Assignment - II

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B.E. Chemical Engineering 
III semester – A Batch 
Chemical Process Calculation 
Assignment - II 
 Faculty: Prof. M.Rajasimman 
DOS: 19.09.20 
 
1. It is required to make 100 kg of 30% NaOH solution by mixing the following liquids; 20% 
NaOH solution and 36% NaOH solution. Calculate the quantities of the two solutions to 
be mixed. [Ans : 
 
2. The waste acid from a nitrating process containing HNO3 24%, H2SO4 56% and H2O 20% 
by weight. This acid is to be concentrated to contain 26% HNO3, 62% H2SO4 by the 
addition of 94% H2SO4 and 90% HNO3. Calculate the weight of waste acid and 
concentrated acids that must be combined to obtain 1000 kg of desired mixture. 
 
3. 5000 kg of mixture of benzene and toluene containing 50 mole% benzene is distilled to get 
an overhead product containing 95 mole% benzene and a residue containing 90 mole% 
toluene. Calculate the weights of benzene and toluene in the feed, distillate and residue. 
 
4. An evaporator is fed with 15000 kg/h of a solution containing 10% NaCl, 15% NaOH and 
rest water. In the operation, water is evaporated and NaCl is precipitated as crystals. The 
thick liquor leaving the evaporator contains 45% NaOH, 2% NaCl and rest water. 
Calculate: (a) kg/h water evaporated, (b) kg/h salt precipitated, (c) kg/h thick liquor. 
 
5. The NH3 - air mixture containing 0.2 kg NH3 per kg air enters into an absorption system 
where ammonia is absorbed in water. The gas leaving the system is found to contain 0.004 
kg NH3 per kg of air. Find the percentage recovery of ammonia. 
 
6. A mixture of phenol and water forms two separate liquid phases, one rich in phenol and 
other rich in water, composition of layers is 70% and 9% (by weight) phenol respectively. 
If 500 kg of phenol and 700 kg of water are mixed and layers allowed to separate, what 
will be the weights of two layers? 
 
7. A multiple-effect evaporator system has a capacity of processing 1000 kg per day of solid 
caustic soda when it concentrates a weak liquor from 4 to 25% by weight caustic soda. 
When the same plant is fed with a 10% weak liquor and if it is concentrated to 50% (both 
on weight basis), find the capacity of the plant in terms of solid caustic soda. Assume that 
the water evaporating capacity to be the same in both cases. 
 
8. The ground nut seeds containing 45% oil and 45% solids are fed to expeller, the cake 
coming out of expeller is found to contain 80% solids and 5% oil. Find the percentage 
recovery of oil. 
 
9. A feed to a continuous fractionating column analyses 28 percent benzene and 72 percent 
toluene by weight. The analysis of the distillate shows 52 weight percent benzene and 5 
weight percent benzene was found in the bottom product. Calculate the amount of distillate 
and bottom product per 1000 kg of feed per hour. Also calculate the percent recovery of 
benzene. 
 
10. In the manufacture of soda-ash by the Le-Blank process, sodium sulphate is heated with 
charcoal and calcium carbonate. The resulting 'black ash' has the following composition 
(on weight basis): 
Sodium carbonate (Na2CO3) = 42%. 
Other water soluble material = 6% 
Insoluble material (charcoal, etc.) = 52% 
The black ash is treated with water in order to extract sodium carbonate. The solid residue 
from this treatment has the following composition (on weight basis): 
Sodium carbonate (Na2CO3) = 4%. 
Other water soluble salts = 0.5% 
Insoluble matter = 85% 
Water = 10.5% 
Calculate the weight of residue remaining from the treatment of 1000 kg of black ash. 
 
11. It is desired to make 100 kg of the solution containing 35% salt by weight. Two solutions 
are available. One contains 15% salt and other contains 60% salt. (a) Calculate the kg of 
each solution to be mixed for preparing the above solution. (b) If 50 kg of each of the 
above solution is mixed, what will be the concentration of the resulting solution? 
 
12. An evaporation crystallisation process is used to obtain solid potassium sulphate from an 
aqueous solution of this salt. The fresh feed to the process contains 18.6 weight% K2SO4. 
The wet filter cake from crystalliser consists of solid K2SO4 crystals and 40% by weight 
K2SO4 solution, in the ratio 10 kg crystals/kg solution. The filtrate from the crystalliser, 
also a 40% by weight K2SO4 solution is recycled to join the fresh feed. Mixed feed enters 
into evaporator where water is evaporated and then concentrated stream from evaporator 
enters into a crystalliser. Of the water fed to the evaporator, 42.66% is evaporated. The 
evaporator has a maximum capacity of 9300 kg water evaporation per hour. Calculate the 
maximum production rate of solid K2SO4, the rate at which fresh feed must be supplied 
to achieve this production rate, the ratio-kg recycle/kg fresh feed and the composition of 
stream entering the crystalliser.