Page 461 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Properties of Hydrocarbon Mixtures 419

For a component in a mixture
(p. = fi
' XiP (645)
The fugacity coefficients are readily calculated from P-V-T data for both,
pure component and mixture.
P-V-T of a fixed composition system can be developed in pressure explicit
forms, i.e.,

P = Q(V,T) (6-46)
The basic equation of state may be transformed to a compressibility factor
Z, but the basic expression given by Equation 644 still applies. Equilibrium K
values are predicted from fugacity, which is related to Gibbs free energy. One
of the basic definitions of fugacity gased K values is

(6-47)

The fugacity coefficient Qi is related to the pressure, volume and temperature by

(6-48)

Applying the SRK equation,

+(Z-l)B~-~(Ai-B~)ln (649)
bRT

or

A
lnQi = -ln(Z - B) + (Z - 1)BI - -(A; - Bl)ln (6-50)
B
where

Bi = bi (6-5 1)
b

Notations are as for Equations 6-11 and 612. For values kr see Tables 6-19
and 6-20. The data in Table 6-19 was prepared for the Peng-Robinson equation,

(text continued on page 422)