Applications of 1-Ethyl-3-methylimidazolium chloride

1-Ethyl-3-methylimidazolium chloride is an imidazolium-based ionic liquid used as a solvent and catalyst in organic synthesis, with high thermal stability and water solubility. It is used as a solvent in many organic reactions due to its unique properties like small vapor pressures, high thermal stabilities and ionic conductivities. This material may be used in the preparation of aluminum chloride-EMIC, zinc chloride-EMIC and EMIC /tetrafluoroborate molten salts, which are useful in electrodeposition studies.

Simultaneous Recovery and Concentration of 1-Ethyl-3-methylimidazolium Chloride

An ionic liquid (IL) is a liquid salt. The melting points of ILs are generally below room temperature, occasionally below 0 °C, and they are classified as molten salts. ILs are characterized, for example, by high thermal and chemical stability, negligible vapor pressure, non-flammability and a wide electrochemical window. ILs are often used for the treatment of environmental samples, such as for the treatment of lignocellulosic biomass. Imidazolium ILs can liquefy lignin, cellulose and therefore wood. A reagent that is commonly used as a solvent for the liquefaction of wood is 1-ethyl-3-methylimidazolium chloride ([Emim]Cl). [Emim]Cl allows lignin and polysaccharides to be liquefied at temperatures around 100 °C. Thus, [Emim]Cl can be used as an alternative solvent in cellulose derivatization reactions, instead of the conventional organic solvents that are characterized by toxicity and volatility. The aim of this work is to investigate the effectiveness of simultaneous recovery and concentration of 1-ethyl-3-methylimidazolium chloride in a laboratory-scale ED module. The influence of the ED parameters on the effectiveness of [Emim]Cl concentration and recovery is discussed in detail. The successful recovery of [Emim] by ED has not yet been demonstrated in the available literature; therefore, it could be a novel way to recover and recycle 1-ethyl-3-methylimidazolium chloride from wastewater.[1]

In the current study, the possibility of simultaneous [Emim]Cl recovery and concentration from aqueous solutions by ED was investigated. It was observed that 1-ethyl-3-methylimidazolium chloride was removed from the diluate effectively using the proposed method. The obtained results proved that a recovery of up to 90.4% is possible. It was also proven that the ED process could be optimized to allow for concentration of the IL. In fact, the [Emim]Cl content in the examined process increased by 2.55 times in comparison to the IL concentration in the initial diluate compartment. At a diluate-to-concentrate volume ratio of 5, a 3.35-fold concentration of 1-ethyl-3-methylimidazolium chloride, with a recovery of 81.7%, could be obtained. It was shown that the IL concentration, applied voltage drop, linear flow velocity and diluate-to-concentrate volume ratio all had an influence on the recovery efficiency and concentration of the chosen IL. The highest ED efficiency for the recovery and concentration of [Emim]Cl was obtained at 20 V applied potential, 2 cm/s linear flow velocity and 0.2 M IL in the feed solution. The performed experiments allowed the operating parameters of [Emim]Cl recovery by ED to be optimized; therefore, the obtained results could be a valuable base to develop and scale-up the method for the recovery and concentration of 1-ethyl-3-methylimidazolium chloride from industrial wastewater. In future, the ED methodology presented here could be a good way to recycle ILs and be a highly valuable wastewater utilization method, especially for wastewater originating from biomass utilization processes or the pharmaceutical industry.

Aqueous Solution Behavior of 1-Ethyl-3-Methylimidazolium Chloride

In the present study, density, speed of sound, and viscosity of 1-ethyl-3-methylimidazolium chloride [C2mim]Cl in pure water as well as in an aqueous solution of potassium chloride, potassium carbonate, and potassium phosphate (ws = 0.11) at T = 298.15–318.15 K were measured. The apparent molar volume, isentropic compressibility, apparent molar isentropic compressibility, and relative viscosity were computed using the experimental data. Transfer apparent molar volume, apparent isentropic compressibility, and viscosity B-coefficient of IL from pure water to aqueous electrolyte solutions were also calculated which provides valuable information regarding the solute–solute and solute–solvent interactions that exist in aqueous IL + electrolyte solutions. The structure-making/breaking nature of the 1-ethyl-3-methylimidazolium chloride in the ternary solutions has been discussed in terms of Hepler's constant and temperature derivative of viscosity B-coefficient (dB/dT). The activation free energy, enthalpy, and entropy were also calculated by the application of transition state theory. The calculated parameters were interpreted in the sense of solvent–solute and solute–solute interactions. The Fourier transform infrared (FTIR) studies and thermal analysis were also performed for the studied systems. The temperature dependency of viscosity was successfully fitted to the Vogel–Fulcher–Tammann (VFT) equation.[2]

The density, speed of sound, and viscosity of 1-ethyl-3-methylimidazolium chloride in water and aqueous KCl, K2CO3, and K3PO4 (ws = 0.11) solutions were measured at T = 298.15–318.15 K. From the experimental data, the apparent molar volume, apparent isentropic compressibility, and relative viscosity have been determined. The limiting apparent molar volume and isentropic compressibility along with viscosity B-coefficient were calculated as well, which were utilized to evaluate the corresponding transfer parameters for [C2mim]Cl from water to aqueous electrolyte solution. The obtained result exhibited a negative transfer volume of [C2mim]Cl from water to the aqueous electrolyte solutions, which decreased by increasing temperature. The isentropic compressibility of all studied systems decreased by increasing the concentration of 1-ethyl-3-methylimidazolium chloride and temperature. The intersection point in isentropic compressibility isotherms may indicate the formation of a clathrate-like structure. Hepler's constant and dB/dT revealed that [C2mim]Cl in pure water and electrolyte solutions acts as a structure maker. The FTIR studies revealed that a change in the wavenumber of the O–H peak in different systems might indicate some structural changes or possible interactions between [C2mim]Cl and electrolyte molecules. The temperature dependency of viscosity was satisfactorily fitted to the VFT equation. The viscosity of 1-ethyl-3-methylimidazolium chloride in aqueous electrolyte solutions is larger than that in pure water and increases with increasing IL concentration and decreases with temperature. The TGA revealed that all the studied systems undergo a two-step thermal decomposition process. By the addition of different electrolytes to the aqueous IL solution, the thermal decomposition temperature of IL was shifted to lower temperatures. The higher the anion charge, the lower the decomposition temperature.

References

[1]Babilas D, Kowalik-Klimczak A, Dydo P. Study on the Effectiveness of Simultaneous Recovery and Concentration of 1-Ethyl-3-methylimidazolium Chloride Ionic Liquid by Electrodialysis with Heterogeneous Ion-Exchange Membranes. Int J Mol Sci. 2021 Dec 1;22(23):13014. doi: 10.3390/ijms222313014. PMID: 34884819; PMCID: PMC8657828.

[2]Sarmad S, Zafarani-Moattar MT, Nikjoo D, Mikkola JP. How Different Electrolytes Can Influence the Aqueous Solution Behavior of 1-Ethyl-3-Methylimidazolium Chloride: A Volumetric, Viscometric, and Infrared Spectroscopy Approach. Front Chem. 2020 Nov 12;8:593786. doi: 10.3389/fchem.2020.593786. PMID: 33282835; PMCID: PMC7688583.