Computation of Tie Lines for Ternary Mixtures

Consider a ternary mixture of hexane, heptane, and methanol. A temperature of 32.85 °C is assumed. This liquid-liquid equilibrium diagram is classified as type II. The Demonstration computes the tie line originating from a user-specified position on the extract curve (i.e., known values of

x

i,1

for

i=1,2,3

are assumed). In effect, one has to find the steady-state solution of the following system of ODEs:

d

x

i,2

dt

=

γ

i,1

x

i,1-

γ

i,2

x

i,2

for

i=1,2,3

, where

x

i,j

is the mole fraction of component

i

in phase

j

(hexane-rich or hexane-lean phases) and

γ

i,j

is the activity coefficient of component

i

in phase

j

predicted using the non-random two liquid (NRTL) model.