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Mass Transfer
Quiz 9
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Q.1
In azeotropic mixture, the equilibrium vapour composition is
More than liquid composition
Less than liquid composition
Same as liquid composition
Independent of pressure
Q.2
When acetone is added in a two layer mixture of methyl isobutyl ketone and water at 30°C, the acetone distributes between the two layers and the composition of the layer follows two solubility curves. For this system,
As the acetone concentration increases, the solubility curves approach each other
Both the phases become identical at a particular common point on both the solubility curves called the plait point
The distribution curve which is a plot between x (acetone concentration in one phase) and y (acetone concentration in other phase) is analogous to x-y curve used in distillation and absorption termina
All of the above
Q.3
Henry's law states that the
Partial pressure of a component over a solution is proportional to its mole fraction in the liquid
Partial pressure of a component over a solution is proportional to the mole fraction in the vapour
Vapour pressure is equal to the product of the mole fraction and total pressure
Partial pressure is equal to the product of the mole fraction and total pressure
Q.4
If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are
Straight
Parallel
Both A & B
Neither A nor B
Q.5
Schimdt number and Lewis number for pure air at atmospheric conditions are respectively
< 1 and ≈ 1
1 and 0
>1 and ≈ 1
0 and ≈ 1
Q.6
Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure.Nitrobenzene will distill off __________ °C.
At < 100
At > 210.6
Between 100 and 210
None of these
Q.7
Rate of leaching increases with increasing
Temperature
Viscosity of solvent
Pressure
Size of the solid
Q.8
Azeotropism for ethyl alcohol-water system disappears by
Increasing temperature
Decreasing pressure
Increasing pressure
No means
Q.9
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
1
0
2
3
Q.10
In case of absorption with exothermic reaction, for fluids having
Pr = Sc; percentage change in heat and mass transfer flux will be the same for a given change in the degree of turbulence
Pr = Sc = 1; total mass, momentum and thermal diffusivity will be the same
Both A & B
Pr = Sc ; there won
Q.11
Pick out the correct statement.
In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity
With increase in temperature, the selectivity of the solvent used in solvent extraction decreases
The selectivity of solvent used in solvent extraction is unity at the plait point
All of the above
Q.12
If a₁ and a₂ are the relative volatilities when the pressure in the distillation column is 1 and 2 atm respectively. Pick out the correct statement.
a₁ = a₂
a₁ = 2a₂
a₁ = 0.5 a₂
None of these
Q.13
Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is
Insoluble in the liquid
Soluble in the liquid
Non-ideal in nature
At a fixed temperature
Q.14
The solvent used in liquid-liquid extraction should have __________ less than one.
Selectivity
Distribution co-efficient
Both A & B
Neither A nor B
Q.15
The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the
Temperature rises
Pressure rises
Temperature falls
Pressure falls
Q.16
For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will
Increase
Decrease
Remain same
Data insufficient, can't be predicted
Q.17
The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will
Increase
Decrease
Remains same
Depend on saturated boiling point; may increase or decrease
Q.18
Antibiotics are best handled in a
Podbielniak extractor
Sieve tray contractor
Rotating disc contactor
Pulsed column extractor
Q.19
Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when
Extracting solvent is cheaply & abundantly available
One of the liquid components is heat sensitive
Viscosity of liquid components is very high
One of the liquid components has very high affinity towards the solvent
Q.20
With increase in the concentration of the adsorbate, the integral heat of adsorption
Increases
Decreases
Remains unchanged
May increase or decrease ; depends on the type of adsorbate
Q.21
Pick out the wrong statement.
Constant pressure distillation can not separate an azeotropic mixture
Relative volatility of a binary mixture changes appreciably with the minor change in temperature
The relative volatility of a binary mixture at azeotropic composition is unity
Flash distillation is practised on wide spread scale in petroleum refinery
Q.22
In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of
1.5
-0.6
-1.5
0.6
Q.23
If the amount of the steam used in steam distillation is increased, the temperature of distillation
Increases
Decreases
Remains unchanged
Depends on relative volatility
Q.24
Heat load in a cooling tower
Means the amount of heat thrown away (KCal/hr.) by the cooling tower
Is equal to the number of kg, of water circulated times the cooling range
Both A & B
Neither A nor B
Q.25
As the reflux ratio decreases, the
Separation becomes more efficient
Number of plates increases
Column diameter increases
None of these
Q.26
For a binary mixture with low relative volatility, continuous rectification to get pure products will require
Low reflux ratio
Less number of trays
Small cross-section column
High reflux ratio
Q.27
Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent?
Cooling and dehumidification
Heating and dehumidification at almost constant wet bulb temperature
Dehumidification with dry bulb temperature remaining constant
None of these
Q.28
For contacting a highly soluble gas with a liquid
Bubble the gas through liquid
Spray the liquid on gas stream
Either A or B would suffice
None of these
Q.29
As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches
That of normal condensation
Integral heat of adsorption
Zero
None of these
Q.30
In case of physical adsorption, the difference between heat of adsorption and heat of normal condensation is
Equal to the heat of formation of surface compound
Equal to the heat of wetting
Zero
Called integral heat of adsorption
Q.31
In a binary system, separation is very efficient, when the relative volatility is
< 1
0.5
1
> 1
Q.32
Steam distillation is used for separation of high boiling
Substances from non-volatile impurities
Volatile impurity from still higher boiling substances
Both A & B
Neither A nor B
Q.33
Fractional solvent extraction
Employs only one solvent
Employs two solvents
Results in low interfacial tension
None of these
Q.34
Diameter to height ratio for a rashig ring is
1
0.5
2
8
Q.35
Large scale usage of flash distillation is practised in
Soap manufacturing
Ammonia synthesis plant
Polymerisation industry
Petroleum refinning
Q.36
Batch tray dryers suffers from the disadvantage of
High maintenance cost
Non-uniform & low production rate
High labour cost & low heat economy
All of the above
Q.37
Flash distillation is
Same as differential distillation
Used for multicomponent systems like crude refining
Same as simple distillation
Most useful for handling binary systems
Q.38
Flooding results in
High tray efficiency
Low tray efficiency
High gas velocity
Good contact between the fluids
Q.39
Ammonia present in the coke oven gas is removed by washing with
Caustic solution
Dilute ammoniacal liquor
Dilute HCl
Ethanolamine
Q.40
The binary diffusivity in gases does not depend upon the
Pressure
Temperature
Nature of the components
None of these
Q.41
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 (α
AB
= 2) does not change appreciably in the coloumn.
5
9
12
28
Q.42
Fenske equation determines the
Maximum number of ideal plates
Height of the distillation column
Minimum number of theoretical plates
Optimum reflux ratio
Q.43
Mass transfer co-efficient is defined as
Flux = Co-efficient/concentration difference
Co-efficient = Flux/concentration difference
Flux=concentration difference/co-effi-cient
None of these
Q.44
Corresponding to Prandtl number in heat transfer, the dimensionless group in mass transfer is the __________ number.
Schmidt
Sherwood
Peclet
Stanton
Q.45
The expression, y(1 - x)/x(1 - y) is for
Absorption factor
Relative volatility
Selectivity
Murphree efficiency
Q.46
The absorption factor is defined as (where, L = liquid flow rate, G = gas flow rate and, m = slope of the equilibrium line)
L/mG
G/mL
ML/G
LG/m
Q.47
__________ is the separation technique used for desalination of sea water.
Thermal diffusion
Reverse osmosis
Adsorption
Absorption
Q.48
__________ extractor uses centrifugal force for separating the two phases.
Treybal
Schiebel
Podbielniak
None of these
Q.49
Schmidt number is given by
Μ/ρD
AB
Re.Pe
Sh x Pe
Re/Pe
Q.50
Which of the following unit operations makes use of Thiele-Geddes equation?
Liquid-liquid extraction
Solid-liquid extraction
Multicomponent absorption with chemical reaction
Multicomponent distillation
0 h : 0 m : 1 s
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