Cation effect of ammonium imide based ionic liquids in alcohols extraction from alcohol-alkane azeotropic mixtures

During recent last years, outstanding properties of ionic liquids such as low melting point, large liquid range and negligible volatility have turned them into possible volatile organic solvents replacers to break alcohol-alkane azeotropic mixtures. On this basis, two ionic liquids, butyltrimethylammoniumbis(trifluoromethylsulfonyl)imide, [BTMA][NTf₂], and tributylmethylammoniumbis(trifluoromethylsulfonyl)imide, [TBMA][NTf₂], were studied through ternary liquid+liquid equilibrium (LLE) of {alkane(1) + alcohol (2) + IL(3)} at T = 298.15 K and atmospheric pressure in order to consider the effect of ionic liquid cation alkyl chain length on the extraction process.The ILs capability as azeotrope breakers was determined by the calculation of parameters such as solute distribution ratio, β, and selectivity, S and this capability was compared with other bis (trifluoromethylsulfonyl)imide based ionic liquids from literature. The consistency of tie-line data was ascertained by applying the Othmer–Tobias and Hand equations. Finally, the experimental LLE were correlated by the Non Random Two Liquid (NRTL) thermodynamic model.     

Application of a group contribution equation of state for the thermodynamic modeling of binary systems (gas + ionic liquids) with bis[(trifluoromethyl)sulfonyl]imide anion

The properties of ionic liquids (ILs) can be modified by appropriate selection of cations and anions. Even if an infinite number of ionic liquids can be generated, only a limited number of families of anions and cations are used. The group contribution equation of state (GC-EoS) is a promising method for calculating the phase behavior of systems with ILs. If the parameters of the characteristic functional group of a IL family are fitted by using data of a reduced number of ILs of the family, then the phase behavior of all the ILs of the same family can be predicted using exclusively the data of the pure components. Previously, the parameters of the IL families with an imidazolium-based cation and the anions PF₆, BF₄NO₃, and Tf₂N were fitted to experimental data [19], and some ternary systems (CO₂ + organics + ionic liquid [bmim][BF₄]) were also modeled [22]. In this work, the GC-EoS was used to calculate phase behavior of gases {(CO₂, O₂, or SO₂) + ionic liquids} with Tf₂N anion and cations of the families 2,3-dimethyl-imidazolium, 1-alkyl-1-methyl-pyrrolidinium, and 1-alkyl-3-methyl-pyridinium. The GC-EoS was able to reproduce experimental data with deviations of the same order of experimental uncertainty. With the correlated parameters it will be possible to predict the phase behavior of systems with ILs of the families considered in this work.     

Electrochemically stable fluorohydrogenate ionic liquids based on quaternary phosphonium cations

Fluorohydrogenate ionic liquids of quaternary phosphonium cations, tri-n-butylmethylphosphonium (P₄₄₄₁) fluorohydrogenate, tetra-n-butylphosphonium (P₄₄₄₄) fluorohydrogenate, and tri-n-butyl-n-octylphosphonium (P₄₄₄₈) fluorohydrogenate, have been synthesized by the metatheses of anhydrous hydrogen fluoride and the corresponding phosphonium chloride precursors. All the obtained salts have melting points below room-temperature with a vacuum-stable composition of P_444m(FH)_2.3F (m = 1, 4, and 8) and were characterized by density, conductivity, and viscosity measurements. Linear sweep voltammetry with a glassy carbon working electrode shows that the P_444m(FH)_2.3Fs have wide electrochemical windows exceeding 5.2 V. In particular, P₄₄₄₁(FH)_2.3F has an electrochemical window of 6.0 V, which is the widest among fluorohydrogenate ionic liquids reported to date. The thermal stability of these ionic liquids is also improved compared to the salts of N-heterocyclic ammonium cations.     

Excess molar volumes of binary mixtures (an ionic liquid + water): A review

This review covers recent developments in the area of excess molar volumes for mixtures of {ILs (1) + H₂O (2)} where ILs refers to ionic liquids involving cations: imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium and ammonium groups; and anions: tetraborate, triflate, hydrogensulphate, methylsulphate, ethylsulphate, thiocyanate, dicyanamide, octanate, acetate, nitrate, chloride, bromide, and iodine. The excess molar volumes of aqueous ILs were found to cover a wide range of values for the different ILs (ranging from −1.7 cm³ · mol⁻¹ to 1.2 cm³ · mol⁻¹). The excess molar volumes increased with increasing temperature for all systems studied in this review. The magnitude and in some cases the sign of the excess molar volumes for all the aqueous ILs mixtures, apart from the ammonium ILs, were very dependent on temperature. This was particularly important in the dilute IL concentration region. It was found that the sign and magnitude of the excess molar volumes of aqueous ILs (for ILs with hydrophobic cations), was more dependent on the nature of the anion than on the cation.     

Prediction of thermophysical properties of novel ionic liquids based on serine [Cnmim][Ser] (n = 3, 4) using semiempirical methods

Two novel ionic liquids based on serine [C_nmim][Ser] (n = 3, 4) were prepared by the neutralization method and their structures were confirmed by ¹H NMR spectroscopy and differential scanning calorimetry (DSC). The density, surface tension, and refractive index of the two ILs were measured from T = (298.15 to 338.15) K. Since these ILs [C_nmim][Ser] (n = 3, 4) could form strong hydrogen bonds with water, small amount of water in the ILs is difficult to removed by common methods. In order to eliminate the effect of trace of water, the standard addition method (SAM) was applied to these measurements. On the basis of the experimental data, the speed of sound (μ), thermal expansion coefficient (α), molecular volume (V_m), standard entropy (S⁰298), entropy of surface (S_a), energy of surface (E_a), parachor (P), molar polarization (R_m), and polarization coefficient (α_p) were calculated, and the relationship between each of these properties of [C_nmim][Ser] (n = 3, 4) and temperatures was discussed. According to the additivity, the average value of anionic parachor, P_−(ave), was 180.81 for [Ser]⁻. At the same time, the surface tension of these serine ionic liquids could be estimated from their parachor and refractive index. The estimated values of the surface tension and the corresponding experimental data were almost identical.     

Liquid range temperature of ionic liquids as potential working fluids for absorption heat pumps

The liquid range temperature of six ionic liquids (ILs) was determined in this work with the aim to propose suitable absorbents for heat pump systems. The selected ILs have three different cations, imidazolium, pyridinium and choline and each was combined with four different anions [NTf₂]⁻, [OTf]⁻, [MeSO₃]⁻ and [BETI]⁻. The lower limit, given by solid − liquid transitions, was determined using differential scanning calorimetry (DSC). The upper limit is given by the degradation temperature. This temperature is determined using thermogravimetric technique (TGA). Dynamic and isothermal methods have been combined to estimate the maximum operation temperature. ILs ageing effect was also analysed in this work.     

Amidinium salts: Towards enabling electrochemistry in non-polar media from alkanes to ionic liquids

There is little known about electrochemical behavior in non-polar media due to lack of compatible, hydrophobic salts. In this work, this difficult challenge has been overcome by following a strategy based on designing and synthesizing a novel family of organic salts with highly-delocalized cations and anions. The salts are based on the amidinium cation with highly-delocalized positive charge and long alkyl groups that enable good miscibility in heptane, an archetypical, non-polar media, while being hydrophobic, room-temperature ionic liquids. The electrolyte solutions show ionic conductivities that span the range 10^− 11–10^− 4 S cm^− 1 and electrochemical activity which enable their application as antistatic agents and also as new type of hydrophobic electrolytes in various electrochemical devices.     

Modification of carbon electrode in ionic liquid through the reduction of phenyl diazonium salt. Electrochemical evidence in ionic liquid

Electrochemical reduction of the 4-nitrophenyl diazonium salt in ionic liquid media has been investigated at carbon electrode. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The cyclic voltammetry study demonstrated the possibility of the electrochemical grafting of the nitrophenyl groups onto carbon electrode after the reduction of its corresponding diazonium in ionic liquid. The electrochemical characterization of the modified electrode achieved on ionic liquid displays the presence of the nitrophenyl group at the carbon surface. Moreover, the surface concentration of the attached group obtained in this media was found to be around 1.7 × 10⁻¹⁰ mol cm⁻², this value may suggest the possibility of the formation of monolayer. Furthermore, the characterization of the modified electrode in [EMIM][TFSI] showed the conversion of some NO₂-phenyl groups to NHOH-phenyl. This observation could indicate the presence of surface interaction between the reduced NO₂-phenyl and the ionic liquid cation, thanks to the presence of acidic proton in the ionic liquid cation.     

Synthesis,physical, and thermodynamic properties of 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Synthesis of new ionic liquids (ILs) viz. 1-butyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [BCN³Py][NTf₂], 1-hexyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN³Py][NTf₂], 1-hexyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN⁴Py][NTf₂], and 1-octyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [OCN³Py][NTf₂] were performed. The specific basic characterization of new compounds by NMR spectra, elementary analysis, water content and glass transition temperature as well as melting temperature, enthalpy of fusion and decomposition of compounds TG/DTA determined by the differential scanning calorimetry, DSC is presented. The heat capacity was measured at three temperatures (298.15, 323.15, and 353.15) K and at pressure 0.1 MPa. The effect of temperature on the density and viscosity is reported over the temperature range from (293.15 to 363.15) K and at 0.1 MPa. The density and viscosity correlation for these systems was provided by an empirical polynomial. From the density–temperature dependence, the isothermal expansion coefficient (volume expansivity), α, was calculated. The surface tension of pure ionic liquids was measured at 0.1 MPa at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15) K. The surface thermodynamic functions such as surface entropy and enthalpy, critical temperatures according to the Eötvös and Guggenheim definition and the total surface energy of the ILs studied were derived from the temperature dependence of the surface tension values. The parachor and speed of sound for pure ionic liquids were described within a range of temperature from (298.15 to 338.15) K. A qualitative analysis on these quantities in terms of molecular interactions is reported.     

Ionic liquid/boric ester binary electrolytes with unusually high lithium transference number

Binary electrolytes composed of ionic liquids and boric esters were prepared by studying compatibility between various combinations of such systems. The study showed that out of various combinations of ionic liquids/boric esters, only TFSI anion (or FSI anion) based ionic liquids/mesityldimethoxyborane (MDMB) systems were found to be miscible. After equimolar amount of lithium salts was added to ionic liquids, the resulting solution showed high ionic conductivity that was comparable to those for ionic liquids. The lithium transference number (t_Li +) of these systems at room temperature was found to be very high. A maximum t_Li + of 0.93 was observed for a binary mixture of AMImFSI [1-allyl-3-methylimidazolium bis(fluorosulfonyl)imide]/MDMB. Further, this binary mixture as electrolyte in Li/electrolyte/Si cell showed good reversible lithiation-delithiation with > 2500 mAh/g of delithiation specific capacity.     

New dicationic piperidinium hexafluorophosphate ILs,synthesis, characterization and dielectric measurements

A new class of dicationic ionic liquids (ILs) were synthesized for electrochemical applications at high temperatures. The syntheses are based on a dialkylation reaction of N-alkylpiperidine followed by anion exchange. The structures of ILs, based on piperidinium combined with hexafluorophosphate anion, were identified by using ¹H, ¹³C, ¹⁹F, ³¹P NMR and FT-IR spectroscopy. ILs’ thermal properties were investigated in the temperature range from −50 to 350 °C by using differential scanning calorimetry (DSC). In the frequency of 10⁻²–10⁶ Hz range, dielectric measurements were performed on ILs’ samples at various temperatures from −80 to 20 °C, i.e. around the glass transition temperature. The peak relaxation was observed near to this temperature. Also, the conductivity was investigated and the energy activation determined. The temperature dependence of the relaxation times was shown to be governed by the Arrhenius equation.     

An acidic cellulose–chitin hybrid gel as novel electrolyte for an electric double layer capacitor

A novel acidic cellulose–chitin hybrid gel electrolyte including binary ionic liquids (ILs) with an aqueous H₂SO₄ solution was prepared for an electric double layer capacitor (EDLC). Its electrochemical characteristics were investigated by galvanostatic charge–discharge measurements. The test cell with a hybrid gel electrolyte shows a specific capacitance of 162 F g^?1 at room temperature, which is higher than that for a cell with an H₂SO₄ electrolyte, 155 F g^?1. This hybrid gel electrolyte exhibits excellent high-rate discharge capability in a wide range of current densities as well as an aqueous H₂SO₄ solution. The discharge capacitance of the test cell can retain over 80% of its initial value in 100,000 cycles even at a high current density of 5000 mA g^?1.     

An electrically heated ionic-liquid/multi-wall carbon nanotube composite electrode and its application to electrochemiluminescent detection of ascorbic acid

A heated composite electrode consisted of multi-wall carbon nanotube (MWNT) and ionic liquids (ILs) was designed and fabricated. The non-conductive binders were replaced by a conductive IL, n-octylpyridinum hexafluorophosphate (OPFP). This heated OPFP/MWNT composite electrode was applied for electrochemiluminescent (ECL) sensor, and the performance of ECL sensor was evaluated by ascorbic acid (AA)/lucigenin ECL system. The new heated electrode combines the advantages of ILs/CNT and heated electrode, showing high thermal stability and conductivity, simple heating setups, improved reproducibility, renewable surface, simplicity of fabrication and enhanced sensitivity with detection limit (S/N = 3) of 0.01 μmol/L for AA.     

Thermophysical properties of 1-methyl-3-methylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate

The density and surface tension of 1-methyl-3-methylimidazolium dimethylphosphate, [C₁mim](CH₃O)₂PO₂ and 1-ethyl-3-methylimidazolium diethylphosphate, [C₂mim](CH₃CH₂O)₂PO₂ ionic liquids have been measured over the temperature range from (283.15 to 338.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 338.15) K. Molecular volume and standard entropies of these ILs were calculated from the experimental density values. The surface properties of ILs were investigated. The critical temperature and enthalpy of vapourization were also discussed.     

Photochromism of 3-butyl-1-methyl-2-phenylazoimidazolium in room temperature ionic liquids

We studied the photochromism of a newly synthesized ionic liquid, [2PA-Bmim]Tf₂N ([2PA-Bmim]⁺: 3-butyl-1-methyl-2-phenylazoimidazolium, Tf₂N^?: bis(trifluoromethanesulfonyl)-amide) which is characterized by a phenylazo group substituted on the imidazolium ring. The melting point of [2PA-Bmim]Tf₂N is 329 K. The absorption spectrum of [2PA-Bmim]⁺ dissolved in conventional organic solvents or in ionic liquids changes drastically upon UV-light irradiation, which is attributed to the photoisomerization of the phenylazo group from E- to Z-forms during irradiation and the backward thermal isomerization from Z- to E-forms in the dark. The E–Z photoisomerization quantum yield, Φ_iso, was determined by 355 nm laser photolysis. The Φ_iso value slightly depends on solvent viscosity, from 0.12 in 3-butyl-1-methylimidazolium PF₆^? (η = 241 cP) to 0.19 in toluene (η < 1 cP). On the other hand, no solvent dependence was observed for Arrhenius parameters of the backward Z–E thermal isomerization. We discuss the isomerization mechanism and the reason why the E–Z photoisomerization yield depends on solvent viscosity.     

Importance of weak interactions and conformational equilibrium in N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide room temperature ionic liquids: Vibrational and theoretical studies

Piperidinium cation-based room temperature ionic liquids (RTILs) constitute an important class of ILs because of their unique electrochemical properties as well as non-aromatic nature of the cation. However, detailed structural studies are yet to be done. In this paper, we discuss the molecular structure and vibrational spectra of N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide, (PIP₁₄NTf₂; where, PIP₁₄ is N-butyl-N-methylpiperidinium and NTf₂ is bis(trifluromethanesulfonyl) imide), obtained with a combined approach of infrared (IR) and Raman spectroscopies in the liquid state and density functional theory (DFT) and Hartree–Fock (H–F) based theoretical calculations. DFT calculations, which are found to produce the most stable geometry compared to other two methods (MP2 and H–F), reproduce the experimental IR and Raman spectra reasonably well. Our findings reveal structural properties that profoundly influence intermolecular interactions and melting point. There exists a large variation in the melting point of the ILs studied. While the bromide salt of the piperidinium derivative (PIP₁₄Br) is solid with very high melting point (241 °C), the corresponding NTf₂ salt is low viscous liquid at room temperature (mp: −25 °C). bmimBr (bmim = 1-butyl-1-methylimidazolium) exhibits a substantially lower melting point of 79 °C than PIP₁₄Br, suggesting that more number of strong classical hydrogen bonding interactions in the latter is primarily responsible for the much higher melting point. In addition, involvement of the alkyl group in PIP₁₄ in H-bonding interaction provides additional rigidity in n-butyl chain which is otherwise absent in bmimBr. Interaction energy for PIP₁₄Br is found to be higher than PIP₁₄NTf₂, showing a positive correlation between interaction energy and melting point. A blue shift in CH stretching wavenumber as evident from IR and Raman spectra of PIP₁₄Br IL is a clear indication of the stronger hydrogen bonding as compared to PIP₁₄NTf₂ IL. Furthermore, we experimentally observe the existence of cisoid–transoid conformational equilibrium of NTf₂⁻ anion in the Raman spectrum of PIP₁₄NTf₂ for the first time and determined that transoid NTf₂⁻ anion to be more stable than the corresponding cisoid conformer by 1.04 kcal/mol using DFT. Examination of various conformational possibilities of the cation shows that the butyl group preferentially exists in gauche conformation.     

Highly selective and stable electro-catalytic system with ionic liquids for the reduction of carbon dioxide to carbon monoxide

In this study, the electrochemical reduction of CO₂ was examined using a Ag-modified Cu catalyst cathode in a series of mixed ionic liquids (ILs) in the presence or absence of cobalt chloride (CoCl₂). These results indicate that the Ag-modified Cu electrode in EMIMBF₄ + BMIMNO₃ with CoCl₂ exhibited the excellent synergy for the electrochemical reduction of CO₂ to CO with a stable area specific activity, with continuous production for at least 150 h. In such a system, a CO selectivity of 98% was achieved. According to the obtained results, a possible mechanism was proposed. The synergistic effect between the Ag-modified Cu electrode, serving as the main catalyst, and CoCl₂ and ILs, serving as the co-catalysts, is probably responsible for the highly selective and stable electrocatalytic reduction of CO₂ to CO.     

Studies on the thermodynamic properties of new ionic liquids: 1-Methyl-3-pentylimidazolium salts containing metal of group III

This paper reports that new ionic liquids (ILs) have been prepared by directly mixing the chloride of group III and 1-methyl-3-pentylimidazolium chloride (PMIC) with molar ratio 1/1 under dry argon atmosphere. The densities and surface tension of these ILs were determined at temperature range of 273.15 K to 343.15 ± 0.1 K. The properties for the ionic liquids were discussed by interstice model and Glasser’s theory.     

Solubility of CO2 in 1-(2-hydroxyethyl)-3-methylimidazolium ionic liquids with different anions

The solubility of carbon dioxide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([hemim]⁺) based ionic liquids (ILs) with different anions, viz. hexafluorophosphate ([PF₆]^?), trifluoromethanesulfonate ([OTf]^?), and bis-(trifluoromethyl)sulfonylimide ([Tf₂N]^?) at temperatures ranging from 303.15 K to 353.15 K and pressures up to 1.3 MPa were determined. The solubility data were correlated using the Krichevsky–Kasarnovsky equation and Henry’s law constants were obtained at different temperatures. Using the solubility data, the partial molar thermodynamic functions of solution such as Gibbs free energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of CO₂ in the ILs studied follows the same behaviour as the corresponding conventional 1-ethyl-3-methylimidazolium ([emim]⁺) based ILs with the same anions, i.e. [hemim][NTf₂] > [hemim][OTf] > [hemim][PF₆] > [hemim][BF₄].     

Li/LiFePO4 batteries with room temperature ionic liquid as electrolyte

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP₁₄TFSI), which showed a wide electrochemical window (?0.1–5.2 V vs. Li⁺/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP₁₄TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO₄ cells initially delivered a discharge capacity of about 127 mAh g^?1 at a current density of 17 mA g^?1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.