Ionic Liquid Solutions Research Articles

Synergistic Effect of Silver-Based Ionic Liquid for Ethylene/Ethane Separation

Separation of ethylene (C2H4) and ethane (C2H6) is one of the most significant processes in the petrochemical industry. In terms of industrial application, silver nitrate aqueous solution is the most widely used absorbent, but the activity of Ag+ and the absorption of C2H4 are not optimistic. Thus, it is urgent to explore new technologies for efficient separation of C2H4 and C2H6. In this work, several silver-based ionic liquid (Ag-IL) solutions are prepared with ionic liquids (ILs), silver salts, and ethylene glycol (EG). Pure and mixed gas absorption experiments were conducted to explore the effects of various anions and cations of ILs, the molar ratio of IL to silver salt, the EG proportion on absorption performance, and recycling of absorbents. Due to the synergy between ILs, EG, and Ag+, the absorption of C2H4 in [Emim][BF4]/AgBF4/EG (2:1:0.1) is up to 101.75 mg/g (2.17 mol C2H4/mol Ag+), which is the highest value of IL absorbents reported so far, and the highest selectivity is 37.8. Furthermore, the cyclic stability kept constant after five cycles of absorption–desorption. The interaction mechanism of Ag-ILs was studied by NMR and FTIR spectroscopies. ILs and EG synergistically weaken the electrostatic effect between the anion and cation of AgBF4 and increase the amount of active silver to enhance the absorption of C2H4. These task-specific Ag-ILs are expected to be a new medium with commercial potential for C2H4/C2H6 separation.

Effects of hydrogen-bonding functional groups of ammonium based-ionic liquids with Tf2N anion on the upper critical solution temperature in aqueous solutions

Ionic liquids (ILs) with an upper critical solution temperature (UCST) are feasible candidates as draw solutions in the forward osmosis process. However, the factors controlling the phase separation of UCST-type ILs in aqueous solutions remain unclear. Here, we focused on the role of hydrogen bonding in the phase separation behavior of UCST-type ILs. The phase separation behavior of aqueous solutions of UCST-type ILs is affected by the hydrogen-bonding functional groups of the ILs. A thermodynamic analysis of the mixing of water and ILs indicated that the phase separation of the aqueous solution of UCST-type ILs is characterized by enthalpy changes of mixing. To investigate the state of hydrogen bond formation in aqueous solutions of ILs, 1H nuclear magnetic resonance spectra were acquired. The data suggest that the hydrophobic parts of the ILs broke the water–water hydrogen bonds, and the hydrogen-bonding functional groups of the IL formed hydrogen bonds in the aqueous IL solution. These hydrogen-bonding states strongly affect the enthalpy changes of mixing. Therefore, water–water and water–IL hydrogen bonds play an important role in the phase separation behavior of UCST-type ILs in aqueous solutions.

Studies on the interference of citrate salts on the ion–solvent interactions of ionic liquid with water at different temperatures through volumetric, viscometric, and acoustic methods

The density, viscosity, and ultrasonic velocity of solutions of imidazolium-based ionic liquid, 1-ethyl-3-methyl imidazolium ethyl sulphate ([EMIm][EtSO4]) with aqueous solutions of sodium and potassium salts of citrate have been measured at five different temperatures i.e., T = (298.15–318.15) K and 0.1 MPa pressure. The experimentally found density (ρ) data have been utilized to compute the different volumetric properties such as apparent molar volume (Vϕ), partial molar volume (Vϕ0), partial molar expansivity (Eϕ0), Hepler’s constant (∂Eϕ0/∂T)p and volume transfer (ΔtrVϕ0). Similarly, the Jones-Dole equation, viscosity B-coefficient, transfer properties of B-Coefficient, (ΔtrB) and thermodynamics of viscous flow were calculated from viscosity consequences. The compression properties such as apparent molar isentropic compressibility (Kϕ,S), partial molar compressibility (Kϕ,S0) and transfer partial molar compressibility (ΔtrKϕ,S0) of IL have been deduced from the ultrasonic velocity. All the derived properties have been used to investigate the impact of citrate salts on the ion–solvent interactions of [EMIm][EtSO4] with water. The positive value of each of Hepler’s constants, and ΔtrKϕ,S0 and the negative sign of (dB/dT) indicates the existence of strong ion–solvent interactions and the cosmotrope nature of [EMIm][EtSO4] in the studied systems at the studied temperature ranges. The ion–solvent interactions of the present IL are found to be more in the solutions of potassium citrate (K3Cit) than sodium citrate (Na3Cit).

Process simulation and energy analysis of synthetic natural gas production from water electrolysis and CO2 capture in a waste incinerator

Power-to-gas (PtG) and carbon capture and utilisation are expected to play a key role in promoting a sustainable energy transition. In this work, a detailed energy analysis of a complete PtG system integrated with a real waste incinerator is performed. A fraction of the renewable electricity and heat produced by the waste incinerator is used in the PtG system to produce hydrogen, which is further converted into SNG by methanation with CO2 recovered from the plant flue gases. A PtG plant able to produce up to 500 m3/h of SNG is considered. A total of six different plant configurations are analysed, obtained by the combination of different electrolysis and post-combustion carbon capture technologies. Specifically, alkaline and PEM electrolysers are considered for the production of hydrogen, while absorption with monoethanolamine solution, absorption with monoethanolamine and ionic liquid solution, and temperature swing adsorption with solid sorbent are selected for carbon capture. The main sections of the PtG system are modelled and the performance of the overall system is evaluated by computing key performance indicators, such as the global energy efficiency and the Specific Plant Energy Consumption for CO2 Avoided (SPECCA). Special attention is also paid to the thermal integration between the methanation unit and the carbon capture unit. The heat produced during the methanation process is sufficient to cover the entire heat demand of the CO2 capture unit in almost all configurations investigated. In particular, thermal integration increases the global energy efficiency by 5–9% and reduces the SPECCA indicator by 5–8%. Considering the thermally integrated configurations, the global energy efficiency is estimated to be between 44.6% and 46.7%, while the SPECCA value ranges from 40.5 MJ/kg to 42.4 MJ/kg. Finally, some technical considerations are given, including the quality of SNG produced and the degradation phenomena in the considered technologies.

Solubility and Stability of Carotenoids in Ammonium- and Phosphonium-Based Ionic Liquids: Effect of Solvent Nature, Temperature and Water.

Ionic liquids (ILs) have arisen as alternatives to organic solvents and been used in natural pigment extraction in recent decades. However, the solubility and stability of carotenoids in phosphonium- and ammonium-based ILs are insufficiently explored. In this work, the physicochemical properties of the ILs, and the dissolution behavior and storage stability of three carotenoids (astaxanthin, β-carotene, and lutein) in the IL aqueous solution were investigated. The results showed that the solubility of the carotenoids in the acidic IL solution is higher than that in the alkaline IL solution, and the optimal pH is about 6. The solubility of astaxanthin (40 mg/100 g), β-carotene (105 mg/100 g), and lutein (5250 mg/100 g) was the highest in tributyloctylphosphonium chloride ([P4448]Cl) due to the van der Waals forces with [P4448]+ and hydrogen bonding with Cl-. A high temperature was beneficial to improve the solubility, but it can reduce the storage stability. Water has no significant effect on the carotenoid stability, but a high water content decreases the carotenoid solubility. A IL water content of 10-20%, an extraction temperature of 338.15 K, and a storage temperature of less than 298.15 K are beneficial for reducing the IL viscosity, improving carotenoid solubility, and maintaining good stability. Moreover, a linear correlation was found between the color parameters and carotenoid contents. This study provides some guidance for screening suitable solvents for carotenoid extraction and storage.

Translational Dynamics of Imidazolium-Based Ionic Liquids in Acetonitrile Solutions

The dynamics of pure ionic liquids and solutions with acetonitrile have been investigated through quasielastic neutron scattering (QENS). The translational diffusive motion of the 1-butyl-3-methyl-imidazolium cation was revealed as a function of concentration and temperature. The diffusion coefficients obtained are in reasonably good agreement with molecular dynamics (MD) computer simulations based on a classical potential. The diffusive mobility of the cation dramatically increases when adding acetonitrile. This increase in diffusivity is directly related to a maximum in conductivity of these ionic liquid solutions and might pave the way for new design of electrolytes. The translational motions in pure ionic liquids are too slow to be resolved by our experiment. However, localized motion resembling rotation on a sphere of the measured proton signal could be identified in the pure ionic liquids.

Interaction between DNA and cationic metalloporphyrins in ionic liquid solutions

We studied the interaction of water-soluble cationic metalloporphyrins, [Formula: see text]Py and TMPyP, with the DNA double helix in ionic liquid solutions using CD and absorption spectra. The dispersibility of their porphyrin complexes was improved by electrostatic interactions of the anions of the ionic liquid. In the case of Cu(II) and Zn(II) complexes, the [Formula: see text]Py complexes with pyridinium cations attached to the meso-phenyl groups via methylene groups intercalated into the DNA double helix, while the compact TMPyP complexes with pyridinium cations at the meso-position could not interact with DNA. Thus, it was suggested that the solvation behavior by ionic liquids depends on the structure of the porphyrin and also affects its interaction with DNA. Neither Mn(III) complexes with axial ligands could interact with DNA, regardless of the presence of the ionic liquids, due to their steric hindrance.

Preparation, thermal properties and electrical conductivity of solutions of pyridinium ionic liquids with tetrachloroferrate anion

Thermal stability of N -alkylpyridinium tetrachloroferrates(III) [C5H5NR]FeCl4 [R = C4H9, (CH2)3CN, CH2C6H5, C8H17, C10H21] in air in the range of 25-600°C was studied, as well as the thermal stability of N -alkylpyridinium chlorides. The equivalent electrical conductivity of N -alkylpyridinium tetrachloroferrates(III) in acetonitrile solution at 25°C was investigated. The ionic association constants K a , the limiting molar electrical conductivity (λ0) and the standard Gibbs energy of the association (Δ G °) in acetonitrile solutions were calculated based on conductometric data by the Lee-Wheaton method.

Liquid-phase exfoliation of titanium disulfide nanosheets in aqueous ionic liquid solutions for highly efficient CO2 electroreduction

Titanium disulfide nanosheets (TiS2 NSs) have attracted considerable research interest due to their eco-friendliness and outstanding electrical transport properties. However, the large scale preparation of TiS2 NSs usually is plagued by the employ of poisonous solvents and low production. Herein, we develop a green, highly efficient and scalable tactic to exfoliate bulk TiS2 powders in aqueous ionic liquids solutions under ambient conditions. This result shows that the exfoliation yield can reach 57.6 %, which surpasses the most values for the liquid-phase exfoliation of TiS2 reported in literatures. The thickness of TiS2 NSs is mainly in the range of 1 nm to 2 nm, and the lateral dimension is up to a few hundreds of nanometers. The molecular geometry and anionic alkalinity of the ionic liquids play key roles in the delamination and stability of TiS2 NSs. In addition, TiS2 NSs have been used as catalysts in the electrocatalytic CO2 to CO conversion with the faradaic efficiency of 68.7 %, which is six times that by the bulk TiS2 powder. Thus, the liquid phase delamination approach reported in this work has a great potential in manufacturing 2D layer materials for high activity electrocatalysis.

Preparation, Thermal Properties, and Electrical Conductivity of Solutions of Pyridinium Ionic Liquids with Tetrachloroferrate Anion

Preparation, Thermal Properties, and Electrical Conductivity of Solutions of Pyridinium Ionic Liquids with Tetrachloroferrate Anion

Thermodynamic and spectroscopic studies of biotin supplement in aqueous solution of biocompatible choline amino acid ionic liquids

Thermodynamic and spectroscopic studies of biotin supplement in aqueous solution of biocompatible choline amino acid ionic liquids

Exploration of Diverse Interactions of l-Methionine in Aqueous Ionic Liquid Solutions: Insights from Experimental and Theoretical Studies.

Here, we have investigated some physicochemical parameters to understand the molecular interactions by means of density (ρ) measurement, measurement of viscosity (η), refractive index(n D) measurement, and conductance and surface tension measurements between two significant aqueous ionic liquid solutions: benzyl trimethyl ammonium chloride (BTMAC) and benzyl triethyl ammonium chloride (BTEAC) in an aqueous l-methionine (amino acid) solution. The apparent molar volume (Φv), coefficient of viscosity (B), and molar refraction (R M) have been used to analyze the molecular interaction behavior associated in the solution at various concentrations and various temperatures. With the help of some important equations such as the Masson equation, the Jones-Doles equation, and the Lorentz-Lorenz equation, very significant parameters, namely, limiting apparent molar volumes (Φv 0 ), coefficient of viscosity (B), and limiting molar refraction (R M 0), respectively, are obtained. These parameters along with specific conductance (κ) and surface tension (σ) are very much helpful to reveal the solute-solvent interactions by varying the concentration of solute molecules and temperature in the solution. Analyses of Δμ1 0#, Δμ2 0#, TΔS 2 0#, ΔH 2 0#, and thermodynamic data provide us valuable information about the interactions. We note that l-Met in 0.005 molality BTEAC ionic liquid at 308.15 K shows maximum solute-solvent interaction, while l-Met in 0.001 molality BTMAC aqueous solution of ionic liquid at 298.15 K shows the minimum one. Spectroscopic techniques such as Fourier transform infrared (FTIR), 1H-NMR, and UV-vis also provide supportive information about the interactions between the ionic liquid and l-methionine in aqueous medium. Furthermore, adsorption energy, reduced density gradient (RDG), and molecular electrostatic potential (MESP) maps obtained by the application of density functional theory (DFT) have been used to determine the type of interactions, which are concordant with the experimental observations.

Simultaneous enhancement of critical heat flux and heat transfer coefficient via in-situ deposition of ionic liquids during pool boiling

Two-phase heat transfer processes such as boiling are required to address waste heat management challenges. Among the various regimes, the nucleate boiling regime, which relies on the ebullition cycle to dissipate large amounts of heat within narrow temperature budgets is desired in such applications. However, an insulating vapor blankets the heater at higher heat fluxes to interrupt this high heat transfer coefficient (HTC) regime. This limiting heat flux beyond which a thermal runaway occurs in boiling systems is known as the critical heat flux (CHF). Accordingly, easy-to-implement and reliable strategies for simultaneous enhancement in HTC and CHF are desired. Typical surface modification/coating strategies used in this regard are often expensive and suffer from the issues of delamination and fouling. Here we utilize aqueous solutions of imidazolium ionic liquids (ImILs) to propose a facile, scalable, and robust strategy to address these issues. We show that the in-situ deposition of short-chain ImILs such as [C2mim][Cl] enhances heater surface wettability to remarkably increase the CHF to ≈1600kW/m2, i.e., ≈1.6× increase compared to the baseline case of pure water. We explain the mechanism of this atypical CHF enhancement with molecular additives via thorough surface tension, foamability, surface, and wettability characterization experiments. We next vary the hydrophobic chain length of the ImILs to facilitate a simultaneous enhancement in CHF and HTC. We perform a quantitative comparison with the existing studies in the literature to demonstrate the potential of our approach. Ease of implementation along with the flexibility to favorably manipulate the heater surface and the boiling fluid properties simultaneously by tuning the structure of ImILs are promising for current and future thermal management challenges.

Aqueous solutions of chiral ionic liquids based on (–)-menthol: An experimental and computational study of volumetric and transport properties

Aqueous solutions of ionic liquids remain at the focus of the physico-chemical and chemical-engineering research due to their interesting behaviour in the bulk and on the molecular level as well as thanks to their possible application potential. Indeed, the molecular structure of the aqueous solutions of ionic liquids is still poorly understood. In this work, imidazolium-based chiral ionic liquids with a (–)-menthol substituent on the cation 1-alkyl-3-[(1R,2S,5R)-(–)-menthoxymethyl]imidazolium chlorides were studied in aqueous solutions. Their volumetric properties and electrical conductivity were measured to better understand their hydration and dissociation. The bulk experimental data were interpreted in the light of MD simulations that enabled us to obtain spatial and radial distribution functions and to estimate the volumetric and transport properties of the studied systems. Experimental data of density and conductivity were analyzed by methods of mathematical gnostics which is naturally robust, is valid for small data set (no coverage factor needed), and does not require prior knowledge of the distribution of the measurement errors. It is therefore applicable in cases where tests of data normality are statistically insignificant or even fail.

Shear-induced phase transition in the aqueous solution of an imidazolium-based ionic liquid.

An ionic liquid (IL) is a salt in the liquid state that consists of a cation and an anion, one of which possesses an organic component. Because of their non-volatile property, these solvents have a high recovery rate, and, hence, they are considered as environment-friendly green solvents. It is necessary to study the detailed physicochemical properties of these liquids for designing and processing techniques and find suitable operating conditions for IL-based systems. In the present work, the flow behavior of aqueous solutions of an imidazolium-based IL, 1-methyl-3-octylimidazolium chloride, is investigated, where the dynamic viscosity measurements indicate non-Newtonian shear thickening behavior in the solutions. Polarizing optical microscopy shows that the pristine samples are isotropic and transform into anisotropic after shear. These shear thickened liquid crystalline samples change into an isotropic phase upon heating, which is quantified by the differential scanning calorimetry. The small angle x-ray scattering study revealed that the pristine isotropic cubic phase of spherical micelles distort into non-spherical micelles. This has provided the detailed structural evolution of mesoscopic aggregates of the IL in an aqueous solution and the corresponding viscoelastic property of the solution.

Controlling Cellulose Membrane Performance via Solvent Choice during Precursor Membrane Formation

Fabrication of cellulose membranes by alkaline hydrolysis of cellulose acetate (CA) membranes is a simple alternative method to preparing cellulose membranes via phase inversion from their ionic liquid solutions. In this study, three different solvent systems were used to fabricate cellulose acetate membranes by phase inversion, which are dimethyl sulfoxide and its mixtures with acetone and acetic acid. Acetone as cosolvent led to an asymmetric morphology with the densest selective layer, whereas acetic acid led to a loose, almost isotropic structure with high porosity and pore connectivity, also reflected in the pure water permeance and molecular weight cutoff (MWCO) of the CA membranes. Comparing the effects of these cosolvents on the phase inversion process, acetic acid decreased the solvent quality, increased nonsolvent–solvent interactions, and in total decreased the polymer solutions’ stability against phase separation. The phase inversion rate when acetic acid was used as cosolvent was also markedly lower, which was attributed primarily to the solvent’s much higher viscosity. After alkaline hydrolysis of the CA membranes, which converted them into cellulose membranes, the permeance and MWCO of large-pore, small-pore, and dense membranes changed in different directions. This was attributed to a changing membrane structure due to partial degradation of cellulose chains in an alkaline medium, which in turn can affect transport through both the pores and the membrane matrix.

Investigation on the Effect of Ionic Liquids and Quaternary Ammonium Salts on the Kinetics of Methane Hydrate

This study investigates the kinetics of gas hydrate (methane gas) in the presence of Ionic Liquids (ILs) and organic Quaternary Ammonium Salts (QASs). Aqueous solutions of eight ILs (five aromatic ILs and three aliphatic ILs) and three QASs have been studied for the kinetics of methane hydrate formation. In this study, five aromatic-based ILs with cations, viz., 1-hexyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-octyl-3-methylimidazolium, and anions such as [Br]−, [Cl]−, and [HSO4]− were selected. Three aliphatic ILs with cations, viz., diethylammonium, tripropylammonium, and tributylammonium, attached with the [HSO4]− anion were also selected. In the case of QASs, varying carbon chain lengths such as tetra-n-methyl-, tetra-n-ethyl-, and tetra-n-butylammonium bromide (TMAB, TEAB, TBAB) have been considered for the study. The kinetics of methane hydrate formation were investigated at a pressure of 7.5 MPa and a temperature of 276.15 K in the presence of aqueous solutions of QASs at 0.05 mf (mass fraction) and 0.1 mf concentrations and ILs at 0.01 mf. The results show that 0.05 mf of TBAB assists the methane hydrate to nucleate very rapidly and enhances the rate of growth. Hence, TBAB at 0.05 mf is observed to be most promising for gas storage and gas separation/processing among all investigated QASs. TMAB and TEAB have shown slow kinetics; therefore, their presence in a gas hydrate system may not aid in hydrate gas storage/gas separation applications; nevertheless, they could be used as an inhibitor for the prevention of hydrates in systems where other inhibitors may become unsuitable. The aqueous solution of aromatic-based ILs generally shows hydrate promotion, except for shorter chain lengths. The shorter chain length of ionic liquid with suitable anion (Cl–) behaved as a hydrate as the inhibitor and with Br– as the promoter. In general, a bigger cation acts as a good nucleating agent. The anion [HSO4]− is common in both the categories of ILs (aromatic and aliphatic), and it looks like the hydrate inhibition (no hydrate formation) may have occurred due to its presence. ILs offer more scope to understand the tunability of cations and anions to derive a better solution for gas hydrate inhibition and promotion, which have more applications in the ares of methane storage and transportation.

Diarylethene-Based Ionic Liquids: Synthesis and Photo-Driven Solution Properties.

In this work, the design and synthesis of a series of photochromic gemini diarylethene-based ionic liquids (GDILs) with different cationic motifs is reported. Several synthetic pathways were optimized for the formation of cationic GDILs with chloride as the counterion. The different cationic motifs were achieved through the N-alkylation of the photochromic organic core unit with different tertiary amines, including different aromatic amines such as imidazole derivatives and pyridinium, and other non-aromatic amines. These novel salts present surprising water solubility with unexplored photochromic features that broaden their known applications. The covalent attachment of the different side groups dictates their water solubility and differences upon photocyclization. The physicochemical properties of GDILs in aqueous and in imidazolium-based ionic liquid (IL) solutions were investigated. Upon irradiation with ultraviolet (UV) light, we have observed changes in the physico-chemical properties of distinct solutions containing these GDILs, at very low concentrations. More specifically, in aqueous solution, the overall conductivity increased with the time of UV photoirradiation. In contrast, in IL solution, these photoinducible changes are dependent on the type of ionic liquid used. These compounds can improve non-ionic and ionic liquids' solutions since we can change their properties, such as conductivity, viscosity or ionicity, only by UV photoirradiation. The electronic and conformational changes associated with these innovative stimuli GDILs may open new opportunities for their use as photoswitchable materials.

Highly selective and rapid removal of metal ions from ionic liquids solutions through size-sieving and ion-exchange strategy

The introduction of metal ion impurities into ionic liquids (ILs) when serving as solvents and catalysts is inevitable, thus the purification and recovery of ILs is essential in view of the quality control of the final products and cost. However, the highly efficient removal of impurity with minimal IL loss is challenging. In this work, the adsorption of metal ions from 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]Dep) solution generated in the cellulose spinning process was investigated. Based on the size-sieving and ion-exchange strategy, the modified molecular sieves (MMSs) were used and the effect of particle size on the adsorption performance was systematically studied. Batch adsorption showed that the MMSs with the smaller size of 1.6 mm exhibited the superior advantages over metal ions with fast removal kinetic and higher selectivity. The removal ratio of K+, Ca2+, Mg2+, Cu2+ and Zn2+ could reach 88.9 %, 98.4 %, 98.9 %, 99.6 % and 99.9 %, respectively. Benefiting from the size-sieving effect, the loss ratio of [Emim]Dep was lower than 0.7 %. Fixed-bed adsorption experiments further suggested the benign long-term separation performance of metal ions from [Emim]Dep aqueous solution. Moreover, the high removal ratios of metal ions from the actual [Emim]Dep aqueous solutions indicated the potential application in the purification of real ionic liquids.

Influence of Pretreatment Severity Factor and Hammett Acidity on Softwood Fractionation by an Acidic Protic Ionic Liquid.

The impact of pretreatment severity in the acidic protic ionic liquid (IL) N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO4] using pine softwood was investigated using a modified severity factor that considers the IL solution acidity based on Hammett acidity. A Box-Behnken experimental design was employed to evaluate pretreatment severity with temperature, pretreatment time, and IL concentration as factors and degree of delignification as the response variable. The optimal pretreatment conditions were found to be at 170 °C, 30 min, and 80 wt % IL, which yielded nearly 90% of delignification and 95% of glucose yield in enzymatic saccharification. The modified severity factor showed an improved correlation with the fractionation indicators relative to the classical pretreatment severity factor, indicating that it can better predict the pretreatment outcomes, particularly for delignification and hemicellulose removal. The fate of hemicellulose, its conversion to humins, and its impact on the precipitated lignin properties were also investigated and correlated to the modified pretreatment severity factor. It was found that such parameters alone cannot be used to predict the fate of dissolved hemicellulose sugars in the IL medium. Furthermore, IL acidity greatly impacts the degradation of the dissolved hemicellulose sugars and the formation of humins.