Water phase equilibria

Munz C, Roberts PV. 1987. Air-water phase equilibria of volatile organic solutes. J Am Water Works Assoc 79 62-69. 

Binary System. The first task is to examine the characteristics of the 2-propanol—water-phase equilibria (VLE, LLE, SLE) to determine the compositions of interest and any critical features. 2-Propanol forms a minimum boiling azeotrope with water (80.4°C at 101.3 kPa (760 torr), 68 mol % 2-propanol). The azeotrope is between the feed and the IPA product and is a distillation boundary, thus it is impossible to obtain both desired products from any single-feed... 

Munz, C., and P. V. Roberts, Air-Water Phase Equilibria of Volatile Organic Solutes. J. Am. Water Works Assoc., 1987 May, 62-69. 

Equilibration Studies, Because the formation of an interfacial layer is a dynamic phenomenon, experiments were conducted to study the effect of oil-water phase equilibria on interfacial properties. Two experiments were carried out where aqueous solutions of 1 1 SLS/LA were equilibrated with both styrene and toluene in sealed containers, without agitation for five weeks. Several important observations were made (a) Despite the presence of mixed emulsifiers,... 

Phase diagrams of monoglyceride-water systems have been reported by Lutton (1966) (C12-C22), Larsson (1967) (C6-C10) and Krog and Larsson (1968) (industrially distilled monoglycerides). The main features of the different monoglyceride-water systems were given in Section 8.2 as an illustration of lipid-water phase equilibria (Fig. 8.12). Only additional comments to this earlier work will be given here. 

Figure 45. Futjural-ethylene glycol-water phase equilibrium diagram.

In the closed system, a limited quantity of a gas becomes distributed between the gas and water phase. Equilibrium concentrations always correspond to the Henry constants but the relative proportions in the gas and water phase depend on the ratio of the volumes of water and gas. Such a closed system may, for example, serve as a model for fog droplets, when under stagnant conditions water droplets are in contact with a liminxl amount of a gas. The assumption of a closed system is often justified in situations where a significant proportion of a volatile substance becomes absorbed in the water phase. 

Figure 8. (A) A water column is divided into fifty equal unit cells and it is assumed there is no liquid or dissolved gas between cells. Each cell originally has the noble gas content of air-equilibrated water and all calculated Ne/Ar ratios are normalized to this value to obtain a fractionation factor F. The column temperature is taken to be 325 K, which for pure water gives Knc = 133245 atm and Kaf= 55389 atm. A gas bubble of constant volume is passed sequentially through the column, equilibrium assumed to occur in each water cell and the Ne and Ar partitioned into the respective gas and water phases (Eqn. 16). The evolution of the Ne/Ar ratio in the gas bubble (bold) and each water phase increment (Faint) is shown for different gas/water volume ratios, Vg/Vi. The gas bubble Ne/Ar ratio approaches the maximum fractionation value predicted for a gas/water phase equilibrium where as Vg/Vi -> 0, F Knc/Kat. The cell Vg/Vi ratio only determines the rate at which this hmit is approached. (B) The same water column with a fixed cell Vg/Vi ratio of 0.01. n subsequent bubbles are passed through the column and the He/Ne distribution between phases calculated at each stage. The gas bubble Ne/Ar ratio evolution for n = 1, 10, 20 and 30 is shown in bold, together with the residual Ne/Ar in the water colunm cells (faint lines). All gas bubbles approach the limit imposed by the phase equilibrium model. The water phase is fractioned in the opposite sense and is fractionated in proportion to the magnitude of gas loss following the Rayleigh fractionation law (Eqn. 24).

Model for Water Phase Equilibrium over a Wide Temperature Range, Journal of Physical Chemistry B 102, 1029-1035... 

Ternary-phase equilibrium data can be tabulated as in Table 15-1 and then worked into an electronic spreadsheet as in Table 15-2 to be presented as a right-triangular diagram as shown in Fig. 15-7. The weight-fraction solute is on the horizontal axis and the weight-fraciion extraciion-solvent is on the veriical axis. The tie-lines connect the points that are in equilibrium. For low-solute concentrations the horizontal scale can be expanded. The water-acetic acid-methylisobutylketone ternary is a Type I system where only one of the binary pairs, water-MIBK, is immiscible. In a Type II system two of the binary pairs are immiscible, i.e. the solute is not totally miscible in one of the liquids. 

Fig. 7. Isothermal cross section of the system H20-CH4-CsH8 on a water-free basis at —3° C. The points represent experimental results and the curves have been obtained from a theoretical analysis. The line AB represents the four-phase equilibrium HiHn ice G the gas G consists of almost pure methane, Hj contains only methane. Consequently, the composition of the latter two phases almost coincide in the figure, and the situation around point A has therefore been drawn separately on an enlarged scale.

An example for a partially known ternary phase diagram is the sodium octane 1 -sulfonate/ 1-decanol/water system [61]. Figure 34 shows the isotropic areas L, and L2 for the water-rich surfactant phase with solubilized alcohol and for the solvent-rich surfactant phase with solubilized water, respectively. Furthermore, the lamellar neat phase D and the anisotropic hexagonal middle phase E are indicated (for systematics, cf. Ref. 62). For the quaternary sodium octane 1-sulfonate (A)/l-butanol (B)/n-tetradecane (0)/water (W) system, the tricritical point which characterizes the transition of three coexisting phases into one liquid phase is at 40.1°C A, 0.042 (mass parts) B, 0.958 (A + B = 56 wt %) O, 0.54 W, 0.46 [63]. For both the binary phase equilibrium dodecane... 

FIG. 34 Phase equilibrium of sodium octane 1-sulfonate/1-decanol/water. 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

The other state variables are the fugacity of dissolved methane in the bulk of the liquid water phase (fb) and the zero, first and second moment of the particle size distribution (p0, Pi, l )- The initial value for the fugacity, fb° is equal to the three phase equilibrium fugacity feq. The initial number of particles, p , or nuclei initially formed was calculated from a mass balance of the amount of gas consumed at the turbidity point. The explanation of the other variables and parameters as well as the initial conditions are described in detail in the reference. The equations are given to illustrate the nature of this parameter estimation problem with five ODEs, one kinetic parameter (K ) and only one measured state variable. 

Carroll J J. and A.E. Mather, "Phase Equilibrium in the System Water-Hydrogen Sulfide Experimental Determination of the LLV Locus", Can. J. Chem. Eng., 67,468-470 (1989a). 

Englezos, P. and S. Hull, Phase Equilibrium Data on Carbon Dioxide Hydrate in the Presence of Electrolytes, Water Soluble Polymers and Montmorillonite , CanJ. Chem. Eng, 72, 887-893 (1994). 

In nonequilibrium systems, chemical processes spontaneously alter the composition or phase of the system until equilibrium is attained. Simple systems, such as a mixture of sodium chloride and water, attain equilibrium quickly, whereas complex systems may reach equilibrium only after decades or eons. 

Chen B, Xing JH, Siepmann JI (2000) Development of polarizable water force fields for phase equilibrium calculations. J Phys Chem B 104(10) 2391—2401... 

Perkins, E. H., 1992, Integration of intensive variable diagrams and fluid phase equilibrium with SOLMINEQ.88 pc/shell. In Y. K. Kharaka and A. S. Maest (eds.), Water-Rock Interaction, Balkema, Rotterdam, p. 1079-1081. 

Equation (4.1) expresses that the ratio of the concentrations of A in the gas phase and the water phase, respectively, is a constant at equilibrium. This constant is temperature dependent but is independent of the quantity of A as long as dilute solutions are dealt with. 

The relative volatility, a, is a constant that under equilibrium conditions can be used to express the distribution of a volatile compound between a gas phase made of A and water vapor and a water phase containing A. This constant is for a component A defined as follows ... 

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