ESCAPE 18

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New configuration for heteroazeotropic batch
distillation I. Feasibility studies

• Peter Lang1, Ferenc Denes1, Xavier Joulia2
• 1BUTE Dept. of Building Services Process
  Engineering
• H-1521 Budapest, Muegyetem rkp. 3-5
• 2LGC-ENSIACET-INPT
• 118 route de Narbonne, 31077 Toulouse, France

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Outline

• 1. Introduction
• 2. Column configurations and the feasibility
  method
• 3. Calculations for a binary heteroazeotropic
  mixture (n-butanol - water)
• 4. Calculations for a ternary mixture
  (isopropanol water benzene)
• 5. Conclusion

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1. Introduction

• The recovery of the organic solvent streams is
  performed mainly by distillation. If components
  of a mixture form a heteroazeotrope or by the
  addition of an entrainer a heteroazeotrope can be
  formed, the azeotropic composition can be crossed
  by decantation.
• In the pharmaceutical and fine chemical
  industries because of the small amount of the
  products and the frequent product changes batch
  processes including the batch heteroazeotropic
  distillation (BHD) are widely applied.

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The objectives of our work
- to study a new double-column heteroazeotropic
batch distillation configuration,
- to investigate the separation of binary and
ternary systems forming heteroazeotrope by
feasibility studies,
- to compare the performance of the new
configuration with that of the usual batch
rectifier.
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Configurations of the heteroazeotropic batch
rectification
2. The column configurations and feasibility
method
Single-column (usual) configuration (batch
rectifier, open system)
Double-column (new) configuration (closed system)
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Processing of a binary heteroazeotropic mixture
(A-B) by usual batch rectifier
Step 1. Production of component A
Step 2. Production of component B
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Processing of a binary heteroazeotropic mixture
(A-B) by the new double-column batch rectifier
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Feasibility method
We made feasibility studies for the separation of
a binary (n-butanol - water) and a ternary
mixture (isopropanol water benzene as
entrainer).
Simplifying assumptions - maximal separation
(azeotropic composition of the top vapour), -
negligible tray and decanter holdup, - constant
molar overflow, - negligible duration of pumping
between the two steps of the BR, - no entrainer
loss in the case of ternary mixture
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We determined for both configurations - the
duration of the processes, - the amount of the
products, - the amount of the byproducts.
In the case of the double-column system the whole
- heat duty Q1 Q2 Q or the vapour
flow rate V1 V2 V ( 20 kmol/h ), - amount
of charge Uch1 Uch2 Uch ( 100 kmol ) is
equal to that of the single-column. For the DCS
both products reach the prescribed purity at the
same time.
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3. Calculations for binary heteroazeotropic
mixture
Boiling and dew point curves of the mixture
n-butanol water
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Calculation results for different compositions
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• In the cases studied the performance of the two
  configurations were nearly the same. In the case
  of the double-column configuration
• - greater recovery of butanol was reached,
• - more water was recovered, and
• - less byproduct was produced.
• However the energy demand increased to a small
  extent.

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4. Calculations for the ternary mixture
Boiling and dew point curves of the isopropanol
water mixture
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In order to produce pure IPA a third component
(entrainer) is added in a small amount to the
binary mixture forming a ternary heteroazeotrope
which splits into an organic and an aqueous
phase. In the latter one the water/IPA ratio is
much higher than in the IPA water azeotrope
(charge).
Residue curve map of the IPA water benzene
mixture at atmospheric pressure
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LLE diagram of the IPA water benzene mixture
at the boiling point of the ternary azeotrope
(65.7 C)
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Calculation results
The mixture studied 100 kmol IPA (A) water
(B) mixture with binary azeotropic composition
(67.4 mol IPA)

• In the case of the double-column system
• - the recovery of IPA is greater,
• - more water is recovered,
• - there is no byproduct.
• However the process was somewhat quicker in the
  case of the single-column configuration (smaller
  energy consumption).

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5. Conclusion
- We suggested and investigated a new
double-column hetroazeotropic batch
distillation configuration.
- For the separation of a binary heteroazeotropic
and for a binary homoazeotropic mixture (with
entrainer) we performed feasibility studies based
on several simplifying assumptions.
- The new configuration proved to be feasible and
in the cases studied competitive with the
batch rectifier.
- After these investigations we made also
rigorous simulation based on much less
simplifying assumptions. (results on poster P019)
- We still have to investigate the operational
and control issues of the new configuration.
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Thank you for your attention.
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References

• - Modla G., P. Lang, K. Molnar, (2001). Batch
  Heteroazeotropic Rectification, 6th WCCE,
  Melbourne, Australia, (10 pages on CD).
• - Modla G., P. Lang , B. Kotai, K. Molnar,
  (2003). AIChE J, 49 (10), 2533.
• - Rodriguez-Donis I, V. Gerbaud, X. Joulia,
  (2002). AIChE J, 48 (6), 1168.
• - Rodriguez-Donis Y., J. Equijarosa, V. Gerbaud,
  X. Joulia, (2003). AIChE J, 49, 3074.
• - Skouras S., V. Kiva , S. Skogestad, (2005a).
  Chem. Eng. Sci., 60, 2895.
• - Skouras S., S. Skogestad, V. Kiva, (2005b).
  AIChE Journal, 51 (4), 1144-1157.
• - Lang P., G. Modla, (2006). Chem. Eng. Sci.,
  61, 4262-4270.