Separation Processes

Question 1

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.

Answer 1

d. Removing nicotine from its water solution by kerosene.

Question 2

Tea percolation employs

Answer 2

leaching

Question 3

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.

Answer 3

73%

Question 4

Which of the following is the most commonly used leaching
solvent in vegetable oil industry?
a. phenol c. furfural
b. hexane d. liquid SO2

Answer 4

b. hexane

Question 5

Leaching of sugar from sugar beets is done using

Answer 5

hot water

Question 6

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?

Answer 6

0.36

Question 7

Rate of leaching increases with increasing

Answer 7

temperature

Question 8

In a counter-current extractor, as the axial mixing increases, the
extraction efficiency

Answer 8

decreases

Question 9

When the solvent dissolves very little of solute, then

Answer 9

large quantity of solvent is required to extract the solute.

Question 10

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?

Answer 10

5 Stages

Question 11

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.

Answer 11

6

Question 12

Leaching of uranium ore and gold ore is done in
a. centrifugal extractor
b. Bollman extractor
c. Pachuka tanks
d. none of these

Answer 12

Pachuka tanks XD

Question 13

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

Answer 13

4

Question 14

Bollman extractor

Answer 14

is used for extraction of oil from oil seed.

Question 15

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

Answer 15

solvent extraction

Question 16

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

Answer 16

absorption

Question 17

Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when

Answer 17

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

Question 18

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

Answer 18

120

Question 19

The solvent used in liquid extraction should not have high latent heat of vaporization, because

Answer 19

its recovery cost by distillation may be prohibitively high.

Question 20

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

Answer 20

50%

Question 21

Which of the following equipment is not used in liquid-liquid
extraction?
a. Pachuka tank
b. Packed towers
c. Agitated vessels
d. Centrifugal extractors

Answer 21

Pachuka tank XD

Question 22

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?

Answer 22

8.96%

Question 23

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

Answer 23

d. None of these

Question 24

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?

Answer 24

9.95x10-3 mg

Question 25

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

Answer 25

rich in S, poor in B, rich in A

Question 26

The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an

Answer 26

pure component

Question 27

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent

Answer 27

a binary mixture.

Question 28

In triangular coordinates, the ternary composition point falls __________ of the triangle.

Answer 28

inside

Question 29

The commonly used solvent in supercritical extraction is

Answer 29

carbon dioxide

Question 30

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?

Answer 30

6

Question 31

Which of the following equipment is not used for liquid dispersion?

Answer 31

Agitated vessels

Question 32

In a counter-current liquid extractor

Answer 32

only one of the liquids may be pumped at any desired rate.

Question 33

The equipment used in the extraction of highly corrosive radioactive liquids is

Answer 33

pulse column

Question 34

Radioactive nuclear waste is treated in

Answer 34

pulsed column extractor

Question 35

Antibiotics are best handled in a

Answer 35

Podbielniak extractor

Question 36

__________ extractor uses centrifugal force for separating the two phases.

Answer 36

Podbielniak

Question 37

Desulfurization of petrol is done in a

Answer 37

rotating disc extractor

Question 38

Which of the following is the most suitable for extraction in a system having very low-density difference?

Answer 38

Centrifugal extractor

Question 39

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).

Answer 39

a. A solution of benzene, toluene and o-xylene

Question 40

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.

Answer 40

67.5% methyl alcohol in liquid and 89.98% methyl alcohol in vapor

Question 41

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.

Answer 41

4.45% water, 12.85% acetic acid and 82.70% acetone

Question 42

A binary mixture of two moles benzene and 8 moles of toluene will boil at

Answer 42

102 0C

Question 43

Boiling point diagram is

Answer 43

affected by pressure.

Question 44

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

Answer 44

sub cooled liquid

Question 45

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

Answer 45

25.5 % increase

Question 46

The ease of difficulty of separating components by distillation is determined by the

Answer 46

relative volatility

Question 47

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

Answer 47

vapor pressure of component A to that of component B.

Question 48

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

Answer 48

Vapor phase obeys Dalton's law and liquid phase obeys Raoult's law.

Question 49

The-relative volatility for separation of a non-ideal binary mixture by distillation should be

Answer 49

> 1

Question 50

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?

Answer 50

1.79

Question 51

The physical separation of components in a miscible mixture by simultaneous evaporation and condensation is

Answer 51

distillation

Question 52

In a batch distillation, the boiling point of the distillate product compared to the residue is

Answer 52

lower

Question 53

In batch distillation with constant reflux, overhead product composition __________ with time.

Answer 53

decreases

Question 54

Increasing the operating pressure of a distilling column

Answer 54

makes separation difficult

Question 55

Determine the relative volatility of n-butane/n-pentane mixture at 300C and 1 atm abs

Answer 55

3.46

Question 56

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.

Answer 56

24.7

Question 57

In distillation, overhead product contains

Answer 57

any number of components

Question 58

Flash distillation is suitable for separating the constituents of a binary system, which

Answer 58

have very wide boiling points.

Question 59

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?

Answer 59

0.4

Question 60

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

Answer 60

the fraction vaporized but not the product composition.

Question 61

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?

Answer 61

95 C

Question 62

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.

Answer 62

steam

Question 63

Steam distillation is used to

Answer 63

avoid thermal decomposition of a component.

Question 64

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?

Answer 64

193

Question 65

In steam distillation, the

Answer 65

product must be immiscible with water.

Question 66

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.

Answer 66

37%

Question 67

In a distilling column, the highest pressure will be at

Answer 67

the bottom

Question 68

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

Answer 68

q = 1

Question 69

When the feed to a distillation column is a saturated liquid, slope of the feed line is

Answer 69

infinity

Question 70

In a binary distillation column, if the feed contains 40 mole % vapor, the q line will have a slope of

Answer 70

-1.5

Question 71

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

Answer 71

3.7

Question 72

At minimum reflux ratio for a given separation

Answer 72

number of plates is infinity.

Question 73

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?

Answer 73

156

Question 74

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 𝛼𝐴𝐵 = 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

Answer 74

1.7

Question 75

Fenske equation determines the

Answer 75

minimum number of theoretical plates.

Question 76

As the reflux ratio decreases, the

Answer 76

number of plates increases.

Question 77

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.

Answer 77

12

Question 78

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.

Answer 78

total

Question 79

In a distillation column, with increase in the reflux ratio, the heat removed in the cooler

Answer 79

increases

Question 80

Fenske's equation for determining the minimum number of theoretical stages in distillation column holds good, when the

Answer 80

relative volatility is reasonably constant.

Question 81

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

Answer 81

300

Question 82

For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will

Answer 82

increases

Question 83

Inside the distillation column, the

Answer 83

driving force for the vapor flow is the pressure drop.

Question 84

Overall efficiency of the distillation column is

Answer 84

the ratio of number of ideal plates to actual plates

Question 85

Can the efficiency of a plate in the distillation tower be greater than 100%?

Answer 85

Never

Question 86

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.

Answer 86

A.

Question 87

Ponchan-Savarit method analyses the fractional equipment based on

Answer 87

both enthalpy and material balances.

Question 88

The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are

Answer 88

both parallel and straight

Question 89

Smoker's equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the

Answer 89

relative volatility is close to one (e.g., separation of close boiling isomers).

Question 90

Design calculation for multiple component distillation is done by

Answer 90

tray to tray calculations

Question 91

Which of the following unit operations makes use of Thiele- Geddes equation?

Answer 91

Multicomponent distillation.

Question 92

In extractive distillation, solvent is

Answer 92

added to alter the relative volatility of the mixture.

Question 93

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

Answer 93

B. ethyl alcohol-water

Question 94

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.

Answer 94

d. Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

Question 95

Azeotropic distillation is employed to separate

Answer 95

constant boiling mixture

Question 96

Positive deviation from Raoult's law means a mixture whose total pressure is

Answer 96

greater than that computed for ideality.

Question 97

The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is

Answer 97

same

Question 98

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.

Answer 98

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

Question 99

The relative volatility of a binary mixture at the azeotropic composition is

Answer 99

1

Question 100

A minimum boiling azeotrope is exemplified by

Answer 100

acetone-carbon disulfide

Question 101

At what percentage (by volume) of alcohol composition, it forms an azeotrope with water?

Answer 101

95

Question 102

Which of the following binary systems is an example of a maximum boiling azeotrope?

Answer 102

water-hydrochloric acid

Question 103

Back-trapping in a distillation column

Answer 103

decreases tray efficiency.