Distillation - Principles of Chemical Separations with Environmental Applications - page 118

4.7 Nomenclature

For a binary system:
D

molar flowrate of liquid distillate

x D mole fraction of most volatile component in distillate

B molar flowrate of liquid bottoms

x B mole fraction of most volatile component in bottoms

F molar flowrate of feed

x F mole fraction of most volatile component in feed

V, L molar flowrates of vapor and liquid streams in enriching section

V , L molar flowrates of vapors and liquid streams in stripping section

n, m number of stages in enriching and stripping sections, respectively

y n , m mole fraction of more volatile component in vapor at stage n , m

x n , m mole fraction of more volatile component in liquid at stage n , m

h F molar enthalpy of feed stream

Q C energy requirement of condenser (should be negative)

Q R energy requirement of reboiler (should be positive)

h D molar enthalpy of distillate

h B molar enthalpy of bottoms

4.8 Problems

4.1 Explain why a partial condenser is an equilibrium stage and a total condenser is not.
4.2 Show the derivation of the q -line equation.
4.3 For steam distillation, derive the equation for the intersection of the operating line
with the diagonal ( y

=

x ) line and the x -axis.
4.4 An existing distillation column has five equilibrium stages, a partial reboiler and a total
condenser. It is planned to use this column to produce a 75 mol% ethanol-25 mol%
water distillate from a 10 mol% ethanol in water feed. The feed is a saturated liquid.
Assume a basis of 100 mol hr. Determine the operating conditions and feed stage for

the column to be used for this application.

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