W.R. Wilcox, Clarkson University, September 2006; revised August 2009
Estimation of binary phase diagrams
Following is a method for estimating binary phase behavior using HYSYS (or UniSim). The
example given is Figure 7.19c of the 2nd edition of Seider, Seader and Lewin's text on Process
and Product Design Principles.
Step 1: Make a list of possible thermodynamic models for the particular mixture being
considered, using, for example the decision tree at
http://people.clarkson.edu/~wilcox/Design/therprop.htm.
Open HYSYS:
Components (di-i-P-Ether and 2-Propanol for Fig. 7.19). Fluid Pkgs. Check Binary Coeffs; if
absent select a different thermodynamic model.
Go to simulation environment and enter two streams going into a mixer, one pure di-i-P-Ether
and one pure 2-Propanol. Set both feed streams to 0 Vapour Fraction (saturated liquid) at 1.01
bar, with unspecified flow rates and temperatures. The mixture coming out of the mixer is
specified as 2 kgmol/hr and the same pressure. Pass the mixture through the heater with the
product specified as the same pressure and 0.5 vapor fraction.
Go to Tools, Databook, Variables, Insert the Molar Flow of the Ether, Add the Temperature of
the final product, the Phase Comp Mole Frac (Vapour Phase - di-i-P-Ether) of the product, and
the Phase Comp Mole Frac (Liquid Phase - di-i-P-Ether) of the product. Go to Case Studies,
Add, give the case study a name, indicate that the Molar Flow of the Ether is the Independent
Variable and the others are Dependent Variables. Click on View, and enter the Low Bound,
High Bound and Step Size for the variation of the Independent Variable. For Display Properties
click on the Dependent Variables. Click on Results, Table. Copy the values in the table to Excel
and plot T versus x and y of di-i-P-Ether to obtain the result as shown on Figures 2 and 3.
If one of the components is water, the liquid composition may show up in an “aqueous phase” in
part of the phase diagram. In that case it will be necessary to include the Phase Comp Mole Frac
of the aqueous phase as a dependent variable, and then in Excel combine the aqueous phase and
liquid phase mole fractions.
82.5
TEMPERATURE (oC)
80
77.5
T-x
75
T-y
72.5
70
67.5
65
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
MOLE FRACTION IPE
Figure 2. TXY phase diagram computed using HYSYS
with the Wilson thermodynamic model.
81
79
TEMPERATURE (oC)
77
75
T-x
T-y
73
71
69
67
65
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
MOLE FRACTION IPE
Figure 3. TXY phase diagram computed using HYSYS
with the PRSV thermodynamic model.
Note that no azeotrope is found, which is contrary to experiment.
Ternary and liquid-liquid equilibria
1