Vapor-liquid equilibrium ratio

K Vapor-liquid equilibrium ratio (K value) P kPa psia... 

For mixtures containing more than two species, an additional degree of freedom is available for each additional component. Thus, for a four-component system, the equihbrium vapor and liquid compositions are only fixed if the pressure, temperature, and mole fractious of two components are set. Representation of multicomponent vapor-hquid equihbrium data in tabular or graphical form of the type shown earlier for biuaiy systems is either difficult or impossible. Instead, such data, as well as biuaiy-system data, are commonly represented in terms of i[Pg.1248]

K-factors for vapor-liquid equilibrium ratios are usually associated with various hydrocarbons and some common impurities as nitrogen, carbon dioxide, and hydrogen sulfide [48]. The K-factor is the equilibrium ratio of the mole fraction of a component in the vapor phase divided by the mole fraction of the same component in the liquid phase. K is generally considered a function of the mixture composition in which a specific component occurs, plus the temperature and pressure of the system at equilibrium. 

K = vapor-liquid equilibrium ratio, y lx, y = gas-phase concentration at equilibrium (mole fraction), x = liquid-phase concentration (mole fraction),... 

VAPOR-LIQUID EQUILIBRIUM RATIOS FOR IDEAL-SOLUTION BEHAVIOR 3.1... 

Determine the relevant vapor-pressure data. Design calculations involving vapor-liquid equilibrium (VLE), such as distillation, absorption, or stripping, are usually based on vapor-liquid equilibrium ratios, or K values. For the tth species, K, is defined as K, = y, /x, where y, is the mole fraction of that species in the vapor phase and x, is its mole fraction in the liquid phase. Sometimes the design calculations are based on relative volatility c/u], which equals K,/Kj, the subscripts i and j referring to two different species. In general, K values depend on temperature and pressure and the compositions of both phases. 

Number of chemical species Distillate flow rate Diffusion coefficient Efficiency Energy flux Energy transfer rate Eeed flow rate Column height Enthalpy Liquid holdup Height of a transfer unit Vapor-liquid equilibrium ratio (K value)... 

Physical Properties The on equilibrium-stage simulation are i and enthalpies these same properties are needed for nonequilibrium models as well. Enthalpies are required for the energy balance equations vapor-liquid equilibrium ratios are needed for the calculation of driving forces for mass and heat transfer. The need for mass- (and heat-) transfer coefficients means that nonequilibrium models are rather more demanding of physical property data than are equilibrium-stage models. These coefficients may depend on a number of other physical properties, as summarized in Table 13-12. 

The Kvalues (vapor-liquid equilibrium ratios) in Equation (13-123) are estimated from the same equation-of-state or activity-coefficient models that are used with equilibrium-stage models. Tray or packed-section pressure drops are estimated from suitable correlations of the type discussed by Kister (op. cit.). 

To evaluate [M] we must differentiate the vapor-liquid equilibrium model with respect to composition. If the vapor liquid equilibrium ratios (A -values) are given by... 

Equation (5.2-3) provides a rigorous (hermodynemic basis for (he prediction of the vapor-liquid equilibrium ratio, Sometimes it can be simplified, as the following special cases demonstrate ... 

The same vapor-liquid equilibrium ratio (AT) charts were used for the rigorous solution as for the shortcut, For the rigorous, however, values of K, were combined with total pressure P, and the Kf product was treated as effective vapor pressure" in the Antoine equation. The rigoroas program was nin in a mal-and-error fashion, with constant reflux ratio of 1.722 (from the shortcut) and with iterations of DIF ratio, total plates, and feed plate location. 

For vapor-liquid equilibrium, a so-called K-value (or vapor-liquid equilibrium ratio) is defined for each species i by... 

Frequently, distillation involves species that cover a relatively narrow range of vapor-liquid equilibrium ratios (X-values). A particularly effective solution procedure for this case was suggested by Friday and Smith and developed in detail by Wang and Henke. It is referred to as the bubble-point (BP) method because a new set of stage temperatures is computed during each iteration from... 

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