Chemical Engineering Society
Council of Student Organizations
De La Salle University – Manila
SEPAPRO QUIZ#4 REVIEWER
Questionnaire:............................................................
I. Multiple Choice
1. The rate of leaching decreases as
a. Pressure decreases
b. Temperature decreases
c. Temperature increases
d. Both (A) and (C)
2. The unit operation by which soluble components of a
liquid mixture are dissolved in a liquid immiscible with
the insoluble components is
a. Gas absorption
b. Solvent extraction
c. Leaching
d. Adsorption
3. Which of the following factor influences the fraction of
liquid retained in the underflow or slude?
a. Boiling point of the solvent
b. The type of pump used for transferring the
underflow
c. Fractional recovery of the solute
d. None of the above
4. In ideal leaching operation, for constant underflow, the
concentration of solute in the overflow is _____ the
concentration of the solute in the solution adhering to
the inert solid in the underflow.
a. Equal to half
b. Less than
c. Equal to
d. More than
5. If the solute concentration (on “solid free basis”) in the
overflow and the overflow are not equal, the
equilibrium (homogeneity) tie-lines are
a. Vertical
b. Horizontal
c. Inclined to the right
d. Inclined to the left
6. Hexane is the most popular solvent for oil extraction
from seeds because
a. It can be easily removed from the extract to
recover the solvent
b. It is non toxic
c.
d.
It is miscibke with plabnt/vegetable oils in all
proportion
All of the above
7. The ideal leaching conditions exist if
a. The solute is infinitely soluble in the solvent
b. Sufficient contact time for the solvent to
penetrate the solute completely is permitted
c. The overflow streams contain some inert
solids, either by entrainment or by partial
solubility in the overflow solution
d. Both (A) and (B)
8. Stage efficiency in leaching process depends on
a. Vapor pressure of the solution
b. Time of contact between the solid and the
solution
c. Rate of diffusion of the solute through the
solid and into the liquid
d. Both (B) and (C)
9. In a determination of the solution retention data, the
mass fraction of the solute in the extract was
determined to be 0.6. The corresponding underflow
analysis showed a retention of 0.6 Kg solvent per Kg of
the inert solid. The mass fraction of solute in the
underflow is most likely
a. 0.6
b. 0.47
c. 0.36
d. 0.27
In a salt recovery plant, rock salt is being leached to
produce industrial salt in a continuous counter current
system consisting of two ideal stages using water as
leaching medium. The average composition of the rock
salt is: inert = 70%, soluble salt = 25%, moisture =5%, all
percentage by weight. The underflow from each stage
contains 0.3 Kg of solution per Kg of inert. The plant
leaches 50 MT/day of rock salt using 50 MT of water per
day. The quantity of soluble salts recovered in MT/day
is:
a. 12.1
b. 13.1
c. 14
d. 15.2
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II. Problem Solving
Answers:…………............................................................
1.
Three hundred fifty Kg per hour of halibut liver is to
be extracted in a counter-current cascade with ethyl
ether to recover oil. The ether which has been
partially purified contains 2% oil. The freshliver
contains 20% oil and is to be extracted to a
composition of 2% oil (on a solvent-free basis).
Solvent used is 150 Kg per hour. All % are weight %.
Use retention/drainage data from Geankoplis page
835, #12.10-4 (right triangular diagram at top of page
and xA in a scale up to 0.6 will suffice to place all
relevant points in the same graph).
a. What % of oil entering with the fresh liver is
recovered in the extract?
b. How many ideal stages are required?
I.
Seeds, containing 20% by mass of oil, are extracted in
a counter-current plant, and 90% of the oil is
recovered in a solution containing 50% by mass of oil.
If the seeds are extracted with fresh solvent and 1 Kg
of solution in the underflow in association with every
2 Kg of insoluble matter, how many ideal stages are
required?
II.
2.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
B
B
D
C
C
D
D
D
C
A
1. Ma
a. 92%
b. 3.6 stages
2. 5 ideal stages
Goodluck sa exam! Kaya niyo yan :)
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