Ionic liquids classification

Because of the way Figure 2.6 reveals the various couplings and decouplings that can be encountered in ionic liquid media, we have used it as a basis for ionic liquid classification. We divide ionic liquids into ideal, subionic (or poor ionic) liquids, and superionic liquids. The subionic liquids may still be good conductors at ambient pressure because their fluidities are high, but the conductivity is much lower than if all the moving particles were cations or anions. 

Oliveri et al. (2009) presented the development of an artificial tongue based on cyclic voltammetry at Pt microdisk electrodes for the classification of olive oils according to their geographical origin the measurements are made directly in the oil samples, previously mixed with a proper quantity of a RTIL (room temperature ionic liquid). The pattern recognition techniques applied were PCA for data exploration and fc-NN for classification, validating the results by means of a cross-validation procedure with five cancellation groups. 

In this entry, solvents are classified into four major categories, viz. organic solvents, aqueous solvents, supercritical solvents, and ionic liquids. This classification is based on the evolutionary approach to solvent design. 

Table 7.3 shows a classification of the liquid membranes on the basis of the configuration and module types employed in gas separation. The liquid membranes can be divided in three main classes (i) supported liquid membrane (SLM), (ii) bulk liquid membrane (BLM), and (iii) supported ionic liquid membrane (SILM). 

Where are ionic liquids in this classification Except for nonpolar groups, we can say that with a proper choice of the anion and the cation, ionic liquids could fit into any of these categories. If we consider the large number of possible anion-cation combinations (see Table 1), the selection of the IL is far from being obvious and a series of problems have to be overcome before development of industrial processes (cf Section 5.1). Some of the properties have to be known when ILs are used for catalysis. 

Polarity is the most common classification for solvents. There is no absolute polarity scale in a first approximation, it can be considered that polar solvents are characterized by their ability to dissolve charged solutes. Since ionic liquids are themselves salts, they are expected to be very polar. 

Given that ionic liquids with similar parameters can behave very differently when used as solvents, a different classification of the polarity has been proposed that takes into account both the hydrogen bond basicity and the dipolarity. The anion has a strong effect on the hydrogen bond basicity of the ionic liquid, whereas the contribution of the cation is negligible. ... 

Classification of Applications of Ionic Liquids in Heterogeneous Catalysis... 

Since Ionic Liquids represent a vast class of various substances, it is not easy to propose a classification. Here are some possibilities ... 

The history of ionic liquids is well documented, and it is widely recognised that the work of Walden produced the first recorded materials that were deliberately ionic and molten at ambient temperature [1]. The classification of ionic liquids as salts that are liquid below 100°C is arbitrary and non-satisfactory because it does not answer the philosophical question When is an ionic liquid not an ionic liquid This seemingly poindess pedantry is inportant, as almost all uses of ionic fluids involve the dissolution of molecular conponents. The issue is therefore how much solute can be added before the molecular character dominates the ionic character. It has been shown by numerous authors that the inclusion of a small amount of certain inpurities can have a profound effect upon the physical and chemical properties of an ionic liquid 12-4]. 

This chapter is devoted to PBI composite membranes involving a polymer matrix, in this case, the PBI, and another compound in the form of filler (solid oxides, solid acids, heteropolyacids and derived heteropolysalts, pyrophosphates, ionic liquids and even carbonaceous materials). A synergic effect between the two elements always appears crucial in order to improve the membrane characteristics. As in die case of Nation membranes, the motivations for fabricating composite PBl-based membranes fall into the following classification ... 

FIGURE 1.2 Ternary diagram for classification of liquids (schematic location of points is conjectural) [bmimjPF represents a room-temperature ionic liquid (see Section 8.3). After Tremillon (1974). 

Fig. 7.1 Classification of ionic liquids/molten salts as a function of melting temperature...

Ionic liquids based on chloroaluminates (the most common form of Lewis acidic or basic ionic liquids) are formed by reacting a quaternary ammonium chloride salt [QAm]" with aluminium chloride (AICI3) in various ratios [94]. Common examples are l-ethyl-3-methyl imidazoUum chloride ([EMIm]Cl) and l-(l-butyl)pyridinium chloride ([BuPy]Cl) [95]. A Lewis base, neutral species or acid is formed by varying the ratio of the two components of the ionic liquid. Using the letter N to represent the mole fraction of AICI3 in the melt [96], the following classification is given for these ionic liquids ... 

In an aqueous solution, the electrode potentials of CO2 reduction correlate with the heats of fusion (HoF) of the electrode metals low-HoF metals (Hg, Tl, Pb, In, Cd and Zn) yield formate, while high-HoF metals (Pt, Pd, Ni, Au, Cu, Ag, Zn, Sn and Ga) form CO [77,87]. The above classification is far from being perfect, and does not cover for all possible scenarios of CO2 electroreduction. As shown later, in the section on the S5mthesis of organic carbonate, when used in an ionic liquid, indium cathodes are efficient in the preparation of dimethyl carbonate. Also, copper-based bimetallic electrodes may exhibit an improved catalytic activity in reducing CO2 to hydrocarbons. Examples include Cu-Ni, Cu-Sn and Cu-Pb alloys. By contrast, for Cu-Ag and Cu-Cd alloy electrodes, the catalytic activity is diluted [81]. 

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