Pressure pseudocritical

The pseudocritical pressure is calculated as a function of other constants ... 

P = saturation pressure for the petroleum fraction at T P = pseudocritical pressure for the petroleum fraction... 

When the critical constants for a pure substance or the pseudocritical constants for a petroleum fraction are known, the vapor pressure for hydrocarbons and petroleum fractions can be calculated using the Lee and Kesler equations ... 

The Law of Corresponding States has been extended to cover mixtures of gases which are closely related. As was brought out in Chapter 2, obtaining the critical point for multicomponent mixtures is somewhat difficult therefore, pseudocritical temperature and pseudocritical pressure have been invented. 

EXAMPLE 3-8 Calculate the pseudocritical temperature and pseudocritical pressure of the gas given in Example 3-5. Use the critical constants given in Appendix A. 

We will see in Chapter 10 that the composition of a petroleum fluid is often given with all components heavier than hexane lumped together as heptanes plus. Pseudocritical pressures and pseudocritical temperatures for heptanes plus for use in Equations 3-42 can be obtained from Figure 3-10.7... 

Determine values of pseudocritical temperature and pseudocritical pressure for the gas given below. 

Values of pseudocritical temperature and pseudocritical pressure are required in the use of Figure 6-4. Methods presented in Chapter 3, including adjustments for carbon dioxide and hydrogen sulfide, can be used to estimate these properties. 

P pc pseudocritical pressure adjusted for nonhydrocarbon components, see Equation 3-45... 

The elevated pressure here requires use of either an equation of state or the Lee/Kesler correlation with pseudocritical parameters. We choose the latter. 

The effect of temperature (or pressure 1 on relative volatility is further illustrated in Fig. 1.2b (29). The diagram clearly shows a reduction in relative volatility as pressure is raised and illustrates that relative volatility approaches unify as the pseudocritical point of the mixture is approached. 

To perform PVT calculations for nonideal gas mixtures, you may use Kay s rule. Determine pseudocritical constants (temperature and pressure) by weighting the critical constants for each mixture component by the mole fraction of that component in the mixture then calculate the reduced temperature and pressure and the compressibility factor as before. 

The values so obtained are the mixture co and pseudocritical temperature and pressure, X Ppc. wliich replace X and P, to definepsendoreducedparameters ... 

In instances where the temperature or pressure of a gas mixture is unknown, it is convenient, to avoid a trial-and-error solution using the generalized compressibility charts, to compute a pseudocritical ideal volume and a pseudoreduced ideal volume as illustrated below. Suppose we have given that the molal volume of the gas mixture in the preceding problem was 326 cm at 90.0 atm. What was the temperature ... 

It would be convenient if the critical temperature of a mixture were the mole weighted average of the critical temperatures of its pure components, and the critical pressure of a mixture were simply a mole weighted average of the critical pressures of the pure components (the concept used in Kay s rule), but these maxims simply are not true, as shown in Fig. 3.22. The pseudocritical temperature falls on the dashed line between the critical temperatures of CO2 and SO2, whereas the actual critical point for the mixture lies somewhere else. The solid line in Fig. 3.22 illustrates how the locus of the actual critical points diverges from the locus of the pseudo critical points. 

Over the years various phases of the initial work have been extended and development of a new characterization scheme using the pseudocompound approach is evolving. Daubert summarizes the traditional and new methods insofar as predicting molecular weights, pseudocritical temperature and pressure, acentric factor, and characterization factors. 

---