Thiocyanate Ionic Liquids Research Articles

The solvation inhomogeneity of sulfur dioxide in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid probed by Raman spectroscopy

AbstractThe different solvation states of SO2 in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid were probed by the detailed analysis of the SO2 symmetric stretching mode, νs(SO2). The band position and linewidth were monitored in function of gas molar fraction, excitation wavelength, and temperature. As expected, the decreasing of the SO2 molar fraction, XSO2, from approximately 0.8 to 0.2, leads to a gradual downshift of the νs(SO2) band, attributed to a more effective charge transfer interaction from thiocyanate anion to SO2. Interestingly, at high gas concentrations (XSO2 = 0.8), a gradual downshift of the νs(SO2) band was noticed as the Raman excitation energy increases, an unexpected behavior because the change in the excitation wavelength in Raman spectroscopy should affect only the band intensities. Such νs(SO2) Raman dispersion can be understood as a consequence of the distinct charge transfer electronic transition energies associated to different SO2 solvation states, whose relative band intensities are modulated by resonance Raman conditions. Moreover, the lowering from room temperature to 100 K showed an increasing in the Raman dispersion effect. The temperature dependence was attributed to the strengthening of the cation–anion interaction, responsible for the increasing of SO2 solvation states distribution. The vibrational spectroscopic data regarding the SO2 solvation inhomogeneity in ionic liquids are showed for the first time, and it may contribute in the understanding of why such liquids are promising solvents for SO2 capture.

Novel solvents based on thiocyanate ionic liquids doped with copper(I) with enhanced equilibrium selectivity for carbon monoxide separation from light gases

Abstract This work focuses on the research of novel carbon monoxide (CO) capture solvents to be applied to the separation of CO from other light components contained in gas streams of the process industry, e.g., nitrogen and hydrogen. More specifically, we examine the use of CO-selective capture solutions composed of the ionic liquid 1-ethyl-3-methylimidazolium thiocyanate ([C 2 mim][SCN]) and the transition metal salt copper(I) thiocyanate (CuSCN) as greener alternatives to the tetrachloroaluminate(III)-aromatic hydrocarbon solutions currently employed for CO separation from gas mixtures. In order to gain insight into the behavior of the selected ionic liquid solutions as chemical solvents for CO, their density and viscosity are characterized with respect to temperature and composition in a wide range of temperatures (273.15–303.15 K), pressures (up to 24 bar) and copper(I) concentrations (0–30 mol%). Moreover, the CO absorption has been assessed and gas-liquid equilibria are successfully described with a thermodynamic model as a function of those variables. The [C 2 mim] x [Cu] 1−x [SCN] solutions exhibit favorable properties in terms of competitive CO sorption capacity and high selectivity towards slightly soluble gases, e.g., 996.1 mmol L −1 and CO/N 2 selectivity of ∼25 at 283.15 K and 23.3 bar, combined with low heat of absorption (−29.5 kJ mol −1 ) as well as easiness of regeneration and reuse. Consequently, these copper(I)-containing ionic liquids are promising for the development of novel and greener CO/N 2 separation processes alternative to the use of flammable and toxic solvents or energy-intensive cryogenic distillations.

Effect of task specific thiocyanate based ionic liquids on relative volatility of cyclohexane and benzene azeotropic mixture

The relative volatilities of cyclohexane (Cy) to benzene (Bz) in the presence of eight task-specific imidazolium thiocyanate ionic liquids (ILs) were measured using headspace gas chromatography. The ILs contain nitrile, ally, benzyl and hydroxyl functional group in their imidazolium cations and thiocyanate as anion. The effects of incorporation of nitrile, allyl, benzyl and hydroxyl functional groups in imidazolium alkyl chain on the relative volatility of Cy to Bz were investigated using experiment and quantum calculations. COSMO-RS model was used to study the polarity (charge distribution) of the ILs and the solutes. Density functional theory (DFT) was employed to investigate the cation-anion interaction energies and IL-Bz/Cy binding energies. The structural variations of the imidazolium cation influence the performance of the ILs. Moreover, the performances of the ILs were compared with two typical conventional entrainers, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). Except two hydroxyl containing ILs, the remaining six ILs show higher Cy to Bz relative volatility values compared to the bench marked conventional solvents.

Effect of addition of 1-butyl-3-methylimidazolium thiocyanate on conductivity of Na-containing polymer electrolyte

Research in the environmentally friendly energy field has grown rapidly due to severe problems such as global warming and climate change. Sodium-ion technology is one of the most promising alternatives to lithium-ion batteries. Use of ionic liquids containing thiocyanate anion has been considered because of their low cost, low viscosity, and nonhazardous nature. In this work, polyethylene oxide (PEO)–sodium perchlorate (NaClO4) samples containing different amounts of 1-butyl-3-methylimidazolium thiocyanate ionic liquid were prepared by a solution casting method. Addition of the ionic liquid to the PEO–NaClO4 electrolyte further increased the ionic conductivity. The electrolyte containing 30 wt% ionic liquid exhibited the maximum ionic conductivity of ~5.0 × 10−4 S/cm at room temperature. Fourier-transform infrared (FT-IR) spectroscopy revealed the interaction between the polymer chain and salt ion complexes for various sodium salt contents. Differential scanning calorimetry (DSC) demonstrated that the crystallinity was reduced by addition of 1-butyl-3-methylimidazolium thiocyanate ionic liquid.

Extraction and recovery process to selectively separate aromatics from naphtha feed to ethylene crackers using 1-ethyl-3-methylimidazolium thiocyanate ionic liquid

Naphtha feed to ethylene crackers is an industrial stream of interest to form part of the habitual main sources of aromatics, pyrolysis and reformer gasolines, in order to reduce the costs caused by the non-converted aromatics in the ethylene crackers. Nonetheless, its lower aromatic concentration (10–25wt. %) in comparison with gasolines (over 50wt.%) has limited the implementation of the now-used technologies. Ionic liquids (ILs) arise as alternative solvents to current-used organic solvents, since the ILs are capable to selectively extract aromatic from a low-concentrated stream as is the naphtha feed to ethylene crackers. Accordingly, 1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]) has been selected to conceptually design the liquid–liquid extraction alternative process to separate BTEX from a naphtha model since this IL has shown the highest values of aromatic/aliphatic selectivity. The process simulation was based on experimental liquid–liquid equilibria (LLE) and vapor–liquid equilibria (VLE) data, the latter destined to plan the hydrocarbon recovery from the extract stream. Kremser method for extraction and a new algorithm for flash distillation units were used to simulate the process and select the most favorable working conditions to increase the purity of aliphatics in the raffinate stream and the purity in the aromatic stream obtained.

Selective alkaline stripping of metal ions after solvent extraction by base-stable 1,2,3-triazolium ionic liquids.

Novel 1,2,3-triazolium ionic liquids with a high base stability were synthesized for use in solvent extraction of first-row transition elements and rare earths from chloride media. The synthesis of these ionic liquids makes use of a recently reported, metal-free multicomponent reaction that allows full substitution of the 1,2,3-triazolium skeleton. The physical and chemical properties of these ionic liquids are compared with those of a trisubstituted analog. Peralkylation of the 1,2,3-triazolium skeleton leads to ionic liquids with superior properties, such as low viscosity, low solubility in water and higher thermal and base stability. Iodide and thiocyanate ionic liquids with peralkylated cations were applied to the solvent extraction of metal ions, and their stability in alkaline media was exploited in the selective stripping of the metals from the loaded ionic liquid phase by alkaline solutions. EXAFS and Raman spectroscopy were performed to gain insight into the extraction mechanism. The applicability of these extraction systems was demonstrated in separations relevant for the recovery of metals from ores and end-of-life products: Fe(iii)/Cu(ii)/Zn(ii) (copper ores, brass scraps) and Fe(iii)/Nd(iii) (rare earth magnets).

Noncovalently functionalized graphene oxide/graphene with imidazolium-based ionic liquids for adsorptive removal of dibenzothiophene from model fuel

Graphene (G) and graphene oxide (GO) were functionalized with 1-methyl-3-octyl-imidazolium hexafluorophosphate ([Omim][PF6]), 1-methyl-3-octyl-imidazolium tetrafluoroborate, and 1-methyl-3-octyl-imidazolium thiocyanate ionic liquids through a non-covalent functionalizing procedure. Different characterization techniques including XRD, AFM, FTIR, SEM/EDX, TGA, XPS, and RAMAN spectroscopy were used to verify the success of functionalization. The functionalized graphenes and graphene oxides were then used as adsorbents to remove dibenzothiophene from a model fuel having decane as the solvent. Among the prepared adsorbents, the functionalized graphene with the ionic liquid of [Omim][PF6] exhibited the highest adsorption capacity of 6.5 mg/g. The results showed that functionalization of graphene and graphene oxide improves their adsorption capacity in comparison to those of graphene (3.2 mg/g) and graphene oxide (2.25 mg/g).

Thermal and conformational stability of insulin in the presence of imidazolium-based ionic liquids

Stabilization of the monomeric form of insulin (In) under condition of low pH has been a recent challenge. This research aims to reveal the effect of a series of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) on the stability of In dissolved in highly acidic solution (pH 2.0). Differential scanning calorimetry was applied to assess the thermal stability of In in the presence of these ILs. In addition, we monitored the IL-induced changes in the In secondary structure using Fourier transformed infrared spectroscopy. The peak of In thermal denaturation was shifted to higher temperatures in the presence of the tested acetate, trifluoroacetate and dicyanamide salts. At the same time, chloride and thiocyanate ILs had no effect on the thermal stability of the insulin, while the tricyanomethanide salt slightly destabilized the protein. The change in the In conformation affected not only the position but also the sharpness and the shape of the transition peak. As a whole, those ILs which were able to preserve or enhance helical structure of In produced stabilizing effect and those which stimulated the formation of unordered and random-coiled structures deteriorated its thermal stability. No aggregation of In in the presence of the imidazolium-based ILs was observed under the tested acidic media.

Efficient separation of transition metals from rare earths by an undiluted phosphonium thiocyanate ionic liquid.

The ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate has been used for the extraction of the transition metal ions Co(ii), Ni(ii), Zn(ii), and the rare-earth ions La(iii), Sm(iii) and Eu(iii) from aqueous solutions containing nitrate or chloride salts. The transition metal ions showed a high affinity for the ionic liquid phase and were efficiently extracted, while the extraction efficiency of the rare-earth ions was low. This difference in extraction behavior enabled separation of the pairs Co(ii)/Sm(iii), Ni(ii)/La(iii) and Zn(ii)/Eu(iii). These separations are relevant for the recycling of rare earths and transition metals from samarium cobalt permanent magnets, nickel metal hydride batteries and lamp phosphors, respectively. The extraction of metal ions from a chloride or nitrate solution with a thiocyanate ionic liquid is an example of "split-anion extraction", where different anions are present in the aqueous and ionic liquid phase. Close to 100% loading was possible for Co(ii) and Zn(ii) up to a concentration of 40 g L(-1) of the transition metal salt in the initial aqueous feed solution, whereas the extraction efficiency for Ni(ii) gradually decreased with increase in the initial feed concentration. Stripping of Co(ii), Zn(ii) and Ni(ii) from the loaded ionic liquid phase was possible by a 15 wt% NH3 solution. The ionic liquid could reused after extraction and stripping.

Separation of propylene and propane by alkylimidazolium thiocyanate ionic liquids with Cu + salt

Abstract Ionic liquids (ILs) coupled with Ag + or Cu + salts to form a new kind of reactive absorbent have been studied to separate light olefin from paraffin recently. In this work, we prepared two halogen-free alkylimidazolium thiocyanate ILs with cheaper cuprous thiocyanate, i.e., [Bmim]SCN–CuSCN and [Emim]SCN–CuSCN (Bmim, 1-butyl-3-methylimidazolium; Emim, 1-ethyl-3-methylimidazolium) and investigated their absorption capability for propylene, propane and mixture of both at 1–7 bar and 298–318 K. The effects of operating parameter including cation nature, temperature, pressure, Cu + concentration and reuse of absorbent were investigated. Propylene shows a chemical absorption while propane does a physical one, and increasing Cu + concentration effectively improves the absorption capability for propylene and the selectivity of propylene/propane. [Bmim]SCN–CuSCN has higher absorption capability and selectivity for propylene than [Emim]SCN–CuSCN, e.g., [Bmim]SCN–CuSCN-1.5 M can absorb 0.12 mol of propylene per liter while 0.012 mol of propane per liter at 1 bar and 298 K, with a selectivity of 10, which is comparable to some other ILs-Ag + salts and better than pure ILs. Such absorbents can be regenerated through temperature and pressure swing without remarkable activity loss. This work shows that alkylimidazolium thiocyanate ILs with Cu + salts are promising reactive absorbents to separate propylene from propane.

Influence of the alkyl group on thermophysical properties of carboxylic acids in 1-butyl-3-methylimidazolium thiocyanate ionic liquid at various temperatures

In the present study, influence of the alkyl group and temperature on the interactions between the carboxylic acid and ionic liquid (IL) mixtures were discussed in term of density and sound velocity measurements. The IL used in this study was 1-butyl-3-methylimidazolium thiocyanate ([BMIM]+[SCN]−). The density (ρ), and sound velocity (u), of the IL, acetic acid, propionic acid, and their corresponding binary systems {[BMIM]+[SCN]− (x1)+acetic or propionic acid (x2)} have been measured at T=(293.15, 298.15, 303.15, 308.15 and 313.15)K and at p=0.1MPa. The excess molar volumes, VmE, isentropic compressibility, κs, and deviation in isentropic compressibility, Δκs, were calculated using experimental density and sound velocity data, respectively. The Redlich–Kister polynomial equation was used to fit the excess/deviation properties. These results are useful for describing the intermolecular interactions that exist between the IL and carboxylic acid mixtures.

SO2 Solvation in the 1-Ethyl-3-Methylimidazolium Thiocyanate Ionic Liquid by Incorporation into the Extended Cation-Anion Network.

We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO2 adduct, the cations create a “cage” around SO2 with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the pi -system. Despite these similarities between the solvation of SO2 and CO2 in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO2 avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO2 can from O(SO2)–H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO2 acts in this way was termed a linker effect by us, because the SO2 can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation)cdots O(SO2) hydrogen bond and a S(anion)–S(SO2) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO2 solubility in these ionic liquids is so high.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-015-0321-5) contains supplementary material, which is available to authorized users.

Thermochromism and switchable paramagnetism of cobalt(II) in thiocyanate ionic liquids.

Temperature-dependent switching of paramagnetism of a cobalt(II) complex is observed in an ionic liquid solution. Paramagnetic and thermochromic switching occur simultaneously due to a reversible change in coordination. This reversible switching is possible in the ionic liquid solution, which enables mobility of thiocyanate anions by remaining mobile at low temperatures and acts as an anion reservoir.

Synthesis, Characterization, and Thermophysical Properties of 1,8-Diazobicyclo[5.4.0]undec-7-ene Based Thiocyanate Ionic Liquids

In this work, synthesis of 12 ionic liquids based on 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) cation with anions such as chloride, bromide, and thiocyanate were performed. The new ionic liquids were characterized using nuclear magnetic resonance spectroscopy and elemental analysis. The effect of alkyl spacer length on the physicochemical properties of DBU based ionic liquids was studied by attaching ethyl, butyl, hexyl, octyl, decyl, and tetradecyl groups to the DBU cation. The effects of temperature on the density and viscosity over a temperature range from 293.15 K to 373.15 K were recorded at atmospheric pressure. From the experimental density values, the thermal expansion coefficient values were calculated. The surface tension of the neat ionic liquids was measured at seven different temperatures (293.15 K, 303.15 K, 313.15 K, 323.15 K, 333.15 K, 343.15 K, and 353.15 K). The surface entropy and surface enthalpy were calculated from the experimental surface tension value at 303.15 K. The thermal behavi...

Phase equilibria study of the (N-octylisoquinolinium thiocyanate ionic liquid + aliphatic and aromatic hydrocarbon, or thiophene) binary systems

Binary liquid+liquid phase equilibria for 8 systems containing N-octylisoquinolinium thiocyanate, [C8iQuin][SCN] and aliphatic hydrocarbon (n-hexane, n-heptane), cyclohexane, aromatic hydrocarbon (benzene, toluene, ethylbenzene, n-propylbenzene) and thiophene have been determined using dynamic method. The experiment was carried out from room temperature to the boiling-point of the solvent at atmospheric pressure. For the tested binary systems the mutual immiscibility with an upper critical solution temperature (UCST) for {IL+aliphatic hydrocarbon, or thiophene} were observed. The immiscibility gap with lower critical solution temperature (LCST) for the {IL+aromatic hydrocarbon} were determined. The parameters of the LLE correlation equation for the tested binary systems have been derived using NRTL equation. The phase equilibria diagrams presented in this paper are compared with literature data for the corresponding ionic liquids with N-alkylisoquinolinium, or N-alkylquinolinium cation and with thiocyanate – based ionic liquids. The influence of the ionic liquid structure on mutual solubility with aliphatic and aromatic hydrocarbons and thiophene is discussed.

Measurements, Correlations, and Predictions of Thermodynamic Properties of N-Octylisoquinolinium Thiocyanate Ionic Liquid and Its Aqueous Solutions

N-Octylisoquinolinium thiocyanate, [C8iQuin][SCN], has been synthesized in our laboratory from [C8iQuin][Br] as a substrate. The compound was characterized using 1H-NMR, 13C-NMR, and elemental analysis. Karl Fisher titration was used to determine the water content. The density and viscosity of pure ionic liquid were determined over a wide temperature range from (288.15 to 348.15) K. The basic thermal properties of the pure IL have been measured using by means of a differential scanning microcalorimetry technique (DSC). Decomposition of the IL was detected by the simultaneous TG/DTA experiments. (Liquid + liquid) phase equilibria (LLE) have been measured for binary mixtures {[C8iQuin][SCN] (1) + water (2)} using a dynamic method at atmospheric pressure. The experiments have been done over a broad range of ionic liquid mole fraction, x1, and temperatures from 250 K to the boiling point of water. Experimental heat capacities and excess enthalpies were determined for {[C8iQuin][SCN] (1) + water (2)} binary mixtures for different IL mole fractions at a wide range of the temperature at ambient pressure. The influence of temperature and composition was assessed, and suitable equations were used to correlate the experimental data. The experimental results were compared with data for other ionic liquids available in the open literature.

Density and Viscosity of Binary Mixtures of Thiocyanate Ionic Liquids + Water as a Function of Temperature

Densities and viscosities have been determined for binary mixtures of the ionic liquids (ILs) 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], or 1-butyl-4-methylpyridinium thiocyanate [BMPy][SCN], or 1-butyl-1-methylpyrrolidinium thiocyanate [BMPYR][SCN], or 1-butyl-1-methylpiperidinium thiocyanate [BMPIP][SCN] with water over wide range of temperatures (298.15–348.15) K and ambient pressure. The thermal properties of [BMPy][SCN], i.e. glass transition temperature and the heat capacity at glass transition, have been measured using a differential scanning microcalorimetry, DSC. The decomposition of [BMPy][SCN] was detected. The density and viscosity correlations for these systems have been made using an empirical second-order polynomial and by the Vogel–Fulcher–Tammann equation, respectively. The concentration dependences have been described by polynomials. The excess molar volumes and deviations in viscosity have been calculated from the experimental values and were correlated by Redlich–Kister polynomial expansions. The variations of these parameters, with compositions of the mixtures and temperature, have been discussed in terms of molecular interactions. A qualitative analysis of the trend of properties with composition and temperature was performed. Further, the excess partial molar volumes, V_{1}^{mathrm{E}} and V_{2}^{mathrm{E}}, were calculated and discussed. The isobaric expansivities (coefficient of thermal expansion), α, and the excess isobaric expansivities, α E, were determined for four ILs and their mixtures with water. The results indicate that the interactions of thiocyanate ILs with water is not as strong as with alcohols, which is shown by the positive/slightly negative excess molar volumes in these binary systems.Electronic Supplementary MaterialThe online version of this article (doi:10.1007/s10953-012-9875-7) contains supplementary material, which is available to authorized users.

Heat capacities and excess enthalpies of the (N-hexylisoquinolinium thiocyanate ionic liquid + water) binary systems

In the present work the binary mixtures containing the ionic liquid N-hexylisoquinolinium thiocyanate, [HiQuin][SCN] and water was considered as a new working pair for absorption refrigeration.Experimental heat capacities and excess enthalpies of the binary mixtures were determined at different ionic liquid mole fractions over a wide range of temperature at ambient pressure. The influence of temperature and composition on measured properties was assessed and suitable equations were used to correlate the experimental data.

Liquid–liquid extraction of aromatics from their mixtures with alkanes using 1-methyl 3-octylimidazolium thiocyanate ionic liquid

Experimental data for liquid–liquid equilibria (LLE) of ternary systems of {aromatic (ethyl benzene or p-xylene)+alkane (hexane or heptane or octane)+ionic liquid} at T=298.15K and atmospheric pressure were studied. The ionic liquid 1-methyl 3-octylimidazolium thiocyanate [Omim][SCN] was used. The tie lines composition was determined by the gas chromatography and mass balance. The selectivity values were calculated from experimental data. The selectivity values are more than unity which indicate the suitability of IL as a new solvent in extraction of aromatics from alkanes. The reliability of the LLE data was tested by the Othmer–Tobias and Hand equations. The NRTL thermodynamic model was applied for correlating the experimental data. The modelling results show the NRTL model can correlate the experimental data with good accuracy.

Estimation of Physicochemical Properties of 1-ethyl-3-methylimidazolium Thiocyanate Ionic Liquid Using Density and Surface Tension

The density and surface tension of the ionic liquid (IL) [C2mim][SCN] (1-ethyl-3-methylimidazolium thiocyanate) were measured in a temperature range from (298.15 to 338.15) K. In terms of Glasser's semiempirical relation theory of ILs, the standard molar entropy and lattice energy of the homologous series of ILs [Cnmim][SCN] of the IL were estimated at 298 K, respectively. Using Kabo's method and Rebelo's method, the molar enthalpy of vaporization of the IL, H(298), at 298 K and, H(Tb), at hypothetical normal boiling point was estimated, respectively. According to the interstice model, the thermal expansion coefficient of the IL was calculated and in comparison with experimental value, it is in good agreement.In terms of semiempirical method, physicochemical properties molecular volume Vm, parachor P, surface tension r, thermal expansion coefficients a, of the homologue of [Cnmim][SCN] (n = 3, 4) were predicted.