Tricyanomethanide Ionic Liquids Research Articles

Solubility of difluoromethane (R-32) and pentafluoroethane (R-125) in 1-alkyl-3-methylimidazolium tricyanomethanide ionic liquids

The recovery of refrigerant blends and the subsequent separation of value-added hydrofluorocarbons (HFCs) for reuse would help to meet the phase-down in the production of virgin HFCs established by the Kigali Amendment to the Montreal Protocol. The use of ionic liquids (ILs) in extractive distillation processes has become particularly relevant. In this process, the selection of the IL is the core element for a technically and economically feasible design. For this purpose, the absorption of the HFCs difluoromethane (R-32) and pentafluoroethane (R-125), components of the equimassic mixture R-410A, in 1-alkyl-3-methylimidazolium tricyanomethanide ILs was studied. The isochoric saturation method was applied to report vapor-liquid equilibrium data over a temperature range of 283.15–323.15 K and up to 0.9 MPa. These data were fitted accurately to the NRTL activity coefficient model and the Henry's law constants, the activity coefficients at infinite dilution, the enthalpies and entropies of solvation and the thermodynamic mixing properties were calculated. Finally, [C2C1im][tcm] ranked as one of the most selective ILs to date, exhibiting a good R-32 absorption capacity that could make it a valuable solvent for the separation of R-410A by extractive distillation.

Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]+[TCM]- in Silica Material SBA-15 Using NMR.

The molecular dynamics of 1-butyl-3-methyl imidazolium tricyanomethanide ionic liquid [BMIM]+[TCM]- confined in SBA-15 mesoporous silica were examined using 1H NMR spin-lattice (T1) relaxation and diffusion measurements. An extensive temperature range (100 K-400 K) was considered in order to study both the liquid and glassy states. The hydrogen dynamics in the two states and the self-diffusion coefficients of the cation [BMIM]+ above the glass transition temperature were extracted from the experimental data. The results were then compared to the corresponding bulk substance. The effects of confinement on the dynamic properties of the ionic liquid clearly manifest themselves in both temperature regimes. In the high-temperature liquid state, the mobility of the confined cations reduces significantly compared to the bulk; interestingly, confinement drives the ionic liquid to the glassy state at a higher temperature Tg than the bulk ionic liquid, whereas an unusual T1 temperature dependence is observed in the high-temperature regime, assigned to the interaction of the ionic liquid with the silica-OH species.

Biodegradable methylcellulose biopolymer-derived activated porous carbon for dual energy application

Activated porous carbon was synthesized from methylcellulose biopolymer through a two-step mechanism involving H3PO4 as an activating agent and then thermally carbonized in a tubular furnace under an inert atmosphere at 850 °C. The product was next rinsed with strong HCl, neutralized with deionized water, and dried in an oven at 80 °C. Then, to fully understand the behavior of the activated porous carbon, it was characterized using techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), RAMAN spectroscopy, Brunauer–Emmett–Teller (BET), and thermal gravimetric analysis (TGA). Additionally, we have created dye-sensitive solar cells and an electric double-layer capacitor (EDLC) using this porous carbon produced from methylcellulose (DSSC). We used the above-mentioned prepared porous carbon for the electrode portion of the Electric Double-Layer Capacitor (EDLC) fabrication, and the maximized polymer electrolyte film made from the methyl cellulose (MC) biopolymer combined with 60 wt.% of 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL), with a maximum conductivity of 1.93 × 10−2 S/cm, for the electrolyte. The fabricated EDLC device shows a specific capacitance of 60.8 F/gm at 5 mV/s scan rate which was confirmed by cyclovoltammetry and a low-frequency impedance plot in the CH electrochemical workstation. The DSSC device was fabricated using the same porous carbon as a material for the counter-electrode and the same composition polymer electrolyte that had been used in the EDLC as the electrolyte for the DSSC which yields an efficiency of 0.86%. The fill factor and other parameters were also calculated from the JV characteristics that had been characterized and obtained in the solar simulator.

Understanding the Molecular Features Controlling the Solubility Differences of R-134a, R-1234ze(E), and R-1234yf in 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids

This work reports a study of the absorption of fluorinated refrigerant gases in ionic liquids (ILs) from a combined experimental and computational approach to gain insights into the solvation of these greenhouse gases. The results allow the selection of solvents for fluorinated gas recovery, based on molecular characteristics, and improve the recyclability of these high-value-added compounds. The solubility of R-134a, R-1234yf, and R-1234ze(E) was measured experimentally in 1-alkyl-3-methylimidazolium tricyanomethanide ILs at 283.15–323.15 K and up to 5 bar to investigate the influence of the alkyl side chain length of the cations in the ILs. Molecular dynamics was used to study solvation environments around refrigerant molecules in terms of radial distribution functions, coordination numbers, and spatial distribution functions. Simulations were carried out with the recent CL&Pol polarizable force field for ILs, which includes polarization effects explicitly. The force field was validated against experimental solubility through free-energy perturbation calculations. The main effects influencing the solubility of fluorinated refrigerants in ILs result from interactions with the anions and with the cation head group alkyl chain, setting a basis for a rational selection and design of ILs for processes to recover and recycle refrigerants in a circular economy model.

SO2 capture by tricyanomethanide ionic liquids: Unraveling anion-gas interactions by resonance Raman spectroscopy

Interactions concerning the high SO2 absorption capacity in 1-butyl-3-methyilimidazolium tricyanomethanide (BMITCM) were analyzed through Raman spectroscopy. The SO2 symmetric stretching band, νs(SO2), remained equal in shape and wavenumber regardless the SO2 molar fraction, suggesting no specific interaction between TCM and SO2. However, by increasing the Raman excitation energy from 568 to 405 nm, a pre-resonance condition was reached, where a shifting and broadening of νs(SO2) is noticed. Such results evidence solvation states where charge transfer interactions between TCM and SO2 prevail, corroborating the high absorption capacity of TCM based ionic liquids.

Carbon Dioxide Solubilities and Diffusivities in 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids: An Experimental and Modeling Study

The solubility and diffusivity of CO2 in a series of 1-alkyl-3methylimidazolium tricyanomethanide ionic liquids ([Cnmim][TCM] with n = 2, 4, 6, 7, 8; ILs) was studied using a magnetic suspension balance at temperatures ranging from 298 to 353 K and pressures up to 2 MPa. The effects of temperature, pressure, and alkyl chain length on CO2 solubility and diffusivity were examined. The electrolyte PC-SAFT (ePC-SAFT) equation of state was used to describe the solubility of CO2 in the ILs. The Henry’s law constant and the excess properties of solvation (Gibbs free energy, enthalpy, and entropy) were calculated. A series of equations derived from Fick’s second law were evaluated, and a Fourier expansion of Fick’s second law of diffusion was found to be the most suitable model for deriving diffusivities from gravimetric data. The diffusivities range from 10–10 to 10–9 m2·s–1 in the temperature and pressure ranges applied. The activation energies for CO2 diffusion (12–16 kJ·mol–1) were found to be in the range of...

Theoretical study of physicochemical properties of ionic liquid [mim][C(CN)3

Intermolecular interactions between cation and anion in methylimidazolium tricyanomethanide ionic liquid [mim][C(CN)3] have been studied at different levels of theory. Structures, interaction energies, hydrogen bonding, physical and topological properties, as well as NMR spectra of the ionic complexes have been investigated. Nucleus-independent chemical shifts were used to characterize the change of aromaticity of the cation ring upon complexation. The effect of different solvents on the stability of complexes and monomers was examined. The obtained natural bond orbital parameters show that in all ion pairs the charge transfer takes place from anion to cation. The LP(N) → σ*(N–H) and LP(N) → σ*(C–H) donor–acceptor interactions are the most important interactions in these complexes. It is predicted that N⋯H–N interaction is stronger than N⋯H–C one.

Molecular simulations of imidazolium-based tricyanomethanide ionic liquids using an optimized classical force field.

Imidazolium-based ionic liquids (ILs) incorporating the tricyanomethanide ([TCM(-)]) anion are studied using an optimized classical force field. These ILs are very promising candidates for use in a wide range of cutting-edge technologies and, to our knowledge, it is the first time that this IL family is subject to a molecular simulation study with the use of a classical atomistic force field. The [C4mim(+)][TCM(-)] ionic liquid at 298.15 K and at atmospheric pressure was used as the basis for force field optimization which primarily involved the determination of the Lennard-Jones parameters of [TCM(-)] and the implementation of three quantum mechanical schemes for the calculation of the partial charge distribution and the identification of the appropriate scaling factor for the reduction of the total ionic charge. The optimized force field was validated by performing simulations of the 1-alkyl-3-methylimidazolium tricyanomethanide ([Cnmim(+)][TCM(-)], n = 2, 4, 6, and 8) IL family at various temperatures. The results for density, self-diffusivity and viscosity are in very good agreement with the available experimental data for all ILs verifying that the force field reliably reproduces the behaviour of the imidazolium-based [TCM(-)] IL family in a wide temperature range. Furthermore, a detailed analysis of the microscopic structure and the complex dynamic behaviour of the ILs under study was performed.

Liquid–liquid extraction of p-xylene from their mixtures with alkanes using 1-butyl-1-methylmorpholinium tricyanomethanide and 1-butyl-3-methylimidazolium tricyanomethanide ionic liquids

Liquid – liquid experimental data for four ternary systems {1-butyl-1-methyl-morpholinium tricyanomethanide, [BMMOR][TCM], or 1-butyl-3-methylimidazolium tricyanomethanide, [BMIM][TCM] + p-xylene + octane, or decane} were determined at T = 298.15 K and atmospheric pressure. The separation of p-xylene from alkanes (octane, or decane) is performed by extraction with the tricyanomethanide - based ionic liquids. Good miscibility of p-xylene and practical complete immiscibility of alkanes in ionic liquids have been observed. Selectivity, S and solute distribution ratio, β at constant temperature for these mixtures were calculated and discussed. These parameters derived from the experimental equilibrium data were compared with the values for other ionic liquids available in the literature. The NRTL and UNIQUAC models were used to correlate experimental LLE data. Agreement between experimental and correlated data was satisfactory. The influence of the cation structure of the ionic liquid on the phase equilibrium and the separation ability of these ionic liquids was discussed. Additionally, the water content and basic physicochemical properties, such as: density, ρ and dynamic viscosity, η were determined for pure ILs at wide temperature range at ambient pressure.

Porous carbons from ionic liquid precursors confined within nanoporous silicas

We propose Vycor® porous glass and various types of enhanced pore size Vycor® (hereafter referred to eps-Vycor®) as hard templates for the development of micro-mesoporous N-doped carbons via nanocasting/thermolytic treatment of 1-alkyl-3-methylimidazolium tricyanomethanide Ionic Liquids (ILs). Vycor® is less costly than mesoporous ordered silicas of the type SBA-15 and MCM-41 which are sometimes employed for the development of micro-mesoporous carbons (CMK-3) as inverse replicas from the solid matrix; in addition Vycor® and eps-Vycor® can also be used in the form of sheets or tubes, thus opening the road for the development of composite carbon/silica substrate membranes with molecular sieving characteristics. We find that the nitrile functional groups in the anion of the IL lead to enhanced carbon yield while nanocasting and nanoconfinement are decisive for producing functional carbons with high levels of microporosity. In addition, the developed functional carbons exhibited extended mesoporosity with characteristic H2 or H1 types of hysteresis in their N2 adsorption isotherms (77 K), solely in the cases when eps-Vycor® was applied as the hard template. The widening of the Vycor® pores, especially of the pore constrictions by treatment in HF for varying periods led to the formation of thicker carbon nanodomains that exhibited the required mechanical stability to retain the inverse structure (replica) upon dissolution of the hard template.

Thermophysical properties of aqueous solutions of the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

Thermophysical behavior of the binary system [water+1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL)] was thoroughly characterized through systematic measurements of (vapor+liquid) equilibria (water activity aw), mixing enthalpy, density, viscosity, and refractive index. The measurements were performed in the entire composition range and/or specifically in the highly dilute IL region, at T=298.15K or as a function of temperature in the range from (288.15 to 318.15)K. Effective experimental methods minimizing IL sample consumption, using flow arrangements, instrument couplings and high degree of automation were preferably employed. In particular, the aw determination based on the chilled-mirror dew point technique and implemented by an AquaLab 4TE instrument was identified as a generally superior approach to study VLE of (water+IL) systems. Excess thermodynamic properties (Gibbs free energy, enthalpy, heat capacity, and volume) and property deviations from the linear mixing rule (viscosity, refractive index) were evaluated, Padé approximants being used to correlate adequately their complex composition dependences. The extensive aw data were processed by a two-step procedure fitting first the temperature dependence at each isopleth and subsequently the composition dependence at each isotherm. Good estimates could be thus obtained for derivative thermal properties (enthalpy, heat capacity). Alternatively, the water activity and excess enthalpy data were correlated simultaneously by a NRTL-type model, providing their compact, thermodynamically consistent and adequate representation. Despite small absolute values of excess Gibbs free energy (GE), the system is revealed to be highly nonideal, the small GE resulting from close compensation of its large enthalpy and entropy contributions. Large endothermic effects and an enhanced increase of entropy upon mixing found for this system indicate relative weakness of interactions between unlike molecules and a massive structure breakage in the solution. Positive values of excess volume and negative values of viscosity and refractive index deviations found in the major part of the composition range corroborate this general energetic and structural pattern, although the situation appears to be more complicated in the highly dilute IL region, where these properties congruently exhibit a sign inversion.

Phase behavior and permeability of Alkyl-Methyl-Imidazolium Tricyanomethanide ionic liquids supported in nanoporous membranes

This work presents an investigation of the CO2 and N2 single and mixed gas phase permeability through supported ionic liquid membranes (SILMs) developed on ceramic nanoporous substrates with different pore size (1, 5 and 10nm). ILs from the 1-alkyl-3-methylimidazolium tricyanomethanide family ([RMIM][TCM], with alkyl group, R: ethyl, butyl or octyl) were used as nanopore modifiers. These ILs exhibit high chemical and thermal stability, low viscosity and enhanced CO2 absorption capacity compared to other imidazolium based ILs. Thermal analysis of the developed SILMs unveiled a drastic liquid-to-solid transition upon confinement of the ILs into the pore channels with a size of 1nm. The IL crystals formed inside these extremely small cavities possessed considerable thermal stability and underwent thermally induced phase transitions that differed significantly from those occurring in the unconfined bulk IL phase or in the IL phase when entrapped into the larger pore channels. The different physical state of the IL under confinement into the pores of different size resulted to significant variation of the flux properties between the developed SILM membranes. The effect of temperature on the CO2 permeability dependend strongly on the crystal thermal stability and microstructure dictated by the confinement into the nanopores.

Corrosion behaviour of mild steel in 1-alkyl-3-methylimidazolium tricyanomethanide ionic liquids for CO2 capture applications

The corrosion behaviour of mild steel (MS) was systematically investigated as a function of the alkyl chain length in the cation of 1-alkyl-3-methylimidazolium tricyanomethanide ([Cnmim]TCM, n = 2, 4, 6 and 8) ionic liquids (ILs) with respect to their potential application as a structural material and solvents for CO2 capture plants respectively. The surface of MS was examined by scanning electron microscopy, energy dispersive X-ray spectroscopy and micro-Raman mapping before and after immersion testing at temperatures of 70 and 80 °C for durations varying from 1 hour to 10 days. Corrosion initiates at the sites of MnS inclusions on the surface of MS, resulting in the formation of cavities due to the MnS dissolution, which may be surrounded by corrosion products containing magnetite (Fe3O4) and maghemite (γ-Fe2O3). The amount of the corrosion products generated around the inclusion sites decreased with the increase of the cation alkyl chain length, following the order [C2mim]TCM > [C4mim]TCM > [C6mim]TCM ≈ [C8mim]TCM. This was attributed to the corrosion inhibition effect of the ILs through adsorption on the metal surface and blocking active sites, with the inhibition efficiency increasing with the alkyl chain length. The underlying mechanism was associated with corrosion processes at active sites on the MS surface, such as sulphide inclusions, in the presence of residual water and oxygen in the IL. It was shown that increase of the water content in the ILs to about 50 000 ppm resulted in faster dissolution of the MnS inclusions. Finally, it was demonstrated that removal of oxygen from the IL significantly reduced the corrosion rate.

Enhanced CO2 Capture in Binary Mixtures of 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids with Water

Absorption of carbon dioxide and water in 1-butyl-3-methylimidazoliun tricyanomethanide ([C4C1im][TCM]) and 1-octyl-3-methylimidazolium tricyanomethanide ([C8C1im][TCM]) ionic liquids (ILs) was systematically investigated for the first time as a function of the H2O content by means of a gravimetric system together with in-situ Raman spectroscopy, excess molar volume (V(E)), and viscosity deviation measurements. Although CO2 absorption was marginally affected by water at low H2O molar fractions for both ILs, an increase of the H2O content resulted in a marked enhancement of both the CO2 solubility (ca. 4-fold) and diffusivity (ca. 10-fold) in the binary [C(n)C1im][TCM]/H2O systems, in contrast to the weak and/or detrimental influence of water in most physically and chemically CO2-absorbing ILs. In-situ Raman spectroscopy on the IL/CO2 systems verified that CO2 is physically absorbed in the dry ILs with no significant effect on their structural organization. A pronounced variation of distinct tricyanomethanide Raman modes was disclosed in the [C(n)C1im][TCM]/H2O mixtures, attesting to the gradual disruption of the anion-cation coupling by the hydrogen-bonded water molecules to the [TCM](-) anions, in accordance with the positive excess molar volumes and negative viscosity deviations for the binary systems. Most importantly, CO2 absorption in the ILs/H2O mixtures at high water concentrations revealed that the [TCM](-) Raman modes tend to restore their original state for the heavily hydrated ILs, in qualitative agreement with the intriguing nonmonotonous transients of CO2 absorption kinetics unveiled by the gravimetric measurements for the hybrid solvents. A molecular exchange mechanism between CO2 in the gas phase and H2O in the liquid phase was thereby proposed to explain the enhanced CO2 absorption in the hybrid [C(n)C1im][TCM]//H2O solvents based on the subtle competition between the TCM-H2O and TCM-CO2 interactions, which renders these ILs very promising for CO2 separation applications.

Solvent extraction of aromatic sulfur compounds from n-heptane using the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

The ionic liquid 1-ethyl-3-methylimidazolium tricyanomethanide ([EMIM][TCM]) has been tested as a solvent for the separation of sulfur compounds from aliphatic hydrocarbon. Liquid–liquid phase equilibrium data have been determined for ternary systems containing the ionic liquid, thiophene or benzothiophene and n-heptane. The influence of temperature on the separation of thiophene from n-heptane was determined. High solubility of sulfur compounds and practical immiscibility of aliphatic hydrocarbon in ionic liquid have been found. The values of selectivity and solute distribution ratios have been calculated for all systems and compared with literature data for other 1-ethyl-3-methylimidazolium-based ionic liquids. High values of selectivity were obtained. The experimental data were correlated using the NRTL equation, and the binary interaction parameters have been reported. The phase equilibria diagrams for the ternary mixtures including the experimental and calculated tie-lines have been presented.

Alkyl-methylimidazolium Tricyanomethanide Ionic Liquids under Extreme Confinement onto Nanoporous Ceramic Membranes

A method to predict the gas permeability of supported ionic liquid membranes (SILMs) was established, using as input the pore structure characteristics of asymmetric ceramic membrane supports and the physicochemical properties of the bulk ionic liquid (IL) phase. The method was applied to investigate the effect of IL nanoconfinement on the CO2 and N2 permeability/selectivity properties of novel SILMs developed on nanofiltration (NF) membranes employing for the first time the 1-ethyl-3-methylimidazolium and the 1-butyl-3-methylimidazolium tricyanomethanide ILs as pore modifiers. The selected ILs exhibit low viscosity, which allows for faster gas solvation rates and ease of synthesis/purification that makes them attractive for large-scale production. In parallel, the use of ceramic supports instead of polymeric ones presents the advantage of operation at elevated temperatures and pressures and offers the possibility to study the “real” permeability of the confined IL phase, avoiding additional contributions...

Ionic Liquids Based on Imidazolium and Pyrrolidinium Salts of the Tricyanomethanide Anion

A novel series of tricyanomethanide ionic liquids have been prepared and characterized for potential use as ionic liquid solvents. Full thermal analyses of all salts at ambient and sub-ambient temperatures are reported (melting points –17° to 160°C). The thermal stability and decomposition temperatures are also presented (Tdecomp ≈ 300°C). An electrochemical window of ~3 V has been established and the conductivity measured over a range of temperatures (20 mS cm–1 at 25°C).