Pressure pseudoreduced

Physical properties of gas mixtures are correlated with pseudoreduced temperature and pseudoreduced pressure in the same manner that properties of pure gases are correlated with reduced temperature and reduced pressure. 

First, calculate the pseudoreduced temperature, pseudoreduced pressure, and determine z. 

Pseudoreduced compressibility is a function of z-factor and pseudore-duced pressure. Thus, a graph relating z-factor to pseudoreduced pressure, Figure 3-7, Figure 3-8, or Figure 3-9, can be used with Equation 6-14 to calculate values of Cpr. 

Examination of Figure 3-7 shows that at moderate pressure, say values of pseudoreduced pressure less than about 6.0, z-factor increases as temperature increases at constant pressure. That is, at pseudoreduced pressures less than about 6.0, the derivative of z-factor with respect to T is positive. 

At high pressure (for instance, at pseudoreduced pressures greater than about 11.0 on Figure 3-7 or Figure 3-8) z-factor decreases as temperature increases. Under these conditions, the derivative of z-factor with respect to T is negative. Thus, Equation 6-23 indicates that temperature increases as pressure decreases. 

The pseudoreduced temperature and pseudoreduced pressure, which replace Tr and P, are determined by... 

Since the dimensions of cg are reciprocal pressure, the product of cg and ppC is dimensionless. This product is called pseudoreduced compressibility, cpr. 

Second, calculate pseudoreduced temperature and psuedoreduced pressure. 

As with single-component gases, if you know V and either T or P you can estimate the ideal pseudoreduced volume = VPj RT and use the other known reduced property to determine the unknown temperature or pressure from the compressibility chart. 

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 ... 

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