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11)11 111 1111 11 111
AL - 241—
B.E. / B.Tech. (Chemical Engineering)
Seventh Semester (CGS)
Chemical Engineering Operations - III
Mass Transfer - II
P Pages : 7
Time : Three Hours
7 CH 01
Max. Marks : 80
Note : 1. Answer three questions from Section A and
three questions from Section B.
2. Due credit will be given to neatness and
adequate dimensions.
3. Assume suitable data wherever necessary.
4. Diagrams and Chemicals equations should
be given wherever necessary.
5. Illustrate your answer necessary with the help
of neat sketches.
SECTION - A
1.
Explain the process of liquid - liquid extraction,
counter current multiple contact with a
single solvent using ternary diagram.
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OR
2.
160cm3/s of a solvent S is used to treat
400cm3/s of a 10 per cent by mass solution
of A in B, in a three-stage countercurrent
multiple-contact liquid-liquid extraction plant.
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What is the composition of the final raffinate ?
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Equilibrium data :
0.15
0.10
kgA/kgB: 0.05
0.258
0.159
kg A / kg S : 0.069
Densities
(kg/m3) :
pA =1200 pB =1000 pS = 800
12.
•
3.
A solution of 5 per cent acetaldehyde in
toluene is to be extracted with water iri a
five stage co- current unit. If 25kg water /
100 kg feed is used, what is the mass of
acetaldehyde extracted and the final
concentration ? The equilibrium relation is
given by :
(kg acetaldehyde / kg water) =
2.20 (kg acetaldehyde / kg toluene)
For a non-ideal system, where the molar
latent heat is no longer constant and where
there is a substantial heat of mixing, the
calculations become much more tedious. For
binary mixtures of this kind. explain the
graphical model developed by RUHEMANN,
PONCHON, and SAVARIT, based on the
use of an enthalpy - composition chart to
find the number of plates in the distillation
column.
1
Aglit******
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•
OR
Explain the process of Differential extraction.
using ternary diagram. Obtain the expression
for final extract Ef and the solvent to be used
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Sf.
4.
Soda ash is mixed with lime and the liquor
from the second of three thickeners and passed
to the first thickener where separation is
effected. The quantity of this caustic solution
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Mole fraction of benzene
in liquid 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Mole fraction of benzene
in vapour 0.22 0.38 0.51 0.63 0.7 0.78 0.85 0.91 0.96
0.
1.
-
. OR
A 50 mole per cent mixture of benzene and .
toluene is fractionated in a batch still which
has the separating power of 8 theoretical
plates. It is proposed to obtain a constant
quality product containing 95 mole per cent
benzene, and to continue the distillation until
the still has a content of 10 mole per cent .
benz.Whatwil rngeofux
ratios used in the process? Show graphically
the relation between the required reflux ratio
and the amount of distillate removed.
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leaving the first thickener is such as to yield 10
Mg of caustic soda per day of 24 hours. The
solution contains 95 kg of caustic soda i 1000
kg of water, whilst the sludge leaving each of
the thickeners consists of one part of solids to
one of liquid.
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Determine :
a) the mass of solids in the sludge,
b) the mass of water admitted to the third
thickener and
c) the percentages of caustic soda in the
sludges leaving the respective thickeners.
OR
6.
A plant produces 100kg/s of titanium dioxide
pigment which must be 99.9 per cent pure
when dried. The pigment is produced by
precipitation and the material, as prepared,
is contaminated with 1 kg of salt solution
containing 0.55 kg of salt / kg of pigment.
The material is washed countercurrenfly with
water in a number of thickeners arranged in
series. How many thickeners will be required
if water is added at the rate of 200kg/s and
the solid discharged from each thickeners
.removes 0.5kg of solvent/kg of pigment ?
A mixture of 60 mole per cent benzene, 30
per cent of toluene and 10 per cent xylene
is handled in a batch still. If the top product
is to be 99 per cent benzene, determine :
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a) the liquid composition on each plate at
total reflux,
b) the composition on the 2nd and 4th plates
for R = 1.5,
The relative volatility of benzene to toluene
may be taken as 2.4. and the relative volatility
of xylene to toluene as 0.43.
OR
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What will be the required number of
thickeners if the amount of solution removed
in association with the pigment varies with
the concentration of the solution in the
thickener as follows :
kg solute / kg solution
0 0.1
02 0.3 0.4 0.5
kg solution / kg pigment
0.30 0.32 0.34 0.36 0.38 0.40
The concentrated wash liquor is mixed with
the material fed to the first thickener.
Mole per cent CS2 in the vapour :
0 8.23 15.55
A continuous fractionating column, operating
at atmospheric pressure, is to be designed
to separate a mixture containing 15.67 per
cent CS2 and 84.33 per cent CCI4 into an
overhead product containing 91 per cent
CS2 and a waste of 97.3 per cent CCI4, all
by mass. A plate efficiency of 70 per cent
and a reflux of 3.16 kmoVkmol of product
may be assumed. Determine the number of
plates required. The feed enters at 290K with
a specific heat capacity of 1.7kJ/kg K and
has a boiling point of 336K. The latent heats
of CS2 and of CCI4 are 25.9MJ/kmol. The
latent heat of CS2 and CCI4 is 25900 kJ/
kmol.
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74.7
82.9 87.8 93.2
Mole per cent CS2 in the liquor :
0 2.96 6.15 11.06 14.35 25.85 39.0 53.18 66.30 75.75 86.011
OR
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8.
The locus of the point of intersection of the
operating lines is of considerable importance,
it is dependent on the temperature and
physical condition of the feed. Explain the
effect of the condition of the feed on the
intersection of the operating lines for a fixed
reflux ratio [q-lines].
SECTION - B
7.
26.6 33.2 49.5 63.4
9.
l∎
A distillation column is fed with a mixture
of benzene and toluene, in which the mole
fraction of benzene is 0.35. The column is
to yield a product in which the mole fraction
of benzene is 0.95, when working with a
reflux ratio of 3.2, and the waste from the
column is not to exceed 0.05 mole fraction
of benzene. If the plate efficiency is 60 per
cent, estimate the number of plates required
and the position of the feed point. The
relation between the mole fraction of
benzene in liquid and in vapour is given by : 1
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