Environmental Engineering Reference
In-Depth Information
100
90
P
80
70
60
50
F
40
30
E
M
20
10
R
0
A
0
10
20
30
40
50
60
70
80
90
100
Water (wt%)
Figure 3.25
Furfural-ethylene glycol-water right triangle diagram.
Example 3.5
Problem:
Mixing oil, vinegar and spices for salad dressing (Figure 3.26).
While this is not an environmental application, this example is a common extraction
situation which illustrates the concept.
Solution:
The mass balance equations could be solved algebraically if an algebraic expression for
the phase equilibrium was known (an equation to relate
y
A
o
and
x
A
o
). Alternatively, the
graphical method can be used to solve the mass balances and equilibrium relationships
algebraically. Suppose the right triangular diagram for the ternary oil-vinegar-spices
system is as shown in Figure 3.27. Here, point
O
i
represents the oil and spices, and
point
V
i
represents the vinegar. Point
F
is where the mixing occurs (note that it is in the
two-phase region). Point
F
separates into two phases along the tie-line (because they
are in equilibrium) with point
O
o
representing the oil and spices layer and point
V
o
representing the vinegar and spices layer. If these layers were separated, an extraction
would have been performed which used vinegar as the solvent to remove some of the
spices (solute) from the oil (diluent).
Suppose one wanted to remove more spices by this same method. The oil and spices
phase from the first equilibrium stage could be mixed with more vinegar. This is the
idea behind a cross-flow cascade of equilibrium stages.
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