Aspen Physical Property System - Physical Property Models

components are mainly through the local interactions with solvents. We can
calculate all three activity coefficients for Henry components as follows:
with
Notice that xH�0 applies to all Henry components in the solution.
NRTLSAC for Segments/Oligomers
130 2 Thermodynamic Property Models
(86)
(87)
(88)
(89)
(90)
(91)
(92)
(93)
(94)
This is the original NRTLSAC model added in version 2006, which requires
that components be defined as oligomers. It is retained for compatibility, but
new models should use the NRTL-SAC model.
NRTL-SAC (patent pending) is a segment contribution activity coefficient
model, derived from the Polymer NRTL model, usable in Aspen Properties and
Aspen Polymers. NRTL-SAC can be used for fast, qualitative estimation of the
solubility of complex organic compounds in common solvents. Conceptually,
the model treats the liquid non-ideality of mixtures containing complex
organic molecules (solute) and small molecules (solvent) in terms of
interactions between three pairwise interacting conceptual segments:
hydrophobic segment (x), hydrophilic segment (z), and polar segments (yand
y+). In practice, these conceptual segments become the molecular
descriptors used to represent the molecular surface characteristics of each
solute or solvent molecule. Hexane, water, and acetonitrile are selected as
the reference molecules for the hydrophobic, hydrophilic, and polar segments,
respectively. The molecular parameters for all other solvents can be
determined by regression of available VLE or LLE data for binary systems of
solvent and the reference molecules or their substitutes. The treatment
results in four component-specific molecular parameters: hydrophobicity X,
hydrophilicity Z, and polarity Y- and Y+. The two types of polar segments, Y-