Chemical Engineering Society
Council of Student Organizations
De La Salle University Manila
SEPAPRO QUIZ#2 REVIEWER
6. Fenskes Equation is used to calculate number of plates
Questionnaire:............................................................ in a distillation column
a. A total reflux
I. Multiple Choice b. For system having constant relative volatility
c. At minimum reflux
1. 100 moles of vapor per hour is leaving the top plate of d. For both (A) and (B) together
a continuous distillation column and overhead product
at the rate of 50 moles/hr is being withdrawn. Then the 7. Which one of the following is not considered an ideal
reflux ratio is stage in distillation concept?
a. 0.5 a. Partial condenser
b. 1.0 b. Total condenser
c. 2.0 c. Reboiler
d. 3.0 d. None of the above
2. Minimum number of ideal stages is required in a 8. When open steam is employed for heating in a
fractionating column when the reflux ratio is equal to continuous distillation column for aqueous solution, the
a. Minimum reflux ratio stripping section operating line in McCabe-Thiele
b. Optimum reflux ratio diagram passes through coordinates (x,y) at the point
c. Zero (xw is the mole fraction of the more volatile component
d. Infinity in the bottom product):
a. (0,0)
3. In a binary distillation column if the feed contains 40 b. (xw, xw )
mol % vapor, the feed line (or q-line) wikll have a slope c. (0, xw )
of d. (xw,0)
a. -1.5
b. -0.6 9. For distillation of an equimolar binary mixture of A and
c. 0.6 B, the equation of the operating lines are:
d. 1.5
Rectifying section: y = 0.663x + 0.32
4. One mole of solute A and B (enthalpy = 900Kcal/Kmol; Stripping section: y = 1.329x 0.013
x=0.4) is mixed with 2 moles of another solution of the
same components (enthalpy = 1200Kcal/Kmol; x=0.8). Where x and y are mole fraction of A in the liquid and
The mole fraction of the mixture is vapor streams respectively. What is the condition of the
a. 0.475 feed?
b. 0.550 a. Saturated liquid
c. 0.667 b. Saturated vapor
d. 0.750 c. Subcooled liquid
d. Supersaturated vapor
5. For the rectification of methanol-water, which of the
followings will increase the number of ideal stages 10. A column for distillation of a mixture of A and B
needed? operates at total reflux. The mole fraction of liquid
a. Uses open steam instead of reboiler leaving the fourth tray from the top is 0.4. If the relative
b. Increases the reflux ratio used volatility is 1.8, what is the mole fraction of the vapor
c. Increases the operating pressure stream leaving the fifth tray from the top?
d. Makes the reflux subcooled a. > 0.72
b. 0.72
c. 0.545
d. 0.4
1
II. Problem Solving Answers:............................................................
1. A total feed of 100 lb-mole/hr having an overall
composition of 40 mole% A and 60 mol% B is to be
I.
fractionated at atmospheric pressure to give a 1. B
distillate containing 95mol % A and a bottoms 2. D
containing 7.5 mol% A. The feed enters the column 3. A
partially vaporized so that 60mol % is liquid and 4. C
40mol % is vapor. The column is to operate at a reflux
ratio of 3 with a total condenser and a reboiler 5. C
wherein the relative volatility of A with respect to B 6. D
can be considered constant at a value of 3. Constant 7. B
molal overflow may be assumed also. Calculate the 8. D
following:
a. lb-mole/hr distillate produced
9. A
b. minimum reflux ratio 10. D
c. theoretical number of plates required
d. actual number of stages if the overall II.
column efficiency is 75% 1.
e. the reboiler heat load (Btu/hr) if the
average molar heat of vaporization of A and a. 37.143lnmole/hr
B is 10,000 Btu/lb-mole b. Rm = 1.5
c. 5.9 theoretical plates + 1 reboiler
2. The molar enthalpies of saturated liquid and vapor d. 8 plates
mixture of A and B at 1 atm total pressure are
e. ...
= 20000 + 4000 (saturated vapor enthalpy, KJ/Kmol)
= 9000 + 1000 (saturated liquid enthalpy, KJ/Kmol) 2. As
a. Condition of the liquid: subcooled
With x,y the mole fraction of A in liquid and vapor Condition of the vapor: superheated
phase respectively. b. x = 0.4, y = 0.67
c. 6.8 ideal stages or 5.8 ideal plates + 1
The relative volatility of A with respect to B is 3. reboiler
d. Qc=2050000 KJ/hr
a. We have 1 Kmol of liquid (x = 0.3, enthalpy
= 8500 KJ.Kmol) and 1 Kmol of a vapor ( y =
0.5, enthalpy = 24000 KJ/Kmol). What is the
condition of the liquid (subcooled,
saturated)? What is the condition of the
vapor (supersaturated, saturated)?
b. If a mixture of saturated liquid and
saturated vapor in equilibrium has an
overall composition of 50 mole% A and an
overall enthalpy of 14000 KJ/Kmol, what is
its x and y values?
c. When a feed described above (b) is fed to a
distillation column at 100Kmol/hr, what
would be the number of ideal stages
needed to produce an overhead product of
90 mol% A and a bottom of 10 mol% A. The
column is equipped with a total condenser
and a reboiler operated at 1 atm with a
reflux ratio of 2. (A scale of enthalpy from
+55000 to -30000KJ/Kmol will suffice to
place all relevant points in the h-x diagram).
d. What is the condenser duty (KJ/hr) fpr
letter (c). Goodluck sa exam! Kaya niyo yan :)
