SEPARATION PROCESSES Flashcards by John Clavines Edradan

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.

D. Removing nicotine from its water solution by kerosene

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Tea percolation employs

a. solvent extraction
b. leaching
c. absorption
d. adsorption

B. leaching

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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%
b. 93%
c. 73%
d. 65%

c. 73%

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Which of the following is the most commonly used leaching
solvent in vegetable oil industry?

a. phenol
b. hexane
c. furfural
d. liquid SO2

B. hexane

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Leaching of sugar from sugar beets is done using

a. hot water
b. hexane
c. dilute H2SO4
d. lime water

A. hot water

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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
b. 0.36
c. 0.47
d. 0.27

B. 0.36

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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
b. 14
c. 13.1
d. 11.2
The composition of salt in weight percent in the final underflow is
a. 0.88%
b. 0.78%
c. 0.98%
d. 0.68%

A. 12.1
A. 0.88%

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Rate of leaching increases with increasing

a. temperature
b. pressure
c. viscosity of solvent
d. size of the solid

A. temperature

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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

B. decreases

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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%
b. 0.18%
c. 0.25%
d. 0.33%
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
b. 0.8 kg/s
c. 0.4 kg/s
d. 0.9 kg/s

C. 0.25%
B. 0.8 kg/s

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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.

C. large quantity of solvent is required to extract the solute.

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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
b. 3
c. 7
d. 2

A. 5

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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
b. 4
c. 5
d. 6

D. 6

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Leaching of uranium ore and gold ore is done in

a. centrifugal extractor
b. Bollman extractor
c. Pachuka tanks
d. none of these

C. Pachuka tanks

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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
b. 5
c. 3
d. 6

A. 4

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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.

B. is used for extraction of oil from oil seed.

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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%
b. 6.54%
c. 3.12%
d. 8.90%
What is the percent recovery?
a. 75.5%
b. 90.8%
c. 85.1%
d. 97.9%

A. 0.13%
D. 97.9%

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Acetic acid will be most economically separated from a dilute
solution of acetic acid in water by

a. solvent extraction
b. evaporation
c. continuous distillation
d. absorption

A. solvent extraction

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Separation of two or more components of a liquid solution cannot
be achieved by

a. liquid extraction
b. absorption
c. fractional crystallization
d. evaporation

b. absorption

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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.

d. one of the liquid components has very high affinity towards the
solvent.

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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
b. 150
c. 120
d. 200

C. 120

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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.

c. its recovery cost by distillation may be prohibitively high.

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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%
b. 70%
c. 50%
d. 90%

c. 50 %

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Which of the following equipment is not used in liquid-liquid
extraction?

a. Pachuka tank
b. Packed towers
c. Agitated vessels
d. Centrifugal extractors

a. Pachuka tank

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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% b. 7.10% c. 9.33% d. 5.52%

A. 8.96%

Which of the following is an undesirable property for an absorbing solvent? a. Low vapor pressure b. Low freezing point c. Low viscosity d. None of these

d. 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, 1. What quantity of iodine remains in the water layer? a. 9.95x10-3 mg b. 6.05x10-3 mg c. 8.86 x10-3 mg d. 5.40 x10-3 mg 2. What quantity of iodine remains in the water layer if only 3 ml of ether is used? a. 0.086 mg b. 0.072 mg c. 0.095 mg d. 0.063 mg 3. How much iodine is left in the water layer if the extraction in (1) is followed by a second extraction, again using 3 ml of ether? a. 4.53x10-3 mg b. 1.37x10-3 mg c. 2.09 x10-3 mg d. 2.88 x10-3 mg

1. A. 9.95x10-3 mg 2. C. 0.095 mg 3. 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

b. 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

d. 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 b. ternary mixture c. binary mixture d. insoluble binary system

a. 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.

b. a binary mixture.

In triangular coordinates, the ternary composition point falls __________ of the triangle. a. in the corners b. on the sides c. inside d. none of these

c. inside

For numbers 38 to 39: 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 following: 1. 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 b. 1.11 kg / 100 kg feed c. 3.36 kg / 100 kg feed d. 2.98 kg / 100 kg feed 2. The final concentration in % weight a. 0.89% b. 0.67% c. 0.54% d. 0.33%

1. a. 4.49 kg / 100 kg feed 2. c. 0.54%

The commonly used solvent in supercritical extraction is a. methyl ethyl ketone b. carbon tetrachloride c. water 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 b. 6 c. 8 d. 4

b. 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. 1. What fraction of the penicillin would be recovered in a single ideal stage? a. 77% b. 65% c. 83% d. 92% 2. What would be the recovery with two-stage extraction using fresh solvent in both stages? a. 88% b. 97% c. 75% d. 69%

1. c. 83% 2. b. 97%

Which of the following equipment is not used for liquid dispersion? a. Wetted wall towers b. Packed tower c. Venturi scrubbers d. Agitated vessels

c. 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.

c. 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 b. mixer settler c. spray column d. baffle tower

a. pulse column

Radioactive nuclear waste is treated in a. mixer-settler extractor b. rotating-disc contactor c. pulsed column extractor d. Bollman extractor

c. 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 1. Equal quantity of chloroform and water is used is a. 10% b. 20% c. 15% d. 30% 2. Twice as much as chloroform as water is used a. 2.6% b. 5.3% c. 3.5% d. 6.0% 3. If extraction as in Problem 1 were followed by an extraction as in Problem 2 is a. 0.53% b. 0.35% c. 0.63% d. 0.73%

1. a. 10% 2. c. 5.3% 3. a. 0.53%

Antibiotics are best handled in a a. Podbielniak extractor b. sieve tray contractor c. rotating disc contactor d. pulsed column extractor

a. Podbielniak extractor

__________ extractor uses centrifugal force for separating the two phases. a. Treybal b. Podbielniak c. Schiebel d. none of these

b. Podbielniak

Desulfurization of petrol is done in a a. Bollman extractor b. rotating disc extractor c. packed extraction column d. plate type extraction column

b. 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

b. 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. 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

a. 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 b. 105 0C c. 110 0F d. 102 0C

d. 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.

b. 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 b. sub cooled liquid c. saturated vapor d. mixture of liquid and vapor

b. 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 b. 25.5 % increase c. 25.5 % decrease d. 10.5% decrease

c. 25.5 % decrease

The ease of difficulty of separating components by distillation is determined by the a. relative volatility b. viscosity c. mole fraction d. weight fraction of the components

a. 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.

a. 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.

d. 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 b. > 1 c. 1 d. < 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 b.1.79 c. 1.69 d. 1.89

The physical separation of components in a miscible mixture by simultaneous evaporation and condensation is a. absorption b. drying c. extraction d. distillation

d. distillation

In a batch distillation, the boiling point of the distillate product compared to the residue is a. the same b. higher c. lower d. half

c. 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.

b. 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

b. makes separation difficult

Determine the relative volatility of n-butane/n-pentane mixture at 300C and 1 atm abs a. 2.55 b. 3.04 c. 3.46 d. 4.28

c. 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 b. 24.7 c. 32.4 d. 48.5

b. 24.7

In distillation, overhead product contains a. only one component b. two components c. any number of components d. only saturated liquid

c. 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. 1. What is the amount of the overhead product if the remaining mixture in the kettle is 80%B? a. 826 mol b. 641 mol c. 725 mol d. 503 mol 2. How much A is in the overhead product? a. 315 mol b. 545 mol c. 495 mol d. 625 mol 3. If 50% of the feed evaporated, how much A remains in the kettle? a. 268 b. 406 c. 354 d. 197

1. c. 725 mol 2. b. 545 mol 3. d. 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.

b. 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 b. 0.6 c. 0.5 d. 0.4

d. 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.

c. 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. 76.5 °C b. 82.10 °C c. 95 °C d. 106 °C

c. 95 °C

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 b. azeotropic c. steam d. none of these

c. 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.

b. 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 b. 114 c. 193 d. 232

c. 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.

c. 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% b. 21% c. 16% d. 54%

a. 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. 1. Calculate the mols of distillate per hundred moles of feed a. 85 b. 62 c. 79 d. 90 2. What is the mole fraction of A in the distillate? a. 0.69 b. 0.78 c. 0.91 d. 0.85 3. What is the mole fraction of A in the residue? a. 0.53 b. 0.37 c. 0.26 d. 0.42

1. a. 85 2. d. 85 3. a. 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

b. 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 b. q = 1 c. q < 1 d. q = 0

b. q = 1

When the feed to a distillation column is a saturated liquid, slope of the feed line is a. zero b. infinity c. unity d. none of these

b. infinity

In a binary distillation column, if the feed contains 40 mole % vapor, the q line will have a slope of a. 1.5 b. -1.5 c. -1.5 d. 0.6

c. -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 b. 1 c. 3.7 d. -3.7

c. 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.

b. 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 b. 43 c. 61 d. 156

d. 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 b. 1.6 c. 1.4 d. 1.5

a. 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. 1. The minimum reflux ratio is a. 1.6 b. 1.5 c. 0.66 d. 0.60 2. The feed is a. at dew point b. superheated vapor c. at bubble point d. partially vapor

1. b. 1.5 2. d. 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.

c. 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 1. Find the minimum number of theoretical stages a. 4.22 b. 6.85 c. 7.85 d. 8.19 2. What is the minimum reflux ratio? a. 1.93 b. 2.10 c. 2.50 d. 1.55

1. c. 7.85 2. a. 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.

b. 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 b. 12 c. 9 d. 28

b. 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 b. operating c. minimum d. maximum permissible

a. 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.

a. 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.

a. 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 b. 400 c. 200 d. 500

a. 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

a. increase

109. 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

a. 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

a. 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.

c. Never

Pick out the correct statement. a. Ponchon-Savarit method is more accurate than McCabe- Thiele 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 McCabe- Thiele 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.

c. 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

c. 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.

a. 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

d. tray to tray calculations

Which of the following unit operations makes use of Thiele- Geddes equation? a. Liquid-liquid extraction b. Solid-liquid extraction c. Multicomponent absorption with chemical reaction d. Multicomponent distillation.

d. 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.

a. added to alter the relative volatility of the mixture.

Pick out the system with minimum boiling azeotrope at 1 atm. a. benzene-toluene b. ethyl alcohol-water c. hydrochloric acid-water d. all of these

b. 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.

d. 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

a. 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.

a. 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

c. 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.

c. Azeotropes obey Raoult's law at all temperature.

The relative volatility of a binary mixture at the azeotropic composition is a. 1 b. 0 c. > 1 d. ∞

a. 1

A minimum boiling azeotrope is exemplified by a. toluene-benzene b. acetone-carbon disulfide c. water-isobutyl alcohol d. none of these

b. acetone-carbon disulfide

At what percentage (by volume) of alcohol composition, it forms an azeotrope with water? a. 90 b. 95 c. 91.5 d. 99

b. 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

a. water-hydrochloric acid

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

a. 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.

b. decreases tray efficiency.

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 each of the following arrangements: 1. Single stage contact A. 665 kg B. 565 kg C. 180 kg D. 70 kg 2. Three-stage batch contact, one third of the solvent will be used in each contact A. 60 kg B. 665 kg C. 210 kg D. 180 kg

1. A. 665 kg 2. D. 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 CaCO 3 . Assuming complete mixing and washing, calculate the NaOH content of the washed and dried limestone in ppm. A. 0.77 ppm B. 0.65 ppm C. 0.82 ppm D. 0.97 ppm

C. 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 B. 22 C. 28 D. 19

A. 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 B. 1/4 C. 1/2 D. 2/3

A. 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

B. 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 following: 1. The total moles of distillate A. 6.36 lbmol B. 5.09 lbmol C. 8.34 lbmol D. 7.75 lbmol 2. The percentage by mol of heptane in the distillate A. 40% B. 50% C. 30% D. 60% 3. The octane concentration of the residue by weight A. 40% B. 50% C. 30% D. 60%

1. A. 6.36 lbmol 2. D. 60% 3. D. 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 B. 0.942 C. 0.894 D. 0.969

C. 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 B. 931 C. 639 D. 1501

C. 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. 1.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 B. 0.06 C. 0.07 D. 0.05 2. 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% B. 90% C. 97% D. 94%

1. B. 0.06 2. C. 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. 1. Amount of solvent required A. 40 kg B. 60 kg C. 50 kg D. 70 kg 2. Number of ideal stages A. 6 B. 4 C. 5 D. 3

1. B. 60 kg 2. A. 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 B. 3 C. 4 D. 5

C. 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 B. 3 C. 4 D. 5

B. 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 B. 1 C. 3 D. 4

A. 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 B. 176 kg/hr C. 195 kg/hr D. 150 kg/hr

B. 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 B. 0.19 C. 0.34 D. 0.48

A. 0.25

At a temperature of 366.4 K, the vapor pressures of n-hexane and octane are 1480 and 278 mmHg, respectively. Assume the hexane-octane system obeys Raoult’s law and the total pressure is 1 atm. Calculate the equilibrium vapor composition (in mole fraction) of the more volatile component. A. 0.94 B. 0.54 C. 0.78 D. 0.25

C. 0.78

The ratio of the solubility of stearic acid per unit volume of n-heptane to that in 97.5% acetic acid is 4.95. How many extractions of a 10 ml solution of stearic acid in 97.5% acetic acid with successive 10 ml portions of n-heptane are needed to reduce the residual stearic acid content of the acetic acid layer to less than 0.5 percent of its original value? A. 2 B. 1 C. 3 D. 4

C. 3

Lambanog (coconut vodka) comes from the fermented sap of the coconut tree. This is then distilled to make the drink more potent. It is clear, colorless spirit, with a neutral taste, potent kick, and a finish with a hint of sweetness. A batch differential distillation is made upon a 25 kg mixture of ethanol-water containing 7% weight alcohol. How many kg of distillate must be collected so that it will have an ethanol content of 30% weight? Assume that the relative volatility of the mixture is equal to 12. A. 9 kg B. 8 kg C. 2 kg D. 5 kg

D. 5 kg

The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is A. 150 B. 0.5 C. 50 D. 2

D. 2

Entrainer used in azeotropic distillation should A. have high latent heat of vaporization. B. have high viscosity to provide high tray efficiency. C. form a new azeotrope of low relative volatility with one of the constituents of the mixture. D. form a low boiling azeotrope with one of the constituents of the mixture.

D. form a low boiling azeotrope with one of the constituents of the mixture.

An ideal single stage extraction process is used to treat 100 mol/s of an organic feed solution. The solute concentration in this solution is to be reduced from 0.5 mol% to 0.1 mol%. A pure solvent S is used. To reduce the solvent requirement by half for the same separation A. add one more ideal co-current stage B. use another pure solvent S* whose partition coefficient is twice that of S C. double the residence time of the solvent S in the contactor D. use solvent S containing 0.02 mole fraction of the solute

B. use another pure solvent S* whose partition coefficient is twice that of S

Tray spacing in a distillation column of dia 10-12 ft. used in petroleum refinery may be around __________ inches. A. 5 B. 100 C. 30 D. 60

C. 30

The charge to a simple batch still consists of an equimolar mixture of hexane and heptane. If the relative volatility of hexane to heptane is 2.0 and 50% of hexane has vaporized, what is the mole fraction of heptane in the total distillate? A. 0.15 B. 0.43 C. 0.29 D. 0.37

D. 0.37

C. 13.7

A binary distillation column is operating with a mixed feed containing 20 mol% vapor. If the feed quality is changed to 80 mol% vapor, the change in the slope of the q-line is A. 0.85 B. 1.50 C. 2.25 D. 3.75

D. 3.75

A counter current multiple contact extraction system is to treat 50 tons/hr of wet beets with fresh water as the solvent. The beets have the following analysis: Components Mass fraction water 0.48 pulp 0.40 sugar 0.12 The strong solution leaving the system is to contain 0.15 mass fraction sugar, 97% of the sugar in the sliced beets is to be recovered. Determine the number of extraction cells required, assuming equilibrium between the underflow and overflow in each cell if each ton of dry pulp retains 3 tons of solution. A. 16 B. 17 C. 15 D. 14

A. 16

A counter current multiple contact extraction system is to treat 50 tons/hr of wet beets with fresh water as the solvent. Repeat if each ton of dry pulp retains 3 tons of solvent. A. 14 B. 16 C. 17 D. 15

C. 17

The orebody of the Union Miniere du Haut-Katanga in the Belgian Congo is composed of malachite, CuCO3 Cu(OH)2 and gangue. Copper is extracted by crushing the ore to -20 mesh, agitating with a dilute solution of sulfuric acid, followed by multiple-contact countercurrent washing to wash the gangue free of the copper-bearing solution. The rich solution from the washing system is treated for removal of dissolved iron and aluminum and then sent to the electrolytic cells for precipitation of the copper. The dilute acid solution from the cells is recycled to the agitators for treatment of more raw ore. The counter current washing operation uses Dorr thickeners for the recovery of the rich solution. The slurry from the agitators, with the copper in the solution as copper sulfate, is fed to the thickeners at the rate of 300 tons per hour. According to operating records, the underflow from each thickener retains 1.22 tons of solution per ton of gangue, and the streams have the following compositions in mass percent. Determine the number of equilibrium stages. Feed to Strong Underflow Leaving Thickener, % Solution, % the System, % CuSO4 6.10 6.69 1.0 Gangue 14.92 - 99 Water 78.98 93.91 99 A. 3 B. 5 C. 4 D. 6

C. 4

Which of the following mixtures does not form an azeotrope at atmosheric pressure? A. Water-alcohol B. None of these C. Methyl alcohol-acetone D. Butyl acetate-water

B. None of these

In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the A. temperature and pressure B. nature of the constituents C. concentration D. None of these

D. None of these

An example of elutioh is A. recovery of vegetable oils from seeds. B. separation of uranium oxide from its ore by H2SO4 in a Pachuca tank. C. dissolution of tannin out of tree barks by water. D. separation of sugar from sugar beet by hot water.

B. separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.

Large scale usage of flash distillation is practiced in A. petroleum refining B. soap manufacturing C. polymerization industry D. ammonia synthesis plant

A. petroleum refining

In an operating distillation column, the A. driving force for the liquid flow is its specific weight. B. vapors and liquids are at their dew point and bubble point respectively C. driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column. D. highest temperature is encountered at the top of the column.

C. driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.

In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapor, because A. saturated steam is used for steam distillation. B. total pressure is less. C. mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition. D. temperature is less.

C. mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.

For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be A. 1 B. 3 C. 0 D. 2

A. 1

__________ is used as an 'entrainer' for the separation of acetic acid-water mixture by distillation. A. Hexane B. Furfural C. Benzol D. Butyl acetate

D. Butyl acetate

For water-ethanol system, the minimum reflux ratio A. is computed from the slope of the upper operating line that is tangent to the equilibrium curve. B. cannot be computed. C. is the optimum reflux ratio. D. is computed from the intercept of the operating line.

A. is computed from the slope of the upper operating line that is tangent to the equilibrium curve.

If Rm is the minimum reflux ratio, the optimum reflux ratio may be around __________ Rm. A. 2.5 to 3 B. 3 to 4 C. 1.2 to 1.5 D. 5

C. 1.2 to 1.5

Solvent used in extractive distillation A. does not alter the relative volatility of the original components. B. forms a high boiling azeotrope. C. forms a low boiling azeotrope. D. is of low volatility.