Page 190 - Separation process principles 2

Exercises 155

(b) When a solution containing 40 mol% isopropanol is slowly of Table 4.4.
vaporized, what will be the composition of the initial vapor
xi = (1 - Kdl(K1 - K2)
formed?
(c) If this same 4.0% mixture is heated under equilibrium condi- X2 = 1 - X1
.
tions until 75 mol% has been vaporized, what will be the composi- YI = (K1K2 - Ki)I(K2 - Ki)
tions of the vapor and liquid produced?
y2 = 1 - y1
VAPOR-LIQUID EQUILIBRIUM FOR ISOPROPANOL = = z~[(Ki - Kz)/(l - K2)l - 1
F K1 - 1
AND WATER AT 1 ATM
4.18 Consider the Rachford-Rice form of the flash equation,
Mol% Isopropanol
Liquid Vapor
1.18 2 1.95
3.22 32.41 Under what conditions can this equation be satisfied? I
8.41 46.20
4.19 A liquid containing 60 mol% toluene and 40 mol% benzene
9.10 47.06
19.78 52.42 is continuously distilled in a single-equilibrium-stage unit at I
atmospheric pressure. What percent of benzene in the feed leaves
28.68 53.44
in the vapor if 90% of the toluene entering in the feed leaves in the
34.96 55.16
45.25 59.26 liquid? Assume a relative volatility of 2.3 and obtain the solution
graphically.
60.30 64.22
4.20 Solve Exercise 4.19 by assuming an ideal solution and
using vapor pressure data from Figure 2.4. Also determine the
temperature.
4.21 A seven-component mixture is flashed at a specified temper-
ature and pressure.
(a) Using the K-values and feed composition given below, make a
Notes: plot of the Rachford-Rice ilash function
Composition of the azeotrope: x = y = 68.54%.
Boiling point of azeotrope: 80.22"C.
Boiling point of pure isopropanol: 82.5"C.
(d) Calculate K-values and values of a at 80°C and 89°C. of ..
at intervals of 9 of 0.1, and from the plot estimate the correct root
(e) Compare your answers in parts (a), (b), and (c) to those ob-
tained from T-x-y and x-y diagrams based on the following vapor (b) An alternative form of the flash function is
pressure data and Raoult's and Dalton's laws.
What do you conclude about the applicability of Raoult's law to
this system?
Vapor Pressures of Isopropanol and Water Make a plot of this equation also at intervals of \I, of 0.1 and
Vapor pressure, torr 200 400 760 explain why the Rachford-Rice function is preferred.
Isopropanol, "C 53.0 67.8 82.5
Component
Water, "C 66.5 83 100
1
2
Section 4.4
3
4.16 Using the y-x and T-y-x diagrams in Figures 4.3 and 4.4, 4
determine the temperature, amounts, and compositions of the equi- 5
librium vapor and liquid phases at 101 kPa for the following condi-
6
tions with a 100-kmol mixture of nC6 (H) and nC8 (C). 7
(a) ZH = 0.5, QJ = V/F = 0.2
4.22 One hundred kilomoles of a feed composed of 25 mol%
(b) ZH = 0.4, YH = 0.6
n-butane, 40 mol% n-pentane, and 35 mol% n-hexane are flashed
(c) ZH = 0.6. xc = 0.7
at steady-state conditions. If 80% of the hexane is to be recovered
(d) ZH = 0.5, q = 0 in the liquid at 240°F, what pressure is required, and what are the
(e) zH = 0.5, \V = 1.0 liquid and vapor compositions? Obtain K-values from Figure 2.8.
(f) ZH = 0.5, T = 20PF 4.23 An equimolar mixture of ethane, propane, n-butane, and
4.17 For a binary mixture of components 1 and 2, show that the n-pentane is subjected to a flash vaporization at 150°F and 205 psia.
equilibrium phase compositions and amounts can be computed What are the expected amounts and compositions of the liquid and
directly from the following reduced forms of Eqs. (5), (6), and (3) vapor products? Is it possible to recover 70% of the ethane'in the