Unformatted text preview: te a 10-stage extraction unit for
the given conditions. The model converged in 12 iterations, with the results given below. The
product compositions differ little from those computed for 1 stage. Also, the interstage flow
rates are almost constant for stages 1 to 7. Thus, a significant separation is not possible for any
number of stages. The reason for this is clear if a line on the above ternary diagram is drawn
from the feed point [30 mol% (2) at 0 mol% (3)] to the solvent point [100 mol% (3)]. This line
is almost collinear with a tie line. Regardless of the number of stages and the number of
equilibrium stages, a significant separation of cyclopentane and cyclohexane can not be made. Exercise 10.43
Subject: Liquid-liquid extraction of acetic acid from water by ethyl acetate at 100oF
Given: Feed of 6,660 lb/h of acetic acid and 23,600 lb/h of water. Solvent of 68,600 lb/h of
ethyl acetate and 2,500 lb/h of water. Ccountercurrent-flow extractor.
Assumptions: NRTL equation for activity coefficients using the following parameters:
Acetic acid BIJ
0.2 Number of equilibrium stages to extract 99.5% of the acetic acid. Analysis: The Extract model of Chemcad was used starting with 2 equilibrium stages and
increasing by one until 99.5% extraction was achieved. For each run, convergence was achieved
in 12 to 13 iterations. The results were:
No. of stages
% Extraction of Acetic acid
The results show that 5 stages are needed, but 6 stages is safer.
Detailed results for 6 stages are: Exercise 11.1 Subject:
Azeotropes and approximate residue curve map for the system n-hexane methanol - methyl acetate at 1 atm
Given:. Ternary system n-hexane - methanol - methyl acetate at 1 atm.
Find: All binary and ternary azeotropes from suitable references. Approximate residue curve
map showing distillation boundaries. Type of node for each azeotrope and pure component.
Analysis: The following azeotrope data were obtained from the "Handbook of Chemistry and
Physics" or the 6th edition of "Perry's Chemical Engineers' Handbook":
At 1 atm, the molecular weights and boiling points of the three components are:
Molecular weight Normal b. pt., oC
Binary azeotropes (all minimum boiling):
Boiling pt., oC
53.5 Wt% A/B
19.0/81.0 Ternary azeotrope (minimum boiling):
Boiling pt., oC
Methyl acetate 47.4 48.6/14.6/36.8 Mol% A/B
35.2/64.8 Mol% A/B/C
37.2/30.1/32.7 An approximate residue curve map on a right triangular diagram, of the type developed in Fig.
11.7, is shown on the next page. From that diagram, which includes approximate distillation
boundaries, the following types...
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