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at the rate of 50 moles/hr is being withdrawn.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