10.32
Spring 2005
EXAM 1
Wednesday, March 2, 2005
1. (40 points) A mixture of three hydrocarbons is at equilibrium at 100°C and 15
atmospheres. The can be assumed to form an ideal mixture in both the liquid and vapor
phases. The composition of the mixture and the constants for the vapor pressure functions
for each component are given below. The vapor pressure functions are of the form
T
D
APln −=
where P is in atmospheres and T is in Kelvins.
Component z A D
C3 0.25 9.816 2260
C4 0.40 9.922 2696
C5 0.35 10.173 3141
a) Determine whether the mixture is a subcooled liquid, a mixture of vapor and liquid,
or a superheated vapor.
b) It is desired to bring the mixture to its bubble point (saturated liquid). If temperature
is maintained at 100°C, to what total pressure must the mixture be subjected to reach
the bubble point?
c) If pressure is maintained at 15 atmospheres, to what temperature must the mixture be
adjusted to reach the bubble point? An answer within a few degrees centigrade is
acceptable.
2. (60 points) We wish to separate a binary mixture of A and B by continuous distillation.
The mixture consists of 20 percent A and 80 percent B at the bubble point. The relative
volatility of A to B is 3.0 and the vapor-liquid equilibrium data are plotted in the attached
figure. The binary mixture is available at 100 pound-mol/hr and we wish to obtain a
distillate product that has a concentration of 95 percent A and that contains half of the
component A in the feed stream.
a) What are the minimum reflux ratio and minimum number of stages required to effect
this separation?
