by the modifiedHildebrand–Scott equation with two energy parameters and anoverall average relative deviation of only 0.92%. The ILs in the studyincluded imidazolium-based, pyridinium-based, and isoquinolinium-basedones, and the cosolvents included methanol, ethanol, 1-propanol, 1-butanol,1-pentanol, acetonitrile, and tetrahydrofuran. Using the energy parametersobtained from the surface tension of a given IL–cosolvent binarysystem at 298.15 K, the surface tension of the same system at otherdifferent temperatures was predicted by the modified Hildebrand–Scottequation, with an overall average relative deviation of 1.06%. [ABSTRACT FROM AUTHOR]

Abstract: Values of the density and viscosity of the pure ionic liquid n-butylammonium nitrate (N4NO3) and its binary mixtures with methanol, ethanol, 1-propanol, and 1-butanol were measured at temperature ranging from T =(293.15 to 313.15)K. The thermal expansion coefficient, molecular volume, standard entropy, and lattice energy of N4NO3 were deduced from the experimental density results. The temperature dependence of the viscosity of N4NO3 was fitted to the fluidity equation. Excess molar volumes V E and viscosity deviations Δη for the binary mixtures were calculated and fitted to the Redlich–Kister equation with satisfactory results. Both excess molar volumes and viscosity deviations show negative deviations for (N4NO3 +alcohol) mixtures. The effect of the temperature and the size of the alcohol on the excess molar volumes and viscosity deviations are discussed and analysed. Other derived properties, such as the apparent molar volume, partial molar volume, excess partial molar volume, thermal expansion coefficient, and excess thermal expansion coefficient of the above-mentioned systems were also calculated. [Copyright &y& Elsevier]

Abstract: Densities (ρ), refractive indices (nD ) and electrical conductivities (κ) of ethylammonium acetate (N2Ac) protic ionic liquid+water and propylammonium acetate (N3Ac) protic ionic liquid+water binary mixtures over the entire composition range were measured at 298.15K under atmospheric pressure. The excess molar volumes (V E), apparent molar volumes (V ϕi ), partial molar volumes () and excess partial molar volumes () of the binary mixtures were calculated from the density data. The refractive index deviations (ΔnD ) of the binary mixtures were determined using the refractive index data. The excess molar volumes and refractive index deviations were correlated with the Redlich–Kister equation. The excess molar volumes of the above-mentioned systems are negative over the whole composition range, while the refractive index deviations are positive. The concentration dependence of electrical conductivity was fitted according to the empirical Casteel–Amis equation. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. [Copyright &y& Elsevier]

Abstract: Densities and viscosities of the pure ionic liquid 1-methylimidazolium acetate ([Mim]Ac) and its binary mixtures with methanol, ethanol, 1-propanol, and 1-butanol were measured at temperature ranging from T =(293.15 to 313.15)K. The thermal expansion coefficient, molecular volume, standard entropy, and lattice energy of [Mim]Ac were deduced from the experimental density results. A simple linear equation was used to correlate the variation of viscosity of [Mim]Ac with temperature. Excess molar volumes V E and viscosity deviations Δη for the binary mixtures at above mentioned temperature were calculated and fitted to the Redlich–Kister equation with satisfactory results. Excess molar volumes for {[Mim]Ac+1-butanol} mixture have an S shape, while those for other mixtures have a negative deviation from ideal behaviour over the entire mole fraction range. Viscosity deviations are all negative deviation for {[Mim]Ac+alcohol} mixtures. The results were interpreted in terms of interactions and structural factors of binary mixtures. [Copyright &y& Elsevier]

Densities and viscosities were determined for the binary mixtures of n-butylammonium acetate ionic liquid (N4AC) with methanol, ethanol, n-propanol, and n-butanol at temperatures of (293.15, 298.15, 303.15, 308.15, and 313.15) K under atmospheric pressure. The refractive indices of the above-mentioned binary mixtures were measured at 298.15 K. Excess molar volumes VE, viscosity deviations Δη, and refractive index deviations ΔnD were obtained from the experimental data and fitted with the Redlich–Kister equation. The correlation results were in good agreement with the experimental data, and optimal fitting parameters were presented. The results were interpreted in terms of interactions and structural factors of N4AC + alkanols mixtures. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) can be used as absorbents and catalysts for NO x absorption and conversion due to their low toxicity, low energy consumption and excellent reusability. The capacity and absorption mechanism of NO x absorption by ILs are presented in this paper. Generally, NO x are physically absorbed by conventional ILs such as imidazolium-based ILs. The absorption capacity is as follows: NO 2 >NO>N 2 O, which is in good agreement with the binding energy between NO x and ILs. Furthermore, low temperature, high pressure and large cation volume are favorable for NO x absorption. The strategies of enhancing NO x capacity through functionalized ILs with metal-containing anions (e.g. [FeCl 4 ]2−), amine groups, sulfonate and carboxylate anions are also concluded. Active N or O sites in functionalized ILs can react with the dimer of NO (N 2 O 2), resulting in high capacity. Moreover, introducing electron-withdrawing substituents such as chlorine and bromine into carboxylate or sulfonate anions reduces desorption residue. Besides NO x absorption, ILs with [NO 3 ]− can activate NO and efficiently catalyze its conversion into HNO 3 in the presence of O 2 and H 2 O, and have better performance than ILs with [Cl]−, [Ac]− and [CF 3 SO 3 ]−, which is attributed to the strong oxidization capability of [NO 3 ]−. In addition, low temperature and high O 2 content can further improve NO conversion. ga1 • Absorption capacity and absorption mechanism of NO x by ILs with different cations and anions is compared. • NO x absorption capacity is as follows: NO 2 >NO>N 2 O, which is in good agreement with bind energy between NO x and ILs. • Functionalized ILs with active N or O sites can effectively improve NO capacity by chemical interaction. • ILs with [NO 3 ]− anion can efficiently catalyze conversion of NO into HNO 3 in the presence of O 2 and H 2 O. [ABSTRACT FROM AUTHOR]

• A series of dual functional ionic liquids were synthesized. • CO 2 absorption capacity enhances by tuning the strength of cation coordination. • Absorption of CO 2 by [K(DGA) 2 [Im] was 1.37 mol CO 2 /mole IL at 333.2 K. • CO 2 reacts first with [Im]− and then with [K(DGA) 2 +. A novel strategy for efficient CO 2 capture by tuning the strength of cation coordination interactions of alkali metal chelated dual functional ionic liquids (DFILs) is reported. CO 2 absorption and viscosity experiment, quantum-mechanical calculations showed that the strengthening of the coordination interactions between alkali metal ions and alkanolamine ligands of DFILs containing imidazolide anion ([Im]−) leads to improve the stability of the cheated cation and weaken the chelated cation-anion interaction, resulting in efficient CO 2 capture capacity and reducing the viscosity of DFILs. Particularly, [K(DGA) 2 [Im] has the stronger cation coordination interactions and lower viscosity (249.8 mPa∙s), exhibiting more efficient CO 2 capture capacity than other DFILs, with an extremely high capacity of CO 2 (∼1.37 mol/mol) in 15 min at T = 333.2 K under atmospheric pressure and good reversibility (5 recycles). Spectroscopic investigations and quantum-mechanical calculations showed that such high CO 2 capacity originates from the fact that both [K(DGA) 2 + and [Im]− of [K(DGA) 2 [Im] react with CO 2. Moreover, [Im]− reacts preferentially with CO 2 over [K(DGA) 2 +. [ABSTRACT FROM AUTHOR]

In order to uncover the micro-structural heterogeneities in the solutions of ammonium-based ionic liquids, diethylamine acetate (DEAA) has been synthesized and concentration-dependent 1 H NMR spectra of three binary solutions, namely DEAA/water, DEAA/DMSO and DEAA/acetone, at different compositions have been measured at 298.15 K. The proton chemical shifts of DEAA have been correlated using the 1 H NMR local composition (LC) model. It has been found that the self-associations of DEAA were predominant instead of DEAA–solvent interactions within DEAA-rich region. However within solvent-rich region, DEAA could mainly interact with solvent molecules, indicating that the network of DEAA has been greatly destroyed by effects of solvents. In addition, the ability of solvents to break down the structure of DEAA followed in such order: water > DMSO > acetone, which was consistent with changes of physicochemical properties of these solutions. [ABSTRACT FROM AUTHOR]

Densities and viscosities of the pure ionic liquid 1,1,3,3-tetramethylguanidine imidazole ([TMG]IM) and its binary mixtures with methanol, ethanol, 1-propanol, and 1-butanol were measured at temperatures from T = (293.15 to 313.15) K. The thermal expansion coefficient, molecular volume, standard entropy, and lattice energy of [TMG]IM were obtained from the experimental density value. The temperature dependence of the viscosity of [TMG]IM was fitted to the fluidity equation. Excess molar volumes V E and viscosity deviations Δ η of the binary mixtures were calculated and fitted to the Redlich–Kister equation with satisfactory results. The result shows that the V E values of the binary mixtures are negative over the whole composition range, while Δ η values have an S-shape deviation. Temperature has little effect on the V E of the systems, but it has significant effect on the Δ η . Furthermore, the absolute values of V E for {[TMG]IM (1) + alcohol (2)} systems at the same temperature decrease with increasing carbon alkyl chain of the primary alcohol. Other derived properties, such as the apparent molar volumes, partial molar volumes, excess partial molar volumes, Gibbs free energy of activation for viscous flow, and excess Gibbs free energy of activation for viscous flow of the above-mentioned systems were also calculated. [ABSTRACT FROM AUTHOR]

• Density, viscosity, and speed of sound of hydroxypyridine anion-based PILs were measured. • CO 2 capture behavior of PILs were determined at 313.2 K and 101.3 kPa. • Effects of the structure on physicochemical properties and CO 2 capture of PILs were studied. • Position of O− in anion plays an important role on properties and CO 2 capture of PILs. • PILs with [2-OP]− exhibits better CO 2 capture capacity due to interaction between CO 2 and O− in anion. Six hydroxypyridine anion-based protic ionic liquids (PILs) were synthesized by equimolar proton transfer of hydroxypyridine with superbase 1,8-diazabicyclo-[5,4,0]undec-7-ene (DBU) or 1,1,3,3-tetramethylguanidine (TMG), namely [DBUH][2-OP], [DBUH][3-OP], [DBUH][4-OP], [TMGH][2-OP], [TMGH][3-OP], and [TMGH][4-OP], and their physicochemical properties including density (ρ), viscosity (η), and speed of sound (u) were measured at T = 293.15–343.15 K to derive thermal expansion coefficient (α p), activation energy for viscous flow, and isentropic compressibility, respectively. CO 2 absorption behavior of PILs at 313.2 K and 101.3 kPa was determined. Effects of the structure on their physicochemical properties and CO 2 absorption were discussed. The results show that the stronger electrostatic interaction and hydrogen bonding originated from the cations with cyclic structure and the anions with long distance between O− and N lead to the lager ρ , η , and u , exhibiting the sequence of [4-OP]− > [3-OP]− > [2-OP]− and [DBUH]+ > [TMGH]+. While CO 2 capture behavior of PILs mainly depends on η , α p and the alkalinity, which are related to the position of O− in anions. When O− appears in the ortho position of N atom, PILs with [2-OP]− have larger free volumes, stronger alkalinity, and lower η , showing excellent carbon capture performance. Additionally, absorption mechanism proved by NMR and FT-IR spectra demonstrates that CO 2 can chemically interact with O− in anion to form the carbonate. In comparison, [DBUH][2-OP] is a good candidate for efficient CO 2 capture. Accordingly, physicochemical properties and CO 2 absorption behavior of can be efficiently regulated by tuning their structure, especially the position of O− in the anions. [ABSTRACT FROM AUTHOR]

In this work, densities and viscosities of aqueous solution of 1,1,3,3-tetramethylguanidine imidazolide ([TMG]IM) ionic liquid were measured at temperatures from T = (293.15 to 313.15) K. Volumetric properties including excess molar volumes V E , apparent molar volumes, partial molar volumes, and excess partial molar volumes were calculated from the experimental density. Viscosity deviations Δ η , Gibbs energy and excess Gibbs energy of activation for viscous flow were deduced from the viscosity. Moreover, electrical conductivities κ and refractive indices of binary mixtures of [TMG]IM with water and alcohols were determined at 298.15 K. The results show that V E values of {[TMG]IM (1) + water (2)} mixture are negative over the whole composition range, while Δ η and refractive index deviations Δ n D values exhibit positive deviations, indicating that the hydrogen bonding interaction between [TMG]IM and water is dominant. The absolute values of V E and Δ η of the mixture decrease with the increasing temperature. The V E , Δ η , and Δ n D can be fitted by the Redlich–Kister equation with satisfactory results. The concentration-dependent κ of the studied systems are fitted to Casteel–Amis equation, showing that the κ values of {[TMG]IM (1) + water (2)} mixture are much higher than those of {[TMG]IM (1) + ethanol (2)} mixture. [ABSTRACT FROM AUTHOR]

Densities and viscosities of binary mixtures of 8-hydrogen-1,8-diazabicyclo[5,4,0]-undec-7-enium imidazolide ([HDBU]IM) and 8-butyl-1,8-diazabicyclo[5,4,0]-undec-7-enium imidazolide ([BDBU]IM) ionic liquids (ILs) with water were measured at temperatures from T = (293.15 to 313.15) K. Excess molar volumes V E and viscosity deviations Δ η of the mixtures were calculated to study the intermolecular interactions and structural factors between ILs and water. The results show that the V E values of the two mixtures are negative over the whole composition range, while the Δ η values have positive deviations, indicating that the hydrogen bonding interactions between IL and water are dominant in the mixtures. Moreover, the absolute values of V E (| V E |) of {[HDBU]IM (1) + H 2 O (2)} system are larger than those of {[BDBU]IM (1) + H 2 O (2)} system at the same condition, indicating that the hydrogen bonding interactions between [HDBU]IM and water are stronger than those between [BDBU]IM and water. Both | V E | and Δ η values of the mixtures decrease with the increasing temperature, resulting from the decreasing the hydrogen bonding interactions between IL and water. Other derived properties of the studied systems, such as the apparent molar volumes, partial molar volumes, excess partial molar volumes, Gibbs free energy of activation for viscous flow, and excess Gibbs free energy of activation for viscous flow were also calculated from the experimental values. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on the molecular descriptors derived from COSMO-SAC, three novel QSPR models were established. • Model I was created to predict the self-diffusion coefficients of 70 ionic liquids. • Model II was established to predict the self-diffusion coefficients of ionic liquids with a fixed anion, [NTf 2 ]. • D B ∞-QSPR model for predicting the mutual diffusion coefficients of 32 ionic liquids was proposed with an AARD of 5.023%. • The effects of temperature and the cavity volume of ions were studied. Quantitative structure–property relationship (QSPR) models can offer theoretical prediction of physicochemical properties of ionic liquids (ILs), and the exploration of molecular descriptors that reflect the structural characteristics of ILs is of primary importance for QSPR models. Here, three novel QSPR models, termed as Model I, Model II and D B ∞ - QSPR model, are developed to predict the diffusion coefficient of ILs by using conductor-like screening model for segment activity coefficient (COSMO-SAC) based descriptors. The established Model I matches well with the experimental data set for both cations and anions, as evidenced by the high values of the coefficient of determination (R 2) (greater than 0.95) in the training set and the testing set. Model II can be used to calculate the self-diffusion coefficients of ILs with a fixed anion of [NTf 2 ], and the corresponding R 2 values are greater than 0.97 in the training set and the testing set. The mutual diffusion coefficients of ILs in water at infinite dilution (D B ∞) can reliably be predicted by D B ∞ - QSPR model, which demonstrates excellent predictive power because of the high values of R 2 (greater than 0.97) in the training set and the testing set. In addition, the value of average absolute relative deviation (AARD) between experimental and calculated D B ∞ is 5.023% in the overall set. According to the afore-mentioned QSPR models, the diffusion coefficient of ILs is positively correlated with temperature and negatively correlated with the cavity volume of ion. [ABSTRACT FROM AUTHOR]

• Influence of introduction of alkyl substituents in primary alkanolamine ligands on DFILs's properties was studied. • Alkyl groups at α or β position adjacent to NH 2 of alkanolamines can increase CO 2 capture capacity of DFILs. • Alkyl groups of alkanolamines at α position have greater influence on DFILs's CO 2 absorption than β position. • CO 2 absorption capacity of [K(AMP) 2 ][Im] was 1.19 mol CO 2 /mole IL at T = 333.2 K. • The saturated CO 2 capacity of DFILs has a linear relation with the thermal expansion coefficient. To reveal the effects of the alkyl substitutions at alpha (α) or beta (β) position adjacent to amino group of primary alkanolamine ligands on CO 2 absorption and physicochemical properties of metal chelated dual functional ionic liquids (DFILs), four DFILs were prepared by reacting potassium imidazole salt (KIm) with alkanolamine ligands, including 2-amino-2-methyl-1-propanol (AMP), 2-amino-1-butanol (AMB), DL-1-amino-2-propanol (DLAMP), and monoethanolamine (MEA). CO 2 absorption behavior and mechanism of DFILs were studied, and density (ρ), speed of sound (u), and viscosity (η) of DFILs were measured to correlate with the CO 2 absorption performance. DFT calculations were employed to explore the influence of the interactions between K+ and alkanolamine on the CO 2 absorption and physicochemical properties of DFILs. The results show that CO 2 capacity at 333.2 K is as follows: [K(AMP) 2 ][Im] > [K(AMB) 2 ][Im] > [K(DLAMP) 2 ][Im] > [K(MEA) 2 ][Im], indicating that the introduction of alkyl group at α or β position of alkanolamines can enhance CO 2 capacity, and the effect of the α position is more significant than the β position. Both ρ and u follow the order: [K(AMP) 2 ][Im] < [K(AMB) 2 ][Im] < [K(DLAMP) 2 ][Im] < [K(MEA) 2 ][Im], while η is in the reverse order. Moreover, the saturated CO 2 capacity of DFILs has an approximately linear relation with the thermal expansion coefficient. DFT calculations show that the presence of the alkyl group at α or β position of alkanolamines reduces the Mulliken charge of N and O atom, thereby weakening the cation coordination interaction between K+ with ligand, resulting in the decrease in ρ and u of DFILs. Moreover, the decrease in the Mulliken charge of N and O atom in alkanolamine leads to the increase of chelated cation-[Im]− interaction, thereby increasing η of DFILs. Consequently, [K(AMP) 2 ][Im] exhibits higher CO 2 capacity and good reversibility, due to the fact that CO 2 can react with the chelated cation and [Im]– simultaneously. The present study provides a new method for effectively regulating the performance of DFILs. [ABSTRACT FROM AUTHOR]