Aspen Physical Property System - Physical Property Models

Additional Parameters
SMLZRA is used in Peneloux-Rauzy volume translation as described in Soave-
Redlich-Kwong. This volume translation feature can be enabled by setting
option code 4 to 1, but is disabled by default (in which case this parameter is
not used).
SMLCMP is the Composition Independent Fugacity Calculation Flag. You can
use this flag to indicate the component for which its fugacity coefficient in the
mixture will be calculated such that it is independent of composition. The
calculated fugacity coefficient of that component is simply the purecomponent
fugacity coefficient. This is a simplification. Enter a value of 1 for
the element i to indicate that the fugacity coefficient of component i is
independent of composition. This parameter defaults to zero.
SRKMLP is a polar parameter for the Mathias alpha function.
SRKGLP is a vector of parameters for the Gibbons-Laughton alpha function.
VPA/IK-CAPE Equation-of-State
The VPA/IK-CAPE equation of state is similar to the HF equation of state but
allows dimerization, tetramerization and hexamerization to occur
simultaneously. The main assumption of the model is that only molecular
association causes the gas phase nonideality. Attractive forces between the
molecules and the complexes are neglected.
There are three kinds of associations, which can be modeled:
� Dimerization (examples: formic acid, acetic acid)
� Tetramerization (example: acetic acid)
� Hexamerization (example: hydrogen fluoride)
To get the largest possible flexibility of the model all these kinds of
association can occur simultaneously, for example, in a mixture containing
acetic acid and HF. Up to five components can associate, and any number of
inert components are allowed. This is the only difference between this model
and the HF equation of state, which account only the hexamerization of HF.
Symbols
In the following description, these symbols are used:
yi = Apparent concentration
zin = True concentration, for component i and degree of
association n=1, 2, 4, 6
zMij = True concentration of cross-dimers of components i
and j, for i,j 1 to 5.
p0 = Reference pressure
k = Number of components
64 2 Thermodynamic Property Models