Systems aniline+cyclohexane

Dobashi et al. [44] found that the data of Figure 9-23 also follow eq 4.4 with / = 0.332 0.001 independent of molecular weight. Figure 9-24 illustrates this fact for three different My,. We see that the range of e in which eq 4.4 holds diminishes with increasing molecular weight. Thus, for the case i, it is restricted to Tc—T < 0.7°C. Dobashi et al. s j3 is consistent with 0.327 0.004 previously obtained by Nakata et al. [45] for a polystyrene with Mw = 1560 x 10 in cyclohexane and also with 0.326 0.003 for methanol + cyclohexane (e < 0.06), 0.328 0.007 for aniline + cyclohexane (e < 0.03), and 0.328 0.004 for isobutyric acid + water (e < 0.006). Dobashi et al. thus concluded that the system polystyrene + methylcyclohexane belongs to the same universality class as binary mixtures of ordinary simple liquids. 

Type 2. Formation of Two Pairs of Partially Miscible Liquids. Refer to the isotherm, Fig. 2.11. In this case, at the temperature of the plot, both the liquid pairs A-B and A-C are partially miscible, while B dissolves in any proportion in C. The area within the band lying across the triangle represents mixtures which form two liquid layers, the compositions of which are at the ends of the tie lines through the points representing the mixtures as a whole. On this type of diagram there can be no plait point. Typical examples are the systems aniline (4)-n-heptane (R)-methyl cyclohexane (C) (58), and water (il)-chlorobenzene (B)-methyl ethyl ketone (C) (35). 

Other examples are (i) Water-aniline (167°), (ii) Benzene-aniline (59.5°) (m)Methyl Alcohol-cyclohexane (45.5°), (iv) Bi-Zn (Metallic system) (85.0°)... 

The effect of dissolved impurities on C.S.T. was observed by Crismer. The C.S.T. of ethanol petroleum system was raised by 17°, by the presence of only 1% of water in ethanol. The C.S.T. of methanol and cyclohexane system is 45.55°. The presence of 0.01 % of water in methanol raises the C.S.T. of the ssytem to 45.65°. The presence of armoatic hydrocarbons in petrol can be detected and estimated by determining the C.S.T. of petrol-aniline system. Similarly, the amount of ceresin in wax can be determined. The biological importance of C.S.T. is in testing the functioning of kidney. A kidney producing urine which raises the C.S.T. of urine-phenol system by 8° is in good order. The kidney is exceedingly well if the C.S.T. is raised by 12° to 16°. 

At the point C the two liquid layers become identical, and this is called the critical solution point or con-solute point. If the total applied pressure is varied, both the critical temperature and composition of the critical mixture alter and we obtain a critical solution line. As an example of this we give in table 16. If the dependence of the critical solution temperature on pressure for the system cyclohexane -f aniline. An increase of pressure raises the critical solution temperature, and the mutual solubility of the two substances is decreased. We saw earlier that the applied pressure had only a small effect on the thermodynamic properties of condensed phases, and we notice in this case that an increase of pressure of 250 atm. alters the critical temperature by only 1.6 °C. 

Effect of Pressure on Critical Mixing Temperature in the System Cyclohexane + Aniline... 

NOTE The system as arranged usually will not produce pure cyclohexane, because the aniline added at the top is added too high up the column and some is carried over with the cyclohexane. This can be improved by adding a small section of bent glass to the separatory funnel tip and adjusting it so the addition is below the top of the condenser and directs the flow to the sidewall of the column. A small amount of aniline impurity will make a rather large change in the refractive index. If you do the distillation slowly, then a fair separation will take place. 

Any attempt to settle the shape of the coexistence curve experimentally is beset by severe problems. In the critical state systems attain equihbrium very slowly this difficulty affects all measurements in the critical region and will be commented on in almost all sections of this work. Another problem for the one-component liquid is the effect of gravity. The effects of impurities are less certain but it has been stated that the coexistence curve of cyclohexane-aniline has a flat top if the components are dry, but that the addition of a small amount of water can destroy the flat portion (see also Reference 134). 

Figure 5.11. Comparison of UNIFAC predictions of liquid-liquid equilibrium with experimental data for two ternary systems, (a) Water-cyclohexane-2-propanol, type-I system. P = plait point, (b) Water-benzene-aniline, type-ll system. (From A. Fredenslund, J. Gmehling, and P. Rasmussen, Vapor-Liquid Equilibria Using UNIFAC, A Group Contribution Method, Elsevier, Amsterdam, 1977.).

Liquid-liquid equilibrium data for the system n-heptane-methyl cyclohexane-aniline at 25°C and at 1 atm (101 kPa)... 

However, the number of phases is not limited to two only. For example, in the case of hetero-azeotropic mixtures like butanol-water or ethanol-water-cyclohexane already two liquid phases exist besides the vapor phase. Hildebrand showed that in the system water-heptane-perfluorokerosene-aniline-phosphorus-gallium-mercury even seven liquid phases are in equilibrium with the vapor phase [2] (see Figure 5.3). 

Effect of Impurities on the Critical Solution Temperature. The addition of even a small amount of a third component to a two-liquid system will ordinarily alter the C.S.T. considerably. Thus, for example, the addition of 0.2 per cent of water to glacial acetic acid raises the C.S.T. with cyclohexane from 4.2 to approximately 8.2 C. Useful methods of analysis have been devised based on such observations. For example, the amount of deuterium oxide in water can be estimated by measuring the C.S.T. with phenol and the aromatic hydrocarbon content of petroleum fractions by the C.S.T. with aniline. In general, the C.S.T. will be raised if the added component is highly soluble in only one of the original components (salting out) and lowered if it is highly soluble in both. Such systems properly must be considered as three-component mixtures, however. 

Illustration 10. Predict the distribution in the Type 2 system w-heptane (il)-aniline (B)-cyclohexane (C), at 25°C. 

Table 3.1 lists several examples of the application of these principles. In each case the components are designated in accordance with Fig. 3.21, and, except for one system, the selectivities expected on the basis of critical solution temperatures actually materialize. In the case of propane-stearic acid-palmitic acid, the inability of propane to extract either of the acids selectively is reflected in the very small difference in C.S.T. s. Note further that, on the basis of the C.S.T. s alone, it would be expected that the selectivity of aniline for cyclohexane in the presence of heptane would be greater than that for methylcyclohexane, but that the reverse is true. 

Illustration 11. A solution containing 50% n-hcptane (A), 50% cyclohexane (C) (on a solvent-free basis) is to be separated into a raffinate containing 95% heptane and an extract containing 95% cyclohexane (both percentages on a solvent-free basis), with aniline (B) as the extracting solvent at 25 C., in a countercurrent multiple contact system with reflux. Feed, reflux, and product streams are to be saturated with solvent, and pure solvent will be added at the mixer and removed from the extract solvent separator. Determine the minimum number of stages and the minimum reflux ratio. 

Hunter and Brown [Zndl. Eng, Chem, 39,1343 (1947)] have determined the equilibrium in the Type 2 system n-heptane (A)-aniline (B)-cyclohexane (C) at 25°C. For each of the equilibrium-data points reported, calculate the constant of Eq. (2.15), and average for the entire system. Plot the data in the manner of Fig. 2.30, together with the Eq. (2.15), using the average value of Comment on the ability of the equation to describe the data. 

Aromatic amines can sometimes be chromatographed successfuly after their conversion to derivatives. For example, isomeric toluidines and aniline, which are poorly separated as salts, can be clearly separated after their conversion to bromo derivatives (105) a series of primary amines can be separated after conversion to arylazo-2-naphthole (p. 342), and for the separation of isomers the products of the reaction of amines with diazonium salts (p. 324) can also be employed. They can be chromatographed in a formamide/hexane system. Thin-layer chromatography of free bases can be carried out on nonadhering layers of alumina (106, 107), or on silica gel G layers using the mobile phase cyclohexane — carbon tetrachloride-ethyl ecetate (10 70 20) ... 

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