Page 108 - Separation process engineering

is more volatile. At equilibrium, if cresol mole fraction in the liquid is 0.3, what is the mole
fraction of cresol in the vapor?
D14. We are feeding 100 kmol/h of a mixture that is 30 mol% n-butane and 70 mol% n-hexane to a

flash drum. We operate with V/F = 0.4 and T drum = 100°C. Use Raoult’s law to estimate K values
from vapor pressures. Use Antoine’s equation to calculate vapor pressure,

where VP is in mm Hg and T is in °C.
n-butane: A = 6.809, B = 935.86, C = 238.73
n-hexane: A = 6.876, B = 1171.17, C = 224.41

Find p drum , x and y i
i
D15.* We have a flash drum separating 50 kmol/h of a mixture of ethane, isobutane, and n-butane. The
ratio of isobutane to n-butane is held constant at 0.8 (that is, z /z = 0.8). The mole fractions of
iC4 nC4
all three components in the feed can change. The flash drum operates at a pressure of 100 kPa and
a temperature of 20°C. If the drum is operating at V/F = 0.4, what must the mole fractions of all

three components in the feed be? Use Figure 2-11 or 2-12 or Eq. (2-30).
D16. A feed that is 50 mol% methane, 10 mol% n-butane, 15 mol% n-pentane, and 25 mol% n-hexane
is flash distilled. F = 150 kmol/h. Drum pressure = 250 kPa, drum temperature = 10°C. Use the
DePriester charts. Find V/F, x, y, V, L.
i
i
D17. We are separating a mixture of acetone (MVC) from ethanol by flash distillation at p = 1 atm.
Equilibrium data are listed in Problem 4.D7. Solve graphically.

a. 1000 kmol/day of a feed that is 70 mol% acetone is flash distilled. If 40% of the feed is
vaporized, find the flow rates and mole fractions of the vapor and liquid products.
b. Repeat part a for a feed rate of 5000 kmol/day.

c. If feed is 30 mol% acetone, what is the lowest possible liquid mole fraction and the highest
possible vapor mole fraction?
d. If we want to obtain a liquid product that is 40 mol% acetone while flashing 60% of the feed,
what must the mole fraction of the feed be?

D18.* We wish to flash distill a feed that is 10 mol% propane, 30 mol% n-butane, and 60 mol% n-
hexane. Feed rate is 10 kmol/h, and drum pressure is 200 kPa. We desire a liquid that is 85 mol%
n-hexane. Use DePriester charts. Find T drum and V/F. Continue until your answer is within 0.5°C

of the correct answer. Note: This is a single trial and error, not a simultaneous mass and energy
balance convergence problem.
D19.* A flash drum operating at 300 kPa is separating a mixture that is fed in as 40 mol% isobutane,
25% n-pentane, and 35% n-hexane. We wish a 90% recovery of n-hexane in the liquid (that is,
90% of the n-hexane in the feed exits in the liquid product). F = 1000 kmol/h. Find T drum , x, y,
j
j
V/F.
D20. A flash drum operating at a pressure of 2.0 bar and a temperature of 0°C is separating a mixture
of ethane (E), n-butane (B), and n-pentane (P). The fraction vaporized is V/F = 0.25. The feed
mole fraction of ethane is z = 0.20. Find the mole fraction of n-butane, z , in the feed. Use the
B
E
DePriester chart.
D21. We wish to flash distill a feed that is 55 mol% ethane and 45 mol% n-pentane. The drum