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We have introduced the concepts of energy of mixing, enthalpy of mixing, and volume of mixing in Section 3.4. We can now relate the mixing behavior to the partial molar properties. The partial molar quantities for ideal gases must be the same as the pure component properties. Entropy for an ideal-gas mixture is more complicated because,…

Generalization of pure-component principles to multicomponent systems requires that we consider how the thermodynamic properties change with respect to changes in the amounts of individual components. For a pure fluid, the natural properties were simply a function of two state variables. In multicomponent mixtures, these energies and the entropy also depend on composition.  These equations…

We introduced some major points about the importance of distillation in Section 3.2. Roughly 80% of separations are done involving distillation and 70% of the capital cost of a chemical plant goes into distillation equipment, and thus the proper application of vapor-liquid equilibria and design are essential. Usually, one distillation column is required to separate any…

Hydrocarbon emission monitoring is an important aspect of environmentally conscious chemical manufacturing and processing. The United States Environmental Protection Agency (EPA) has published guidelines8,9,10 on the calculations of emissions of volatile organic compounds (VOCs), and VOC emissions are monitored in the U.S. Most of the emission models apply the ideal gas law and Raoult’s law and thus the calculation…

Extending our equations to multicomponent systems is straightforward. For a bubble calculation we have For a dew calculation we have These equations may be used for bubble- or dew-pressure calculations without iterations. For bubble- or dew-point temperatures, iteration is required. A first guess may be obtained from one of the following formulas: But these are…

For a small class of mixtures where the components have very similar molecular functionality and molecular size, the bubble-pressure line is found to be a linear function of composition as shown in Figs. 10.2 and 10.3. As was noted in Section 10.1, the T-x-y and P-x-y diagram shapes are related qualitatively by inverting one of the diagrams. Because the bubble pressure is a…

Classes of VLE Calculations Depending on the information provided, one may perform one of several types of vapor-liquid equilibrium (VLE) calculations to model the vapor-liquid partitioning. These are: bubble-point pressure (BP), dew-point pressure (DP), bubble-point temperature (BT), dew-point temperature (DT), and isothermal flash (FL) and adiabatic flash (FA). The specifications of the information required and the information to be computed are tabulated below in Table 10.1. Also shown…

Before we delve into the details of calculating phase equilibria, let us introduce elementary concepts of common vapor-liquid phase diagrams. For a pure fluid, the Gibbs phase rule shows vapor-liquid equilibrium occurs with only one degree of freedom, F = C – P + 2 = 1 – 2 + 2 = 1. At one atmosphere pressure, vapor-liquid equilibria will occur at only one…