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)
Use solvent S containing 0.02 mole
fraction of the solute
(D)
Double the residence time of the solvent
S in the contactor
GATE 2006
Answer: (B)
Common statement for the next two
questions
Consider the diffusion of a reactant A through a
cylindrical catalyst pore of radius R and length L>>R. Reactant A
undergoes a zero order reaction on the cylindrical surface of the pore. The
following equation describes changes in the concentration of A within the pore
due to the axial diffusion of A and the disappearance of A due to reaction d2CA/dx2=K,
where CA is the concentration of A at a distance from the pore
entrance and K is a constant.
The minimum pore length for A to be completely
converted within the pore is
(A)
(CA0/K)1/2
(B)
(CA0/2K)1/2
(C)
(2CA0/K)
(D)
(2CA0/K)1/2
GATE 2006
Answer: (D)
If the concentration of A at the pore entrance (x =
0) is CA0 and x = L is a dead end where no reaction occurs, the
concentration profile of A in the pore is given by
(A)
CA(x) = Kx2/2 –
KLx + CA0
(B)
CA(x) = Kx(x-L)/2 – CA0x/L
+ CA0
(C)
CA(x) = CA0
(D)
CA(x) = CA0((L-x)/L)
GATE 2006
Answer: (B)
The
ratio of diffusion coefficient in a gas to that in a liquid is of the order of
(A)
105
(B)
10-5
(C)
10-2
(D)
102
GATE 2005
Answer: (A)
In
a tray column, separating a binary mixture, with non-ideal stages. One of the
following statement is TRUE.
(A)
Point efficiency can exceed 100%
(B)
Murphree efficiency cannot exceed 100%
(C)
Murphree efficiency can exceed 100%
(D)
Both Murphree and point efficiencies can
exceed 100%
GATE 2005
Answer: (C)
A
distillation column at a pilot plant is scaled up by 3 times for industrial use
at steady state. After scaling up
(A)
The number of theoretical trays
increases by 3 times
(B)
The minimum reflux ratio is increased by
three times
(C)
The feed flow rate and product flow
rates are increased by three times
(D)
The feed composition and product
compositions are increased by three times
GATE 2005
Answer: (C)
A separation column for vapour-liquid contact
processes 200 kmol/hr of vapour. The flooding velocity is 3 m/s. If the column
operates at 85% of flooding velocity and the down comer area is !0% of the
total cross sectional area, what is diameter of the column? Average density of
vapour = 2 kg/m3 and its molecular weight = 44.
(A)
0.82 m
(B)
0.72 m
(C)
0.78 m
(D)
1 m
GATE 2005
Answer: (A)
Match
the variation of mass transfer coefficient given by the theory in Group –I with
the appropriate variation in Group –II
(A)
P – 1, Q – 2, R – 3
(B)
P – 2, Q – 1, R – 3
(C)
P – 1, Q – 3, R – 2
(D)
P – 3, Q – 2, R – 1
GATE 2005
Answer: (C)
Two
solid discs of benzoic acid (molecular weight = 122) of equal dimensions are
spinning separately in large volumes of water and air at 300 K. the mass
transfer coefficients for benzoic acid in water and air are 0.9×10-5
and 0.47
10-2 m/s
respectively. The solubility of benzoic acid in water is 3 kg/m3 and
the equilibrium vapour pressure of benzoic acid in air is 0.04 Kpa. Then the
disc
(A)
Dissolves faster in air than in water
(B)
Dissolve faster in water than in air
(C)
Dissolves at the same rate in both air
and water
(D)
Does not dissolve either in water or in
air
GATE
2005
Answer: (B)
For
a two phase feed, where 80% of the feed is vaporized under column conditions,
the feed line slope in the Mcabe-Thiele method for distillation column design,
is
(A)
-1/4
(B)
+1/4
(C)
+4
(D)
- 4
GATE 2005
Answer: (A)
In
the triangular diagram represented below for a batch separation process, a
stream F, is mixed with a solvent B to produce products R and E. Substance A is
the carrier liquid and c is the solute to be extracted. The amounts of B and E
are 1 kg and 1.20 kg respectively. The length FM is 3.1 and length FB is 8.5
units on the figure. The ratio R/E is estimated to be
(A)
1.285
(B)
2
(C)
0.751
(D)
2.5
GATE 2005
Answer: (A)
A
filter cake is dried with air at wet and dry bulb temperatures of 300 and 323 K
respectively. The heat transfer coefficient is 11 W/(m2K) and the
latent heat of vaporization of water is 2500 KJ/kg. Mass transfer does not
limit the process. Select the drying rate during the constant rate period.
Neglect conduction through the solid and radiation effects.
(A)
1.32×10-2 Kg m-2 s-1
(B)
0.71×10-2 Kg m-2 s-1
(C)
4.53×10-2 Kg m-2 s-1
(D)
0.10×10-3 Kg m-2 s-1
GATE
2005
Answer: (D)
Common
Statement for the next two questions
A binary gas mixture of a solute and a
carrier gas is treated in a countercurrent gas absorption column, containing
ideal trays, using a solvent. The compositions y and x (see figure below) are
the mole fractions of the solute in the gas and liquid respectively. Also V and
L are the molar flow rates of the gas liquid respectively. Assume that the
carrier gas is insoluble in the solvent and that the vapour pressure of the
solvent is very low at the given conditions of the column. Further the gas and
liquid streams are sufficiently dilute that L and v may assumed to be constant
throughout the column. The equilibrium relation is given by y* = mx, where m is
a positive constant.
For any value of m, the change in liquid composition
across a tray is independent of the tray location if
(A)
(L/V) =
1
(B)
(mL/V)
= 1
(C)
(m/LV)
= 1
(D)
(L/mV)
= 1
GATE 2005
Answer: (D)
Under the correct condition corresponding to
part (a), the number of ideal trays in the column is given by
GATE
2005
Answer: (C)
In
a distillation operation, what is the effect of the temperature of the reflux
stream (given) on the condenser and reboiler loads?
Reflux
conditions: (i) reflux stream is completely liquid and is at its bubble point
(ii) reflux
stream is below its bubble point
(A)
Condenser and reboiler loads are the
same in both cases
(B)
Reboiler load is the same in both the
cases but condenser load is higher in case (ii)
(C)
Condenser load is the same in both the
cases but reboiler load is higher in case (ii)
(D)
Both condenser and reboiler loads are
higher in case (ii) as compared to case (i)
GATE
2004
Answer: (D)
A
long cylinder and a sphere both of 5 cm diameter are made from the same porous
material. The flat ends of cylinder are sealed. Both the cylinder and sphere
are saturated with the same solution of sodium chloride. Later, both the
objects are immersed for a short and equal interval of time in a large tank of
water, which is well agitated. The fractions of salt remaining in the cylinder
and the sphere are Xc and Xs respectively. Which of the
following statements is correct?
(A)
Xc > Xs
(B)
Xc = Xs
(C)
Xc < Xs
(D)
Xc is greater /less than Xs
depending on the length of the cylinder
GATE 2004
Answer: (C)
At
equilibrium, the concentration of water in vapour phase (C*) in kg/m3
of air space and the amount of water (m) adsorbed per kg of dry silica gel are
related by C* = 0.0667m. To maintain dry conditions in a room of air
space 100 m3 containing 2.2 kg of water vapour initially, 10 kg of
dry silica gel is kept in the room. The fraction of initial water remaining in
the air space after long time (during which the temperature is maintained
constant) is
(A)
0.0
(B)
0.2
(C)
0.4
(D)
1.0
GATE
2004
Answer: (C)
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