Page 220 - Separation process principles 2

Exercises 185

8, single-section membrane cascades increase purity of one the number of unique variables and the number of independent
and recovery of the main component in that product. equations that relate the variables. For a single-section, counter-
current cascade, the recovery of one component can be specified.
9. Hybrid systems of different types reduce energy expenditures,
make possible separations that are otherwise difficult, andlor For a two-section countercurrent cascade, the recoveries of two
improve the degree of separation. components can be specified.
10. The number of degrees of freedom (number of specifications)
for a mathematical model of a cascade is the difference between

REFERENCES
f
1. BERDT, R.J., and C.C. LYNCH, Am. Chem. Soc., 66,282-284 (1944). 6. PRASAD, R., E NOTARO, and D.R. THOMPSON, J. Membrane Science, 94,
J.
I Issue 1,225-248 (1994).
2. KREMSER, A., Natl. Petroleum News, 22(21), 4349 (May 21, 1930).
7. BERRY, D.A., and K.M. NG,AIC~E J., 43,1751-1762 (1997).
3. EDMISTER, W.C., AIChE J., 3,165-171 (1957).
4. SMITH, B.D., and W.K. BRINKLEY, AIChE J., 6,446450 (1960). 8. KWAUK, M., AIChE J., 2,240-248 (1956).
P
and
5. LYSTER, W.N., S.L. SULLIVAN, D.S. BILLINGSLEY, C.D. HOLLAND, 9. GILLILAND, E.R., and C.E. REED, Ind. Eng. Chem., 34,55 1-557 (1942).
Jr.,
petroleum Refinel; 38(6), 221-230 (1959).
EXERCISES
/ Section 51 where 100 mg each of solutes A and B are dissolved in 100 ml of
water. After adding 100 ml of an organic solvent that is more
t 5.1 Devise an interlinked cascade of the type shown in Fig-
ure 5.2e, but consisting of three columns for the separation of a selective for A than B, the distribution of A and B becomes that
L shown for equilibration 1 with vessel 1. The organic-rich phase is
four-component feed into four products.
transferred to vessel 2 (transfer), leaving the water-rich phase in
5.2 A liquid-liquid extraction process is conducted batchwise as vessel 1 (transfer). Assume that water and the organic solvent are
shown in Figure 5.23. The process begins in vessel 1 (original),
immiscible. Next, 100 ml of water is added to vessel 2, resulting in
the phase distribution shown for vessel 2 (equilibration 2). Also,
100 ml of organic solvent is added to vessel 1 to give the phase
Vessel 1
Organic 1 I distribution shown for vessel 1 (equilibration 2). The batch
Aqueous [Ei] Original process is continued by adding vessel 3 and then 4 to obtain the
results shown.
(a) Carefully study the process in Figure 5.23 and then draw a
66.7 A
Organic corresponding cascade diagram, labeled in a manner similar to
Equilibration 1
33.3 A Figure 5.2(b).
Aqueous 66.7 B
(b) Is the process of the cocurrent, countercurrent, or crosscurrent
Vessel 2
type?
66.7 A
Organic
33.3 B (c) Compare the separation achieved with that for a single-batch
Transfer
Aqueous equilibrium step.
(d) How could the process be modified to make it a countercurrent
cascade [see 0. Post and L.C. Craig, Anal. Chem., 35,641 (1963)l.
Equilibration 2
5.3 Nitrogen is to be removed from a gas mixture with methane
by gas permeation (see Table 1.2) using a glassy polymer mem-
Vessel 3
brane that is selective for nitrogen. However, the desired degree of
Organic separation cannot be achieved in one stage. Draw sketches of two
Transfer different two-stage membrane cascades that might be considered to
Aqueous perform the desired separation.
29.6 A
7.4 A 29.6 A fj !
Organic Section 5.2
Equilibration 3 I
3.7A 14.8A 14.8A 5.4 In Example 4.9, 83.25% of the oil in soybeans is leached by I
Aqueous 29.6 B 29.6 B
benzene using a single equilibrium stage. Calculate the percent I
. - - - - .
Vessel 4 .
extraction of oil if: 1
29.6 A
Organic
Transfer (a) Two countercurrent equilibrium stages are used to process
Aqueous 5,000 kg/h of soybean meal with 5,000 kgh of benzene.
(b) Three countercurrent equilibrium stages are used to process the
same flows as in part (a).
(c) Also, determine the number of countercurrent equilibrium
stages required to extract 98% of the oil if a solvent rate of twice
I
Figure 5.23 Liquid-liquid extraction process for Exercise 5.2. the minimum value is used.
I