MASS TRANSFER Flashcards
FOR REVIEW HIKHIK
The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives
low pressure drop and high hold up.
high pressure drop and low hold up.
low pressure drop and low hold up.
high pressure drop and high hold up.
low pressure drop and low hold up.
f the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be __________ percent.
100
> 100
< 100
none of these
> 100
Raoult’s law is applicable to the
ideal solutions
real solutions
mixture of water and alcohol
non-ideal gases
ideal solutions
Weeping in a distillation column
increases tray efficiency.
provides large interfacial surface for mass transfer.
results due to very high gas velocity.
results due to very low gas velocity.
results due to very low gas velocity.
In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of
area between operating line and 45° diagonal x-y diagram.
condenser and reboiler surfaces.
tower cross-section.
none of these.
area between operating line and 45° diagonal x-y diagram.
molal diffusivity.
volumetric co-efficient.
mass transfer co-efficient.
none of these.
mass transfer co-efficient.
In McCabe-Thiele method, at infinite reflux ratio —–
the overhead product is minimum.
both the operating lines coincide with diagonal.
both (a) and (b).
neither (a) nor (b).
the overhead product is minimum.
With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency
increases
decreases
remains same
may increase or decrease ; depends on individual design
Answer: Option
increases
Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the
packing may be crushed due to thermal expansion/contraction of the components of the equipment.
pressure drop in the equipment will be very high.
viscosity variation of the fluids may cause channeling/flooding.
none of these.
packing may be crushed due to thermal expansion/contraction of the components of the equipment.
The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is
more
less
same
either more or less; depends on the system
same
Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
wetted wall
bubble cap
perforated tray
packed
wetted wall
Pick out the system with minimum boiling azeotrope at 1 atm.
benzene-toluene
ethyl alcohol-water
hydrochloric acid-water
all (a), (b) and (c)
ethyl alcohol-water
Free flowing granular materials can be best dried in a __________ drier.
rotary
cylinder
drum
freeze
rotary
In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction.
inversely
linearly
exponentially
none of these
linearly
Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.
Sherwood
Schmidt
Peclet
Stanton
Sherwood
Molarity is defined as the number of gm moles of solute per __________ of solution.
liter
kg
gm
c.c
liter
An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)
less number of trays are required.
composition of the residue remains unchanged.
more number of trays are required but the residue composition remains unchanged.
more number of trays are required and the residue composition is more dilute in methanol.
less number of trays are required.
The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.
exponential
parabolic
linear
cubic
exponential
Which of the following binary systems is an example of a maximum boiling azeotrope ?
Water-hydrochloric acid.
Acetone-carbon disulphide.
Water-ethyl alcohol.
n-heptane-n-octane.
Water-hydrochloric acid.
(NRe . NSc) is termed in mass transfer operation as the __________ number.
Stanton
Sherwood
Peclet
none of these
Peclet
he binary diffusivity in gases and liquids vary respectively as
T3/2 and T
T and T3/2
T and T3/2
T3/2 and T
T3/2 and T
Pick out the correct statement.
The slope of the stripping line is always less than unity.
For a given separation in a binary distillation column, with increase in reflux ratio (above the minimum reflux ratio), the fixed cost of the distillation column first increases and then decreases.
In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.
Kremsor-Brown-Souder’s equation is used to calculate the efficiency of a plate tower.
In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.
Pick out the correct statement.
Dialysis process is used for the production of fresh water from brine.
Electrodialysis is used in the manufacture of NaOH.
Electrodialysis is used for the refining/purification of petrol.
both (b) and (c).
Electrodialysis is used in the manufacture of NaOH.
Pick out the correct statement.
Bound moisture is removed during constant rate drying period.
Free moisture is removed during falling rate drying period.
The sum of free moisture and equilibrium moisture in a solid is called the critical moisture.
The driving force for mass transfer in a wet solid is its free moisture content.
The driving force for mass transfer in a wet solid is its free moisture content.
Very tall packed towers are divided into series of beds to—-
reduce the overall pressure drop
avoid channeling
reduce liquid hold-up
avoid flooding
avoid channeling
Moisture contained by a substance in excess of the equilibrium moisture is called the __________ moisture.
unbound
free
critical
bound
free
With increase in temperature, the solubility of gases in liquids, at fixed pressure
increases
decreases
remains same
either (a) or (b), depends on the system
decreases
In most of the vacuum crystallizer, vacuum is generally produced by means of a
suction pump
compressed air jet
steam jet ejector with a barometric condenser
none of these
steam jet ejector with a barometric condenser
On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in
greater degree of separation with a fixed number of trays
increased reboiler load
increased reflux ratio
None of these.
greater degree of separation with a fixed number of trays
__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.
Wetted wall
Packed
Plate
Spray
Plate
Deairation (removal of O2) of water is done by
rectification
absorption
ion-exchange
adsorption
ion-exchange
Pick out the wrong statement.
The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.
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.
Azeotropes obey Raoult’s law at all temperature.
The relative volatility of a binary mixture at the azeotropic composition is 1.
Azeotropes obey Raoult’s law at all temperature.
Make up water is supplied during cooling tower operation to compensate for water losses due to
evaporation
blowdown
entrainment
all (a), (b)&(c)
ALL
A minimum boiling azeotrope is exemplified by
toluene-benzene
acetone-carbon disulphide
water-isobutyl alcohol
none of these
acetone-carbon disulphide
Which of the following solutions will follow Raoult’s law most closely ?
A solution of benzene, toluene and oxylene.
35% solution of camphor in water.
35% solution of NH3 in water.
A solution of polar organic compounds (not of homologs of a series).
A solution of benzene, toluene and oxylene.
Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)
increases pressure drop, increases surface area.
increases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
decreases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
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.
that of normal condensation.
‘Absorption with chemical reaction’ is involved in the removal of
carbon dioxide from gaseous stream using alkaline solution.
benzol from coke oven gas using solar oil/wash oil.
ammonia from coke oven gas using refrigerated water.
tar from coke oven gas in primary gas coolers using chilled water.
carbon dioxide from gaseous stream using alkaline solution.
The-relative volatility for separation of a non-ideal binary mixture by distillation should be
0
1
> 1
< 1
> 1
Pick out the wrong statement:
Reboiler is not used in open steam distillation.
The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
Freeze drying is used for the drying of fish.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
In paper industry, paper is dried in a __________ dryer.
tunnel
heated cylinder
conveyor
festoon
heated cylinder
Pick out the wrong statement.
Critical moisture content is not a property of the material itself.
A sharp increase in pressure drop gives an indication of the flooding in a distillation column.
Separation of components is not possible in liquid extraction, if selectivity is unity.
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.
Only small amount of evaporation of water produces large cooling effects because of its
large latent heat
low viscosity
small latent heat
none of these
large latent heat
The most common packing used in industrial operations is __________ rings.
raschig
lessing
cross-partition
single spiral
raschig
When the feed to a distillation column is a saturated liquid, slope of the feed line is
zero
unity
infinity
none of these
infinity
Leaching of sugar from sugar beets is done by
hot water
hexane
dilute H2SO4
lime water
hot water
Absorption factor method is used to calculate the number of ideal stages, when
operating line lies above the equilibrium line.
operating line lies below the equilibrium line.
both operating and equilibrium lines are parallel.
pressure drop in the column is very high.
both operating and equilibrium lines are parallel.
Flights in a rotary dryer are provided to
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
reduce the residence time of solid.
increase the residence time of the solid.
none of these.
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that
the system comprises of partially miscible liquids.
the system comprises of miscible liquids.
the system comprises of an azeotrope.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
Dry bulb temperature of unsaturated air is more than its __________ temperature.
dew point
wet bulb
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
The reciprocal of stripping factor is termed as
selectivity index
relative volatility
absorption factor
Murphree efficiency
absorption factor
Ponchan-Savarit method analyses the fractional equipment based on
enthalpy balance only.
material balance only.
both enthalpy and material balances.
the assumption of constant molal overflow.
both enthalpy and material balances.
The binary diffusivity in gases at atmospheric conditions is about
10^-9 cm/sec
10^-1 cm^2/sec
10^-3 sec/cm
10^-4 cm^2/sec^2
10^-1 cm^2/sec
Percentage saturation is __________ the relative saturation.
always smaller than
always greater than
not related to
none of these
always smaller than
In case of a desorber (stripper), the
operating line always lies above the equilibrium curve.
operating line always lies below the equilibrium curve.
temperature remains unaffected.
temperature always increases.
operating line always lies below the equilibrium curve.
What is the reflux ratio at total reflux ?
Zero
Infinity
Unity
Data insufficient
Infinity
Under conditions of flooding in packed tower, the gas pressure drop
decreases rapidly
increases rapidly
remains constant
is maximum
is maximum
For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).
1-5
10-60
200-300
> 500
10-60
The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its
integral heat of adsorption.
heat of wetting.
differential heat of adsorption.
heat of normal condensation.
integral heat of adsorption.
The minimum number of theoretical plates is required for achieving a given separation in distillation column with
no reflux
total reflux
zero reflux ratio
minimum reflux ratio
total reflux
A good solvent used for absorption should not have very high
viscosity
vapor pressure
freezing point
all (a), (b) & (c)
all (a), (b) & (c)
In a counter-current liquid extractor
both liquids flow at fixed rate.
both liquids can have any desired flow rate.
only one of the liquids may be pumped at any desired rate.
liquid’s flow rate depends upon the temperature and pressure.
only one of the liquids may be pumped at any desired rate.
The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
M.T.C. of individual components in a liquid-liquid system.
M.T.C. of liquid in liquid-gas system.
the overall M.T.C. of the system.
individual mass transfer co-efficient (M.T.C.) in gaseous system.
Weight of 1 cum of humid air as compared to 1 cum of dry air, under the same conditions, is
less
more
same
unpredictable
less
Positive deviation from Raoult’s law means a mixture whose total pressure is
greater than that computed for ideality.
less than that computed for ideality.
less than the sum of the vapour pressure of the components.
none of these.
greater than that computed for ideality.
With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent —-
increases
decreases
decreases linearly
remains unaffected
increases
Prandtl number for water at 20°C is about
7
70
0.7
150.
7
Boiling point diagram is
not affected by pressure.
affected by pressure.
a plot of temperature vs. liquid composition.
a plot of temperature vs. vapour composition.
affected by pressure.
Steam distillation is used to
reduce the number of plates.
avoid thermal decomposition of a component.
increase the efficiency of separation.
increase the total pressure of distillation.
avoid thermal decomposition of a component.
Freundlich equation applies to the adsorption of solute from
dilute solutions, over a small concentration range.
gaseous solutions at high pressure.
concentrated solutions.
none of these.
dilute solutions, over a small concentration range.
For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.
no change in theoretical
marginal decrease in the number of
major decrease in the number of
none of these
marginal decrease in the number of
The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an
pure component
binary mixture
ternary mixture
insoluble binary system
pure component
A slurry is to be dried to produce flaky solid. Which dryer would you recommend?
Spray dryer
Drum dryer
Rotary dryer
Dielectric dryer
Spray dryer
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.
Heating and dehumidification at almost constant wet bulb temperature.
The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is
1
∞
0.5
2
1
Pick out the wrong statement
Co-current absorbers are usually used, when the gas to be dissolved in the liquid is a pure substance.
In case of gas absorption, HETP is equal to HTU, when both the operating line & the equilibrium lines are parallel.
Hatta number is important in case of gas absorption with chemical reaction.
In actual practice, absorption is an endothermic process, while stripping is an exothermic process.
In actual practice, absorption is an endothermic process, while stripping is an exothermic process.
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.
continuous
steam
azerotropic
none of these
steam
Large scale drying of wheat is done in a __________ dryer.
fluidised bed
spouted bed
tray
vacuum rotary
spouted bed
Azeotropic distillation is employed to separate —-
constant boiling mixture.
high boiling mixture.
mixture with very high relative volatility.
heat sensitive materials.
constant boiling mixture.
The drying time between fixed moisture content within diffusion controlled ‘falling rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )
sqrt. T
T
T^2
T^3
T^2
At the boiling point of the liquid at the prevailing pressure, the saturated absolute humidity becomes
1
0
∞
none of these
∞
Use of natural draft cooling tower is practised, when the air has low
humidity
temperature
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
Pressure drop through plate tower as compared to that through packed tower, for the same duty will be
less
more
equal
either (a) or (b); depends on the packing height
more
Dimension of mass diffusivity is the same as that of
kinematic viscosity
dynamic viscosity
surface tension
pressure
kinematic viscosity
Dorr thickener is an equipment used for
classification
sedimentation
clarification
leaching
sedimentation
Steam distillation is used to separate
azeotropes.
high boiling substances from nonvolatile impurities.
heat sensitive materials.
mixtures of low relative volatility.
high boiling substances from nonvolatile impurities.
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
q > 1
q < 1
q = 1
q = 0
q = 1
Which of the following is an undesirable property in a tower packing ?
Large surface per unit volume.
Large free cross-section.
Low weight per unit volume.
Large weight of liquid retained.
Large weight of liquid retained.
Water entrained by circulating air in cooling towers is termed as
drift
blow down
vapor load
none of these.
drift
With increase in temperature, the rate of leaching increases, because the
diffusivity of solute increases.
viscosity of solvent decreases.
thermal conductivity of solute increases.
none of these.
diffusivity of solute increases.
Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.
molal
relative
percentage
none of these
molal
The Kundsen diffusivity is proportional to (where, T = absolute temperature)
sqt T
T^2
T
T^4
sqt T
In an absorption coloumn, the flooding velocity for random packing is __________ that for stacked/regular packing.
greater than
smaller than
equal to
either (a), or (b) ; depends on the type of packing
smaller than
The relation among various mass transfer co-efficients (M.T.C) for ideal gases is given by (where, Kc & Km are M.T.C. for equimolar counter diffusion with concentration & mole fraction respectively as the driving force. and, Kp = M.T.C. for diffusion of a gas through a stagnant inert gas with pressure as driving force.)
Kc = Kp = Km
Kc = Kp/RT = Km . RT/P
Kc = Kp . RT = Km . RT/p
none of these
Kc = Kp . RT = Km . RT/p
With increase in temperature, the leaching rate increases because of the
increased diffusivity.
decreased viscosity of liquid.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Leaching of uranium ore and gold ore is done in
centrifugal extractor
Pachuka tanks
Bollman extractor
none of these
Pachuka tanks
Blowdown in a cooling tower
means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.
increases the scale forming tendencies of water.
is undesirable.
all (a), (b) & (c).
means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.
Antibiotics are best handled in a
Podbielniak extractor.
sieve tray contractor.
rotating disc contactor.
pulsed column extractor.
Podbielniak extractor.
The fixed cost of a distillation column at minimum reflux ratio is
minimum
infinite
optimum
none of these
infinite
__________ extractor uses centrifugal force for separating the two phases.
Treybal
Schiebel
Podbielniak
None of these
Podbielniak
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
-1.5
Pick out the wrong statement.
Mechanical agitation is required, if the system has low interfacial tension.
Seive tray towers are generally used for systems having low interfacial tension.
When Henry’s law constant is very small, then the mass transfer rate is controlled by the gas film resistance.
Taylor-Prandtl analogy for heat and mass transfer considers the transfer through both laminar and turbulent layers.
Mechanical agitation is required, if the system has low interfacial tension.
Acetic acid will be most economically separated from a dilute solution of acetic acid in water by
solvent extraction
continuous distillation
evaporation
absorption
solvent extraction
Design calculation for multiple component distillation is done by
Ponchon-Savarit method
Mccabe-Thiele method
enthalpy concentration method
tray to tray calculations.
tray to tray calculations.
To get high tray efficiency
interfacial surface between liquid and gas phase should be large.
time of contact between the two phases should be less.
gas velocity should be very low.
liquid entrainment should be severe.
interfacial surface between liquid and gas phase should be large.
The mass transfer co-efficient for a solid sphere of radius ‘a’ dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is
D/a
D/2a
proportional to sqrt. D
dependent on the Reynolds number
proportional to sqrt. D
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.
one of the liquid components has very high affinity towards the solvent.
Inside the distillation column, the
driving force for the vapour flow is the pressure drop.
liquids are not always at their bubble points.
pressure increases gradually from bottom to the top of the column.
none of these
driving force for the vapour flow is the pressure drop.
Diffusivity in concentrated solutions differs from that in dilute solutions, because of the changes in
viscosity with concentration.
degree of ideality of the solution.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Occurrence of ‘case hardening’ during drying of a high moisture solid cake __________ the drying rate.
increases
decreases
does not affect
exponentially increases
decreases
Which of the following is not a continuous drier ?
Drum drier
Spray drier
Tunnel drier
Tray drier
Tray drier
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
insoluble in the liquid
__________ is the temperature at which a gas-vapor mixture becomes saturated, when cooled at constant total pressure out of contact with a liquid.
Dew point
Bubble point
Dry bulb temperature
Wet bulb temperature
Dew point
Rate of leaching increases with increasing
temperature
viscosity of solvent
pressure
size of the solid
temperature
An azeotropic mixture is a __________ mixture.
binary
ternary
constant boiling point
none of these
constant boiling point
Molecular seives are regenerated by heating to __________ °C.
< 150
200-330
> 500
> 1000
200-330
In a counter-current extractor, as the axial mixing increases, the extraction efficiency
increases
decreases
remains unchanged
depends on the pressure of the system
decreases
Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer.
indirect tray
spray
freeze
none of these
freeze
In extractive distillation, solvent is
added to alter the relative volatility of the mixture.
of high volatility.
present in overhead stream.
of high viscosity to give high tray efficiency.
added to alter the relative volatility of the mixture.
Radioactive nuclear waste is treated in
mixer-settler extractor
rotating-disc contactor
pulsed column extractor
Bollman extractor
pulsed column extractor
Large scale drying of sugar is done in a __________ dryer.
spouted bed
tray
rotary
truck
rotary
__________ temperature is the steady state temperature attained by a small amount of liquid evaporating into a large quantity of unsaturated gas-vapor mixture.
Dry bulb
Wet bulb
Dew point
none of these
Wet bulb
The drying time between fixed moisture contents within the ‘constant rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )
sqrt. T
T
T^1.5
T^3
T
__________ equation applies to diffusivities in liquids.
Gilliland
Hirschfelder
Wilke and Chang
none of these
Gilliland
A packed tower compared to a plate tower for a particular mass transfer operation
incurs smaller pressure drop.
allows installation of cooling coils.
is less costly when built in large sizes/diameters.
is more suitable, if suspended solids are present in fluid streams.
incurs smaller pressure drop.
Which of the following is the most commonly used leaching solvent in vegetable oil industry?
Phenol
Hexane
Furfurol
Liquid SO2
Hexane
Large quantity of silica gel is normally dried in a __________ dryer.
freeze
through circulation
rotary vacuum
tray
through circulation
For the same system, if the same liquid used in an absorber is decreased, the tower height will
increase
decrease
remain unaffected
decrease or increase ; depends on the type of liquid
increase
Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant.
agitated vessel
sieve tray column
bubble cap column
packed tower
agitated vessel
Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent
a pure component.
a binary mixture.
a ternary mixture.
partially miscible ternary system.
a binary mixture.
In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when
saturated feed is not used.
an azeotrope forms.
the latent heat of vaporisation of the more and less volatile components are greatly different.
a total condenser is used.
a total condenser is used.
In an interphase mass transfer process, the lesser the solubility of a given solute in a liquid, the higher are the chances that the transfer process will be
liquid phase resistance-controlled.
gas phase resistance controlled.
impossible.
driven by a non-linear driving force.
gas phase resistance controlled.
As the reflux ratio decreases, the
separation becomes more efficient.
number of plates increases.
column diameter increases.
none of these.
number of plates increases.
Which of the following equipments is not used for gas dispersion ?
Agitated vessels
Bubble cap tray towers
Perforated sieve tray towers
Spray towers
Spray towers
One mole feed of a binary mixture of a given composition is flash vaporised at a fixed P and T. If Raoult’s law is obeyed, then changing the feed composition would effect
the product composition but not the fraction vaporised.
the product composition as well as the fraction vaporised.
the fraction vaporised but not the product composition.
neither the product composition nor the fraction vaporised.
the fraction vaporised but not the product composition.
With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop
decreases
remains unchanged
increases
decreases exponentially
increases
Which of these columns incurs the lowest pressure drop ?
Packed column (with stacked packing)
Packed column (with dumped packing)
Bubble plate column
Pulse column
Packed column (with stacked packing)
In the desorption of highly soluble gas from the liquid, the main resistance will be in the __________ phase.
gas
liquid
both (a) & (b)
neither (a) nor (b)
liquid
If G = insoluble gas in gas stream and L = non-volatile solvent in liquid stream, then the slope of the operating line for the absorber is
L/G
G/L
always < 1
none of these
L/G
Which of the following remains constant during evaporative cooling process with recirculated water supply ?
Relative humidity
Partial pressure of vapour
Wet bulb temperature
None of these
Wet bulb temperature
For stripping of a gas in a counter current stripper, the operating line
lies above the equilibrium curve.
lies below the equilibrium curve.
can lie above or below the equilibrium curve.
is always parallel to the equilibrium curve.
can lie above or below the equilibrium curve.
Which of the following same diameter columns gives lowest pressure drop per unit height ?
Bubble-cap column
Sieve-plate column
Packed column (stacked)
Randomly packed column
Packed column (stacked)
Diffusion in concentrated solutins differs from that in dilute solutions, because of the change in the __________ with the concentration of the solution.
degree of ideality
viscosity
both ‘a ‘& ‘b’
neither ‘a’ nor ‘b’
both ‘a ‘& ‘b’
Stage efficiency in a leaching process depends on the
time of contact between the solid and the solution
rate of diffusion of the solute through the solid and into the liquid
both (a) and (b)
vapour pressure of the solution
both (a) and (b)
Operating velocity in a packed tower is usually __________ the flooding velocity.
half
twice
equal to
more than
half
The Knudsen diffusivity is dependent on the
molecular velocity only.
pore radius of the catalyst only.
molecular mean free path only.
molecular velocity and por radius of the catalyst.
molecular velocity and pore radius of the catalyst.
Minimum possible diameter of a packed coloumn is decided mainly by the
flooding
gas viscosity
liquid density
liquid hold up
flooding
Solvent used in extractive distillation
is of low volatility.
forms a low boiling azeotrope.
forms a high boiling azeotrope.
does not alter the relative volatility of the original components.
forms a low boiling azeotrope.
Capacity of a rotary dryer depends on its
r.p.m
inclination with ground surface
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
The cooling effect in a cooling tower can be speeded up by
increasing the air velocity and area of exposed wet surface.
reducing the barometric pressure.
reducing the humidity of the air.
all (a), (b) and (c).
all (a), (b) and (c).
Perforated plate towers are unique for solvent extraction because, they provide
higher contact area.
better contact of the phase.
repeated coalescence & redispersion of the drop phase.
none of these.
repeated coalescence & redispersion of the drop phase.
In case of absorption & stripping, the interface of the liquid & gas phases are present in equilibrium, when the diffusional resistance of __________ is zero.
interface
gas phase
liquid phase
all ‘a’, ‘b’ & ‘c’
interface
Swenson-Walker crystalliser is a __________ unit
continuous
batch
semi-batch
cooling (adiabatic)-cum-evaporation
continuous
With increase in temperature, the mutual solubility of two liquids ____________.
increases
decreases
remains unchanged
decreases exponentially
increases
The relative volatility of a binary mixture at the azeotropic composition is
1
> 1
0
∞
1
Relative volatility varies with the concentration of component for an ideal solution. The relative volatity of a binary mixture may be defined as the ratio of vapor pressure of component ‘A’ to that of component ‘B’, when _____________.
only vapor phase follows Raoult’s law.
only liquid phase obeys Dalton’s law.
liquid phase obeys Dalton’s law and vapor phase obeys Raoult’s law.
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.
__________ extractor is used for the concentration of radioactive nuclear waste.
Pulsed column
Seive plate
Mixer-settler
Ballman
Pulsed column
Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture.
free
unbound
equilibrium
bound
equilibrium
All moisture in a non-hygroscopic material is the __________ moisture.
free
equilibrium
unbound
bound
unbound
Pick out the correct relationship. (where, Ri = internal reflux ratio Ro = external reflux ratio. )
(1 + Ro) = Ro/Ri
(1 - Ro) = Ro/Ri
(1 + Ri) = Ro/Ri
(1 - Ri) = Ro/Ri
(1 + Ro) = Ro/Ri
Separation of __________ employs gaseous diffusion process.
N2 and O2 from air
isotopes of uranium
isotopes of helium
SO2 and air
isotopes of uranium
For water-ethanol system, the minimum reflux ratio
is computed from the slope of the upper operating line that is tangent to the equilibrium curve.
is computed from the intercept of the operating line.
cannot be computed.
is the optimum reflux ratio.
is computed from the slope of the upper operating line that is tangent to the equilibrium curve.
Experimental determination of __________ is done by wetted wall column method.
diffusion co-efficient
mass transfer co-efficient
NTU
none of these
mass transfer co-efficient
In liquid extraction, if the selectivity is unity, then
separation of the constituents is the most effective.
no separation will occur.
amount of solvent required will be minimum.
solvent flow rate should be very low.
no separation will occur.
Paper industry employs __________ driers.
cylinder
rotary
spray
fluidised bed
cylinder
Leaching of coarse solid lumps is also termed as
decoction
dissolution
percolation
agitation and settling
percolation
The main reason for dividing a tall packed tower into series of small towers is to
minimise the overall pressure drop.
avoid flooding.
reduce liquid hold up.
avoid channeling.
avoid channeling.
Co-current absorbers are usually used when the gas to be dissolved in the liquid is
sparingly soluble
highly soluble
a pure substance
a mixture
a pure substance
At what percentage (by volume) of alcohol composition, it forms an azeotrope with water ?
90
91.5
95
99
95
Measurement of the interfacial area of mass transfer is achieved easily & accurately in case of a __________ coloumn.
spray
packed
bubble cap plate
wetted wall
wetted wall
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.
Co-efficient = Flux/concentration difference.
When an unsaturated air-water mixture is heated at constant pressure, then
the partial pressure of water vapour increases.
the specific humidity decreases.
The relative humidity increases.
the relative humidity decreases.
the relative humidity decreases.
At a fixed pressure, the humidity depends upon the partial pressure of vapor in the mixture. Humidity of a vapour free gas is __________ percent.
100
0
50
between 0 and 100
0
Large scale usage of flash distillation is practised in
soap manufacturing
ammonia synthesis plant
polymerisation industry
petroleum refinning
petroleum refinning
High pressure at the bottom of a distillation tower handling heat sensitive materials results in
thermal decomposition of bottoms.
increased relative volatility.
erosion of the tower.
very efficient operation.
thermal decomposition of bottoms.
Alcohol is dehydrated using __________ distillation.
extractive
azeotropic
steam
molecular
azeotropic
Separation of two volatile liquids by distillation makes use of their
selectivity
relative volatility
solubility
density difference
relative volatility
Dried finished product sampled from various parts of a __________ dryer exhibits non-uniformity in the moisture content.
rotary
tray
freeze
none of these
tray
__________ is used as an ‘entrainer’ for the separation of acetic acid-water mixture by distillation.
Furfural
Benzol
Butyl acetate
Hexane
Butyl acetate
Rotary dryers cannot handle __________ materials.
free flowing
dry
sticky
grannular
sticky
An example of elution is
separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.
separation of sugar from sugar beet by hot water.
dissolution of tannin out of tree barks by water.
recovery of vegetable oils from seeds.
separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.
The operating line for an absorber is curved, when plotted in terms of
mole fractions
mole ratios
partial pressure
mass fractions
partial pressure
For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.
tunnel
tray
rotary
none of these
rotary
Moisture in a substance exerting an equilibrium vapour pressure less than that of pure liquid at the same temperature is called the __________ moisture.
bound
unbound
critical
none of these
bound
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
high reflux ratio
Detergent solution is dried to a powder in a
spray dryer
spouted bed dryer
tunnel dryer
pan open to atmosphere
spray dryer
During bottling of cold drinks (e.g. Pepsi), the main resistance to mass transfer for the absorption of carbon dioxide in water lies in the
gas film
liquid film
liquid-gas interface
none of these
liquid film
The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by
increasing the gas film co-efficient.
increasing the liquid film co-efficient.
increasing the total pressure.
decreasing the total pressure.
increasing the gas film co-efficient.
Flooding results in
high tray efficiency
low tray efficiency
high gas velocity
good contact between the fluids
low tray efficiency
he suitable evaporator for concentration of foaming liquids is a __________ evaporator.
long tube
short tube
vacuum
falling film
long tube
