Homework 2 Debriefing

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Homework 2 -Debriefing

• CH EN 5253
• Design II
• Terry Ring

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Problem 1a

• Determine the best distillation sequence by the
  heuristics.

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Separation Train Heuristics

• 1. Remove thermally unstable, corrosive, or
  chemically reactive components early in the
  sequence.
• 2. Remove final products one by one as
  distillates (the direct sequence).
• 3. Sequence separation points to remove, early in
  the sequence, those components of greatest molar
  percentage in the feed.
• 4. Sequence separation points in the order of
  decreasing relative volatility so that the most
  difficult splits are made in the absence of the
  other components.
• 5. Sequence separation points to leave last those
  separations that give the highest-purity
  products.
• 6. Sequence separation points that favor near
  equimolar amounts of distillate and bottoms in
  each column.

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1. Remove thermally unstable, corrosive, or
chemically reactive components early in the
sequence.
Benzene is a carcinogen! For medical/beverage
applications of the other materials, They would
have purity requirement with respect to benzene
that are lt 1 ppm. EPA limits in drinking water
are 5 ppb. Direct Sequence to remove early.
Indirect sequence to make other products clean.
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2. Remove final products one by one as
distillates (the direct sequence).
Direct Sequence if B and T are final products
B T E P M O
T E P M O
E P M O
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3. Sequence separation points to remove, early in
the sequence, those components of greatest molar
percentage in the feed.
This conflicts with Heuristic 2! One product with
a flow of 600 kmole/hr should be removed first
not Benzene and Toluene first using Heuristic 2.
This argues for
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4. Sequence separation points in the order of
decreasing relative volatility so that the most
difficult splits are made in the absence of the
other components.
No information on relative volatilities is given
but you can gage the difficult splits by the
separation of the boiling points. The most
difficult separation is that between Ep-m- and o-
which would be the last in the direct sequence.
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5. Sequence separation points to leave last those
separations that give the highest-purity
products.
Product purities are not stated in the problem.
Using Direct sequence, o-xylene would be the
most pure, but this is also the most difficult
split which may lower it purity a bit. Using
Indirect sequence the Benzene would be the most
pure.
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6. Sequence separation points that favor near
equimolar amounts of distillate and bottoms in
each column.
200 kmole/h
B T E P M O
B T
Argues for the hybrid sequence as it did with
Heuristic 3 Or indirect sequence but Certainly
not the direct sequence
E P M O
800 kmole/h
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Problem 1b

• Marginal Vapor Rate Method

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Simplified Marginal Vapor Rate Method
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Problem 2

• Distillation system to separate a mixture with
  multiple azeotropes.
• 50ºC and 1 bar
• 100 kmole/hr acetone
• 200 kmole/hr chloroform
• 150 kmole/hr ethanol
• Must use sophistocated Physical Property Package

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NRTL, UNIQUAC and their variances
Figure 2
LL?
WILSON, NRTL, UNIQUAC and their variances
ij?
UNIFAC LLE
P?
LL?
UNIFAC and its extensions
Schwartentruber-Renon PR or SRK with WS PR or SRK
with MHV2
LL?
Liquid/Liquid
ij?
P?
Pressure
PSRK PR or SRK with MHV2
ij?
Interaction Parameters Available
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Wilson, NRTL, UNIQUAC, or UNIFAC with special
EOS for Hexamers
Figure 3
DP?
Wilson, NRTL, UNIQUAC, UNIFAC with Hayden
OConnell or Northnagel EOS
VAP?
Wilson, NRTL, UNIQUAC, or UNIFAC with ideal Gas
or RK EOS
VAP?
Vapor Phase Association
UNIFAC and its Extensions
DP?
Degrees of Polymerizatiom
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Bob Seaders Recommendations
     
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Physical Property Data Base

• There are several
• NRTL
• Uniquac
• Use most sophisticated data base
• Second set of coefficients
• Non-ideal gas for gt 10 bar

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Distillation Sequence
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Concepts of Sequence
Acetone
B2

• B1 or B11
• Azeotrope in D
• EtOH in B
• Mix to move off Azeotrope
• B12
• Chloroform in D
• Acetone in B

D1
F2
F1
B1
D2
Ethanol
Chloroform
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Distillation

• XB, XF and YD form a line for a Distillation
  Column
• XD is on tie line to residue curve and the
  tangent takes you to YD