Unformatted text preview: he values of relative volatility, the separation of p-xylene from m-xylene by
distillation is not practical. The other two separations are practical by distillation, but
require large numbers of stages.
(b) From Reference 10, the following properties are obtained: Property
van der Waals volume, m3/kmol
van der Waals area, m2/kmol x 10-8
Dipole moment, debye
Radius of gyration, m x 1010
Normal melting point, K
Normal boiling point, K
Critical temperature, K
Critical pressure, MPa m-xylene
3.511 From the table, the difference of 61.1 K in melting points is very significant and can be
exploited in melt crystallization. The difference in dipole moments of 0.30, while not
large, makes possible the use of adsorption or distillation with a solvent
(c) Explanations are cited in Part (b). Exercise 1.20
Subject: Separation of a near-azeotropic mixture of ethyl alcohol and water.
Given: A list of possible methods to break the azeotrope.
Find: Reasons why the following separation operations might be used:
(a) Extractive distillation
(b) Azeotropic distillation
(c) Liquid-liquid extreaction
(e) Pervaporation membrane
Melting point, oC
Dipole moment, debye Ethanol
1.85 (a) Extractive distillation is a proven process using ethylene glycol.
(b) Heterogeneous azeotropic distillation is possible with benzene, carbon
tetrachloride, trichloroethylene, and ethyl acetate.
(c) Liquid-liquid extraction is possible with n-butanol.
(d) Crystallization is possible because of the large difference in the melting
(e) Pervaporation is possible using a polyvinylalcohol membrane.
(f) Adsorption is possible using silica gel or activated alumina to adsorb the
water. Exercise 1.21
Subject: Removal of ammonia from water.
Given: 7,000 kmol/h of water containing 3,000 ppm by weight of ammonia at 350 K
and 1 bar.
Find: A method to remove the ammonia.
Analysis: From Perry's Handbook, 7th edition, page 2-87, the volatility of ammonia is
much higher than that of water. Therefore, could use distillation or air stripping. Also,
could adsorb the ammonia on a carbon molecular sieve or use a liquid organic membrane
containing an acidic complexing agent to form an ion-pair with the ammonia ion, NH4+. Exercise 1.22
Subject: Separation of a mixture of distillation by a sequence of distillation columns.
Given: Feed stream containing in kmol/h: 45.4 C3, 136.1 iC4, 226.8 nC4, 181.4 iC5,
and 317.4 nC5. Three columns in series, C1, C2, and C3. Distillate from C1 is C3-rich
with a 98% recovery. Distillate from C2 is iC4-rich with a 98% recovery. Distillate from
C3 is nC4-rich with a 98% recovery. Bottoms from C3 is C5s-rich with a 98% recovery.
Find: (a) Process-flow diagram like Figure 1.9.
(b) Material-balance table like Table 1.5.
(c) Mole % purities in a ta...
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