UNIT-III
1. Write about drying and crystallization.
2. The spent acid from a nitrating process contains 33% H 2SO4 36%
HNO3 and 31% water by weight. This acid is to be strengthened by the
addition of concentrated sulphuric acid containing 95% H 2SO4and
concentrated nitric acid containing 78% HNO 3. The strengthened
mixed acid is to contain 40% H 2SO4 and 43% HNO3. Calculate the
quantities spent and concentrated acids that should be mixed
together to yield 1500 kg of the desired mixed acid.
ANSWER:
y=556.1 kg
z=726.6 kg.
3. A solution of potassium dichromate in water contains 16% K2Cr2O7
by weight, 1000 kg of this solution is evaporated to remove some
amount of water. The remaining solution is cooled to 20 oC. If the yield
of K2Cr2O7 crystals is 80%, calculate the amount of water evaporated.
Solubility of K2Cr2O7 is 0.390 kg mole per 1000 kg water (at 20 oC).
ANSWER:
Amount of water evaporated = 561 kg.
4. 1000 kg of sodium carbonate solution containing 25% Na 2CO3 is
subjected to evaporative cooling, during which process 15% of the
water present in the solution is evaporated. From the concentrated
solution Na2CO3.10H2O crystallizes out. Calculate how much crystals
would be produced if the solubility of Na 2CO3.10H2O is 21.5 gm per
100gm of water.
Crystals formed (C)= 479.4 kg.
5. 9000 kg of KCl are present in a saturated solution at a temperature
of 80C. The solution is cooled to 20C in an open tank. The
solubilities of KCl at 80C and 20C are 55.0 and 35.0 parts per 100 of
water respectively. Calculate:
(a) Assuming water equal to 3% by weight of solution is lost by
evaporation, weight of crystals obtained.
(b) The yield of crystals neglecting loss by evaporation.
KCL crystallizes without any water of crystallization.
(a) E = 0.03, C = 3550.32 kg.
(b) When E = 0, C = 3284.485 kg.
6) A saturated solution of MgSO4 at 80 ºC is cooled to25 ºC. During this
process 5% of the original water is lost. Find the weight of water lost, mother
liquor leaving and feed, if 1500 kg of MgSO 4.7H20 crystallizes. Solubility data:
At 80 ºC: 64.28 g MgSO4 per 100 g water.
At 25 ºC: 40.88 g MgSO4 per 100 g
water.
Amount of water evaporated=82.35 kg
Amount of Mother Liquor =1122.85 kg
Feed = 2705.2 kg
7) The waste acid from a nitrating process contains 21% HNO3, 55% H2SO4
& 24% H2O. This acid is to be concentrated to 28% HNO3, 62% H2SO4 by the
addition of concentrated sulfuric acid containing 93% H2SO4 and
concentrated nitric acid containing 90% HNO3. Calculate the weight of acids
needed to obtain 10000 kg of desired acid.
Weight of waste (spent) acid = 127 kg
Weight of conc. H2SO4 = 592 kg
Weight of conc. HNO3 = 281 kg
8) Feed to a crystallizer contains 6420 kg of aqueous solution containing
29.6% anhydrous sodium sulfate by weight at 104 ºC. The solution is cooled to
20 ºC to crystallize out the desired Glauber’s salt. The mother liquor is found
to contain 16.1% anhydrous sulfate. Estimate the weight of mother liquor.
Mother liquor = 3324.64 kg.
9) A vacuum crystallizer is to produce 10,000 kg of FeSO 4.5H2O crystals per
hour. The feed solution contains 38.9 parts FeSO4/ 100 parts of water. The
feed enters at 70 ºC and is cooled to 27 ºC. The solubility at 27 ºC is 30.3
FeSO4/ 100 Parts water. Determine the quantity of feed and water lost as
vapour.
Feed = 83078.34 kg.
10) A crystallizer is charged with 9000 kg of an aqueous solution of 20%
NaSO4 and it is subjected to evaporative cooling and 10% of original water
evaporates. Glauber’s salt crystallizes. The mother liquor leaves with 16%
salt. Calculate the weights of a) water loss b) the mother liquor leaving and c)
crystals formed.
a) Water loss =720 kg
b) Mother liquor leaving = 6589 kg
c) Crystals formed= 1691 kg
11) Methanol is produced by the reaction of CO with H2 according to the equation
CO+ 2H2→ CH3OH. Only 15% of the CO entering the reactor is converted to
methanol. The methanol product is condensed and separated from the unreacted
gases, which are recycled. The feed to the reactor contains 2 mole of H 2 for every
mole of CO. The fresh feed enters at 35 ºC and 300 atm. To produce 6600 kg/h of
methanol calculate:
a) Volume of fresh feed gas
b) The recycle ratio.
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