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Unformatted text preview: equired: A sketch of the membrane device.
Analysis: A sweep fluid is generally required. In some cases, a vacuum could be pulled
on the permeate side. The membrane device is shown below. Exercise 1.10
Wanted: The differences, if any, between adsorption and gas-solid chromatography.
Analysis: Adsorption can be conducted by many techniques including fixed bed, moving
bed, slurry, and chromatography. In chromatography, unlike the other adsorption
techniques, an eluant is used to carry the mixture through the tube containing the sorbent.
Multiple pure products are obtained because of differences in the extent and rate of
adsorption, resulting in different residence times in the tube. The tube is made long
enough that the residences do not overlap. Exercise 1.11
Wanted: Is it essential in gas-liquid chromatography that the gas flows through the
packed tube in plug flow?
Analysis: Plug flow is not essential, but it can provide sharper fronts and, therefore, the
chromatographic columns can be shorter. Exercise 1.12
Wanted: The reason why most small particles have a negative charge.
Analysis: Small particles can pick up a negative charge from collisions in glass ware. In
an aqueous solution, inorganic and polar organic particles develop a charge that depends
on the pH of the solution. The charge will be negative at high pH values. Exercise 1.13
Wanted: Can a turbulent-flow field be used in field-flow fractionation?
Analysis: Field-flow fractionation requires a residence-time distribution of the
molecules flowing down the tube. This is provided best by laminar flow. The residencetime distribution with turbulent flow is not nearly as favorable. Turbulent flow would not
be practical. Exercise 1.14
Subject: Sequence of three distillation columns in Fig. 1.9 for separating light
Given: Feed to column C3 is stream 5 in Table 1.5. Alter the separation to produce a
distillate containing 95 mol% iC4 at a recovery of 96%.
Find: (a) Component flow rates in the distillate and bottoms from column C3.
(b) Percent purity of nC4 in the bottoms.
(c) Percent recovery of iC4, for 95 mol% iC4 in the distillate, that will
maximize the percent purity of nC4 in the bottoms. Assumptions: Because of the relatively sharp separation in column C3 between iC4 and
nC4, assume that all propane in the feed appears in the distillate and all C5s appear in the
Analysis: (a) Isobutane to the distillate = (0.96)(171.1) = 164.3 lbmol/h
Total distillate rate = 164.3/0.95 = 172.9 lbmol/h
Normal butane to the distillate = 172.9 - 2.2 - 164.3 = 6.4
Material balance around column C3, in lbmol/h:
272.6 (b) % Purity of nC4 in bottoms = (220.2/272.6) x 100% = 80.8%
(c) Let x = lbmol/h of nC4 in the distillate
y = lbmol/h of iC4 in the distillate
P = mole fraction purity of nC4 in the bottoms
226.6 − x
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.
- Spring '11
- The Land