Page 195 - Separation process principles 2

160 Chapter 4 Single Equilibrium Stages and Flash Calculations

4.64 A vapor mixture having equal volumes of NH3 and N2 is 4.68 A gas containing 50 mol% propylene in propane is to be
to be contacted at 20°C and 1 atm (760 tom) with water to absorb a separated with silica gel having the equilibrium properties shown
portion of the NH3. If 14 m3 of this mixture is brought into contact in Figure 4.30. The final products are to be 90 mol% propylene and
with 10 m3 of water and if equilibrium is attained, calculate the 75 mol% propane. If 1,000 lb of silica geMbmol of feed gas or less
percent of the ammonia originally in the gas that will be absorbed. is used, can the desired separation be made in one equilibrium
Both temperature and total pressure will be maintained constant stage? If not, what separation can be achieved?
during the absorption. The partial pressure of NH3 over water at
20°C is as follows: Section 4.10

Partial Pressure Grams of Dissolved 4.69 Repeat Example 4.17 for 90% evaporation of the water.
of NH3 in Air, torr NHd100 g of Hz0 4.70 A 5,000-kglh aqueous solution of 20 wt% Na2S04 is fed to
an evaporative crystallizer operating at 60°C. Equilibrium data are
given in Figure 4.24. If 80% of the Na2S04 is to be crystallized,
calculate:
(a) The kilograms of water that must be evaporated per hour
(b) The crystallizer pressure in ton
4.71 Calculate the dew-point pressure, secondary dew-point
pressure, and bubble-point pressure of the following mixtures at
50°C, assuming that the liquid aromatics and water are mutually
insoluble:
(a) 50 mol% benzene and 50 mol% water.
(b) 50 mol% toluene and 50 mol% water.
(c) 40 mol% benzene, 40 mol% toluene, and 20 mol% water.
Section 4.9 4.72 Repeat Exercise 4.71, except compute temperatures for a
4.65 Repeat Example 4.15 for temperatures corresponding to the pressure of 2 atrn.
following vapor pressures for solid PA: 4.73 A liquid containing 30 mol% toluene, 40 mol% ethylben-
(a) 0.7 torr zene, and 30 mol% water is subjected to a continuous, flash distil-
lation at a total pressure of 0.5 atm. Assuming that mixtures of
(b) 0.4 torr
ethylbenzene and toluene obey Raoult's law and that the hydrocar-
(c) 0.1 torr
bons are completely immiscible in water and vice versa, calculate
Plot the percent recovery of PA versus the solid vapor pressure for
the temperature and composition of the vapor phase at the bubble-
the range from 0.1 torr to 1.0 torr. point temperature.
4.66 Nitrogen at 760 torr and 300°C contains 10 mol% 4.74 As shown in Figure 4.8, water (W) and n-butanol (B) can
anthraquinone (A). If this gas is cooled to 200°C, calculate the
form a three-phase system at 101 kPa. For a mixture of overall com-
percent desublimation of A. Vapor pressure data for solid A are as
position of 60 mol% W and 40 mol% B, use a simulation computer
follows:
program and the UNIFAC method to estimate:
T, "C: 190.0 234.2 264.3 285.0 (a) Dew-point temperature and composition of the first drop of
Vapor pressure, torr: 1 10 40 100 liquid.
(b) Bubble-point temperature and composition of the first bubble
These data can be fitted to the Antoine equation (2-39) using the
of vapor.
first three constants.
(c) Compositions and relative amounts of all three phases for
4.67 At 25°C and 101 kPa, 2 mol of a gas containing 35 mol%
50 mol% vaporization.
propylene in propane is equilibrated with 0.1 kg of silica gel adsor-
bent. Using the equilibrium data of Figure 4.30, calculate the moles 4.75 Repeat Example 4.19 for a temperature of 25°C. Are the
and composition of the gas adsorbed and the equilibrium composi- changes significant?
tion of the gas not adsorbed.