Mixtures of liquids

System in which the solid phases consist of the pure components and the components are completely miscible in the liquid phase. We may now conveniently consider the general case of a system in which the two components A and B are completely miscible in the liquid state and the solid phases consist of the pure components. The equilibrium diagram is shown in Fig. 1,12, 1. Here the points A and B are the melting points of the pure components A and B respectively. If the freezing points of a series of liquid mixtures, varying in composition from pure A to pure B, are determined, the two curves represented by AC and BC will be obtained. The curve AC expresses the compositions of solutions which are in equilibrium, at different temperatures, with the solid component A, and, likewise, the curve BC denotes the compositions... 

The process of distillation is aimed at the separation of components from a liquid mixture. This process depends on the differences in boiling points of the individual components. Also, depending on the concentrations of the components present, the liquid mixture will have different boiling point characteristics. This means that distillation processes depends on the vapor pressure characteristics of liquid mixtures. 

Distillation is probably Ihe most widely used separation (mass transfer) process in the chemical and allied industries. Its applications range from the rectification of alcohol, which has been practiced since antiquity, lo the fractionation of crude oil. The separation of liquid mixtures by distillation is based on differences in volatility between the components. The greater the... 

HK = Heavy key component in volatile mixture h = Enthalpy of liquid mixture or pure compound at tray conditions of temperature and pressure, or specified point or condition, Btu/lb mol, or Btu/lb... 

V Z V" and the measurement of the actual component volumes V becomes a difficult undertaking. In these systems, a volume change—either shrinkage or expansion—is experienced upon mixing of the components. In addition, thermal effects may accompany the formation of the mixture or solution. The volumetric composition of liquid mixtures is expected to vary with temperature owing to the density dependence on temperature. 

There are two very important generalisations which may be established in connexion with the second type of liquid mixtures investigated by Regnault, e.g., mixtures of ether and water. 

In general, the thermal conductivities of liquid mixtures, and gas mixtures, are not simple functions of composition and the thermal conductivity of the components. Bretsznajder (1971) discusses the methods that are available for estimating the thermal conductivities of mixtures from a knowledge of the thermal conductivity of the components. 

The specific heats of liquid mixtures can be estimated, with sufficient accuracy for most technical calculations, by taking heat capacities of the components as additive. 

The separation of liquid mixtures by distillation depends on differences in volatility between the components. The greater the relative volatilities, the easier the separation. The basic equipment required for continuous distillation is shown in Figure 11.1. Vapour flows up the column and liquid counter-currently down the column. The vapour and liquid are brought into contact on plates, or packing. Part of the condensate from the condenser is returned to the top of the column to provide liquid flow above the feed point (reflux), and part of the liquid from the base of the column is vaporised in the reboiler and returned to provide the vapour flow. 

The system methanol-cyclohexane can be modeled using the NRTL equation. Vapor pressure coefficients for the Antoine equation for pressure in bar and temperature in Kelvin are given in Table 4.176. Data for the NRTL equation at 1 atm are given in Table 4.186. Assume the gas constant R = 8.3145 kIkmol 1-K 1. Set up a spreadsheet to calculate the bubble point of liquid mixtures and plot the x-y diagram. 

Dimplon, W. Estimating Specific Heat of Liquid Mixtures, Chemical Engineering, Oct. 2, 1972, p. 64. 

Temperature Two modes of temperature parametric-pumping cycles have been defined—direct and recuperative. In direct mode, an adsorbent column is heated and cooled while the fluid feed is pumped forward and backward through the bed from reservoirs at each end. When the feed is a binary fluid, one component will concentrate in one reservoir and one in the other. In recuperative mode, the heating and cooling takes place outside the adsorbent column. Parametric pumping, thermal and pH modes, have been widely studied for separation of liquid mixtures. However, the primary success for separating gas mixtures in thermal mode has been the separation of propane/ethane on activated carbon [Jencziewski and Myers, Ind. Eng. Chem. Fundam., 9, 216-221 (1970)] and of air/S02 on silica gel... 

V.L. Tal Rose, G.V. Karpov, I.G. Grdetskii and V.E. Skurat, Capillary system for the introduction of liquid mixtures into an analytical mass spectrometer, Russian J. Phys. Chem., 42 (1968) 1658-1664. 

Membrane composition PVA/PAA Composition of liquid mixture Permeation rate / / (g m"2 h"1) T/ C Separation factor... 

Composition of the membrane PAA.HC1/PVA/GA Composition of liquid mixture Water flux / / (kgm 2h 1) T/°C Separation factor... 

Composition of the membrane PVA/PAcr.Ac Composition of liquid mixture fusel oil Permeation rate/ /(gm-2h- ) T/°C Separation factor Permeate activation energy Ea / (kJ mol 1)... 

Also very promising are the monolithic separation media prepared directly in situ within the confines of the capillary by a free-radical polymerization of liquid mixtures [44]. They are easy to prepare and completely eliminate packing of beads which, for the very small beads, might require new technical solutions. In addition, the in situ prepared monoliths appear to be the material of choice for the fabrication of miniaturized microfluidic devices that represent the new generation of separation devices for the twenty-first century [202,203]. 

A rams, D. S., and J. M. Prausnitz, "Statistical Thermodynamics of Liquid Mixtures A New Expression for the Excess Gibbs Energy of Partly or Completely Miscible Systems," AIChE J., 1975, 21, 116. 

According to the complexity of the phenomenon of solvation, experimental results which might have bearings for its understanding are spread throughout the literature. Gas-phase investigations of intermolecular interactions are of a basic interest 23 ) and a large amount work has been done on the thermodynamics and spectroscopic properties of liquid mixtures 29,237-239)... 

Theoretical considerations based upon a molecular approach to solvation are not yet very sophisticated. As in the case of ionic solvation, but even more markedly, the connection between properties of liquid mixtures and models on the level of molecular colculations is, despite all the progress made, an essentially unsolved problem. Even very crude approximative approaches utilizing for example the concept of pairwise additivity of intermolecular forces are not yet tractable, simply because extended potential hypersurfaces of dimeric molecular associations are lacking. A complete hypersurface describing the potential of two diatomics has already a dimensionality of six In this light, it is clear that advanced calculations are limited to very basic aspects of intermolecular interactions,... 

In accordance with the limited aim of this article, in the following subsections we shall consider only two of the individual contributions to the highly complex solvation process dealing with structural problems of solutions. No attempt is made to treat other aspects, which might well be of considerable theoretical interest, like electronic spectra 189 244> or dynamic properties 13> of liquid mixtures. 

Calado and Gomes de Azevedo (11) have measured the molar volume of liquid mixtures of ethane and ethene at 161.39 K. Their values are shown in Table 18.7. 

TABLE 18.7. Molar Volume of Liquid Mixtures of Ethane and Ethene at 161.39 K... 

Gillespie equilibrium still analychem A recirculating equilibrium distillation apparatus used to establish azeotropic properties of liquid mixtures. ga Ies-pe, e-kw3 llbre-om, stil ... 

Thickening agent. A hydrophilic substance used to increase the viscosity of liquid mixtures and solutions and to aid in maintaining stability of their emulsifying properties. 

Furlan, LT., Chaves, B.C., and Santana, C.C. (1992) Separation of liquid mixtures of p-xylenes and o-xylenes in X zeolites the role of water content on the adsorbent selectivity. Ind. Eng. 

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