College of Engineering
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Department of
Chemical Engineering
College of Engineering |
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| Florida A&M University | Florida State University |
Experiment 300: Distillation
[ Theory] [ Data] [ Back Home]
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There are essentially two parts to the theoretical background regarding the
analysis of the distillation column in our laboratory. The first
area of interest is predicting values of the bottoms and distillate
ethanol mole fractions based on the theoretical minimum number of stages
and minimum reflux ratio based on
the measured values of the bottoms and distillate ethanol mole
fractions, not at total reflux.
The theoretical minimum number of stages is the number of stages needed
to reach a desired separation. The theoretical number of stages at
total reflux may be calculated using the Fenske Equation and the
McCabe Thiele Model.
The
Fenske equation may be used to calculate the theoretical minimum
number of stages, Nm,
at total reflux for a distillation column with a total
condenser.
XD=mole
fraction of desired product in distillate XB=
mole fraction of desired product in bottoms a1
= relative volatility of the overhead vapor aw=
relative volatility of the bottoms liquid McCabe Thiele Model The McCabe Thiele model may also be
used to determine the number of theoretical stages at total reflux.
The following steps will enable one to determine the number of
stages: Draw the equilibrium line on an
x-y plot. Draw the y=x line. Plot the measured bottoms and
distillate ethanol mole fractions along the y = x line. For total
reflux this line will be your operating
line. Draw a horizontal line from the
distillate mole fraction on the operating line to the equilibrium
line, followed by a vertical line drawn back down to the operating
line. Repeat this until the desired bottoms composition is reached. Count the number of times the
horizontal line hits the equilibrium line to get the number of
stages. Note: The last stage is the reboiler.
NUmber
Fenske Equation
