Continuous Gas Dehydration Using the Hygroscopic Ionic Liquid [EMIM][MeSO3] as a Promising Alternative Absorbent

Continuous gas drying experiments with the hygroscopic ionic liquid [EMIM][MeSO₃] show that it can be a very promising alternative drying agent to the absorbent triethylene glycol (TEG) commonly used in industrial gas drying processes. The HTU/NTU model in combination with the correlations of Onda et al. for mass transfer coefficients can be applied for the design of an absorption process with [EMIM][MeSO₃]. The major advantage of this ionic liquid (IL) is that well‐known problems associated with the regeneration of the absorbent TEG can be avoided using [EMIM][MeSO₃] due to extremely low vapor pressure and possible regeneration with air. The drying capacity of the IL system is about two times higher compared to TEG. Hence, a simple plant design comparable to that of industrial adsorption plants might be applied.     

Air-drying with ionic liquids

Ionic liquids (ILs) are employed for air-drying for the first time. The experimental gas–liquid equilibrium (EQ) of N₂/O₂ + [EMIM][BF₄] and N₂/O₂ + [EMIM][BF₄] + H₂O systems under a broad temperature range are measured. The new modified UNIFAC-Lei model is successfully extended to predict the N₂/O₂-IL-H₂O system based on extensive phase EQ data. The air-drying experiment using [EMIM][BF₄] as an absorbent is conducted, confirming that this new technology is effective and efficient. © 2018 American Institute of Chemical Engineers AIChE J, 65: 479–482, 2019     

Thermodynamic properties of 1‐ETHYL‐3‐methylimidazolium methanesulphonate with aromatic sulphur,nitrogen compounds at T = 298.15–323.15 K and P = 1 bar

This work investigates the ability of 1‐ethyl‐3‐methylimidazolium methanesulphate ([EMIM][MeSO₃]) as a green and tuneable solvent for denitrification and desulphurisation studies. Experimental density, surface tension and refractive index data have been measured for the following systems: [EMIM][MeSO₃] (1) + pyridine (2), [EMIM][MeSO₃] (1) + pyrrole (2), [EMIM][MeSO₃] (1) + quinoline (2), [EMIM][MeSO₃] (1) + indoline (2), [EMIM][MeSO₃] (1) + thiophene (2) and [EMIM][MeSO₃] (1) + water (2) over the entire mole fraction of [EMIM][MeSO₃] at T = 298.15–323.15 K and P = 1 bar. Further from experimental density, surface tension and refractive index, coefficient of thermal expansivity, excess molar volume, deviation of surface tension and refractive index deviation were also calculated. It was found that the heteroaromatic nitrogen/sulphur compounds are completely miscible in [EMIM][MeSO₃]. The surface tension values were found to increase while the refractive index decreases with increasing mole fraction of [EMIM][MeSO₃]. The experimental values for surface tension increased in the order: pyridine > thiophene > pyrrole > indoline > quinoline > water and for refractive index: pyridine > pyrrole > indoline > quinoline > thiophene > water. It was found that the composition of [EMIM][MeSO₃] has a greater influence than temperature in deciding the surface, optical and thermodynamic properties for similar molecular interaction such as IL–thiophene and IL–pyrrole than dissimilar molecules such as IL–water. Further quantum chemical‐based COSMO‐RS tool was used to estimate the activity coefficient at different composition. © 2012 Canadian Society for Chemical Engineering     

Effect of small amount of water on the dynamics properties and microstructures of ionic liquids

A series of systems of 1‐butyl‐3‐methylimidazolium acetate ([Bmim][Ac]), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF₄]), and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf₂N]) with a small amount of water were simulated. Viscosities of systems were obtained by nonequilibrium molecule dynamics simulation and the results show that the viscosities change in different ways: for [Bmim][BF₄] and [Bmim][Tf₂N], viscosities decrease rapidly in the first stage, and then decrease slowly with the increase of water content. But for [Bmim][Ac], the viscosities increase first and then decrease. The unique phenomenon of [Bmim][Ac] can be attributed to the formation of chain‐like structure of anion???water???anion???. Hydrogen bond (HB) interaction between ion pairs is weakened, but the number of HB between water and anions increases with increase of water content. Besides, the microstructures of water in ionic liquids‐water systems were compared and found that the distribution of water is more concentrated in [Bmim][Tf₂N]‐H₂O system, while it is isotropy in [Bmim][Ac]‐H₂O system. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2248–2256, 2017     

Modified COSMO-UNIFAC model for ionic liquid–CO2 systems and molecular dynamic simulation

A new predictive molecular thermodynamic model (i.e., modified COSMO-SAC-UNIFAC) was first proposed and extended to predict the solubility of CO₂ in pure and mixed ionic liquids (ILs) at the temperatures down to 263.2 K. It is interesting to discover that with equimolar amounts, the solubility of CO₂ in such 1:1 IL pairs, that is, [A₁][B₁] + [A₂][B₂] and [A₁][B₂] + [A₂][B₁], was consistent at the same temperature and pressure in the case of exchanging their respective cations and anions. The molecular dynamic (MD) simulation for CO₂ + mixed ILs was performed to deeply analyze and explain this intriguing phenomenon. Not only the CO₂ gas drying experiment with the ILs ([C2mim][OAc], [C2mim][dca], and [C2mim][OAc] + [C2mim][dca]) as absorbents but also the corresponding process simulation and optimization were made to stress the effectiveness and applicability of the new thermodynamic model. Thus, this work ranges from molecular level to systematic scale.     

UNIFAC model for ionic liquid‐CO (H2) systems: An experimental and modeling study on gas solubility

The universal quasichemical functional‐group activity coefficients (UNIFAC) model for ionic liquids (ILs) has become notably popular because of its simplicity and availability via modern process simulation softwares. In this work, new group binary interaction parameters (α_mn and α_nm) between CO (H₂) and IL groups were obtained by correlating the solubility data in pure ILs at high temperatures (above 273.2 K) collected from the literature. the solubility of CO in [BMIM]⁺[BF₄]^?, [OMIM]⁺[BF₄]^?, [OMIM]⁺[Tf₂N]^?, and their mixtures, as well as that of H₂ in [EMIM]⁺[BF₄]^?, [BMIM]⁺[BF₄]^?, [OMIM]⁺[Tf₂N]^?, and their mixtures, at temperatures from 243.2 to 333.2 K and pressures up to 6.0 MPa were measured. The UNIFAC model was observed to well predict the solubility in pure and mixed ILs at both high (above 273.2 K) and low (below 273.2 K) temperatures. Moreover, the selectivity of CO (or H₂) to CO₂ in ILs increases with decreasing temperature, indicating that low temperatures favor for gas separation. © 2014 American Institute of Chemical Engineers AIChE J 60: 4222–4231, 2014     

Self‐healing imidazolium‐based ionene‐polyamide membranes: an experimental study on physical and gas transport properties

A new series of six imidazolium‐based ionenes containing aromatic amide linkages has been developed. These ionene‐polyamides are all constitutional isomers varying in the regiochemistry of the amide linkages (para, meta) and xylyl linkages (ortho, meta, para) along the polymer backbone. The physical properties as well as the gas separation behaviors of the corresponding membranes have been extensively studied. These ionene‐polyamide membranes show excellent thermal and mechanical stabilities, together with self‐healing and shape memory characteristics. Most importantly, [TC‐API(p)‐Xy][Tf₂N] and [IC‐API(m)‐Xy][Tf₂N] membranes (TC, terephthaloyl chloride; API, 1‐(3‐aminopropyl)imidazole; Xy, xylyl; Tf₂N, bis(trifluoromethylsulfonyl) imide; IC, isophthaloyl chloride), where the amide and xylyl linkages are attached at para and meta positions, exhibit superior selectivity for CO₂/CH₄ and CO₂/N₂ gas pairs. We also demonstrate the transport properties and diverse applicability of our newly developed ionene‐polyamides, particularly [TC‐API(p)‐Xy][Tf₂N], for various industrial applications. © 2019 Society of Chemical Industry     

Thermal conductivity of the ionic liquid [HMIm][Tf2N] with compressed carbon dioxide

The liquid thermal conductivity of the ionic liquid (IL), 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), saturated with compressed vapor and supercritical carbon dioxide was measured over three isotherms (298.15, 323.15, and 348.15 K) and pressures up to approximately 20 MPa using a transient hot-wire technique. Pure [HMIm][Tf₂N] thermal conductivity was also measured over a temperature range of 293.15–353.15 K at ambient pressure and with hydrostatic pressure to approximately 20 MPa. Literature vapor–liquid equilibrium data were used to predict the liquid CO₂ composition at the conditions investigated. Initially, the liquid thermal conductivity slightly decreased with pressure/composition of CO₂ followed by a gradual increase that is mainly attributed to hydrostatic pressure effects. Simple composition-based mixing rules for mixture properties are not qualitatively nor quantitatively accurate. These data could be used to engineer heat transfer equipment required for a variety of proposed IL applications in CO₂ capture, absorption refrigeration, biphasic CO₂/IL reaction platforms, etc.     

CO2 absorption properties of Brønsted acid-base ionic liquid composed of N,N-dimethylformamide and bis(trifluoromethanesulfonyl)amide

The solubilities of CO₂ and the liquid densities in a Brønsted acid-base ionic liquid, [DMFH][Tf₂N], composed of N,N-dimethylformamide (DMF) and bis(trifluoromethanesulfonyl)amide (HTf₂N) have been investigated at high pressures and at different temperatures. The results were compared with those in DMF and a typical 1-butyl-3-methylimidazolium analogue with the same anion, [BMIM][Tf₂N]. The mole fraction scaled solubilities of CO₂ in the three liquids showed a slight increase in the following order, DMF < [DMFH][Tf₂N] < [BMIM][Tf₂N], whereas more remarkable difference was observed in the volume scaled concentrations of CO₂, [BMIM][Tf₂N] < [DMFH][Tf₂N] « DMF, mainly due to the bulkiness of liquid entities.     

Molecular insight into the effect of ion structure and interface behavior on the ammonia absorption by ionic liquids

Molecular dynamics simulations were performed to elucidate the roles of ion structure and interface behavior in absorption of gases (NH₃, N₂, H₂) by ILs (protic IL [Bim][Tf₂N] and conventional IL [Bmim][Tf₂N]). The results indicated that NH₃ compete with [Tf₂N]⁻ to interact with N3-H site of [Bim]⁺ cation, forming a strong N3 H∙∙∙N(NH₃) hydrogen bond with the energy of −79 kJ/mol, which is twice as much as the energy of the hydrogen bond between C2 H of [Bmim]⁺ and NH₃ (−33.2 kJ/mol). Moreover, there is a dramatic increase in the number density of cations near the IL-gas interface, resulting in the NH₃ molecules permeate into the bulk rapidly and effectively and achieving the high selective absorption of NH₃ to H₂ and N₂. Considering the inevitable trace water in the raw gases, the influence of water was studied and it was shown that trace water can enhance the absorption of NH₃ by [Bim][Tf₂N].     

Ionic liquid mediated surface micropatterning of polymer blends

A polymer of intrinsic porosity (i.e., PIM‐1) has been blended with different ionic liquids (ILs) in order to evaluate the effect of the ILs on the microstructure of the polymer blend. [C₈MIM][Cl], [BMIM][DCa], [BMPyr][DCa], and [BMIM][Tf₂N] have been selected and were mixed with PIM‐1. Polymer blends containing up to 80 wt % of ILs were prepared by a casting method with chloroform as solvent. SEM images show that during the film formation a structuring of the surface appears depending on the nature and the concentration of ILs, with appearance of well‐defined microstructure in the case of [BMIM][Tf₂N] and [BMIM][DCa]. In the case of [BMIM][Tf₂N]/PIM‐1 film, the lower IL concentration induces the denser film with small micropatterns onto the surface. AFM analysis indicates that the ILs are well dispersed on the surface. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and water contact angle measurements show that a gradient of IL concentration is observed across the film thickness. It is demonstrated that ILs are versatile co‐solvents for inducing controlled micropatterns in polymer membrane surfaces. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46109.     

Ionic liquids for highly efficient methyl chloride capture and dehydration

A new methyl chloride (CH₃Cl) capture and dehydration process using two ionic liquids (ILs) was designed and systematically studied. ILs [EMIM][Ac] and [EMIM][BF₄] were screened out as CH₃Cl capture and drying absorbents through the COSMO-RS model. The result of solubility experiment suggests [EMIM][Ac] has an excellent solvent capacity for CH₃Cl at mild operation conditions. The bench-scale CH₃Cl absorption experiments further confirmed the outstanding CH₃Cl capture ability of [EMIM][Ac]. Besides, the water content of outlet gas can be decreased to 452 ppm (mass fraction) using [EMIM][BF₄] in the dehydration experiment. The industrial-scale CH₃Cl capture and dehydration process was simulated and optimized. Compared to the benchmarked triethylene glycol process, IL process has higher product purity (99.99 wt%), and lower energy consumption. The quantum chemical calculations clearly revealed the relationship between hydrogen bond and separation performance. This study provides a decision-making basis for designing green process associated with volatile organic compounds.     

Liquid‐liquid phase split in ionic liquid + toluene mixtures induced by CO2

High pressure carbon dioxide was dissolved in ionic liquid + toluene mixtures to obtain the conditions of pressure and composition where a liquid‐liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf₂N]^?) anion were selected: 1‐hexyl‐3‐methylimidazolium ([hmim]⁺), 1‐hexyl‐3‐methylpyridinium ([hmpy]⁺), triethyloctylphosphonium ([P₂₂₂₈]⁺), and tetradecyltrihexylphosphonium ([P₆₆₆₁₄]⁺). The solubility of CO₂ was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO₂ in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf₂N]. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2968–2976, 2015     

Aromatic sulfur‐nitrogen extraction using ionic liquids: Experiments and predictions using an a priori model

The tie‐line composition of three quaternary system namely 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]) ([EMIM][OAc]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM][EtSO₄]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium methylsulphonate ([EMIM][MeSO₃]) (1) + thiophene (2) + pyridine (3) + toluene (4) were experimentally determined at 298.15 K. The measured tie‐line data were successfully correlated with the nonrandom two liquid and UNIversal QUAsiChemical model prediction which gave less than 1% root mean square deviation (RMSD). [EMIM][MeSO₃] looks to be a promising solvent for the simultaneous separation having distribution ratios less than unity for both thiophene and pyridine. The quantum chemical‐based conductor like screening model for real solvent (COSMO‐RS) model was then used to predict the tie‐line composition of quaternary systems. COSMO‐RS gave the RMSD for the studied systems to be 8.41, 8.74, and 6.53% for the ionic liquids, respectively. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4806–4815, 2013     

A new approach of ionic liquid containing polymer sorbents for post-combustion CO2 scrubbing

Room temperature task-specific ionic liquids (TSIL) of 1-(2-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Im₂₁OH][Tf₂N]) or 2-hydroxyethyl(dimethyl)-isopropylammonium bis(trifluoromethylsulfonyl)imide ([N_ip,211OH][Tf₂N]) with superbase, 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU), has been combined with Torlon^® powders (<106 um) to simulate the potential benefits of integrating equimolar amounts of ionic liquids and superbase into hollow fibers in terms of both sorption uptake and kinetics. Approximately 44 wt% of an equimolar [Im₂₁OH][Tf₂N]-DBU in Torlon^® powders achieved CO₂ sorption uptake of 0.57 mmol CO₂/g at a CO₂ feed pressure of 0.1 atm and at 35 °C. Similar amounts of an equimolar [N_ip,211OH][Tf₂N]-DBU in Torlon^® powders showed CO₂ sorption uptake of 0.45 mmol CO₂/g at the same condition. The half time (time to reach M_t/M_∞ of 0.5) for Torlon^®, Torlon^®(62 mg)/[Im₂₁OH][Tf₂N]-DBU(48 mg) and [Im₂₁OH][Tf₂N]-DBU at low feed pressure (～1.5 psia CO₂) was approximately 4, 55, and 298 s, respectively demonstrating that imbibing an equimolar [Im₂₁OH][Tf₂N]-DBU into polymer powders substantially improved sorption kinetics compared to the neat counterpart. The sorption half time is expected to be even shorter for fibers with smaller characteristic polymer morphology domains. The current study also demonstrates a new experimental approach to characterize CO₂ sorption in an equimolar mixture of ionic liquids and superbase.     

Influence of ionic liquids under controlled water activity and low halide content on lipase activity

Room-temperature ionic liquids (ILs) can be used as reaction media for nonaqueous biocatalysis. However, the purity of ILs should be considered to understand the influence of ILs on enzyme activity. The major impurities in ILs are water and halide. In the transesterification of benzyl alcohol with vinyl acetate, the optimal water activities for lipases in [Omim][Tf₂N] were similar to those in organic solvents. The chloride impurity in [Omim][Tf₂N] seriously influenced the activity of lipase. In this work, the effect of ILs on lipase activity was investigated under controlled initial water activity and low halide content. The activity of lipase was highly dependent upon the anion structure of ILs. The initial reaction rate of lipases followed the order [Tf₂N]⁻>[PF6]⁻>[TfO]⁻>[SbF₆]⁻≈[BF₄]⁻. All tested lipases showed the highest activities in ILs containing [Tf₂N] anion. Particularly, [AAIM][Tf₂N] was shown as a suitable reaction medium for biocatalysis. Lipozyme IM showed the highest activity in this IL among tested ILs. Thermal stability of lipase was also investigated. The higher thermal stability of Novozym 435 was obtained in hydrophobic and water-immiscible ILs such as [Bmim][Tf₂N], [Edmim][Tf₂N], and [Bmim][PF₆].     

Synergistic Extraction of Lanthanides (III) with Mixtures of TODGA and Hydrophobic Ionic Liquid into Molecular Diluent

The extraction of lanthanides(III) from aqueous nitric acid solutions with N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and with mixtures of TODGA and the hydrophobic ionic liquid (IL) [C₄mim][Tf₂N] into 1,2-dichloroethane (DCE) has been investigated. The extraction efficiency of Ln(III) ions was greatly enhanced by the addition of a small amount of IL to an organic phase containing TODGA. The synergistic effect comes from the higher hydrophobicity of Ln(III) extracted species formed by TODGA and the weakly coordinating Tf₂N^? anions compared with those formed by TODGA and NO₃^? ions as the counter-anions. The partition of Tf₂N^? anions between the organic and aqueous phases is the dominant factor governing the extractability of lanthanides(III) with mixtures of TODGA and [C₄mim][Tf₂N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C₄mim][Tf₂N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C₄mim][Tf₂N], the partition of Tf₂N^? between two immiscible phases and the interaction between HTf₂N and TODGA in the organic phase should be taken into account. Possible reasons of the antagonistic effect in the TODGA–[C₄mim][Tf₂N] extraction system are discussed.     

Enhanced stability of <Emphasis Type="Italic">Candida antarctica</Emphasis> lipase B in ionic liquids

The activity and stability of lipase from Candida antarctica were investigated in the kinetic resolution of (R,S)-1-phenylethanol with vinyl acetate using ionic liquids (ILs) as reaction media. Among ILs tested, the highest activity of lipase was observed in [Edmim][Tf₂N]. In hydrophobic ILs such as [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim] [PF₆], lipase could retain its activity after 5 times reuse, while the activity of lipase in hydrophilic ILs and organic solvents was drastically decreased. The activities of lipase in [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim][PF₆] were also well maintained after 1 day incubation at 80 °C. The lipase suspended in [Edmim][Tf₂N] could be successfully reused 6 times without loss of activity.     

Solubility of carbon dioxide in ammonium-based ionic liquids: Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide

Solubility results of carbon dioxide (CO₂) in two ammonium-based ionic liquids, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N4,1,1,1][Tf₂N]) and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N1,8,8,8][Tf₂N]), are presented at pressures up to approximately 45 MPa and temperatures ranging from 303.15 K to 343.15 K. The solubility was determined by measuring bubble point pressures of mixtures of CO₂ and ionic liquid using a high-pressure equilibrium apparatus equipped with a variable-volume view cell. Sharp increase of equilibrium pressure was observed at high CO₂ compositions. The CO₂ solubility in ionic liquids increased with the increase of the total length of alkyl chains attached to the ammonium cation of the ionic liquids. The experimental data for the CO₂+ionic liquid systems were correlated using the Peng-Robinson equation of state.     

Power generation from waste heat: Ionic liquid-based absorption cycle versus organic Rankine cycle

Aspen Plus® simulations using the Peng-Robinson (PR-EOS) and the COSMO-SAC models were performed to study absorption power cycles (APCs) using mixtures of R-134a with two ionic liquids, [C₂C₁im][Tf₂N] or [C₆C₁im][Tf₂N], and compared against an R-134a organic Rankine cycle (ORC) operating under similar conditions. The PR-EOS results were in agreement with calculations from a PR model fitted to the R-134a + IL experimental phase equilibrium data. The APCs have similar efficiencies and outperform the ORC by 3%–46%, with the largest differences observed when operating with lower grade (lower T_H) heating sources, lower quality cooling (higher T_L), and lower subcooling in the pump inlet stream. The PR-EOS and the Conductor-like Screening Model Segment Activity Coefficient (COSMO-SAC) results follow similar trends, but numerical discrepancies are observed in the cycle efficiencies and stream flow rates and compositions due to differences in solubilities and enthalpy changes between both models, suggesting that improvements are needed to increase the accuracy of COSMO-SAC for these systems.