1. Vapor-liquid-liquid equilibrium (VLLE)
Chapter 14- Part VI

2. LLE binodal curves
intersect VLE diagram
At the 3-phase point
F= 2 – p + N
F = 2 – = 1
At constant P,
T and compositions are fixed

4. Corresponding P-x diagram (constant T)

5. Calculation of VLLE VLE is calculated in the same way as before
The liquid phase cannot be assumed ideal
LLE is expected, therefore NRTL, UNIFAC, and UNIQUAC are the best choices

7. Low Pressure VLLE

8. Two equations (of the 4) are preferred
You can show that both g1∞ and g2∞  ∞
Then, your equations should not include g1a
Similarly, your equations should not include g2b

9. To avoid g1∞ ∞ and g2∞ ∞
y1* can be also calculated

11. Calculations of VLE for Fig. 14.21
Region I:
y1(I)P=P1sat
Region II:
y2(II)P=[1-y1(II)]P=P2sat