Separation Processes Flashcards
The distribution equilibrium for A between an extract solvent S and a
raffinate solvent B is given Y=2X where Y=mass of A per unit mass of S,
X=mass of A per unit mass of B. The extract and raffinate solvents are
immiscible with each other at all concentrations of A. From these data,
calculate the amount of extract solvent needed per 100 kg solution containing
30% A in B in 95% of A is to be removed for Single stage contact
A. 665 kg
C. 180 kg
B. 565 kg
D. 70 kg
665 kg
The distribution equilibrium for A between an extract solvent S and a
raffinate solvent B is given Y=2X where Y=mass of A per unit mass of S,
X=mass of A per unit mass of B. The extract and raffinate solvents are
immiscible with each other at all concentrations of A. From these data,
calculate the amount of extract solvent needed per 100 kg solution containing
30% A in B in 95% of A is to be removed for Three-stage batch contact, one third of the solvent will be used in
each contact
A. 60 kg
C. 210 kg
B. 665 kg
D. 180 kg
180 kg
Powdered limestone (CaCO3) containing 10000 ppm NaOH is to be washed in a
two-step continuous counter current washing system to remove most of the
NaOH. Two cells and 100000 L of water per 10 MT/day of limestone feed are
used. The slurry discharged and removed from the underflow contains 0.091 MT
of water per MT CaCO3. Assuming complete mixing and washing, calculate the
NaOH content of the washed and dried limestone in ppm.
A. 0.77 ppm
C. 0.82 ppm
B. 0.65 ppm
D. 0.97 ppm
0.82 ppm
Ten kg of a solid containing 45% of soluble material were treated with 15
kg of a solvent containing the same solute at 2% concentration in a vessel
under constant agitation. After a long time, the solution and the solid were
separated by pressing. The solid analyzed 0.8 kg of solvent per kg of inert
solid. The extract quantity obtained in kg was therefore
A. 14
C. 28
B. 22
D. 19
14
It is desired to produce an overhead product containing 80 mol% benzene
from a feed mixture of 68 mol% benzene and 32 mol% toluene. If the mixture
is subjected to equilibrium distillation at 1 atm, what is the fraction of
the liquid that is vaporized?
A. 1/3
C. 1/2
B. 1/4
D. 2/3
1/3
A vessel contains a liquid mixture of 50% benzene and 50% toluene by
weight at 1000C. Calculate the average molecular weight of the vapor in
contact with the solution.
A. 85 g/mol
C. 84 g/mol
B. 82 g/mol
D. 86 g/mol
82 g/mol
A 537 kg solution of 50% wt octane and 50% wt heptane is batch-distilled
until only 4.74 lbmols remain in the still. Assuming α=2.0, calculate the
total moles of distillate
A. 6.36 lbmol
C. 8.34 lbmol
B. 5.09 lbmol
D. 7.75 lbmol
. 6.36 lbmol
A 537 kg solution of 50% wt octane and 50% wt heptane is batch-distilled
until only 4.74 lbmols remain in the still. Assuming α=2.0, calculate the percentage by mol of heptane in the distillate
A. 40%
C. 30%
B. 50%
D. 60%
60%
A 537 kg solution of 50% wt octane and 50% wt heptane is batch-distilled
until only 4.74 lbmols remain in the still. Assuming α=2.0, calculate the octane concentration of the residue by weight
A. 40%
C. 30%
B. 50%
D. 60%
60%
The vapor pressures of n-heptane and toluene at 373 K are 106 and
73.7kN/m2 respectively. What is the mole fraction of n-heptane in the vapor
phase at 373 K if the total pressure is 101.3kN/m2?
A. 0.856
C. 0.894
B. 0.942
D. 0.969
0.894
It is desired to reduce the concentration of pyridine in 500 kg of
aqueous solution from 20 weight percent to 5 wt percent in a single batch
extraction using chlorobenzene as solvent. Equilibrium compositions (end
points of the tie line) in terms of weight percent of pyridine-waterchlorobenzene are (5, 95, 0) and (11, 0, 89). The amount of pure solvent
required in kg for the operation is
A. 607
C. 639
B. 931
D. 1501
639
One hundred kg of a solid containing 40% solute A and 60% inert B is treated
with solvent C in a single stage single contact extraction. The extracted
solids are then screw pressed. The pressed solids contain 1.2 kg solution
per kg of inert. Entrainment of solids in the extract may be neglected.
The mass fraction of the solute in the extract if 90% of the solute in
the feed is to be recovered in a single stage contact is
A. 0.03
C. 0.07
B. 0.06
D. 0.05
0.06
One hundred kg of a solid containing 40% solute A and 60% inert B is treated
with solvent C in a single stage single contact extraction. The extracted
solids are then screw pressed. The pressed solids contain 1.2 kg solution
per kg of inert. Entrainment of solids in the extract may be neglected.
The percent recovery of the solute if the extraction is carried out in
two crosscurrent stages if 50% of the solvent amount in problem no. 12 is
used in each stage is
A. 95%
C. 97%
B. 90%
D. 94%
97%
Cod liver oil is obtained from crushed livers by extraction with an organic
solvent. A sample that contains 0.335 kg of oil per each kg of exhausted
liver is fed into a multistage extractor that operates under countercurrent,
where pure organic solvent is employed. It is desired to recover 90% of the
oil in the final overflow, with a composition 60% in weight of oil. If
retention of the solution is 2 kg per each 3.2 kg of insoluble solids,
calculate the amount of solvent required and the number of ideal stages
required to carry out the desired extraction. Calculations are made assuming
that 100 kg of food is introduced into the extractor.
Amount of solvent required
A. 40 kg
C. 50 kg
B. 60 kg
D. 70 kg
60 kg
Cod liver oil is obtained from crushed livers by extraction with an organic
solvent. A sample that contains 0.335 kg of oil per each kg of exhausted
liver is fed into a multistage extractor that operates under countercurrent,
where pure organic solvent is employed. It is desired to recover 90% of the
oil in the final overflow, with a composition 60% in weight of oil. If
retention of the solution is 2 kg per each 3.2 kg of insoluble solids,
calculate the amount of solvent required and the number of ideal stages
required to carry out the desired extraction. Calculations are made assuming
that 100 kg of food is introduced into the extractor.
15. Number of ideal stages
A. 6
C. 5
B. 4
D. 3
6
A countercurrent extraction battery is used to extract NaOH from
theoretical feed of NaOH and CaCO3 produced by the causticization of lime,
but with 4 lb H2O per lb CaCO3. The final extract solution is to contain 10%
NaOH on recovery of 98% of the NaOH. How many theoretical stages will be
required? The underflow may be assumed constant at 2 lb solution per lb
CaCO3.
A. 2
C. 4
B. 3
D. 5
4
If the operation of the extraction units could be improved so that the
underflow contained only 1 lb solution per lb CaCO3, how many stages would
be required?
A. 2
C. 4
B. 3
D. 5
3
A multiple contact extraction is to treat 1.25 tons per hour of dry black
ash containing 40% Na2CO3 and 60% insoluble matter with 30 gpm of water. If
5% of the Na2CO3 remains unextracted, calculate the number of stages. The
mass ratio of insoluble matter to solvent in the underflow from the stage is
1:2.
A. 2
C. 3
B. 1
D. 4
2
Two ideal cross-current stages operate to extract P from a feed
containing P and Q. The mass flowrates of P and Q fed to stage 1 are 1000
kg/h and 10000 kg/h, respectively. Pure solvent (S) is injected at mass
flowrates of 5000 kg/h and 15000 kg/h to stages 1 and 2, respectively. The
equilibrium relation is given by Y* = 1.5X, where Y is the mass of P per
unit mass of S in the extract, which is in equilibrium with the raffinate.
The mass flowrate of P (in kg/hr) in the raffinate from stage 2 is _____
A. 188 kg/hr
C. 195 kg/hr
B. 176 kg/hr
D. 150 kg/hr
176 kg/hr
.Streptomycin is used as an antibiotic to fight bacterial diseases, and is
produced by the fermentation of a bacterium in a biological reactor with a
nutrient of glucose and amino acids. After the fermentation process,
Streptomycin is recovered by contacting the fermentation broth with an
organic solvent in an extraction process. The extraction process is able to
recover the Streptomycin because Streptomycin has a greater affinity for
dissolving in the organic solution than in the aqueous solution.
Determine the mass fraction of Streptomycin in the exit organic solvent
assuming that no water exits with the solvent exits with the aqueous
solution. Assume that the density of the aqueous solution is 1 g/ml and
the density of the organic solvent is 0.6 g/ml.
A. 0.25
C. 0.34
B. 0.19
D. 0.48
0.25
Which of the following operations does not involve leaching?
a. Dissolving gold from ores.
b. Dissolving pharmaceutical products from bark or roots.
c. Dissolving sugar from the cells of the beet.
d. Removing nicotine from its water solution by kerosene.
Removing nicotine from its water solution by kerosene.
Tea percolation employs
a. solvent extraction
c. absorption
b. leaching
d. adsorption
leaching
Neem oil is a traditional plant product which possesses
spermicidal properties. A group of students working on their
investigatory project wanted to test how effective the said oil was
as contraceptive by using it as a component for contraceptives.
The students were able to gather 5 kg of Neem Tree Seeds that
contains 30% of soluble oil and 70% inert solids and they decided
to use 5 kg of pure hexane to extract the oil. What percentage of
oil will they be able to recover given that the ratio of the liquid to
solid components in the underflow is 0.5? Assume ideal
leaching.
a. 88%
c. 73%
b. 93%
d. 65%
c. 73%
Which of the following is the most commonly used leaching
solvent in vegetable oil industry?
a. phenol
c. furfural
b. hexane
d. liquid SO2
hexane
Leaching of sugar from sugar beets is done using
a. hot water
c. dilute H2SO4
b. hexane
d. lime water
hot water
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. 0.60
c. 0.47
b. 0.36
d. 0.27
0.36
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: inerts = 70%, soluble salts = 25%,
moisture = 5%, all percentage by weight. The underflow from
each stage contains 0.3 kg of solution per kg of inerts. The plant
leaches 50 MT of rock salt per day using 50 MT of water.
The quantity of soluble salts recovered in MT/day is
a. 12.1
c. 13.1
b. 14
d. 11.2
12.1
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: inerts = 70%, soluble salts = 25%,
moisture = 5%, all percentage by weight. The underflow from
each stage contains 0.3 kg of solution per kg of inerts. The plant
leaches 50 MT of rock salt per day using 50 MT of water.
The composition of salt in weight percent in the final underflow is
a. 0.88%
c. 0.98%
b. 0.78%
d. 0.68%
a. 0.88%
Rate of leaching increases with increasing
a. temperature
c. viscosity of solvent
b. pressure
d. size of the solid
temperature
In a counter-current extractor, as the axial mixing increases, the
extraction efficiency
a. increases
b. decreases
c. remains unchanged
d. depends on the pressure of the system
decreases
0.4 kg/s of dry sea-shore sand, containing 1 per cent by mass of
salt, is to be washed with 0.4 kg/s of fresh water running counter
currently to the sand through two classifiers in series. It may be
assumed that perfect mixing of the sand and water occurs in each
classifier and that the sand discharged from each classifier
contains one part of water for every two of sand by mass. If the washed sand is dried in a kiln dryer, what percentage of salt
will it retain?
a. 0.47%
c. 0.25%
b. 0.18%
d. 0.33%
0.25%
0.4 kg/s of dry sea-shore sand, containing 1 per cent by mass of
salt, is to be washed with 0.4 kg/s of fresh water running counter
currently to the sand through two classifiers in series. It may be
assumed that perfect mixing of the sand and water occurs in each
classifier and that the sand discharged from each classifier
contains one part of water for every two of sand by mass
What wash rate would be required in a single classifier in order to
wash the sand to the same extent?
a. 0.5 kg/s
c. 0.4 kg/s
b. 0.8 kg/s
d. 0.9 kg/s
b. 0.8 kg/s
When the solvent dissolves very little of solute, then
a. solvent of low latent heat of vaporization should be used.
b. solvent of low freezing point should be used.
c. large quantity of solvent is required to extract the solute.
d. very small quantity of solvent is required.
large quantity of solvent is required to extract the solute.
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 is removed in the underflow in
association with every 2 kg of insoluble matter, how many ideal
stages are required?
a. 5
c. 7
b. 3
d. 2
5
Ground roasted coffee contains 8% soluble solids, 2% water, and
90% inert insoluble solids. In order to obtain an extract with high
soluble solids content without having to concentrate it for spray
drying, a countercurrent extraction process is to be used to
prepare the extract. It is desired that the final extract contains 0.15
kg soluble/ kg water and that the soluble of the spent coffee
grounds not to exceed 0.008 kg/kg dry inert solids. The coffee
grounds carry 1 kg water/ kg of soluble free inert solids and this
quantity is constant with the solute concentration in the extract.
Determine the number of extraction stages needed for this
process.
a. 3
c. 5
b. 4
d. 6
6
Leaching of uranium ore and gold ore is done in
a. centrifugal extractor c. Pachuka tanks
b. Bollman extractor
d. none of these
Pachuka tanks
Tung meal containing 55% oil is to be extracted at a rate of 4000
kg/hr using n-hexane containing 5% wt oil as solvent. A counter
current multiple stage extraction system is to be used. The meal
retains 2 kg solvent per kg of oil free meal while the residual
charge contains 0.11 kg oil per kg oil free meal while the product
is composed of 15 weight percent of oil. The theoretical number
of stages is
a. 4
c. 3
b. 5
d. 6
4
Bollman extractor
a. is a static bed leaching equipment.
b. is used for extraction of oil from oil seed.
c. is a centrifugal extractor.
d. employs only counter-current extraction.
is used for extraction of oil from oil seed.
One thousand pounds of roasted copper ore containing 10
percent CuSO4, 85 percent insoluble gangue and 5 percent
moisture is to be extracted by washing it three times with 2000-lb
batches of fresh water. It has been found that the solids retain 0.8
lb of solution per pound of gangue.
What is the percent CuSO4 of the final underflow sludge after
three washings?
a. 0.13%
c. 3.12%
b. 6.54%
d. 8.90%
0.13%
One thousand pounds of roasted copper ore containing 10
percent CuSO4, 85 percent insoluble gangue and 5 percent
moisture is to be extracted by washing it three times with 2000-lb
batches of fresh water. It has been found that the solids retain 0.8
lb of solution per pound of gangue.
What is the percent recovery?
a. 75.5%
c. 85.1%
b. 90.8%
d. 97.9%
97.9%
The unit operation by where two immiscible or partly miscible
liquids are brought in contact with each other so that the soluble
substance(s) in one liquid passes into other liquid by diffusion.
Liquid-Liquid Extraction
A unit operation in which a soluble component is removed from
an inert solid by a solvent which preferentially dissolves the
soluble matter is known as
Leaching
Acetic acid will be most economically separated from a dilute
solution of acetic acid in water by
a. solvent extraction
c. continuous distillation
b. evaporation
d. absorption
solvent extraction
Separation of two or more components of a liquid solution cannot
be achieved by
a. liquid extraction
c. fractional crystallization
b. absorption
d. evaporation
absorption
Solvent extraction is the terminology applied to the liquid-liquid
extraction, which is preferred for the separation of the
components of liquids, when
a. extracting solvent is cheaply and abundantly available.
b. one of the liquid components is heat sensitive.
c. viscosity of liquid components is very high.
d. one of the liquid components has very high affinity towards the
solvent.
one of the liquid components has very high affinity towards the
solvent.
The distribution coefficient of solute A between solvents B and S
is given by Y = 2.5X where Y = mass of A / mass of S in extract
and X = mass of A / mass of B in raffinate. S and B are mutually
immiscible. A solution containing 25% A in B is to be extracted in
a single stage contact with a recovery of 80%. The amount of S
in kg required per 100 kg of solution is nearly
a. 100
c. 120
b. 150
d. 200
120
The solvent used in liquid extraction should not have high latent
heat of vaporization, because
a. the pressure drop and hence the pumping cost will be very
high.
b. it cannot be recovered by distillation.
c. its recovery cost by distillation may be prohibitively high.
d. it will decompose while recovering by distillation.
its recovery cost by distillation may be prohibitively high.
Compound A is extracted from a solution of A + B into a pure
solvent S. A co-current unit is used for the liquid-liquid extraction.
The inlet rate of the solution containing A is 200 moles of B/hr-m2
and the solvent flow, rate is 400 moles of S/m2-hr. The equilibrium
data is represented by Y = 2x, where Y is in moles of a A/moles
of B and X is in moles A/moles of S. The maximum percentage
extraction achieved in the unit is
a. 25%
c. 50%
b. 70%
d. 90%
50%
Which of the following equipment is not used in liquid-liquid
extraction?
a. Pachuka tank
c. Agitated vessels
b. Packed towers
d. Centrifugal extractors
Pachuka tank
A liquid mixture of acetaldehyde and toluene contains 8 lb of
acetaldehyde and 90 lb of toluene. Part of the acetaldehyde in
this solution is to be extracted using pure water as the extracting
agent. The extraction is to be performed in two stages, using 25
lb of fresh water for each stage. The raffinate layer from the first
stage is treated by fresh water in the second stage. The extraction
takes place at 170C and the equilibrium equation Y=2.2X may be
employed. Assuming toluene and water is immiscible, what would
be the weight percent of acetaldehyde in a mixture of the extracts
from both stage if each of the extraction were theoretically
perfect?
a. 8.96%
c. 9.33%
b. 7.10%
d. 5.52%
8.96%
Which of the following is an undesirable property for an absorbing
solvent?
a. Low vapor pressure
c. Low viscosity
b. Low freezing point
d. None of these
None of these
The solubility of iodine per unit volume is 200 times greater in
ether than in water at a particular temperature. If an aqueous
solution of iodine, 30 ml in volume and containing 2 mg of iodine
is shaken with 30 ml of ether and the ether is allowed to separate,
what quantity of iodine remains in the water layer?
a. 9.95x10-3 mg
c. 8.86 x10-3 mg
b. 6.05x10-3 mg
d. 5.40 x10-3 mg
9.95x10-3 mg
What quantity of iodine remains in the water layer if only 3 ml of
ether is used?
a. 0.086 mg
c. 0.095 mg
b. 0.072 mg
d. 0.063 mg
0.095 mg
How much iodine is left in the water layer if the extraction in (31)
is followed by a second extraction, again using 3 ml of ether?
a. 4.53x10-3 mg
c. 2.09 x10-3 mg
b. 1.37x10-3 mg
d. 2.88 x10-3 mg
a. 4.53x10-3 mg
Which method is more efficient, a single large washing or
repeated small washing?
a. single large washing
b. repeated small washing
c. either single large or repeated small washing
d. none of these
repeated small washing
A solution of solute (A) in diluent (B) is mixed with solvent (S).
The component (B) is slightly soluble in (S). The resulting extract
will be
a. rich in S, poor in B, poor in A
b. poor in S, rich in B, poor in A
c. rich in S, rich in B, rich in A
d. rich in S, poor in B, rich in A
rich in S, poor in B, rich in A
The apex of an equilateral-triangular coordinate (in ternary liquid
system) represents a/an
a. pure component
c. binary mixture
b. ternary mixture
d. insoluble binary system
pure component
Sides of equilateral-triangular co-ordinates (on which ternary
liquid system is plotted) represent
a. a pure component.
b. a binary mixture.
c. a ternary mixture.
d. partially miscible ternary system
a binary mixture.
In triangular coordinates, the ternary composition point falls
__________ of the triangle.
a. in the corners
c. inside
b. on the sides
d. none of these
inside
A solution of 5% acetaldehyde in toluene is to be extracted with
water in a five-stage concurrent unit. If 25 kg water per 100 kg of
feed is used, calculate the mass of acetaldehyde extracted if the equilibrium relation is
given by: kg acetaldehyde per kg water = 2.20 (kg acetaldehyde
per kg toluene).
a. 4.49 kg / 100 kg feed c. 3.36 kg / 100 kg feed
b. 1.11 kg / 100 kg feed d. 2.98 kg / 100 kg feed
4.49 kg / 100 kg feed
A solution of 5% acetaldehyde in toluene is to be extracted with
water in a five-stage concurrent unit. If 25 kg water per 100 kg of
feed is used, calculate the final concentration in % weight
a. 0.89%
c. 0.54%
b. 0.67%
d. 0.33%
0.54%
The commonly used solvent in supercritical extraction is
a. methyl ethyl ketone c. water
b. carbon tetrachloride d. carbon dioxide
d. carbon dioxide
To plan a liquid–liquid extraction we need to know the solute’s
distribution ratio between the two phases. One approach is to
carry out the extraction on a solution containing a known amount
of solute. After extracting the solution, we isolate the organic
phase and allow it to evaporate, leaving behind the solute. In one
such experiment, 1.235 g of a solute with a molar mass of 117.3
g/mol is dissolved in 10.00 mL of water. After extracting with 5.00
mL of toluene, 0.889 g of the solute is recovered in the organic
phase. How many extractions will we need to recover 99.9% of
the solute?
a. 5
c. 8
b. 6
d. 4
6
By extraction with amyl acetate, Penicillin F is recovered from an
aqueous fermentation broth using 6 volumes of solvent per 100
volumes of the aqueous phase. At pH = 3.2, the distribution
coefficient KD is 80.
What fraction of the penicillin would be recovered in a single ideal
stage?
a. 77%
c. 83%
b. 65%
d. 92%
83%
By extraction with amyl acetate, Penicillin F is recovered from an
aqueous fermentation broth using 6 volumes of solvent per 100
volumes of the aqueous phase. At pH = 3.2, the distribution
coefficient KD is 80.What would be the recovery with two-stage extraction using fresh
solvent in both stages?
a. 88%
c. 75%
b. 97%
d. 69%
97%
Which of the following equipment is not used for liquid
dispersion?
a. Wetted wall towers c. Venturi scrubbers
b. Packed tower
d. Agitated vessels
Venturi scrubbers
In a counter-current liquid extractor
a. both liquids flow at fixed rate.
b. both liquids can have any desired flow rate.
c. only one of the liquids may be pumped at any desired rate.
d. liquid’s flow rate depends upon the temperature and pressure.
only one of the liquids may be pumped at any desired rate.
The equipment used in the extraction of highly corrosive
radioactive liquids is
a. pulse column
c. spray column
b. mixer settler
d. baffle tower
pulse column
Radioactive nuclear waste is treated in
a. mixer-settler extractor
b. rotating-disc contactor
c. pulsed column extractor
d. Bollman extractor
pulsed column extractor
Benzoic acid is 9 times more soluble in chloroform than in water.
The percent benzoic acid that will remain from a water solution of
benzoic acid if
Equal quantity of chloroform and water is used is
a. 10%
c. 15%
b. 20%
d. 30%
10%
Benzoic acid is 9 times more soluble in chloroform than in water.
The percent benzoic acid that will remain from a water solution of
benzoic acid If Twice as much as chloroform as water is used
a. 2.6%
c. 3.5%
b. 5.3%
d. 6.0%
5.3%
Benzoic acid is 9 times more soluble in chloroform than in water.
The percent benzoic acid that will remain from a water solution of
benzoic acid if If extraction Equal quantity of chloroform and water is used were followed by an extraction as
Twice as much as chloroform as water is used
is
a. 0.53%
c. 0.63%
b. 0.35%
d. 0.73%
0.53%
Antibiotics are best handled in a
a. Podbielniak extractor c. rotating disc contactor
b. sieve tray contractor d. pulsed column extractor
Podbielniak extractor
extractor uses centrifugal force for separating the
two phases.
a. Treybal
c. Schiebel
b. Podbielniak
d. none of these
Podbielniak
Desulfurization of petrol is done in a
a. Bollman extractor
b. rotating disc extractor
c. packed extraction column
d. plate type extraction column
rotating disc extractor
Which of the following is the most suitable for extraction in a
system having very low-density difference?
a. Mixer-settler extractor
b. Centrifugal extractor
c. Pulsed extractor
d. Packed extraction tower
Centrifugal extractor
Which of the following solutions will follow Raoult’s law most
closely?
a. A solution of benzene, toluene and o-xylene
b. 35% solution of camphor in water
c. 35% solution of NH3 in water
d. A solution of polar organic compounds (not of homologs of a
series).
A solution of benzene, toluene and o-xylene
Calculate the equilibrium compositions of the liquid and the vapor
phases for the mixture of methyl alcohol in water at a temperature
of 500C and under a pressure of 40 kPa. Assume that both the
liquid and the vapor behave ideally. At 500C, the vapor pressure
of methyl alcohol is 53.32 kPa and that of water is 12.33 kPa.
a. 67.5% methyl alcohol in liquid and 89.98% methyl alcohol in
vapor
b. 50.2% methyl alcohol in liquid and 77.60% methyl alcohol in
vapor
c. 61.1% methyl alcohol in liquid and 62.12% methyl alcohol in
vapor
d. 54.6% methyl alcohol in liquid and 94.33% methyl alcohol in
vapor
67.5% methyl alcohol in liquid and 89.98% methyl alcohol in
vapor
Determine the composition of the equilibrium vapor over a liquid
mixture consisting of 10 mol % water, 50 mol % acetic acid and
40 mol % acetone at 800C, assuming that the component obey
Raoult`s law. The vapor pressures of components at 800C are:
water – 47.33 kPa, acetic acid – 27.32 kPa and acetone – 219.77
kPa.
a. 2.55% water, 10.35% acetic acid and 87.10% acetone
b. 4.45% water, 12.85% acetic acid and 82.70% acetone
c. 3.50% water, 15.00% acetic acid and 81.50% acetone
d. 5.60% water, 11.75% acetic acid and 82.65% acetone
b. 4.45% water, 12.85% acetic acid and 82.70% acetone
A binary mixture of two moles benzene and 8 moles of toluene
will boil at
a. 110 0C
c. 110 0F
b. 105 0C
d. 102 0C
102 0C
Boiling point diagram is
a. not affected by pressure.
b. affected by pressure.
c. a plot of temperature vs. liquid composition.
d. a plot of temperature vs. vapor composition.
affected by pressure
A 50 % by weight benzene – toluene mixture is fed to a column
at 180 0F and 1 atm. The condition of the feed is called
a. saturated liquid
c. saturated vapor
b. sub cooled liquid
d. mixture of liquid and vapor
sub cooled liquid
The percentage change in the boiling point of a 20 mole benzene
– toluene solution when the pressure is increased from 1 atm to
2 atm is
a. 10.5 % increase
c. 25.5 % decrease
b. 25.5 % increase
d. 10.5% decrease
25.5 % decrease
The ease of difficulty of separating components by distillation is
determined by the
a. relative volatility
c. mole fraction
b. viscosity
d. weight fraction of the components
relative volatility
When the liquid phase and vapor phase of a binary system obeys
Raoult’s and Dalton’s law respectively, the relative volatility is the
ratio of
a. vapor pressure of component A to that of component B.
b. vapor pressure of component A to the total pressure.
c. vapor pressure of component A to the partial pressure of A.
d. partial pressure of component A to the total pressure.
vapor pressure of component A to that of component B.
Relative volatility varies with the concentration of component for
an ideal solution. The relative volatility of a binary mixture may be
defined as the ratio of vapor pressure of component ‘A’ to that of
component ‘B’, when
a. only vapor phase follows Raoult’s law.
b. only liquid phase obeys Dalton’s law.
c. liquid phase obeys Dalton’s law and vapor phase obeys
Raoult’s law.
d. Vapor phase obeys Dalton’s law and liquid phase obeys
Raoult’s law.
Vapor phase obeys Dalton’s law and liquid phase obeys
Raoult’s law.
The-relative volatility for separation of a non-ideal binary mixture
by distillation should be
a. 0
c. 1
b. > 1
d. < 1
b. > 1
A liquid mixture of ethyl alcohol and water is in equilibrium with a
vapor containing ethyl alcohol and water at a total pressure of 760
mmHg. A sample of the vapor indicates that it contains 3.3 mol of
ethyl alcohol for every 1.7 mol of water. If the liquid has a mol
fraction of 0.52 ethyl, what is the relative volatility for the mixture?
a.1.59
c. 1.69
b.1.79
d. 1.89
b.1.79
The physical separation of components in a miscible mixture by
simultaneous evaporation and condensation is
a. absorption
c. extraction
b. drying
d. distillation
distillation
In a batch distillation, the boiling point of the distillate product
compared to the residue is
a. the same
c. lower
b. higher
d. half
lower
In batch distillation with constant reflux, overhead product
composition __________ with time.
a. increases
b. decreases
c. does not vary
d. may increase on decrease, depends on the system
decreases
Increasing the operating pressure of a distilling column
a. does not make a difference in components separation
b. makes separation difficult
c. sharpens separation
d. requires less heat in the feed heater
makes separation difficult
Determine the relative volatility of n-butane/n-pentane mixture at
300C and 1 atm abs
a. 2.55
c. 3.46
b. 3.04
d. 4.28
3.46
One hundred mols of 15% by mole n-butane/n-pentane mixture
is distilled until the residual liquid contains 45.5 mols. Using the
value of the relative volatility obtained in problem no.71, find the
average concentration of the distillate in mol% butane.
a. 20.6
c. 32.4
b. 24.7
d. 48.5
24.7
In distillation, overhead product contains
a. only one component
b. two components
c. any number of components
d. only saturated liquid
any number of components
Given a relative volatility of 4,600 mols of A and 400 mols of B
are fed in a kettle for distillation. A is more volatile than B.
What is the amount of the overhead product if the remaining
mixture in the kettle is 80%B?
a. 826 mol
c. 725 mol
b. 641 mol
d. 503 mol
725 mol
Given a relative volatility of 4,600 mols of A and 400 mols of B
are fed in a kettle for distillation. A is more volatile than B.
How much A is in the overhead product?
a. 315 mol
c. 495 mol
b. 545 mol
d. 625 mol
545 mol
Given a relative volatility of 4,600 mols of A and 400 mols of B
are fed in a kettle for distillation. A is more volatile than B.
If 50% of the feed evaporated, how much A remains in the kettle?
a. 268
c. 354
b. 406
d. 197
197
Flash distillation is suitable for separating the constituents of a
binary system, which
a. form minimum boiling azeotrope.
b. have very wide boiling points.
c. have very close boiling points.
d. form constant boiling azeotrope.
have very wide boiling points.
A mixture of 60 mole % A and 40 mol % B is subject to flash
distillation at a separator pressure of 1 atm. The relative volatility
of A with respect to B is constant 3. What fraction of the feed must
be vaporized to have the composition of the vapor leaving the
separator be 75 mol % A?
a. 0.3
c. 0.5
b. 0.6
d. 0.4
0.4
One mole feed of a binary mixture of a given composition is flash
vaporized at a fixed P and T. If Raoult’s law is obeyed, then
changing the feed composition would effect
a. the product composition but not the fraction vaporized.
b. the product composition as well as the fraction vaporized.
c. the fraction vaporized but not the product composition.
d. neither the product composition nor the fraction vaporized.
the fraction vaporized but not the product composition.
An equimolal mixture of benzene and toluene is subjected to flash
distillation at a separator pressure of 1 atm. If 40% of the charge
is vaporized, at what temperature will the vapor and liquid
separate?
a. 76.50C
c. 950C
b. 82.100C
d. 1060C
c. 95 0C
When the mixture to be distilled has a very high boiling point and
the product material is heat sensitive, the separation technique to
be used is __________ distillation.
a. continuous
c. steam
b. azeotropic
d. none of these
steam
Steam distillation is used to
a. reduce the number of plates.
b. avoid thermal decomposition of a component.
c. increase the efficiency of separation.
d. increase the total pressure of distillation
avoid thermal decomposition of a component
Nitrobenzene is to be open-steam distilled at 125.80C at a
vacuum of 26 “ Hg. How many pounds of steam will be
theoretically required to collect 2000 pounds of pure
nitrobenzene?
a. 93
c. 193
b. 114
d. 232
193
In steam distillation, the
a. temperature is 100°C.
b. temperature is more than 100° C.
c. product must be immiscible with water.
d. temperature is higher than the boiling point of either
component.
product must be immiscible with water.
Glycerin is steam distilled at 1820C and under a 26 in Hg vacuum.
A test shows that one lb of steam is consumed per lb of glycerine
distilled. What percent excess steam is actually used than
theoretical? Vapor pressure of glycerine at 1820C is 21 mmHg.
a. 37%
c. 16%
b. 21%
d. 54%
37%
It is planned to feed continuously 100 mol per hour of a solution
containing 80 mol of A and 20 mol of B to an externally fired
kettle by which there is good agitation due to boiling. The residue
and vapor will be withdrawn continuously, the vapor condensed,
cooled and sent to storage. There is no return of residue or
condensate to kettle, hence, this will be continuous simple
distillation. It is planned to regulate the heat supply that D grams
of distillate per hour will contain 72 mol of the more volatile
component A which is five times more volatile than B.
86. Calculate the mols of distillate per hundred moles of feed
a. 85
c. 79
b. 62
d. 90
85
It is planned to feed continuously 100 mol per hour of a solution
containing 80 mol of A and 20 mol of B to an externally fired
kettle by which there is good agitation due to boiling. The residue
and vapor will be withdrawn continuously, the vapor condensed,
cooled and sent to storage. There is no return of residue or
condensate to kettle, hence, this will be continuous simple
distillation. It is planned to regulate the heat supply that D grams
of distillate per hour will contain 72 mol of the more volatile
component A which is five times more volatile than B. What is the mole fraction of A in the distillate?
a. 0.69
c. 0.91
b. 0.78
d. 0.85
0.85
It is planned to feed continuously 100 mol per hour of a solution
containing 80 mol of A and 20 mol of B to an externally fired
kettle by which there is good agitation due to boiling. The residue
and vapor will be withdrawn continuously, the vapor condensed,
cooled and sent to storage. There is no return of residue or
condensate to kettle, hence, this will be continuous simple
distillation. It is planned to regulate the heat supply that D grams
of distillate per hour will contain 72 mol of the more volatile
component A which is five times more volatile than B. What is the mole fraction of A in the residue?
a. 0.53
c. 0.26
b. 0.37
d. 0.42
0.53
In a distilling column, the highest pressure will be at
a. the top
b. the bottom
c. the feed plate
d. between the feed plate and the top
the bottom
In distillation where q is defined as the moles of liquid flow in the
stripping section per mole of feed introduced, for saturated liquid
feed
a. q > 1
c. q < 1
b. q = 1
d. q = 0
q = 1
When the feed to a distillation column is a saturated liquid, slope
of the feed line is
a. zero
c. unity
b. infinity
d. none of these
infinity
In a binary distillation column, if the feed contains 40 mole %
vapor, the q line will have a slope of
a. 1.5
c. -0.6
b. -1.5
d. 0.6
-1.5
A benzene-toluene feed with (40 mol% benzene and 60 mol%
toluene) to a distillation column is at a temperature of 200C. The
molar heat capacity of the feed is 159.2 kJ/kmol-K. Molar latent
heats of vaporization of benzene and toluene are 30 813 and 33
325 kJ/kmol, respectively. The bubble point of the mixture is 95
0C. The slope of the q line is closest to
a. 0
c. 3.7
b. 1
d. -3.7
3.7
At minimum reflux ratio for a given separation
a. number of plates is zero.
b. number of plates is infinity.
c. minimum number of the theoretical plates is required.
d. separation is most efficient.
number of plates is infinity
One hundred kgmol/hr of 40 mol% benzene-toluene mixture is
fractionated in a plate column at 1 atm. The overhead product
must contain 95 mol% benzene and the bottoms must contain 95
mol% toluene. The feed is saturated liquid. If the reflux ratio is to
be twice the minimum, determine the kgmol per hour of the
overhead vapor?
a. 38
c. 61
b. 43
d. 156
156
A binary mixture with components A and B is to be separated in
a distillation column to obtain 95 mol% A as the top product. The
binary mixture has a constant relative volatility 2. The
column feed is a saturated liquid containing 50 mol% A. Under
the usual simplifying assumptions such as constant molal
overflow, negligible heat loss, ideal trays, the minimum reflux ratio
for this separation is
a. 1.7
c. 1.4
b. 1.6
d. 1.5
1.7
A binary feed mixture containing equimolar quantities of
components S and T is to be distilled in a fractionating tower at
atmospheric pressure. The distillate contains 96 mol % S. The
q-line (feed line) intersects the equilibrium line at x’ = 0.46 and
y’= 0.66, where x’ and y’ are mole fraction s. Assume that the
McCabe-Thiele method is applicable and the relative volatility is
constant.
The minimum reflux ratio is
a. 1.6
c. 0.66
b. 1.5
d. 0.60
1.5
A binary feed mixture containing equimolar quantities of
components S and T is to be distilled in a fractionating tower at
atmospheric pressure. The distillate contains 96 mol % S. The
q-line (feed line) intersects the equilibrium line at x’ = 0.46 and
y’= 0.66, where x’ and y’ are mole fraction s. Assume that the
McCabe-Thiele method is applicable and the relative volatility is
constant.The feed is
a. at dew point
c. at bubble point
b. superheated vapor d. partially vapor
. partially vapor
Fenske equation determines the
a. maximum number of ideal plates.
b. height of the distillation column.
c. minimum number of theoretical plates.
d. optimum reflux ratio.
minimum number of theoretical plates.
An ideal mixture of A and B is to be distilled continuously. If the
relative volatility is constant at 1.75 and
feed = saturated liquid with 50 mol% A
feed rate = 200 lbmol/hr
distillation composition = 90% A
bottoms composition = 10% A
Find the minimum number of theoretical stages
a. 4.22
c. 7.85
b. 6.85
d. 8.19
7.85
An ideal mixture of A and B is to be distilled continuously. If the
relative volatility is constant at 1.75 and
feed = saturated liquid with 50 mol% A
feed rate = 200 lbmol/hr
distillation composition = 90% A
bottoms composition = 10% A
What is the minimum reflux ratio?
a. 1.93
c. 2.50
b. 2.10
d. 1.55
1.93
As the reflux ratio decreases, the
a. separation becomes more efficient.
b. number of plates increases.
c. column diameter increases.
d. none of these.
number of plates increases.
According to the Fenske equation, what will be the minimum
number of plates required in a distillation column to separate an
equimolar binary mixture of components A and B into an
overhead fraction containing 99 mol% A and a bottom fraction
containing 98 mol% B. Assume that relative volatility (αAB = 2)
does not change appreciably in the column.
a. 5
c. 9
b. 12
d. 28
12
In McCabe-Thiele method of theoretical plate calculation for a
distillation column, the operating lines of stripping and rectifying
sections coincide with the diagonal at __________ reflux.
a. total
c. minimum
b. operating
d. maximum permissible
total
In a distillation column, with increase in the reflux ratio, the heat
removed in the cooler
a. increases.
b. decreases.
c. remains unaffected.
d. and the heat required in reboiler decreases.
increases
In a distillation column, with increase in the reflux ratio, the heat
removed in the cooler
a. increases.
b. decreases.
c. remains unaffected.
d. and the heat required in reboiler decreases.
increases
Fenske’s equation for determining the minimum number of
theoretical stages in distillation column holds good, when the
a. relative volatility is reasonably constant.
b. mixture (to be separated) shows negative deviation from
ideality.
c. mixture (to be separated) shows positive deviation from
ideality.
d. multicomponent distillation is involved.
relative volatility is reasonably constant.
In continuous rectification column is used to separate a binary
mixture of A and B. Distillate in produced at 100 kgmol/hr
containing 98 mole % A. The mole fractions of A in the liquid and
in the vapor, x and y respectively, from two adjacent ideal plates
in the enriching section are as follows
x
y
0.65
0.82
0.56
0.76
If the latent heat of vaporization is the same for all mixtures and
if the feed is a saturated liquid, calculate the rate in the striping
section in kg moles per hour
a. 300
c. 200
b. 400
d. 500
300
In continuous rectification column is used to separate a binary
mixture of A and B. Distillate in produced at 100 kgmol/hr
containing 98 mole % A. The mole fractions of A in the liquid and
in the vapor, x and y respectively, from two adjacent ideal plates
in the enriching section are as follows
x
y
0.65
0.82
0.56
0.76
If the latent heat of vaporization is the same for all mixtures and
if the feed is a saturated liquid, calculate the rate in the striping
section in kg moles per hour
a. 300
c. 200
b. 400
d. 500
300
For the same feed, feed quality and separation (in a distillation
column), with the increase of total pressure, the number of ideal
plates will
a. increase
b. decrease
c. remains same
d. data insufficient, can’t be predicted
increase
Inside the distillation column, the
a. driving force for the vapor flow is the pressure drop.
b. liquids are not always at their bubble points.
c. pressure increases gradually from bottom to the top of the
column.
d. none of these
driving force for the vapor flow is the pressure drop.
Overall efficiency of the distillation column is
a. the ratio of number of ideal plates to actual plates
b. the ratio of number of actual plates to ideal plates
c. same as the Murphree efficiency
d. always more than the point efficiency
the ratio of number of ideal plates to actual plates
Can the efficiency of a plate in the distillation tower be greater
than 100%?
a. Yes
b. Normally not; but is possible if infinite number of plates are put.
c. Never
d. Yes; if the reflux ratio is maximum.
Never
Pick out the correct statement.
a. Ponchon-Savarit method is more accurate than McCabeThiele method to determine the number of theoretical stages
required for the separation of non-ideal binary system by
distillation.
b. A sharp decrease in pressure drop is an indication of flooding
in a distillation column.
c. Solvent used in extractive distillation should be of high volatility.
d. Flash distillation is suitable for separating components which
have very close boiling temperature.
a. Ponchon-Savarit method is more accurate than McCabeThiele method to determine the number of theoretical stages
required for the separation of non-ideal binary system by
distillation.
Ponchan-Savarit method analyses the fractional equipment
based on
a. enthalpy balance only.
b. material balance only.
c. both enthalpy and material balances.
d. the assumption of constant molal overflow
both enthalpy and material balances.
The assumption made in Elis method in distillation is that enthalpy
concentration lines of vapor and liquid are
a. parallel
b. straight
c. both parallel and straight
d. neither parallel nor straight
both parallel and straight
Smoker’s equation for the calculation of number of equilibrium
stages in a continuous binary distillation column is used, when
the
a. relative volatility is close to one (e.g., separation of close boiling
isomers).
b. feed is not at its bubble point.
c. number of equilibrium stages in only stripping section is to be
calculated.
d. number of equilibrium stages required is likely to be very small.
relative volatility is close to one (e.g., separation of close boiling
isomers).
Design calculation for multiple component distillation is done by
a. Ponchon-Savarit method
b. Mccabe-Thiele method
c. enthalpy concentration method
d. tray to tray calculations
tray to tray calculations
Which of the following unit operations makes use of ThieleGeddes equation?
a. Liquid-liquid extraction
b. Solid-liquid extraction
c. Multicomponent absorption with chemical reaction
d. Multicomponent distillation.
Multicomponent distillation.
. In extractive distillation, solvent is
a. added to alter the relative volatility of the mixture.
b. of high volatility.
c. present in overhead stream.
d. of high viscosity to give high tray efficiency.
added to alter the relative volatility of the mixture.
Pick out the system with minimum boiling azeotrope at 1 atm.
a. benzene-toluene
c. hydrochloric acid-water
b. ethyl alcohol-water
d. all of these
ethyl alcohol-water
Pick out the wrong statement.
a. Critical moisture content is not a property of the material itself.
b. A sharp increase in pressure drop gives an indication of the
flooding in a distillation column.
c. Separation of components is not possible in liquid extraction, if
selectivity is unity.
d. Dehydration of ethyl alcohol is most economically done by
molecular distillation at very high vacuum.
Dehydration of ethyl alcohol is most economically done by
molecular distillation at very high vacuum.
Azeotropic distillation is employed to separate
a. constant boiling mixture
b. high boiling mixture
c. mixture with very high relative volatility
d. heat sensitive materials
constant boiling mixture
Positive deviation from Raoult’s law means a mixture whose total
pressure is
a. greater than that computed for ideality.
b. less than that computed for ideality.
c. less than the sum of the vapour pressure of the components.
d. none of these.
greater than that computed for ideality.
The equilibrium liquid composition compared to the vapor
composition in case of azeotropic mixture is
a. more
b. less
c. same
d. either more or less; depends on the system
same
Pick out the wrong statement.
a. The mole fraction of solute is directly proportional to the
molality of a ‘dilute’ solution.
b. For a non-reacting binary mixture of ideal gases, the partial
pressure distribution of both components is nonlinear in the case
of steady state unimolal unidirectional diffusion.
c. Azeotropes obey Raoult’s law at all temperature.
d. The relative volatility of a binary mixture at the azeotropic
composition is 1
Azeotropes obey Raoult’s law at all temperature.
The relative volatility of a binary mixture at the azeotropic
composition is
a. 1
c. > 1
b. 0
d. ∞
1
. A minimum boiling azeotrope is exemplified by
a. toluene-benzene
b. acetone-carbon disulfide
c. water-isobutyl alcohol
d. none of these
acetone-carbon disulfide
At what percentage (by volume) of alcohol composition, it forms
an azeotrope with water?
a. 90
c. 91.5
b. 95
d. 99
95
Which of the following binary systems is an example of a
maximum boiling azeotrope?
a. water-hydrochloric acid
b. acetone-carbon disulfide
c. water-ethyl alcohol
d. n-heptane-n-octane
water-hydrochloric acid
Back-trapping in a distillation column
a. increases tray efficiency.
b. decreases tray efficiency.
c. reduces pressure drop.
d. is desirable, as it provides improved vapor-liquid contact.
decreases tray efficiency.
