Binary systems vapour pressure

Figure A2.5.11. Typical pressure-temperature phase diagrams for a two-component fluid system. The fiill curves are vapour pressure lines for the pure fluids, ending at critical points. The dotted curves are critical lines, while the dashed curves are tliree-phase lines. The dashed horizontal lines are not part of the phase diagram, but indicate constant-pressure paths for the T, x) diagrams in figure A2.5.12. All but the type VI diagrams are predicted by the van der Waals equation for binary mixtures. Adapted from figures in [3].

If he selects the still pressure (which for a binary system will determine the vapour-liquid-equilibrium relationship) and one outlet stream flow-rate, then the outlet compositions can be calculated by simultaneous solution of the mass balance and equilibrium relationships (equations). A graphical method for the simultaneous solution is given in Volume 2, Chapter 11. 

J. G. WOJTASINSKI. J. Chem. Eng. Data, 1963 (July), pp. 381-385. Measurement of total pressures for determining liquid-vapour equilibrium relations of the binary system isobutyraldehyde-n-butyraldehyde. 

At present there are two fundamentally different approaches available for calculating phase equilibria, one utilising activity coefficients and the other an equation of state. In the case of vapour-liquid equilibrium (VLE), the first method is an extension of Raoult s Law. For binary systems it requires typically three Antoine parameters for each component and two parameters for the activity coefficients to describe the pure-component vapour pressure and the phase equilibrium. Further parameters are needed to represent the temperature dependence of the activity coefficients, therebly allowing the heat of mixing to be calculated. 

The parameters were optimised to represent the critical data p and T, the vapour pressure from room temperature up to the critical point and the saturated vapour and liquid molar volumes. Account was also taken of the representation of the binary systems H20-CH. to C.H.q. Initially the method of Powell... 

Using a recent equation of state of the van der Waals type developed to describe non-polar components, a model is presented which considers water as a mixture of monomers and a limited number of polymers formed by association. The parameters of the model are determined so as to describe the pure-component properties (vapour pressure, saturated volumes of both phases) of water and the phase equilibria (vapour-liquid and/or liquid-liquid) for binary systems with water including selected hydrocarbons and inorganic gases. The results obtained are satisfactory for a considerable variety of different types of system over a wide range of pressure and temperature. 

Vapour pressure investigations of the systems here under discussion have frequently been carried out (cf. Olah, 1963). However, many of these studies are concerned with the question of the composition of the complexes formed in binary or ternary systems (Van Dyke, 1950 Brown and Pearsall, 1952 Brown and Brady, 1949, 1952 Brown and Wallace, 1953a, b Lieser and Pfluger, 1960a, b). To answer this question, the vapour pressm-e diagrams were recorded as a function of the composition of the binary or ternary system. The direct evaluation of the Henry s law constant, however, also permits the basicity of the unsaturated hydrocarbons to be determined. 

It is convenient to use phase diagrams [46] to represent the thermodynamic properties that determine the stability and equilibrium composition of water-containing aerosols. The properties of interest are the temperature, the vapour pressure and composition of the various components in the condensed phases. This is particularly important with respect to the composition and stability of the various hydrates formed at low temperature in the nitric acid-water [47] and sulfuric acid-water binary systems [48], and the ternary systems HjSO/HNOj/HjO and HjSO/HCl/HjO [49],... 

Several authors [3-9] studied the solubility of polymers in supercritical fluids due to research on fractionation of polymers. For solubility of SCF in polymers only limited number of experimental data are available till now [e.g. 4,5,10-12], Few data (for PEG S with molar mass up to 1000 g/mol) are available on the vapour-liquid phase equilibrium PEG -CO2 [13]. No data can be found on phase equilibrium solid-liquid for the binary PEG S -CO2. Experimental equipment and procedure for determination of phase equilibrium (vapour -liquid and solid -liquid) in the binary system PEG s -C02 are presented in [14]. It was found that the solubility of C02 in PEG is practically independent from the molecular mass of PEG and is influenced only by pressure and temperature of the system. 

The examination of a binary system involving a solute (1) and solvent (2) allows more insight into the problem (Figure 6.13). For the solvent the reference-state // may be seen as real, because this is always a liquid with negligible vapour pressure at the working temperature. The fugacity of the component 2 can be approximated by an ideal... 

It can be seen from the preceding statements that tellurium dihalides do not exist in the solid state. The materials under investigations, if actually binary, with great certainty consisted of more than one phase. On the other hand, there is no doubt about the existence of dihalide molecules in the vapour phase. This is confirmed by a numl r of investigations on the vapour pressure in the respective systems 21,35,36,3 , by experiments concerning the chemical transport of tellurium with iodine and by electron diffraction studies (II.D). 

There has been some confusion concerning the existence of Tel2 in the vapour phase. An early vapour pressure determination of the Te—I system resulted in the statement that the only binary molecular species in the gaseous state is Tel4. On the other hand, in the course of the chemical transport of tellurium with iodine (2) it was shown by mass spectroscopy ° that the main species in the gas phase is Tel2 if a tellurium-rich binary system is heated under vacuum. 

Gas-Liquid Critical Curves of Binary Systems. In Figure la the pressure-temperature-composition surface is represented schematically for the gas-liquid equilibria of a binary system in a simple case. The dashed lines are the vapour pressure curves of the pure components they end at the critical points CP I and CP II of the pure components I and II. Some pressure-composition cuts for constant temperature are given. The critical point of the binary system is situated at the extreme value of each p x) isotherm or (not shown in Figure la) at the extreme value of each T x) isobar. The line that connects the critical points of all binary mixtures is the critical curve in a pressure-temperature projection the critical curve is the envelope of all p T) curves for constant composition (so-called isopleths). At temperatures and pressures beyond the critical curve the constituents are miscible in all proportions. 

Figure 23 piX) projections of the phase diagrams of binary fluid CO + alkane mixtures (solid line = critical curve of binary system dashed line = vapour pressure curve of pure component, Cg = octane, Qj = tridecane, Qe = hexadecane, Qq = 2,6,10,-15,19,23-hexamethyltetracosane) ... 

B. Hydrocarbon + Water Systems.—In Figure 28 the critical phase behaviour of binary aqueous solutions of several hydrocarbons and fluorobenzene is shown according to data taken from the literature. The dashed curve is the vapour pressure curve of pure water and the solid lines are the branches of the critical curves of the binary systems that start from the critical point of pure water CP(H20). Except for naphthalene -I- H2O and biphenyl + H2O the critical... 

In Figure 36 parts of the critical curves of some binary He systems and of the vapour-pressure curves of the pure less volatile components are plotted making use of a compilation by Streett. Whereas He + Na, He + Ar, and... 

It is well known that coexistence curves for binary mixtures are frequently more nearly symmetric in a T, representation than in a T, x representation." Simon, Fannin, and Knobler found, in analysing their vapour-pressure measurements on the system CH4 + CF4, that plots of A vs. [where their definition of takes the molar volumes in equation (28) as those of the pure... 

The three variables that can affect the phase equilibria of a binary system are temperature, pressure and concentration. The behaviour of such a system should, therefore, be represented by a space model with three mutually perpendicular axes of pressure, temperature and concentration. Alternatively, three diagrams with pressure-temperature, pressure-concentration and temperature-concentration axes, respectively, can be employed. However, in most crystallization processes the main interest lies in the liquid and solid phases of a system a knowledge of the behaviour of the vapour phase is only required... 

Figure 5. Critical curves for several binary aqueous systems in the vicinity of the critical point of pure water. The shaded side of the curves indicates the two-phase regions. Tlie CeHn-curve is not shaded only because of clarity. The not shaded heavy solid line near the bottom left represents the vapour pressure curve of pure water, ending at the critical point (c.p.) [81]...

Any deviation of an intcrmetallic compound from the strict stoichiometric composition always means that there is a disturbance in the ideal order of the crystal lattice. That is to say, defects are present. Suppose that the isothermal activity of metal A (i.e. the relative vapour pressure compared to the pure material) is measured in a binary system A-B in which inter-metallic compounds with finite ranges of homogeneity exist. Then, for an arbitrarily chosen phase diagram, a plot of activity versus composition as shown schematically in Fig. 1-4 results. 

Nissema, A. Karvo, M. Thermodynamic properties of binary and ternary systems. Part V. Vapour pressures and thermodynamic excess functions of toluene + dimethyl sulphoxide mixtures Finn. Chem. Lett. 1977, (8), 222-226... 

Wheatley, C. J. 1986. A Theory cf Heterogeneous Equilibrium between Vapour and Liquid Phases of Binary Systems and Formulae for the Partial Pressures of HF and Vapour, SRD-R357, UK Atomic... 

The theories of solutions were first applied to mixtures of n-alkanes for several reasons the components interact only through dispersion forces, the number of combinations between components is large, the difference between systems is small, and such data as vapour pressures, second virial coefficients, etc., required for the calculation of correct activity coefficients and for application of solution theories, are available for a large number of pure n-alkanes. Moreover, the heats and volumes of mixing have been determined by experiments carried out on a large number of binary systems [93]. 

The diagram refers to the enthalpy relationships of a completely miscible binary system at a constant pressure of 1 atm. The mole fraction of component B is plotted horizontally from left to right and the enthalpy of the mixture, relative to the pure components in chosen reference states, is plotted vertically. Curve CD represents the enthalpy of the liquid phase, at its boiling-point, as a fimction of composition. Curve EF represents the enthalpy of the vapour above the boiling liquid as a function of its own composition. (Thus CE and DF are the enthalpies of vaporization of A and B respectively.) OH and IJ are typical tie-lines, i.e. a boiling liquid of composition ( is in equilibrium with vapour of composition H,... 

In the case of a binary system the Gibbs-Duhem (or Duhem-Margules) equation can be put into a useful form in terms of the total pressure. Let x be the mole fraction of component A in the condensed phase and let y be its mole fraction in the vapour phase. It will be assumed that the system contains components A and B only, i.e. there is no inert gas. Then... 

As shown in the last section, R W>ult s and Henry s laws are permissible solutions of the differential expression (7 40) which governs vapour-liquid equilibria at constant temperature and constant (or effectively constant) total pressure. However, these laws are not the only functional relationships connecting and Xi which are compatible with (7 40), and in the present section we shall discuss some alternative relationships for the special case of a binary system. 

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