Ionic Liquid Solutions Research Articles

Experimental study on chemical structure and wetting influence of imidazole ionic liquids on coal

Three imidazole ionic liquid solutions were selected to handle coal with distinct degrees of metamorphism to research the influences of cation and anion ions in ionic liquids on functional groups and the relationship between functional groups and coal wettability. The chemical framework of coal was researched by FTIR and the wetting peculiarity of the coal was researched by contact angle meter. FTIR analysis showed that the cation and anion ions in ionic liquids significantly altered the framework of the coal. The contact angle measurement results demonstrated that compared with coal using pure water, the coal handled with ionic liquids showed a smaller contact angle. Finally, the relationship between contact angle and functional group content was analyzed. The results showed that the anions and cations of different ionic liquids can increase the content of hydrophilic groups in coal dust with different metamorphisms, such as OH···O, CO, and CO, and destroy the hydrophobic groups in the dissolved coal structure, such as CH2, CH and the benzene ring 3 substitutions. And 2 % [Emim][BF4] can effectively reduce the coal contact angle and improve the wettability of coal dust. The content of CO and OH···O groups had the greatest correlation with the contact angle, which were 0.845 and 0.754, respectively. By studying the influence of anions and cations in ionic liquids on the content of functional groups in coal, the effect of specific anions and cations on coal structure was further discovered, which provides a theoretical basis for the development of new ionic liquids with specific functions, and provides guiding significance for ionic liquid solutions to improve the wettability of coal and reduce the dust concentration.

Ionic-Liquid-Based Aqueous Two-Phase Systems Induced by Intra- and Intermolecular Hydrogen Bonds.

In recent years, aqueous two-phase systems (ATPSs) have been widely used in different fields and have become an increasingly attractive subject due to their application in the separation and purification of biomolecules. In this work, the aqueous phase behavior of ionic liquids (ILs) was modulated by changing the cis-trans structure of the anion in ILs. With the same tetra-butyl-phosphine as the cation, the cis-anion exhibited upper critical solution temperature (UCST) phenomena. In contrast, the trans-anion exhibited lower critical solution temperature (LCST) phenomena. The proposed mechanism shows that the main factors responsible for these phenomena include variations in the dissociation degree with temperature and the steric hindrance of the ILs. This phase behavior combines the chemical equilibrium in a solution with the microstructure of the molecule and is useful for constructing new chemical dynamic equilibria in ATPS. As an example of its application, aqueous solutions of both ILs can be used for the efficient separation and extraction of specific amino acids. The two ATPS systems reported in this work highlight a simple, effective, and environmentally friendly method for separating small biological molecules.

Recent Research Progress of Ionic Liquid Dissolving Silks for Biomedicine and Tissue Engineering Applications.

Ionic liquids (ILs) show a bright application prospect in the field of biomedicine and energy materials due to their unique recyclable, modifiability, structure of cation and anion adjustability, as well as excellent physical and chemical properties. Dissolving silk fibroin (SF), from different species silkworm cocoons, with ILs is considered an effective new way to obtain biomaterials with highly enhanced/tailored properties, which can significantly overcome the shortcomings of traditional preparation methods, such as the cumbersome, time-consuming and the organic toxicity caused by manufacture. In this paper, the basic structure and properties of SF and the preparation methods of traditional regenerated SF solution are first introduced. Then, the dissolving mechanism and main influencing factors of ILs for SF are expounded, and the fabrication methods, material structure and properties of SF blending with natural biological protein, inorganic matter, synthetic polymer, carbon nanotube and graphene oxide in the ILs solution system are introduced. Additionally, our work summarizes the biomedicine and tissue engineering applications of silk-based materials dissolved through various ILs. Finally, according to the deficiency of ILs for dissolving SF at a high melting point and expensive cost, their further study and future development trend are prospected.

Explication of molecular interactions between leucine and pharmaceutical active ionic liquid in an aqueous system: Volumetric and acoustic studies

Ionic liquids and their performance for industrial objectives have focused on some of the most academic and scientific research efforts in the last decade. The densities and sound velocities of amino acid (L-leucine) in an aqueous solution of a pharmaceutically active ionic liquid 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIm][PF6] were measured at different temperatures (293.15 K to 318.15 K) under atmospheric pressure. The experimental results were further used to compute apparent and partial molar volumes, partial molar expansion, Hepler’s constant, apparent and partial molar isentropic compression, alongwith corresponding empirical constants (Sv and Sk), intermolecular free length Lf and acoustic impedance Z. The negative values are obtained for partial molar volume of transfer, ΔtVΦo at all temperatures, and become more negative by increasing the concentration of ionic liquid which indicates predominance of strong electrostriction. The obtained values of these parameters show the structure-making/breaking ability of leucine in solutions of ionic liquid that favours solute–solvent interactions.

Modeling of CH4/CO2 hydrate phase behavior in organic and electrolyte inhibitors by dickens’ model

The main purpose of this study is investigating a reliable and convenient model based on Dickens and Quinby-Hunt approach to predict CH4/CO2 gas hydrate equilibrium temperature in presence of organic inhibitors (e.g., methanol, ethanol, ethylene glycol, triethylene glycol, glycerol), and electrolyte inhibitors (e.g., NaCl, KCl, NaBr, KBr, CaCl2, CaBr2, MgCl2, EMIM-Cl, BMIM-Cl, BMIM-Br, BMIM-I, BMIM-DCA, EMIM-HSO4, EMIM-EtSO4, and EMIM-MeSO4). This model named as Dickens’ model is an activity-based model and to calculate water activity of organic solutions the nonrandom two-liquid (NRTL) and Margules was used. Also, Pitzer model was employed to calculate activity of water in electrolyte solutions. A correlation was suggested to determine enthalpy of hydrate dissociation in terms of inhibitor weight percent and equilibrium pressure. Due to no data in open literature, the virial coefficients of Pitzer model in ionic liquid solutions were adjusted. The model results were compared with available experimental data from open literature and observed to be in good agreement with the reported literature.

Microheterogeneity-Induced Vibrational Spectral Dynamics of Aqueous 1-Alkyl-3-methylimidazolium Tetrafluoroborate Ionic Liquids of Different Cationic Chain Lengths.

We have monitored the impacts of an increment in the alkyl chain length of the imidazolium-based tetrafluoroborate ionic liquids on the local deuteroxyl probe modes of interest. For this study, we have taken 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIm][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4], 1-octyl-3-methylimidazolium tetrafluoroborate [OMIm][BF4], and 1-decyl-3-methylimidazolium tetrafluoroborate [DMIm][BF4] ionic liquid solutions with 5% HOD in H2O as the vibrational reporter of the associated ultrafast system dynamics. Classical molecular dynamics (MD) simulations were employed to determine molecular structure and dynamic properties, while the spectral profiles were derived by applying the wavelet analysis of classical trajectories. Spatial distribution functions reveal the heterogeneity within the molecular structures of the ionic liquids (ILs) with varying alkyl chain lengths. The intense position of the spectral peak, the frequency corresponding to the shoulder peak, and the spectral linewidth of the O-D stretch distribution are not influenced by the increment in the cationic chain length. In addition, the ionic liquid (IL) [BMIm][BF4] exhibits a notable trend; the dynamic timescales are longer than the other studied systems. Therefore, we have performed the Voronoi decomposition analysis of the ionic and the polar-apolar domains, symmetrically increasing the length of alkyl chains on the IL cations. Domain analysis reveals structural microheterogeneity; the anions form discrete domains, and the ionic liquid constituting cations form continuous domains irrespective of the alkyl chain length on the imidazolium cations. Therefore, this computational ultrafast spectroscopy study aids in forming a molecular-level picture of the ionic liquid cations and anions in the liquid phase, providing a detailed interpretation of the spectral properties of the probe stretching vibrations.

Soluble Hybrid Ionic Semiconductor and Its Photovoltaic Effect in Solution.

Semiconductor materials were adopted in their solid states for photovoltaic applications owing to their nonsolubility and/or breaking of the photogenerated carrier transfer pathway in solution. The liquid-state photovoltaic device fills in a gap between currently prevailing full-solid-state and solid-liquid-state solar cells; however, reports on the photovoltaic effect from realistic semiconductor solution are absent so far. Herein, we report a hybrid inorganic-organic ionic semiconductor [Ni(Phen)3][V14O34Cl]Cl (Phen = 1,10-phenanthroline) and observe its photovoltaic effect in ionic liquid solution. This photovoltaic effect arises as a result of charge transfer between the coordination cation and inorganic polyoxovanadate in solution under illumination and subsequent transfer to electrodes. The liquid-state photovoltaic device (cell configuration: carbon cloth||[Ni(Phen)3][V14O34Cl]Cl in ionic liquid||Al foam) yields an open-circuit voltage of ca. 1.199 V and a photocurrent density of 3.268 mA cm-2 upon illumination using an air mass of 1.5 (100 mW cm-2) at 80 °C with a fill factor of 42.48% and an efficiency of 1.665%. This novel type of hybrid ionic semiconductor possesses great structural tunability for an optimized photovoltaic performance.

Cooperative catalytic effects between aqueous acidic ionic liquid solutions and polyoxometalate-ionic liquid in the oxidative depolymerization of alkali lignin

The oxidative depolymerization of alkali lignin can be achieved by using Keggin structure polyoxometalate-ionic liquid (POM-IL) as catalyst under aerobic conditions. The effects of catalysts such as [HC4im]3PMo12O40, [HC4im]5PV2Mo10O40, [HC2im]5PV2Mo10O40, and [HC4im]4SiMo12O40 (abbreviated as POM-IL1, POM-IL2, POM-IL3, and POM-IL4, respectively), the acidity of aqueous IL solutions on lignin conversion, and aromatic product distribution were investigated. Under optimized conditions, phenolic products (mainly m (p)-cresol, veratrole, vanillin) had the highest yield and the selectivity was as high as 75.0% using POM-IL1 as the catalyst. POM-IL2 and POM-IL3 were used as the catalysts, the highest conversion of 76.0% of lignin was achieved, and the overall yield of ketone products were higher on lignin samples, in which the main products include acetovanillone, 3-methoxyphenol, and 4-methylcatechol, and the highest selectivity of ketone products was 76.8%. The results show that the lignin fragments could be successfully oxidized into platform compounds in aqueous acidic ILs (AILs) solutions catalyzed by Keggin structure POM-IL. In addition, the role of AILs and POM-ILs in the oxidative depolymerization of alkaline lignin was analyzed, and the possible reaction mechanism between AIL-water/POM-IL/lignin system was speculated.

Quantifying the anion effect of gas solubility within ionic liquids using the solvation affinity index

The solubility of gas molecules within ionic liquids (ILs) is strongly dictated by the anion effect and the free volume effect, and of these two influences, the anion effect can be challenging to predict. We evaluate a wide range of different gas solutes (O2, NH3, CH4, H2S, SO2, Ar, H2, N2, CO2) in different ILs, and we find that the solubility is strongly correlated to one of three different IL properties, which can be directly calculated from the anion electrostatic potential (ESP) surfaces. Thus, the solutes can be grouped into three fundamental types, leading to a general descriptor, the solvation affinity index (SAI), which can identify the affinity between a wide range of gas solutes and IL solvents. The SAI of nine common industrial gases with 47 common anions are generated. This can provide a fast approach for pre-screening IL solvents or even for ILs embedded within porous supports.

Effect of 1-Butyl-1-methylpyrrolidinium trifluoromethanesulfonate on water activity of ternary aqueous ionic liquid solutions containing [BMIm]Br, [BMIm]Cl, [HMIm]Br, and [HMIm]Cl, at 298.15 K

In improved isopiestic method, the effect of 1-butyl 1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][TfO]) on the activity of water of aqueous solutions of 1-butyl 3-methyl imidazolium bromide ([BMIm]Br), 1-butyl 3-methyl imidazolium chloride ([BMIm]Cl), 1-hexyl 3-methyl imidazolium bromide ([HMIm]Br), and 1-hexyl 3-methyl imidazolium chloride ([HMIm]Cl) was determined. Some quantities of vapor liquid equilibrium were calculated from the experimental values. The activity coefficients of [BMIm]Br, [BMIm]Cl, [HMIm]Br, and [HMIm]Cl in binary and ternary systems were calculated by the results obtained from correlating the activity of water measured in these systems with TNRF-mNRTL local composition based model. Through it, the transfer of these ionic liquids from water to aqueous ternary solutions containing [BMP][TfO] was investigated with respect to the transfer Gibbs energy. The interactions between solute and solvent were highlighted using the transfer Gibbs energy, water activity and partial pressure of water data.

Exploring the optimal two-step selenization process to enhance the performance of ionic liquid solution based Cu2ZnSn(S,Se)4 thin film solar cells

Two-step selenization process has been proved to control Cu 2 ZnSn(S,Se) 4 (CZTSSe) crystallization growth, helping to fabricate a homogeneous large-grain structure of CZTSSe absorber. The two-step selenization process is usually composed of the low-temperature nucleation (LT) and high-temperature grain growth reaction (HT) processes. Here, an exploration of optimizing the annealing conditions at each step in the two-step process is reported to obtain the excellent structure of ionic liquid solution based Cu 2 ZnSn(S,Se) 4 absorber, boosting performance of the solar cell. Based on the basic requirement of an absorber candidate for solar cells (the compact films), three effective kinds of two-step process are confirmed (LT400–10&HT540–10, LT400–10&HT550–10, and LT400–10&HT560–10). We further explore the other properties of sample prepared by one-step and these three kinds of two-step process, respectively, and the optimal two-step process can be identified as LT400–10&HT550–10, which also confirms a homogeneous large-grain structure of CZTSSe absorber. Finally, CZTSSe solar cell with the highest efficiency of 9.24% can be achieved, which can be improved 67% than one by one-step annealing process (5.54%). • The detail optimization of annealing conditions at each step in the two-step selenization process is explored. • Homogeneous large-grain structure of Cu 2 ZnSn(S,Se) 4 absorber can be fabricated at the optimal two-step selenization condition. • The best efficiency of corresponding device can be obtained to be 9.24%, increased by 67% compared with one-step process.

NMR-monitoring of H/D exchange reaction of ketones in solutions of imidazolium ionic liquids

NMR spectroscopy was used to study hydrogen–deuterium exchange in CH3, CH2 and CH moieties of ketones dissolved in mixtures of solvents containing exchangeable deuteriums and imidazolium ionic liquids (IL) acting as catalysts. Factors affecting the efficiency of the exchange, as well as the role of the deuterated solvent, temperature and concentration, were investigated. Depending on the sample composition and temperature, the degree of deuteration can reach different values at equilibrium state, and the exchange rate can vary from several minutes to several months. ILs with OAc anions and with ethyl chain cations exhibit significant catalytic properties and high degrees of deuteration (up to 98%), which can be achieved by consecutive deuteration cycles. A convenient practical protocol for monitoring the exchange process by NMR spectroscopy and calculating the degree of deuteration was developed and can be used for various molecular systems.

Toward green and efficient recycling of Au(III), Pd(II) and Pt(IV) from acidic medium using UCST-type ionic liquid

The development of efficient ionic liquids (ILs) for disposable separation and recovery of various precious metals was of great importance, but still faced difficult challenges. A phase change temperature-controlled system composed of IL and HCl solution was developed for the extraction and separation of Au(III), Pd(II) and Pt(IV) from secondary resources. UCST (upper critical solution temperature)-type IL ([1,4,7-TMTA][Tf2N]) possessed outstanding selectivity of precious metals and the property of temperature-controlled phase transition. The ability of ILs to form solvated hydrogen bonds was confirmed by quantum-chemical calculation to be correlated with their corresponding UCST. Different experimental parameters were optimized to explore the extraction behavior of IL. It is noteworthy that homogeneous liquid-liquid extraction system (HLLE) constructed by UCST-type IL could significantly enhance the extraction kinetic of Au(III), Pd(II) and Pt(IV) by decreasing phase interface resistance. For Au(III), Pd(II) and Pt(IV), when the system temperatures were higher than 40 °C, 49 °C and 65 °C, the maximum values were 98.5%, 98.3% and 93.2% at the highest efficiency. In addition, the extraction mechanism of anion exchange was revealed by UV–vis, IR, NMR and LC-MS spectrometry. At last, Au(III), Pd(II) and Pt(IV) could be selectively separated from multi-metal solutions where impurity ions coexist by K2C2O4, NH3·H2O and CS(NH2)2/HCl, respectively. After 5 cycles, the extraction performance of [1,4,7-TMTA][Tf2N] maintained. In summary, this paper overcame the obstacle of slow kinetics of solvent extraction technology, and pointed out a way for polymetallic co-extraction and separation in HLLE system.

Evaluation of the interfacial activity of imidazolium-based ionic liquids and their application in enhanced oil recovery process

Ionic liquids (ILs) are a growing trend in Enhanced Oil Recovery (EOR) studies as alternatives to commercial surfactants due to their environmentally friendly nature, and their resistance in harsh temperatures and salinities. ILs are customizable and come in an immense variety, and therefore, it is vital that different combinations of cation/anion be investigated for use in the industry. In this work, experiments are designed and performed to evaluate novel ILs’ surface activity and performance in a lab-scale EOR set-up, compatible with Iranian oil reservoir conditions. Three imidazolium-based ionic liquids were used, namely, butyl-methylimidazolium nitrate, hexyl-methylimidazolium nitrate, and octyl-methylimidazolium nitrate. Nitrate anions have a less environmental impact than the often-used halogen anions, but their performance in EOR have not yet been investigated. Aqueous and saline solutions of these ILs were prepared, and subsequently, interfacial tension (IFT) tests and emulsion stability tests were carried out while the IL concentrations were kept to a minimum to account for the procedure’s feasibility. A high reduction in IFT between the saline IL solution, [C8MIm][NO3], and oil was observed compared to ILs with similar alkyl chain length in previous studies. Glass micromodels are exceptional in representing oil reservoirs under chemical EOR, and thus, were utilized to predict the ILs’ contributions to sweep efficiency and recovery factor. Up to 80% oil recovery was obtained in the micromodel flooding tests with a strong sweep efficiency. Tests were repeated at two different temperatures (30 and 75 °C) and several salinities, and it was concluded that the ILs are resistant to harsh reservoir conditions, and can, potentially, improve the production efficiency of oil fields.

PPDN and NTCDA radical anions formation in EMIM-DCA, BMIM-BF4, EMIM-Ac ionic liquid solutions under the steady state UV and Vis light illumination: A combined X-, K-band EPR and DFT study

The radical anion of Pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN) in blends with imidazolium based room temperature ionic liquids (RTIL): EMIM-DCA, BMIM-BF4, EMIM-Ac has been detected by X-band continues wave (CW) electron paramagnetic resonance (EPR) under steady state Xe-lamp illumination in the temperature interval from 190 to 340 K. The radical anion of 1,4,5,8-Naphthalenetetracarboxylic dianhydride (NTCDA) was registered by X- and K-band CW EPR at room temperature under the visible light CW diode laser operated at 532 nm, and Xe-lamp as well. The experimental hyperfine coupling data of both anion radicals were confirmed by DFT calculation. The formation of PPDN•– NTCDA•– and fullerene derivative (FD) radical anions is attributed to the photoelectron transfer from an IL anion to PPDN, NTCDA and FD electron acceptors. Here, the electron transfer leads to an irreversibility of these reactions due to photo-induced decomposition of the IL anions in the presence of an effective electron acceptor and is supported in the above RTILs solutions by means of EPR. For the indirect confirmation of the EMIM-DCA, EMIM-AC, BMIM-BF4 anion degradation in solutions with PPDN and NTCDA up to the transient radical state, similar data of acetate anion [OCOCH3]– decomposition, under CW Xe-Lamp photolysis resulting in •CH3 formation and its stabilization at 77 K in EMIM-Ac suspension with some FD dissolved in DCB are introduced as well. However, the main goal of this study is dedicated to the features of rotational and translational diffusion kinetics of PPDN and NTCDA radical anions in IL solutions as well to the evaluation of their application as a spin probes in ILs study in liquid phase.

A novel X-ray diffraction approach to assess the crystallinity of regenerated cellulose fibers.

Here, a new accurate approach is presented to quantify the degree of crystallinity of regenerated cellulose textile fibers using wide-angle X-ray scattering. The approach is based on the observation that the contributions to the scattering from crystalline and amorphous domains of the fibers can be separated due to their different degree of orientation with respect to the fiber direction. The method is tested on Ioncell-F fibers, dry jet wet spun with different draw ratios from an ionic liquid solution. The analysis output includes, apart from an accurate estimate of the fiber crystallinity, the degrees of orientation of the cellulose nanocrystals and the cellulose chains in the amorphous domains.

Rheological Characterization of Mixed Aqueous Solutions of Enzymatic Hydrolysis Lignin and Ionic Liquid

AbstractHere we present a rheological study of enzymatic hydrolysis lignin (EH lignin) in 1‐butyl‐3‐methylimidazolium chloride ([C4min]Cl) aqueous solutions. The effects of ionic liquid mass fraction, shear rate and temperature on the viscosity and macromolecular chain configuration of EH lignin / C4min] Cl aqueous solution were studied. The results showed that the viscosity of the aqueous solutions increased with the increase of lignin content. The mass percentages of overlapping and winding, responding to divisions of lignin macromolecules existence state, were varied with changing in the temperature and mass percentages of ionic liquid. Increasing the mass of ionic liquid will significantly change the viscosity of lignin solution. Most of the lignin solutions had shear thinning behavior, suggesting that macromolecular chains of lignin moved with orientation to the fluid, and disentangled under the shear force. The viscosity of lignin solution decreased with the increase of temperature, and the viscosity activation energy increased with the increase of lignin or ionic liquid mass fraction.

Interfacial Water and Microheterogeneity in Aqueous Solutions of Ionic Liquids.

In this work, aqueous solutions of two prototypical ionic liquids (ILs), [BMIM][BF4] and [BMIM][TfO], were investigated by UV Raman spectroscopy and small-angle neutron scattering (SANS) in the water-rich domain, where strong heterogeneities at mesoscopic length scales (microheterogeneity) were expected. Analyzing Raman data by a differential method, the solute-correlated (SC) spectrum was extracted from the OH stretching profiles, emphasizing specific hydration features of the anions. SC-UV Raman spectra pointed out the molecular structuring of the interfacial water in these microheterogeneous IL/water mixtures, in which IL aggregates coexist with bulk water domains. The organization of the interfacial water differs for the [BMIM][BF4] and [BMIM][TfO] solutions, being affected by specific anion–water interactions. In particular, in the case of [BMIM][BF4], which forms weaker H-bonds with water, the aggregation properties clearly depend on concentration, as reflected by local changes in the interfacial water. On the other hand, stronger water–anion hydrogen bonds and more persistent hydration layers were observed for [BMIM][TfO], which likely prevent changes in IL aggregates. The modeling of SANS profiles, extended to [BPy][BF4] and [BPy][TfO], evidences the occurrence of significant concentration fluctuations for all of the systems: this appears as a rather general phenomenon that can be ascribed to the presence of IL aggregation, mainly induced by (cation-driven) hydrophobic interactions. Nevertheless, larger concentration fluctuations were observed for [BMIM][BF4], suggesting that anion–water interactions are relevant in modulating the microheterogeneity of the mixture.

Experimental performance of a three-fluid desiccant contactor using a novel ionic liquid

• Novel Ionic Liquid that is not corrosive to aluminum is used as liquid desiccant. • New three-fluid fin-tube desiccant contactor fabricated using aluminum. • Experimental performance of the fin-tube contactor using IL solution is investigated. • The fin–tube contactor showed superior performance than the packed bed contactor. • Lower solution flow rates and pumping power is expected using the fin–tube contactor. The experimental performance of a new three-fluid fin–tube contactor using a novel ionic liquid desiccant solution is investigated and compared with those of an adiabatic packed bed contactor with LiCl solution for liquid desiccant air conditioning system applications. Owing to the compatibility of the ionic liquid solution with aluminum, a fin–tube contactor is manufactured to exploit internal cooling from a third fluid. The results indicate the superior dehumidification performance of the fin–tube contactor, which yielded an outlet air humidity ratio of 10.5 g w ·kg da -1 at a solution mass flux of 3.06 kg·m −2 ·s −1 , as compared to a similar humidity ratio at a solution mass flux of 4.98 kg·m −2 ·s −1 achieved by the packed bed contactor. In terms of cooling performance, the outlet air temperature of the fin–tube contactor is 21.9 °C, which is lower than that of the packed bed contactor even at its highest solution mass flux. This indicates that the cooling performance of the fin–tube contactor has minimal dependence on the solution mass flux in achieving cooling effect, owing to the cooling medium flowing inside the tubes. Relatively lower solution pumping power than that of the packed bed contactor can be expected from the fin–tube contactor, in addition to the ability to achieve comfortable and hygienic indoor air at a cooling medium temperature of 17 °C or higher, the ionic liquid desiccant and three-fluid fin–tube contactor pair for liquid desiccant air conditioning system is elevated a step higher as an alternative to vapor compression air conditioning system.

Mechanism study on CO2 capture by ionic liquids made from TFA blended with MEA and MDEA

Ionic liquids are presenting a great potential to increase the efficiency and reduce the cost of CO2 capture process. TFA was selected as anion in the produced ionic liquids to study its absorption capacity, and CO2 capture by [3-AP][TFA] and [MDEA][TFA] were tested under different conditions with various solvents such as water, MEA and MDEA. Results showed that ionic liquids blended with MEA improved the absorption capacity up to 0.50 mol CO2/mol absorbent, which was much higher than that of aqueous ionic liquid solution (less than 0.30 mol CO2/mol absorbent), and the aqueous solution of ionic liquids blended with MDEA could improve its absorption capacity up to 0.93 mol CO2/mol absorbent. Different ratios of ionic liquids blended with MDEA were investigated, and ratios of ionic liquids versus MDEA was set from 2:1 to 1:6. The CO2 absorption capacity reached the maximum of 0.91 mol CO2/mol IL at ratio 1:6 for [3-AP][TFA] and 0.93 mol CO2/mol IL at ratio 1:4 for [MDEA][TFA], which indicated that the CO2 absorption capacity increased with ascending amount of MDEA. Characterizations of aqueous blends were performed by FT-IR and 13C NMR, which showed that the formation of bicarbonate was observed, indicating the mechanism of CO2 absorption was a two-step reaction via the formation of zwitterion. The produced zwitterions contributed to CO2 absorption by increasing both the capacity and reaction rate. Reaction of MDEA with CO2 in water was considered to be a catalyzed hydrolysis, because the lack of eliminating hydrogen atom prevented MDEA from forming carbamate but produced bicarbonate instead.