DISTILLATION

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DISTILLATION

• A Key Process in Chemical Engineering Studies

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INTRODUCTION

• Distillation is the separation process of fluid
  mixtures
• The mixture can either be liquid-liquid,
  liquid-gas, or gas-gas
• The mixture can contain 2 or more components with
  varying boiling points
• The component with the higher boiling point is
  called the more volatile component (MVC)
• There are 2 basic methods of distillation

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FLASH DISTILLATION

• Flash distillation works by boiling a mixture to
  vaporize the lower boiling point component
• Then component is then condensed without any
  liquid returning to the system
• The system has no reflux (all the condensate is
  drawn off as product)

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FLASH DISTILLATION
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FLASH DISTILLATION

• Advantages
• The process is fast and low-cost
• Can be run in batches or continuously
• Disadvantages
• Only effective for components with large
  difference in boiling points
• Not so useful for equally volatile components

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DISTILLATION WITH REFLUX

• Also known as rectification
• A part of the condensate is returned to the
  distillation column
• The returning liquid comes into close contact
  with the vapor
• The returning of liquid is termed reflux

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DISTILLATION WITH REFLUX

• Advantages
• Able to separate components with similar boiling
  points
• Can achieve high separation
• Disadvantages
• The process is slower
• The system is usually more expensive

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Distillation Column Types

• Packed Column rings, balls, saddles, etc.
• Sieve tray/plate
• Bubble cap
• Main objective to increase efficiency

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VAPOR-LIQUID EQUILIBRIUM (VLE)

• When a mixture is boiled, the components have
  different liquid and vapor compositions
• The compositions are determined by the
  temperature and pressure
• An equilibrium curve can be plotted for
  compositions at specific temperatures and
  pressures

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VAPOR-LIQUID EQUILIBRIUM (VLE)
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VAPOR-LIQUID EQUILIBRIUM (VLE)

• This curve is important because it is used to
• determine the phase compositions of a component
  at a particular temperature/pressure
• determine the maximum achievable separation
• estimate the number of plates needed in a
  continuous distillation column with reflux

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BOILING-POINT DIAGRAM

• A diagram similar to the VLE curve is the boiling
  point diagram
• It relates the liquid and vapor phase
  compositions to temperature

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BOILING-POINT DIAGRAM
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RECTIFICATION AND STRIPPING

• Rectification is simply continuous distillation
  with reflux
• When a mixture is fed to center of a column, the
  rising vapor strips it of the MVC, leaving the
  less volatile component to flow down
• When combined, a highly pure top and bottom
  product can be obtained

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DISTILLATION IN THE INDUSTRY

• Petroleum refineries use multi-stage continuous
  distillation to separate crude oil
• Ethanol is distilled from fermented carbohydrates
  such as rice, corn, wheat, barley etc.
• Air is distilled to obtain argon, a useful inert
  gases and liquid nitrogen