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The last decade saw an explosion of interest in using amine-functionalized materials for CO2 capture and conversion, and it is of great importance to elucidate the relationship between the molecular structure of amine-functionalized materials and their CO2 capacity. In this work, based on a new quantitative analysis method for the CO2 absorption mechanism of amino-acid ionic liquids (ILs) and quantum chemical calculations, we show that the small difference in the local structure of amine groups in ILs could lead to much different CO2 absorption mechanisms, which provides an opportunity for achieving higher CO2 capacity by structure design. This work revealed that the actual CO2 absorption mechanism by amino-acid ILs goes beyond the apparent CO2 /amine stoichiometry; a rigid ring structure around the amine group in ILs creates a unique electrostatic environment that inhibits the deprotonation of carbamic acid and enables actually equimolar CO2 /amine absorption., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Here we report a novel self-assembly induced solubilization strategy with nanostructured ionic liquids as solvents. Highly ordered mesoscopic structures featuring the solute as a key component, such as liquid crystals, were formed via self-assembly in nanostructured long-chain carboxylate ionic liquids, resulting in extremely high solubilities for sparingly soluble drug molecules.

The basicity of ionic liquids (ILs) underlies many important IL-based processes including the dissolution and conversion of cellulose, the capture of CO2, and metal catalysis. In this work, we have disclosed the nature of the basicity of ILs, i.e., the difference between the basicity of IL and the basicity of the molecular solvent and inorganic salt, through a quantitative electrostatic and electronic analysis of the molecular surface for the first time. The results reveal one of the distinctive properties of ILs (enhanced basicity over molecular solvents and inorganic salts with the same basic site) stemming from their special electrostatic environment and microstructure. The enhancement is significant, from either the electrostatic aspect or the covalent aspect of basicity. The peculiar electrostatic environment of ILs leads to stronger basicity than similar molecular solvents, and the relatively freer microstructure of ILs contributes to the enhancement of basicity over their inorganic analogues. These results are highly instructive for better understanding the unique value of ILs and designing novel ILs to improve the efficiency of basicity-related processes.

Ionic liquids (ILs) with relatively strong basicity often show impressive performance in chemical processes, so it is important to enhance the basicity of ILs by molecular design. Here, we proposed two effective ways to enhance the basicity of ILs: by weakening the cation-anion interaction strength and by employing the anion-tethered strategy. Notably, two quantum-chemical parameters, the most negative surface electrostatic potential and the lowest surface average local ionization energy, were adopted as powerful tools to demonstrate the electrostatic and covalent aspects of basicity, respectively, at the microscopic level. It was shown that, for the ILs with the same anion (acetate or trifluoroacetate), the basicity of the ILs could be enhanced when the cation-anion interaction strength was weakened. For the acetate anion-based ILs, the hydrogen-bonding basicity scale (β) increased by 29% when the cation changed from 1-butyl-3-methylimidazolium ([Bmim]) to tetrabutylphosphonium ([P4444]), achieving one of the highest reported β values for ILs. Moreover, it was also demonstrated that, when an amine group was tethered to the anion of the IL, its basicity was stronger than when it was tethered to the cation. These results are highly instructive for designing ILs with strong basicity and for improving the efficiency of IL-based processes, such as CO2 capture, SO2 and acetylene absorption, dissolution of cellulose, extraction of bioactive compounds, and so on.

A selective separation of vitamin D₃ and tachysterol₃ by solvent extraction with 7 organic solvents and 11 ionic liquids (ILs) has been reported. Among organic solvents sulfolane showed optimal extraction performance, giving only a selectivity of 1.44 for tachysterol₃ over vitamin D₃. ILs with unsaturated bonds demonstrated high selectivity probably due to their different π-π interactions with the two compounds. A pyrrolidinium-based ionic liquid, for example, [BMPr][NTf2], provided the highest selectivity up to 1.77. Acceptable selectivity and distribution coefficients were observed by a combination of organic solvents and ILs as extracting agents. In this work, the effects of concentrations, anions, cations, and substituent of ILs were investigated, which may provide a rational strategy for the design of novel ILs for extractive separation of structural analogues. The purification and recovery of vitamin D₃3 via continuous multistage extractions were simulated, indicating that IL-based liquid-liquid extraction might be superior to traditional organic solvents in practical production.

The room-temperature ionic liquids (RTILs) have potential in realizing the ethylene (C(2)H(4)) and acetylene (C(2)H(2)) separation and avoiding solvent loss and environmental pollution compared with traditional solvents. The interaction mechanisms between gases and RTILs are important for the exploration of new RTILs for gas separation; thus, they were studied by quantum chemical calculation and molecular dynamics simulation in this work. The optimized geometries were obtained for the complexes of C(2)H(4)/C(2)H(2) with anions (Tf(2)N(-), BF(4)(-), and OAc(-)), cation (bmim(+)), and their ion pairs, and the analysis for geometry, interaction energy, natural bond orbital (NBO), and atoms in molecules (AIM) was performed. The quantum chemical calculation results show that the hydrogen-bonding interaction between the gas molecule and anion is the dominant factor in determining the solubility of C(2)H(2) in RTILs. However, the hydrogen-bonding interaction, the p-π interaction in C(2)H(4)-anion, and the π-π interaction in C(2)H(4)-cation are weak and comparable, which all affect the solubility of C(2)H(4) in RTILs with comparable contribution. The calculated results for the distance of H(gas)···X (X = O or F in anions), the BSSE-corrected interaction energy, the electron density of H(gas)···X at the bond critical point (ρ(BCP)), and the relative second-order perturbation stabilization energy (E(2)) are consistent with the experimental data that C(2)H(2) is more soluble than C(2)H(4) in the same RTILs and the solubility of C(2)H(4) in RTILs has the following order: [bmim][Tf(2)N] > [bmim][OAc] > [bmim][BF(4)]. The calculated results also agree with the order of C(2)H(2) solubility in different RTILs that [bmim][OAc] > [bmim][BF(4)] > [bmim][Tf(2)N]. Furthermore, the calculation results indicate that there is strong C(2)H(2)-RTIL interaction, which cannot be negligible compared to the RTIL-RTIL interaction; thus, the regular solution theory is probably not suitable to correlate C(2)H(2) solubility in RTILs. The molecular dynamics simulation results show that the hydrogen bond between the H in C2 of the imidazolium cation and the anion will weaken the hydrogen-bonding interaction of the gas molecule and anion in a realistic solution condition, especially in the C(2)H(4)-RTIL system.

The separation of structurally similar compounds, such as cholic acid (CA) and deoxycholic acid (DCA), is challenging due to their nearly identical physicochemical properties. This study demonstrates a synergistic 'push and pull' strategy with an ionic liquid (IL) biphasic system for significantly enhanced CA/DCA separation efficiency. Ethyl acetate was selected as the feed solvent to 'push' CA into the IL-rich extractant phase, while the IL 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) was chosen to 'pull' CA due to their strong hydrogen bonding interaction. This 'push and pull' system yielded a remarkable CA/DCA selectivity up to 47.8, much higher than the case using n-butanol which pulls both CA and DCA. The underlying separation mechanism was elucidated through computational screening with COSMO-RS, NMR analysis, and solvatochromic measurements. Results revealed the critical roles of specific hydrogen bonding between the chloride anion of [EMIM]Cl and the hydroxyl/carboxyl groups of CA/DCA, along with nonspecific interactions between the feed solvent and CA/DCA. Thermodynamic analysis of the phase transfer process confirmed the 'push and pull' synergy is energetically favorable for preferentially transferring CA from the ethyl acetate feed solution into the IL-rich extractant phase. Multi-stage simulation indicated that 99% purity and recovery of both CA and DCA can be obtained through this biphasic system under optimized conditions. Overall, strategically tuning both the feed solvent and IL extractant could significantly enhance the separation efficiency of structurally similar compounds while minimizing solvent and energy consumption. This 'push and pull' approach may shed light on improving separation processes for other structural analogues. [ABSTRACT FROM AUTHOR]

Ionic liquid (IL)‐stabilized metal nanoparticles (NPs) have attracted increased attention as novel catalysts for various reactions due to their excellent stability and high activity. However, the high viscosity of ILs limits their applications. Here, for the first time, we reported an NPs@IL‐cosolvent liquid–liquid biphasic system for metal NPs catalysis. The NPs were successfully confined to IL phase, and abundant IL droplets containing NPs were generated under the reactant flow. The NPs@IL droplets served as microreactors for the catalysis; while the low viscosity organic phase enabled the rapid mass transfer of substances. The biphasic system exhibited improved performance for acetylene hydrochlorination than that of the pure IL system. An acetylene conversion of 98% and a selectivity of 99.5% were achieved along with a 90% decrease on IL usage. The tolerable gas hourly space velocity in the biphasic system for a satisfactory conversion was almost double that of the pure IL system. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2536–2544, 2018 [ABSTRACT FROM AUTHOR]

The selective separation of strongly hydrophilic structurally related compounds in aqueous solutions is a long‐standing challenge due to a trade‐off between separation selectivity and capacity. This work shows a new method to separate strongly hydrophilic structurally related compounds through hydrophobic ionic solution‐based liquid‐liquid extraction, with L‐ascorbic acid 2‐glucoside (AA‐2G) and L‐ascorbic acid as model compounds. Extraordinary distribution coefficient, superb molecular selectivity, large extraction capacity and good recyclability without using strong acids and salts were all achieved, with a small consumption of phosphonium bromide ionic liquid and aprotic molecular diluent. The essence of this method is the successful combination of both strong hydrogen‐bond basicity and good hydrophobicity along with significant preferential solvation phenomena of the constructed ionic solutions. Even if at a high feed concentration of 100 mg/mL, the purity of AA‐2G could be greatly elevated from 50% to 96.2% with an ultrahigh yield of almost 100% after five‐stage countercurrent extraction. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1373–1382, 2018 [ABSTRACT FROM AUTHOR]

Ionic liquid (IL) supported metal-organic framework (MOF) was utilized to efficiently separate acetylene from ethylene. A common IL, 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]), was encapsulated into a hydrothermally stable MOF, namely MIL-101(Cr). Characterization techniques including FTIR, Powder X-ray diffraction, BET, and thermal gravimetric analysis were used to confirm successful encapsulation of the IL within MIL-101(Cr). Adsorption isotherms of acetylene and ethylene in the IL-encapsulated MOF were tested. From the results, the MOF composite retained a relatively high adsorption capacity. Remarkably, the adsorption selectivity of acetylene/ethylene has dramatically increased from 3.0 to 30 in comparison with the parent MIL-101(Cr). Furthermore, the potential of industrial practice was examined by breakthrough and regeneration experiments. It not only satisfies the industrial production of removal of low level of acetylene from ethylene, but also is notably stable during the adsorption-desorption process. The high designability of ILs combined with richness of MOFs' structures exploits a novel blueprint for gas separation. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2165-2175, 2017 [ABSTRACT FROM AUTHOR]

Water is an ideal green solvent for the solubilization and separation of valued-added bioactive compounds in various chemical and biological processes, partly because water has a minimal impact on the environment and few safety issues. However, many bioactive compounds exhibit hydrophobic properties, which leads to their limited solubility in water and substantially hinders the development of green separation technologies using aqueous media. In this study, we construct a family of new water/ionic liquid (IL) mixtures with amphiphilic, anionic functional long-chain carboxylate ionic liquids (LCC-ILs) for the solubilization and extraction of hydrophobic bioactive compounds (HBCs). The LCC-ILs integrate both weak polarity and strong hydrogen-bonding basicity and, more importantly, have excellent lipophilicity while still being water-miscible; therefore, the water/LCC-IL mixtures exhibit extremely high solubilities for various HBCs. The quantitative solubilities (g g−1) of various HBCs, including tocopherol, perillyl alcohol, rutin, and ginkgolides, are as high as 1.46, 0.71, 0.39 and 0.43, respectively, at 35 °C in water/LCC-IL mixtures, which are the highest solubilities in aqueous solutions ever reported. The water/LCC-IL mixtures also exhibit excellent performance in the extraction of tocopherols from biomass with a yield 2 to 12 times that in common solvents. The microscopic solvent properties and dissolution mechanism were investigated. Nano-micelles were observed when tocopherol was dissolved in water/LCC-IL mixtures, and their dissolution ability was dependent on the alkyl chain length and the concentration of LCC-ILs. These results demonstrated the considerable potential of water/LCC-IL mixtures as promising green solvents for the solubilization and separation of HBCs. [ABSTRACT FROM AUTHOR]

The last decade saw an explosion of interest in using amine-functionalized materials for CO2 capture and conversion, and it is of great importance to elucidate the relationship between the molecular structure of amine-functionalized materials and their CO2 capacity. In this work, based on a new quantitative analysis method for the CO2 absorption mechanism of amino-acid ionic liquids (ILs) and quantum chemical calculations, we show that the small difference in the local structure of amine groups in ILs could lead to much different CO2 absorption mechanisms, which provides an opportunity for achieving higher CO2 capacity by structure design. This work revealed that the actual CO2 absorption mechanism by amino-acid ILs goes beyond the apparent CO2/amine stoichiometry; a rigid ring structure around the amine group in ILs creates a unique electrostatic environment that inhibits the deprotonation of carbamic acid and enables actually equimolar CO2/amine absorption. [ABSTRACT FROM AUTHOR]

A class of new ionic liquid (IL)-based nonaqueous lyotropic liquid crystals (LLCs) and the development of an efficient IL extraction process based on LC chemistry are reported. The nonaqueous LLCs feature extraordinarily high extraction capacity, excellent separation selectivity, easy recovery, and biocompatibility. This work also demonstrates that the introduction of self-assembled anisotropic nanostructures into an IL system is an efficient way to overcome the intrinsically strong polarity of ILs and enhances the molecular recognition ability of ILs. The distribution coefficients of IL-based LLCs for organic compounds with H-bond donors reached unprecedented values of 50-60 at very high feed concentrations (>100 mg mL−1), which are 800-1000 times greater than those of common ILs as well as traditional organic and polymer extractants. The IL-based nonaqueous LLCs combining the unique properties of ILs and LCs open a new avenue for the development of high-performance extraction methods. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) have been proposed as promising solvents for separating C2H2 and C2H4, but screening an industrially attractive IL with high capacity from numerous available ILs remains challenging. In this work, a rapid screening method based on COSMO-RS was developed. We also present an efficient strategy to improve the C2H2 capacity in ILs together with adequate C2H2/C2H4 selectivity with the aid of COSMO-RS. The essence of this strategy is to increase molecular free volume of ILs and simultaneously enhance hydrogen-bond basicity of anions by introducing flexible and highly asymmetric structures, which is validated by a new class of tetraalkylphosphonium ILs featuring long-chain carboxylate anions. At 298.1 K and 1 bar, the solubility of C2H2 in ILs reaches 0.476 mol/mol IL, very high for a physical absorption, with a selectivity of up to 21.4. The separation performance of tetraalkylphosphonium ILs to the mixture of C2H2/C2H4 was also evaluated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2016-2027, 2015 [ABSTRACT FROM AUTHOR]

Separation of high value bioactive compounds is a viable route to make full use of the biomass resources and improve the profitability. However, the sparing aqua- and lipo-solubility of the bioactive compounds makes their separation really challenging. Considering that ionic liquids show good solubility of biomass and could easily form biphasic systems with organic solvents, an ionic liquid (IL)-based biphasic system consisting of ionic liquid, water and ethyl acetate is proposed in this study. Ginkgolide homologues were selected as model compounds to evaluate its practicality. Adequate distribution coefficients, relatively high extraction capacity and selectivity were obtained with the novel biphasic system. The improved distribution coefficients of the ginkgolides are mainly attributed to the multiple interactions between ginkgolide and IL, which were confirmed by means of quantum chemistry calculations. Moreover, the effect of the interactions between ginkgolides and the extraction solvent on the selectivity coefficient was studied by measuring the Kamlet–Taft parameters of the extraction solvent. Based on the results of fractional extraction, which was simulated by calculation and validated by experiments, as well as the comparison of organic solvent consumption, the employed IL-based extraction would be a valid and clean method as an alternative to chromatographic methods for separating bioactive compounds in large-scale operations. It is noteworthy that the amount of organic solvents consumed with this method was supposed to be less than 1/11 of the most widely used chromatographic method. [ABSTRACT FROM AUTHOR]

Thedesign of a biphasic system is important for the developmentof liquid–liquid extraction and biphasic catalysis. In thiswork, we report a series of ternary biphasic systems that consistof hydrophilic ionic liquid (IL), water, and ethyl acetate. The effectsof the structure of the ILs (cation, anion, and substituent group),IL/water ratio, and temperature on the phase equilibrium of thesebiphasic systems were investigated. The mutual solubility was lowerin the IL/water–ethyl acetate biphasic system than in the water–ethylacetate system when ILs with strong hydration ability were introduced,such as [EMIm]OAc, [EMIm]Cl, [EMIm]NO3, [EMIm]EtSO4, and [HOEMIm]Cl. In addition, the hydrogen-bonding basicityof the IL-containing phase could be tuned by changing the IL structureor IL/water ratio. These novel IL/water-ethyl acetate biphasic systemsmay present another option in addition to hydrophobic IL–waterand aqueous biphasic systems for liquid–liquid extraction. [ABSTRACT FROM AUTHOR]

As environmentally friendly and designablesolvents, ionic liquids (ILs) have great potential in the separationof C2H4and C2H2, whichis quite important in chemical industry. The microscopic insight intothe intermolecular interaction and the diffusion dynamics at a molecularlevel is crucial for designing more efficient ILs. In this work, theinteraction mechanism and diffusion dynamics for C2H4/C2H2absorption and separation withfive ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium acetate ([bmim][OAc]), 1-butyl-3-methylimidazoliumtrifluoroacetate ([bmim][TFA]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([bmim][Tf2N]), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide([bmpyrr][Tf2N]), were investigated by molecular dynamics(MD) simulation. The result suggests that the van der Waals interactionbetween C2H4and cation plays an important rolein C2H4dissolution in ILs, but the hydrogenbonding interaction between C2H2and anion isforemost in C2H2dissolution. Moreover, theinteraction energy analysis matches better with the experimental solubilitythan our previous quantum chemical calculation, indicating the superiorityof the MD simulation approach in studying the interaction mechanismof IL-based systems where multiple interactions are often present.The self-diffusion coefficients of cations and anions of ILs do notchange obviously after adding C2H4, while theyhave a significant increase after dissolving C2H2, particularly in relatively strong hydrogen bonding systems [bmim][OAc]–C2H2. [ABSTRACT FROM AUTHOR]

Abstract: The solution of ionic liquid (IL) bmimCl and polar organic solvent formamide (FA) were used to form nonaqueous microemulsions in cyclohexane by the aid of surfactant Triton X-100 (TX-100). The phase behavior of the bmimCl–FA/TX-100/cyclohexane system at 25±0.1°C was studied. Electrical conductivity measurement was used to identify the microstructures of the nonaqueous microemulsions. Based on the phase diagram, the reverse microemulsions containing bmimCl–FA as the internal phase were investigated by the dynamic light scattering (DLS) and UV–vis spectroscopy. The result of DLS experiments confirmed the formation of reverse microemulsions of bmimCl–FA in cyclohexane. The UV–vis studies with methyl orange (MO) and methylene blue (MB) as absorption probes further confirmed the existence of reverse microemulsions. UV–vis studies using CoCl2 as probe also indicated that the reverse microemulsions could dissolve metal salt. [Copyright &y& Elsevier]

A study was carried out concerning the effects of anionic liquid(IL) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) on the properties of nonionic surfactant-based H2O +Triton X-100 (TX-100) + hexanol + cyclohexane microemulsions. Severalproperties of microemulsions, such as polarity, conductivity, viscosity,and droplet size, were investigated with the massratio of TX-100/hexanol/cyclohexane = 3:2:7. With the addition ofIL, the polarity of the microemulsions increases. Conductivity resultsreveal that the onset water content of electrical percolation decreaseswith the presence of IL and continues to decrease as the amount ofIL increases. The viscosity of microemulsions increases with the increasingamount of IL. Dynamic light scattering (DLS) measurements indicatethat the droplet sizes of microemulsions increase with the additionof IL. All results presented in this study suggest that the IL issolubilized into the polar core of microemulsions. [ABSTRACT FROM AUTHOR]

Abstract: The effect of ionic liquids (ILs) on temperature-induced percolation of water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane microemulsions was investigated. Several properties of microemulsions, including percolation temperature threshold (T p), viscosity, and droplet size were used to demonstrate the effect of the structure of ILs on percolation phenomena. Percolation phenomena of microemulsions were clearly observed after the addition of IL, and the T p of microemulsions increased with increases in the ILs concentration. In addition, T p was greatly affected by the alkyl side-chain length of imidazolium cation and increased with increases in chain length. However, T p was slightly affected by the ILs anions due to the charge exclusion caused by the head group of surfactant. Additionally, the viscosity and droplet size of microemulsions decreased with the addition of ILs, and the observed decrease correlated roughly with an increase in T p. These results also confirm the influence of ILs on percolation phenomena of the microemulsions. [Copyright &y& Elsevier]

Abstract: This article tries to provide a feasible approach to solving current problems of ionic liquid (IL) mediated liquid–liquid extraction such as large viscosity, relatively high polarity and considerable cost. The performance of IL–cosolvent mixtures instead of pure ILs as extractant was systematically studied for the first time, taking the extractive separation of tocopherol homologs as an example. The adjustment of separation efficiency through both the structures of IL and cosolvent and their relative amount was conducted. Moreover, the synergistic effect between IL and cosolvent was revealed. A large separation selectivity, adequate distribution coefficient, low viscosity, and low consumption of IL can be simultaneously achieved in the IL–cosolvent–hexane biphasic system. For example, while using the 2:98 [bmim]Cl–acetonitrile mixture (molar ratio) as the extractant (viscosity was only about 0.44mPas) at 303.15K, the selectivity of δ-tocopherol to α-tocopherol was 11.3, four times larger than that using pure acetonitrile, and the distribution coefficients of δ-, β&γ-, and α-tocopherol were 4.07, 2.02, and 0.36, respectively, at least eighteen times larger than those using pure [bmim]Cl. A quantitative correlation between the selectivities of different tocopherol homologs and the hydrogen-bond basicity of IL–cosolvent mixtures was established with a linear equation. Overall, this work demonstrated that improved separation efficiency might be achieved by using IL–cosolvent mixtures as extractant compared to using pure IL or pure cosolvent. [Copyright &y& Elsevier]