The Path Ahead for Ionic Liquids

Abstract

Ionic liquids are designer molecules which can efficiently replace the conventional organic solvents used in chemical processes and operations. Although a number of such applications have been reported in the literature for almost a decade, very few have actually been commercialized. This paper details the different applications claimed and examines the issues and barriers which obstruct the rapid commercialization of ionic liquids. It identifies further courses of action required for the assessment and realization of the advantages of ionic liquids. PreambleFor the past ten years, ionic liquids (ILs) have been looked upon as a revolutionary replacement for conventional organic solvents, as a medium which can be designed and used to carry out a number of chemical reactions and operations at comparatively lower temperature and pressure conditions, and which do not affect the environment. However, thus far only a few ILs have been manufactured and utilized on a commercial scale. This paper examines the claimed uses of ILs, the issues and barriers for their commercialization and the course of action required to explore their utilization. Ionic LiquidsIonic liquids are defined as room temperature fluids composed entirely of ions that are typically large organic cations and small inorganic or organic anions [1]. The thermodynamics and reaction kinetics of processes carried out in ionic liquids are different from those in conventional media. This creates new opportunities for catalytic reactions, separations, electrochemistry and combined reaction/separation processes. ILs have negligible vapor pressures near room temperature and the emission of volatile organic compounds, which is substantial for conventional organic solvents, is negligible for ILs. This leads to cleaner chemical processes and operations.Ionic liquid salts can be mixed with other salts including inorganic salts to form multicomponent ILs. Suitable cations and anions can be chosen to obtain ILs with the desired properties for specific application and there can be innumerable mixtures. It is possible to design an IL for a particular application by combining a cation with an organic or inorganic anion, as shown in Fig. 1, to obtain desired melting points, viscosity, density, hydrophobicity, miscibility, etc. The estimated number of IL mixtures currently available is 1018 [2]. PropertiesBy choosing the anion or alkyl chain of the cation, one can vary the hydrophobicity, viscosity, density, and solvation of the ionic liquid system. The contamination of ILs by impurities such as water, halides, and metal ions often affects the physical properties. The physical and thermodynamic properties of some ILs are given in Tab. 1 [3] 1) . DensityIonic liquids generally have a higher density than water. Traces of water in the ionic liquids appear to act as a diluent, and therefore, lower the density. However, such traces have a relatively small effect. ViscosityViscosity is an important physical property. ILs are generally viscous, compared to molecular solvents. How...

Ionic liquids in microemulsions

“…Ionic liquids (ILs) continue to attract interest as environmentally benign solvents for green chemistry and electrolytes [1][2][3]. Since the melting points of ILs are low, ILs can act as solvents for diverse reactions, and because the liquid is made of ions rather than molecules, such reactions often give different selectivity and reactivity compared with conventional organic solvents.…”

Thermal and kinetic analysis of pure and contaminated ionic liquid: 1-butyl-2.3-dimethylimidazolium chloride (BDMIMCl)

“…Where k is the rate coeffi cient which can be described by the Arrhenius equation as follows: (5) In case of a linear heating rate β, equation (3) and equation (5) can be combined as follows: (6) The integration of equation (6) by Coats Redfern method formulates the following relation: (7) where A is the apparent pre-exponential factor, R is the universal gas constant (8.314 J/mol.K), β is the constant heating rate (K/min), E is the apparent activation energy (kJ/mol.K) and T is the absolute temperature in K and; (8) where f(α) is a function of the degradation process and function g(α) depends on the reaction mechanism. Sub-stituting a plot of the left hand side of equation (7) versus 1/T gives a straight line with slope equal to -E/R and y-intercept equal to ln (AR/βE).…”

“…In spite of numerous advantages of ILs, this is worrying to know that far only few ILs have been manufactured and utilized on commercial scale. One of the reasons is the lack of information about thermal behavior of these ionic liquids 8 . Moreover, the investigation of thermal properties of ILs is imperative for design and evaluation, to set the feasible temperature operating range in a chemical process and to estimate heating and cooling requirements as well as heat-storage capacity.…”

Radio Frequency‐Based In Situ Determination of the Mass Loss of Supported Ionic Liquids

“…The solubility characteristics, as well as other chemical and physical properties, depend on the anion-cation combination [1,3]. Considering the large number of available ILs, a suitable one for a particular application can, therefore, be rationally selected [3].…”

“…Ionic liquids (ILs) find growing interest in many areas of chemical technology, e.g., for catalysis and separation processes [1][2][3][4][5][6][7][8][9]. By definition, they are salts with a melting point below 100°C; many of them are even liquid at room temperature [1,2].…”