Liquid ranges, solvents

Solvent Liquid range CC) Dielectric constant Viscosity Supporting (cP) electrolytes ... 

Instead of concentrating on the diffiisioii limit of reaction rates in liquid solution, it can be histnictive to consider die dependence of bimolecular rate coefficients of elementary chemical reactions on pressure over a wide solvent density range covering gas and liquid phase alike. Particularly amenable to such studies are atom recombination reactions whose rate coefficients can be easily hivestigated over a wide range of physical conditions from the dilute-gas phase to compressed liquid solution [3, 4]. 

They are readily available, have convenient liquid ranges (p. 559), are fairly easy to handle, have low viscosities r], moderately high dielectric constants e and good solvent properties (Table 13.8). 

The other hydrogen halides are less tractable as solvents, as might be expected from their physical properties (p. 813), especially their low bps, short liquid ranges, low dielectric constants and negligible self-dissociation into ions. Nevertheless, they have received some attention, both for comparison with HF and as preparative media with their own special advantages.In particular, because of their low bp and consequent ease of removal, the liquid HX solvent systems have provided convenient routes to BX4, BF3C1 ,... 

Ionic liquids possess a variety of properties that make them desirable as solvents for investigation of electrochemical processes. They often have wide electrochemical potential windows, they have reasonably good electrical conductivity and solvent transport properties, they have wide liquid ranges, and they are able to solvate a wide variety of inorganic, organic, and organometallic species. The liquid ranges of ionic liquids have been discussed in Section 3.1 and their solubility and solvation in... 

Table 1 shows various solvents (in alphabetical order) used in lithium batteries. The table contains the names of the solvents, their acronyms, the liquid range represented by melting (0m,°C) and boiling points (0m,°C), and the physical properties at 25 °C unless otherwise noted, permittivity s, viscosity rjl cP), and density >o/( kg L 1). The data are taken from Ref. [15], where the original literature is cited, or from more recent references given in the table. 

A solvent that resembles water in many ways is liquid hydrogen fluoride. The molecule is polar, there is some autoionization, and it is a fairly good solvent for numerous ionic solids. Although the boiling point of liquid HF is rather low (19.5 °C), it has a liquid range that is comparable to that of water, partially as a result of extensive hydrogen bonding. One of the problems associated with the use of liquid... 

HF is that it attacks glass, so containers must be made of some inert material such as Teflon, a polytet-rafluoroethylene. The data for this nonaqueous solvent are shown in Table 10.4. As expected from the rather high heat of vaporization (which lies between the values for water and liquid ammonia) liquid HF has a liquid range that spans over 100 °C and a relatively high boiling point. 

Liquid range of solvent The solvent should be in the liquid state near the operating conditions. To ensure this following limits on boiling point and melting point are placed. 

The lower boundary of the liquid range, on the other hand, does usually serve as the low-temperature limit for the electrolytes. The mp of LiPFe/EC/ DMC was determined as a function of solvent composition by Tarascon and Guyomard, who concluded that LiPFe/EC/DMC could be used in the solvent compositions between 3 7 and 8 2 at temperatures down to —25 °C. The mp-dependence on solvent composition that was reported in the work, however, does not seem to be rational, since it shows a long plateau at -10 °C in 30-90% DMC after an initial drop from 20 °C at 20% DMC, whereas a typical simple eutectic feature would be expected instead. When a closer comparison is made between the results by Tarascon and Guyomard and the more recent studies by Ding et it becomes... 

Typically, the liquidus lines of a binary system curve down and intersect with the solidus line at the eutectic point, where a liquid coexists with the solid phases of both components. In this sense, the mixture of two solvents should have an expanded liquid range with a lower melting temperature than that of either solvent individually. As Figure 4 shows, the most popular solvent combination used for lithium ion technology, LiPFe/EC/DMC, has liquidus lines below the mp of either EC or DMC, and the eutectic point lies at —7.6 °C with molar fractions of - 0.30 EC and "-"0.70 DMC. This composition corresponds to volume fractions of 0.24 EC and 0.76 DMC or weight fractions of 0.28 EC and 0.71 DMC. Due to the high mp of both EC (36 X) and DMC (4.6 X), this low-temperature limit is rather high and needs improvement if applications in cold environments are to be considered. 

In addition to linear carbonates, PC was also considered as a cosolvent that could help to improve the low-temperature performance of the electrolytes, mainly due to its wide liquid range and solvation ability to lithium salts. This latter property seems to be a merit relative to the linear carbonates, whose dielectric constants are generally below 10 and whose displacement of EC usually causes the solubility of lithium salts to decrease in such mixed solvents, especially at low temperatures. 

There are properties of liquids used as solvents, such as the liquid range, viscosity, surface tension, and vapor pressure that, although important from the practical and technical points of view, are not listed in Table 2.1. These can be found in Refs. [1,2]. Tables 12.2, 13.1, and 13.2 list solvents used in extraction with some further information. 

The spectrum of physical and chemical properties of ionic liquids is much larger than that of classical organic or inorganic solvents. As well as wide liquid ranges, they offer ranges of physical properties such as density and viscosity and also have high heat conductivities. In addition, the miscibilities of ionic liquids with organic... 

The reactions that have been observed so far in ionic liquids represent the tip of the iceberg. In the future, research will involve efforts to optimize such phenomena as the relative solubilities of the reactants and products, the reaction kinetics, the liquid range of the solvent, the cost of the solvent, the intrinsic catalytic behavior of the... 

Relative Permittivities (Dielectric Constants) D and Normal Liquid Ranges of Common Solvents... 

There are several physical properties of a solvent that are of importance in determining its behavior. Two of the most important from a pragmatic point of view are the melting and boiling points. These determine the liquid range and hence the potential range of chemical operations. More fundamental is the permittivity (dielectric constant). A high permittivity is necessary if solutions of ionic substances are 10 form readily. Coulombic attractions between ions are inversely proportional to the permittivity of the medium ... 

HSO3F has a wide liquid range (mp=— 89.0°C, bp =+162.7°C), making it advantageous as a superacid solvent for the protonation of a wide variety of weak bases. 

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