Mass transfer solucionario

1.2a. Concentration of a liquid solution fed to a distillation column.
A solution of carbon tetrachloride (1) and carbon disulfide (2) containing 50% by weight each is to be continuously distilled at the rate of 4,000 kg/h Determine:
a) The concentration of the mixture in terms of mole fractions.

Solution

Basis: 100 kg mixture
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b)The average molecular weight of the mixture.

Solution
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c) Calculate the feed rate in kmol/h.

Solution
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1.1a. Concentration of a gas mixture.
A mixture of noble gases [helium (1), argon (2), krypton (3), and xenon (4)] is at a total pressure of 200 kPa and a temperature of 400 K. If the mixture has equal mole fractions of each of the gases, determine:
a)The composition of the mixture in terms of mass fractions.

Solution:
Basis: 100 kmole of the mixture
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b) The average molecular weight of the mixture.

Solution
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c) The total molar concentration.

Solution
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d) The mass density.

Solution
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1.3a.Concentration of liquified natural gas.
A sample of liquified natural gas, LNG, from Alaska has the following molar composition: 93.5% CH4, 4.6% C2H6, 1.2% C3H8, and 0.7% CO2. Calculate:
a) Average molecular weight of the LNG mixture.

Solution
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b) Weight fraction of CH4 in the mixture.

Solution

Basis: 100 kmoles of LNG
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c) The LNG is heated to 300 K and 140 kPa, and vaporizes completely. Estimate the density of the gas mixture under these conditions.

Solution
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1.4b. Concentration of a flue gas.
A flue gas consists of carbon dioxide, oxygen, water vapor, and nitrogen. The molar fractions of CO2 and O2 in a sample of the gas are 12% and6%, respectively. The weight fraction of H2O in the gas is 6.17%. Estimate the density of this gas at 500 K and 110 kPa.

Solution
Basis: 100 kmole of gas mixture

Let x = molar fraction of water in the mixture (as a percent)
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Initial estimate
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From the given water weight fraction (0.0617):
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1.5b. Material balances around an ammonia gas absorber.
A gas stream flows at the rate of 10.0 m3/s at 300 K and 102 kPa. It consists of an equimolar mixture of ammonia and air. The gas enters through the bottom of a packed bed gas absorber where it flows countercourrent to a stream of pure liquid water that absorbs 90% of allof the ammonia, and virtually no air. The absorber vessel is cylindrical with an internal diameter of 2.5 m.
a) Neglecting the evaporation of water, calculate the ammonia mol fraction in the gas leaving the absorber.

Solution:
Basis: 1 second
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A = ammonia B = air
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b)Calculate the outlet gas mass velocity (defined as mass flow rate per unit empty tube cross-sectional area).

Solution:
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1.6b. Velocities and fluxes in a gas mixture.
A gas mixture at a total pressure of 150 kPa and 295 K contains 20% H2, 40% O2, and 40% H2O by volume. The absolute velocities of each species are -10 m/s, -2 m/s, and 12 m/s, respectively, allin the direction of the z-axis.
a) Determine the mass average velocity, v, and the molar average velocity, V, for the mixture.

Solution
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Molar average velocity, V
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Mass average velocity, vm

Basis: 1 kmole of gas mixture
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b) Evaluate the four fluxes: jO2, nO2, JO2, NO2.

Solution:
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