Significance of solvent properties

The prerequisite for the safe and commercially satisfactory handling of used solvents is knowledge of the make-up of the solvents involved. The only sure source of this information is the user of the solvent. The user must be depended upon to describe the material correctly in the first place and, almost more importantly, report changes in its quality if they should occur subsequently. 

This is often chosen initially so that the user of the solvent will find it familiar. Often this means that a mixture will be known by a letter or number code or by a nickname. While the codes are of little assistance the nickname can be positively harmftil or misleading. 

Thus a typical instance is the use of IPA to denote either isopropanol or isopropyl acetate. The former is fully water miscible while the latter is not and the technique for dealing with a fire or spillage is therefore different. 

Even worse, because of the large diiference in toxicity between them, benzin, the German name for paraffinic solvent fractions, is easy to confuse with benzene. 

Other pitfalls that have been experienced in solvent recovery operations are dimethylamine, dimethylac-etamide and dimethylamine abbreviated to DMA and formic acid and hydrofluoric add to HE 

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Table 13.9 Upper critical solution temperature (°C) Significance of solvent properties 189... 

We now consider a type of analysis in which the data (which may consist of solvent properties or of solvent effects on rates, equilibria, and spectra) again are expressed as a linear combination of products as in Eq. (8-81), but now the statistical treatment yields estimates of both a, and jc,. This method is called principal component analysis or factor analysis. A key difference between multiple linear regression analysis and principal component analysis (in the chemical setting) is that regression analysis adopts chemical models a priori, whereas in factor analysis the chemical significance of the factors emerges (if desired) as a result of the analysis. We will not explore the statistical procedure, but will cite some results. We have already encountered examples in Section 8.2 on the classification of solvents and in the present section in the form of the Swain et al. treatment leading to Eq. (8-74). 

Solvent vapor pressure also has a significant effect on the cavitation phenomenon because the intensity of cavitation decreases as the vapor pressure of the solvent increases. This is because more vapor is enclosed in the microbubble, which cushions the collapse, leading to lower collapse temperatures and pressures. On the other hand, solvents with low vapor pressure tend not to diffuse into the growing microbubble thereby reducing the size of the bubble, which lessens the intensity of bubble collapse. Thus, a delicate balance of solvent properties must be achieved to attain the desired sonication conditions. 

Distillation By-Products. Of the CTO distiHation by-products, ie, pitch, heads, and DistiHed TaH Oil (DTO), only the last, a unique mixture of rosin and fatty acids, has significant commercial value. Pitch and heads are used as fuel the former has a fuel value of 41,800 kj/kg. TaH oil heads have outstanding solvent properties, but also have a bad odor, which is hard to remove. They contain a relatively high fraction of palmitic acid which can be recovered by crystallization. 

Properties of the activation product. The two decylamine-activation products (luciferins) showed similar absorption characteristics (A.max 372 nm in water, and 375 nm in ethanol), which clearly differ from the absorption peak of the natural luciferin (320 nm) reported by Kuwabara and Wassink (1966). The fluorescence emission of the activation products varied significantly by solvents, showing a peak at 460 nm in neutral aqueous solution and a broad peak at 485-522 nm in ethanol. They emitted chemiluminescence (A.max 580 nm) in the presence of CTAB, H2O2 and Fe2+ (Fig. 9.13), in resemblance to the (NH4)2S04-activation product of panal (A.max 570 nm). 

In the last two decades experimental evidence has been gathered showing that the intrinsic properties of the electrolytes determine both bulk properties of the solution and the reactivity of the solutes at the electrodes. Examples covering various aspects of this field are given in Ref. [16]. Intrinsic properties may be described with the help of local structures caused by ion-ion, ion-solvent, and solvent-solvent interactions. An efficient description of the properties of electrolyte solutions up to salt concentrations significantly larger than 1 mol kg 1 is based on the chemical model of electrolytes. 

In processing, it is frequently necessary to separate a mixture into its components and, in a physical process, differences in a particular property are exploited as the basis for the separation process. Thus, fractional distillation depends on differences in volatility. gas absorption on differences in solubility of the gases in a selective absorbent and, similarly, liquid-liquid extraction is based on on the selectivity of an immiscible liquid solvent for one of the constituents. The rate at which the process takes place is dependent both on the driving force (concentration difference) and on the mass transfer resistance. In most of these applications, mass transfer takes place across a phase boundary where the concentrations on either side of the interface are related by the phase equilibrium relationship. Where a chemical reaction takes place during the course of the mass transfer process, the overall transfer rate depends on both the chemical kinetics of the reaction and on the mass transfer resistance, and it is important to understand the relative significance of these two factors in any practical application. 

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