Aspen Physical Property System - Physical Property Models

I, J = Component index
i, j, m = Conceptual segment indexx, y-, y+, z
�I = Activity coefficient of component I
�I C = �I FH = Flory-Huggins term for combinatorial contribution to �I
�I R = �I lc = NRTL term for local composition interaction contribution to
132 2 Thermodynamic Property Models
�I
�I = Segment mole fraction of component I
pI = Effective component size parameter
sI and �I = Empirical parameters for pI
rI = Total segment number of component I
xI = Mole fraction of component I
rI,m = Number of conceptual segment m containing in component
I
xi = Segment mole fraction of conceptual segment i in mixtures
�im = NRTL binary non-randomness factor parameter for
conceptual segments
�im = NRTL binary interaction energy parameter for conceptual
segments
NRTL binary parameters for conceptual segments
The NRTL binary parameters between conceptual segments in NRTLSAC are
determined by available VLE and LLE data between reference molecules
defined above.
Segment 1 x x y- y+ x
Segment 2 y- z z z y+
� 12
� 21
� 12 = � 21
1.643 6.547 -2.000 2.000 1.643
1.834 10.949 1.787 1.787 1.834
0.2 0.2 0.3 0.3 0.2
Parameters used in NRTLSAC
Each component can have up to four parameters, rI,x, rI,y-, rI,y+, and rI,z
although only one or two of these molecular parameters are needed for most
solvents in practice. Since conceptual segments apply to all molecules, these
four molecular parameters are implemented together as a binary parameter,
NRTLXY(I, m) where I represents a component (molecule) index and m
represents a conceptual segment index.
In addition, the Flory-Huggins size parameter, FHSIZE , is used in NRTLSAC
to calculate the effective component size parameter, pI. The Flory-Huggins
combinatorial term can be turned off by setting �I = 0 for each component in
mixtures.