Destilación Azeotropica

Azeotropic Distillation
Post-IFAC Conference

I-Lung Chien Department of Chemical Engineering National Taiwan University of Science and Technology Taipei 106, TAIWAN

July 14, 2008
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Typical methods for separating mixtures with azeotrope
˙Not adding third component
- Pressure-swing distillation (THF-H2O) - Mixtures with binary heterogeneous azeotrope (n-butanol-H2O) - Hybriddistillation with pervaporation (membrane) - Hybrid distillation with adsorbent (molecular sieve)

˙Adding third component
- Homogeneous azeotropic distillation (IPA-H2O+DMSO) - Heterogeneous azeotropic distillation
(Two systems: IPA-H2O+CyH and HAc-H2O+IBA)

- Salt distillation (saline extractive distillation)
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Thermodynamic Model
˙Extremely important for any design study ˙Check yourapplication and select the proper class of property method ˙Use Aspen Plus built-in model parameters or the parameters from literature to predict VLE (Txy, xy), LLE, and azeotropic compositions and azeotropic temperatures ˙Verify from data in DECHEMA, Azeotropic Data – III (Horsely, 1973), Azeotropic Data (Gmehling, 2004), and also from literatures ˙You may need to re-fit model parameters using parameterestimation capability in Aspen Plus
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Pressure-Swing Azeotropic Column System
(Example from: Luyben’s book “Plantwide Dynamic Simulators in Chemical Processing and Control”)

˙ Can be used in systems where there is significant change in the azeotropic composition with pressure. ˙ Azeotrope: @20 psia → 80.6 mol% THF, 164ºF @115 psia → 65.1 mol% THF, 280ºF ˙ Minimum-boiling homogeneousazeotrope varies with pressure.

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Design Flowsheet

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Remarks about the Design Flowsheet
˙Two pressures are design variables to be optimized, as well as the number of trays in each column and feed-tray locations. ˙The larger the difference in the two pressures, further apart the azeotropic compositions, less recycle is required and the lower of the energy consumption. ˙However, the lowerthe pressure in the low-pressure column, the larger the diameter and the coolant required in the condenser. The higher the pressure in the high-pressure column, the higher the pressure of the steam that must be used in the reboiler and other problems with high temperature at reboiler. ˙Possible heat integration of the condenser (HPCOL) and the reboiler (LPCOL).
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Isobaric Phase Diagrams forBinary Azeotropic Mixtures

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Separation of a Binary Heterogeneous Azeotropic Mixture
(Example from Doherty and Malone, “Conceptual Design of Distillation Systems)

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Design when Feed Composition is in miscible Region (e.g. 20% water)

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Examples of Binary Mixture Systems
• No need to add entrainer as in pressure-swing azeotropic distillation system. • Examples include:purifying water-hydrocarbon mixtures (e.g., water with any one of the following components: C4-C10, benzene, toluene, xylene, etc.). • Water-alcohol mixtures (e.g. butanol, pentanol, etc.) as another example.
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Homogeneous Azeotropic Distillation
(Minimum-boiling azeotrope with intermediate-boiling entrainer example)

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Extractive Distillation
• Separating minimum-boiling binary azeotropeby using heavy entrainer. • Two-column sequence with first extractive column separating out light product and second entrainer recovery column separating out entrainer and another product. • Most widely used form of homogeneous azeotropic distillation in industries • Examples include: n-butane-butadiene using furfural; dehydration of ethanol using ethylene glycol; acetonemethanol using water;pyridine-water using bisphenol.
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Case Study of an Homogeneous Azeotropic Distillation System
• Isopropyl Alcohol (IPA) is widely used in semi-conductor industry as a cleaning agent, thus the recovery of IPA from waste solvent stream is an important issue worthy of study. • Dehydration of IPA using Dimethyl Sulfoxide (DMSO) as entrainer. • Minimum-boiling azeotrope with heavy entrainer, thus...