The DePriester charts check this quite well (see Figures 8-4A and B, and Figure 8-3D). For n-pentane at convergence pressure of 3,000 psia (nearest chart) the K-value reads 0.19. įor a temperature of 100☏, the convergence pressure is approximately 2,500 psia (dotted line) for the pseudo system methane-n-pentane (see Figure 8-3C). Regression equations and coefficients for various versions of the GPA convergence-pressure charts are available from the GPA. The widespread availabihty and utihzation of digital computers for distillation calculations have given impetus to the development of analytical expressions for i regression equation and accompanying regression coefficients that represent the DePriester charts of Fig. It is analogous to the critical point for a pure component in the sense that the two. An alternative measure of composition is the convergence pressure of the system, which is defined as that pressure at which the Kvalues for aU the components in an isothermal mixture converge to unity. The Kellogg and DePriester charts and their subsequent extensions and generahzations use the molar average boiling points of the liquid and vapor phases to represent the composition effect.
SI versions of these charts have been developed by Dadyburjor. For K as a function of T and P only, the DePriester charts provide good starting values for the iteration. One cannot calculate K values until phase compositions are known, and those cannot be known until the K values are available to calculate them. Ī trial-and- error procedure is required with any K-value correlation that takes into account the effect of composition. The Kellogg charts, and hence the DePriester charts, are based primarily on the Benedict-Webb-Rubin equation of state, which can represent both the liquid and the vapor phases and can predict K values quite accurately when the equation constants are available for the components in question. These charts are a simplification of the Kellogg charts and include additional experimental data.
The easiest to use are the DePriester charts, which cover 12 hydrocarbons (methane, ethylene, ethane, propylene, propane, isobutane, isobutylene, /i-butane, isopentane, /1-pentane, /i-hexane, and /i-heptane). For example, several major graphical i light-hydrocarbon systems. However, for mixtures of compounds of similar molecular structure and size, the K value depends mainly on temperature and pressure. 4, the i complex function of temperature, pressure, and equilibrium vapor- and hquid-phase compositions. And please make sure to include important information in the question body.As discussed in Sec. These numbers came from somewhere, it would have been nice if you'd provided the calculations. Or are they just showing there isn't VLE with that given property?Ĭould you give an example of where this was done? I have a hunch where you are going with Ok an example,we have mole fractions and temperature, and we want dew pressure, so we take two arbitrary pressures and calculate summation of y/k, which y=z because we are in dew point,and k earned by DePriester,so if we try this summation in 100psi we get 0.828 and if we try it in 150psi we get 1.174, and finally if we try 126psi we get 1 and thats the dew pressure,i wanna know about those 1.174 and 0.828,do they give us some physical signs about which regions are we in,by that pressure? = psi sum of y/kĭo the values for the pressures above and below the dew point pressure have a physical meaning?įor example, showing us that we are in two-phase, SH vapor or SC liquid region? If I wanted to calculate the dew point pressure at a given temperature and I take arbitrary pressures (including the dew point pressure) I get the following results. My question is about those values, are they showing some physical property? Now there are sometimes that we get some K's and using the summation of $y/k$ we get some quantities that are not 1, like 0.9 or 1.2. Using DePriester Chart and Given one of mole fractions ($z$), pressure and temperature we can acquire K-values for that properties and bubble and dew properties.