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Posted By: sunil Member Level: Diamond Posted Date: 25 Jun 2008
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2008 Jawaharlal Nehru Technological University Chemical engineering III B.Tech II Semester Regular Examinations, Apr/May 2008 MASS TRANSFER OPERATIONS-II Question paper
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Code No: R05320801
Set No. 2
III B.Tech II Semester Regular Examinations, Apr/May 2008
MASS TRANSFER OPERATIONS-II
(Chemical Engineering)
Time: 3 hours
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
Max Marks: 80
1. A coal gas is freed of its light oil content (benzene) by absorption into an a absorbent
oil. The inlet gas contains 2% benzene by volume and 95% removal is required.
Inlet gas ?ow rate=0.25cu.m/s; Pressure =1.07 ×105N/sq.m; Temperature = 26
0C; Oil inlet ?ow rate (Ls) =1.787× 10- 3k mol/s; Solute content of inlet oil=0.005
mole fraction benzene; Average molecular weight of oil = 260. Equilibrium data
Y=0.125 x (mole fraction units). Determine the number of trays required
(a) Graphically,
(b) By Kremser equation.
[16]
2. Water containing 6 ppm trichloroethane (TCE) is to puri?ed by stripping with
air at 200C. The product must contain less than 4.5 ppb TCE to meet emission
standards. Calculate the minimum air rate in standard cubic meters of air per
cubic meter of water and the number of transfer units if the air rate is the 1.6 times
the minimum value. Henry’s law coe?cient for TCE in water at 200C is 0.0075
m3atm/mol. Assume density of water is 1 gm/cc.
[16]
3. It is required to extract picric acid from a dilute aqueous solution containing 0.1
mole picric acid per litre of solution using benzene as solvent with a recovery of 80%
of the picric acid originally present .Determine the quantity of benzene required per
litre of aqueous solution by employing
(a) single stage extraction and
(b) three stage extraction (cross current ) using equal amounts of fresh solvent in
each stage. The equilibrium data for benzene - picric acid - water system at
250C is given by
CB×102
0.0932 0.225
1
2
5
10
18
m= CB/CA2.23 1.45 1.705 0.505 0.32 0.24 0.187
where CB, CAare the equilibrium concentrations of picric acid in benzene and
aqueous phases respectively in mole per litre. Assume benzene-water are completely
immiscible.
[16]
4. Explain in detail for the estimation of number of stages for continuous counter
current extraction with out re?ux using rectangular graph sheets and also write
the relevant equations.
5. (a) Explain the concept of HETP and HTU.
1 of 2
[16]
Code No: R05320801
Set No. 2
(b) With the help of a neat sketch explain the construction and working of cen-
trifugal extractor.
6. (a) Explain about various Industrial adsorbents.
[8+8]
(b) Prove that for crosscurrent two-stage treatment of liquid solutions by contact
?ltration, when the adsorption isotherm is linear, the least total adsorbent
results if the amounts used in each stage are equal.
7. (a) Explain the working of Higgin‘s contactor with a neat sketch.
(b) Distinguish between ?uidized and teeter beds.
[6+10]
[8+8]
8. A 1 meter diameter tank ?tted with a false bottom and canvas ?lter is partly
?tted with 10 kg (dry weight) of sea sand wet with sea water. The sand is allowed
to drain until it stops dripping whereupon 750 kg of fresh water is added and
recirculate to reach a uniform salt concentration Estimate the salt concentration
of the wash water. The sand particle have an average size of 0.4 mm, particle
density of 8660kg/cu.m. and a bulk density of 1490 kg/cu.m. ad surface tension of
0.0736N/m. The sea water contains 3.5% salt and its density is 1018 kg/cu.m.
[16
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