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

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

Corresponding P-x diagram (constant T)

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

Low Pressure VLLE

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

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

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