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Modeling
Finally, Figure III.24 presents the results obtained for the CO2/decalin mixture.
This mixture presents a region of liquid-liquid equilibria as reported by Tiffin et al. (1978).
The upper critical solution temperature (UCST), identified by the star in the figure, occurs
at 316.45 K. Both versions overestimate the liquid-liquid region by predicting a LLE at a
temperature above the UCST. However, it can be observed that the polar soft-SAFT gives
better predictions at lower and higher temperatures than the original soft-SAFT EoS.
Table III.11 compares the adjusted binary parameters when the quadrupole moment
is considered explicitly and in an effective way. As observed before, when the polar term is
included, the binary energy and size parameters are consistently closer to unity than when
the non-polar soft-SAFT EoS is used for the same reasons mentioned above. Also, the
CO2/alkane mixtures were found to be more sensitive to the size binary parameter and
although slightly differences are found between them, it was decided not to fix the
parameter in order to obtain a quantitative description of the experimental data.
P / MPa
40
35
30
25
20
15
10
5
0
0 0.2 0.4 0.6 0.8 1
x, y CO2
Figure III.24. Predictions of the vapor-liquid equilibrium of CO2/decalin system at 298, 348 and
423 K. Legend as in Figure III.23. Binary parameters were adjusted at 323 K. The star indicates the
upper critical solution temperature of this mixture.
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