SETK 1123-MASS BALANCE
Exercises 1
Name: ________________________________________________________
Question 1
In the concentration of orange juice, a fresh extracted and strained juice containing 7.08
wt % solids is fed to a vacuum evaporator. In the evaporator, water is removed and solids
content increased to 50 wt% solids. For 1000 kg/h entering, calculate the amounts of the
outlet streams of concentrated juice and water.
Question 2
A gas stream contains 18 mole % hexane and the remainder nitrogen. The stream flows
to a condenser, where its temperature is reduced and some of the hexane is liquefied. The
hexane mole fraction in the gas stream leaving the condenser is 0.050. Liquid hexane
condensate is recovered at rate of 1.50 L/min.
(a) What is the flow rate of the gas stream leaving the condenser in mol/min?
(ans:83.8 mol/min; 72.3 mol/min)
(b) What percentage of the hexane entering the condenser is recovered (mole outlet/
mole inlet) as a liquid? (ans: 76%)
Question 3
A liquid mixture of benzene and toluene contains 55% benzene by mass. The mixture is
to be partially evaporated to yield a vapor containing 85 % benzene and a residual liquid
containing 10.6 % benzene by mass. Draw and label a process flow chart, then determine
the expected value of the flow rate of the vapor and liquid product streams, respectively.
(ans: 59.7 kg/h; 40.3 kg/h)
Question 4
Three hundred gallons of a mixture containing 75.0 wt % ethanol (ethyl alcohol) and 25
wt % water (mixture SG =0.877) and a quantity of a 40.0 wt % ethanol-60.0 wt % water
mixture (mixture SG= 0.952) are blended to produce a mixture containing 60.0 wt %
ethanol.
(a) Draw and label a flowchart of the mixing process and do degree-of-freedom
analysis
(b) Calculate the required volume (in gallons) of the 40 wt % ethanol-60.0 wt % water
mixture. (ans: 207 gal)
Dr. Jamarosliza binti Jamaluddin
1
SETK 1123-MASS BALANCE
Question 5
Wet air is a mixture of water vapor (H2O) and dry air (DA), containing 4.0 mole % water vapor
is passed through a column of calcium chloride pellets. The pellets adsorb 97.0 % of the water
and none of the other constituents of the wet air. The column packing (pellets) was initially
dry and had a mass of 3.40 kg. Following 5.0 hours of operation, the pellets are reweighed
and found to have mass of 3.54 kg. Do the degree of freedom analysis and calculate the molar
flow rate (mol/h) of the feed gas and mole fraction of water vapor in product gas. (ans: 40.1
mol/h; 1.2 x 10-5 mol H2O/mol
Question 6 (Test 1 2019/2020-2)
One of the steps in the recovery of ethanol from fermentation is distillation. The continuous
distillation column is operated at steady state at a feed rate of 1500 kg/h. The feed is mainly
water with 8.0 wt% ethanol. The top stream (distillate) contains 90 wt% ethanol and
represents 80% of the ethanol in the feed. (Ethanol, Mw = 46.07 kg/kmol and water, Mw= 18
kg/kmol).
(a) Draw and label a flow chart of the distillation column completely.
(7 Marks)
(b) Perform the degree of freedom analysis to prove that the problem can be solved.
(3 Marks)
(c) Calculate the molar flow rate of ethanol (kmol/h) in the top product stream and the
mole fraction of ethanol in the bottom product stream.
(10 Marks)
Question 7 (Test 1 2019/2020-2)
A gas mixture containing 72 mol% methane (CH4) (Mw = 16.04 g/mol) and 28 mol% hydrogen
sulfide (H2S) (Mw = 34.08 g/mol) is to be purified in an absorber by contacting the gas with
a liquid solvent. The gas is fed at 3200 mol/h and the gas feed rate/solvent feed rate ratio is
3:1. The solvent (Mw = 119 g/mol) absorbs 97.2% of the H 2S in the gas feed stream. CH4 is
not absorbed in the solvent at all, and no solvent leaves with the gas.
(a) Draw and label the process flow diagram completely
(5 Marks)
(b) Perform the degree of freedom analysis to show that the problem is completely
specified.
(3 Marks)
(c) Calculate the flow rates (kg/h) and composition (wt%) of both output streams. (ans:
32wt%;68 wt%; 45 wt%; 55 wt%; 74 kg/h; 46.77 kg/h)
(12 Marks)
Question 8 (Test 1 2019/2020-2)
To make tomato paste, 100 kg tomato pulp containing one-fifth water by mass is conveyed
through an evaporator in which 70.0% of the entering water is vaporized.
(a) Draw and label the process flow diagram completely.
(5 Marks)
(b) Calculate the mass fraction of water in the tomato paste, leaving the evaporator and
the ratio of kg H2O vaporized/kg tomato paste leaving the evaporator. (ans:0.07 kg
water/kg)
(9 Marks)
(c) If 3000 tons/day of tomato pulp are fed to the evaporator, (i) determine the mass
fraction of each stream and justify your answer and (ii) how much water (tons/day)
must be removed from the tomato pulp. (ans: 420 ton/day
(6 Marks)
Dr. Jamarosliza binti Jamaluddin
2
SETK 1123-MASS BALANCE
Question 9 (ans: 170 kg; 800 kg; 500 kg)
Question 10 (ans: 54 Ton/hr; 80 Ton/hr; 84 Ton/hr)
Question 11
Lately a lot of fish hobbyists want to have salty fish species in their aquarium. Currently
a 10-gallon fish aquarium contains 2 percent salt by mass. This concentration is not
suitable for the fish and can make them sick. You need to add pure salt to increase the
concentration to 3.5 percent by mass. Assume the salt water having same density as
water.
(a) Draw and label the process
(b) How much dry salt (Ibm) must be added to the aquarium
(c) If we change the 10 gallon aquarium to 10 liter aquarium, does the final
concentration in the aquarium need to change? Justify your answer
Question 12
A solution, containing 3.7 mol % ethyl acetate, 2.6 mol % acetic acid, 5.4 mol % ethanol,
and water, is fed to a splitter at 97 kmol/h. The splitter operates at steady state and has
three output streams. 27 % of the flow exits in the first stream, 54 % exits in the second
stream, and the remainder exits in the third stream. Calculate the flow rates (kmol/h) and
compositions (mol %) of the three output streams.
Dr. Jamarosliza binti Jamaluddin
3