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Adsorption: A surface phenomenon

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It is a surface phenomenon i.e. the interior of adsorbent ... Very favourable. Favourable. Unfavourable. Linear. Adsorption isotherms. y. q. Linear. Freundlich ... – PowerPoint PPT presentation

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Title: Adsorption: A surface phenomenon


1
Adsorption A surface phenomenon
Adsorbate
Adsorbent
Selective solute binding
Removal of bound material is called desorption
i.e. opposite of adsorption
2
Selectivity of adsorption Criteria
  • Molecular weight or size
  • Solute shape
  • Polarity
  • Electrostatic charge

Steric
Chemical properties
Interactions involved in adsorption
  • van der Waals forces
  • Electrostatic interactions
  • Hydrophobic interactions
  • Hydrogen bonding
  • Chemical bond formation (chemisorption)

Non-covalent interactions
3
Adsorbents
  • Natural or synthetic
  • Amorphous or microcrystalline structure
  • Very high specific surface area
  • Examples
  • Charcoal
  • Kaolin
  • Bentonite
  • Activated carbon
  • Silica gel
  • Activated alumina
  • Zeolite (molecular sieves),

4
Adsoprtion
  • Advantages
  • High selectivity (e.g. affinity adsorption)
  • Ability to handle very dilute feed concentrations
  • Disadvantages
  • It is a surface phenomenon i.e. the interior of
    adsorbent is not available
  • Batch or semi-batch operations only
  • Adsorbent regenerated
  • Loss of product quality

5
Adsoprtion Applications
  • Gas separation using molecular sieves by pressure
    swing adsorption
  • Removal of toxic gases from air (e.g. gas masks)
  • Fractionation of industrial chemicals using gas
    or liquid chromatography
  • Removal of phenolics and other toxic chemical
    from waste water
  • Removal of chlorinated hydrocarbons from waste
    gas streams
  • De-hydration or de-humidification of gases
  • Water purification by deionization and
    ion-exchange
  • Ion exchange separation of proteins and nucleic
    acids
  • Affinity separations

6
Adsoprtion Isotherms
  • Relationship between bound and free solute
    concentrations at equilibrium
  • Analogous to equilibrium line in extraction
  • Isotherm refers to data being obtained at
    constant temperature

Irreversible
Very favourable
Linear
Solute Concentration on adsorbents surface (q)
Favourable
Unfavourable
Solute concentration in solution (y)
7
Adsorption isotherms
Linear
Freundlich
Langmuir
Freundlich
q
Linear
Langmuir
y
8
Determination of isotherm constants
Linear Determine K from plot of q versus
y Freundlich Determine K and n from plot of
(log q) versus (log y) Langmuir Determine q0
and K from plot of (1/q) versus (1/y)
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