Physical Chemistry , 1st ed.

Fractional distillations are among the most important and energy-demanding

processes, especially in the petrochemical industry.

Phase diagrams can also be plotted in terms of temperature—usually the

boiling point (BP) of the liquid—versus composition. However, unlike the

pressure-composition phase diagram, there is no simple straight-line equation

to express one of the lines, so in temperature-composition phase diagrams

both bubble point and dew point lines are curved. An example is shown in

Figure 7.10, which corresponds to Figure 7.5. Notice that the higher compo-

nent of vapor pressure, component 2, has the lower boiling point for the pure

7.3 Two Components: Liquid/Liquid Systems 177

Figure 7.9 Some fractional distillation apparatus. (a) A laboratory scale fractional distillation

apparatus. (b) A microscale fractional distillation setup. Microscale equipment uses small

amounts, so it is appropriate when only small amounts of material are available. (c) Fractional

distillation on an industrial scale is a common process. This shows the hardware for large-scale

distillations.

T(BP 2 )

T(BP 1 )

Temperature

0.5

x 1 , y 1

0.0 1.0

T(BP) vs. x 1 :

the bubble point line

T(BP) vs. y 1 :

the dew point line

Figure 7.10 Temperature-composition

phase diagrams are more common than

pressure-composition diagrams. Notice,

however, that neither line is straight, and

that the lines indicating the boiling process

and the condensation process are switched

from the pressure-composition diagrams.

Compare to Figure 7.5.

© William Wright/Fundamental Photographs

Receiving

flask

Condenser

Thermometer

Sample

flask

Fractional

distillation

column Water

(a)

(b)

(c)