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Adsorption

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The physical and chemical properties of the gas or vapor (adsorbate) ... Chemical adsorption occurs when there is sharing of electrons between adsorbent and ... – PowerPoint PPT presentation

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Title: Adsorption


1
Adsorption
2
What is Adsorption?
  • Adsorption is the transfer of a material from one
    liquid or gaseous state to a surface.
  • The substance that is transferred to the surafce
    is the adsorbate.
  • The material on which the adsorbate deposits is
    the adsorbent.
  • Example Silica gel, Activated carbon, Alumina,
    Zeolites and molecular sieves, Polymers.

3
Factors affecting the process
  • The physical and chemical properties of the gas
    or vapor (adsorbate).
  • The temperature at which the process occurs.
  • The properties of the adsorbent.
  • The adsorption isotherm or equilibrium adsorption
    data.

4
Physical and chemical adsorption
  • Physical adsorption occurs when the bonding
    forces are dispersion and coulombic type.
  • The amount of heat released during this process
    is equal to the heat of condensation.
  • Chemical adsorption occurs when there is sharing
    of electrons between adsorbent and adsorbate.
  • The amount of heat released during this process
    is equal to the heat of reaction.

5
Single-component Monolayer models
  • The following two isotherms are more commonly
    used
  • 1. Langmuir equation qA (QKCA/ 1KCA)
  • qA equilibrium uptake of adsorbate
  • Q weight of adsorbate
  • CA concentration of adsorbate A
  • K constant
  • 2. Freundlich equation qA K(CA)1/n
  • qA equilibrium uptake of adsorbate
  • CA concentration of adsorbate A
  • K, n constants

6
Single compartment multilayer models
  • The following model is most commonly referred
    to
  • BET equation
  • P/V(Ps P) 1/VmC ((C-1)P)/(CVmPs)
  • V Volume adsorbed
  • Ps saturation pressure
  • P pressure at which V is adsorbed
  • Vm volume occupied in a monolayer
  • C a constant

7
Multicomponent models
  • Such a model is employede when the adsornber is
    to remove two or more pollutants.
  • Markham and Benton model The equation for an n
    component system
  • qi QiKiPi/(1?KjPj) (for j1 to n)
  • Pi partial pressure of component i
  • Qi amount adsorbed for component I
  • Ki a constant.
  • Total quantity adsorbed
  • qT ?qi ?QjKjPj/(1 ?KjPj)
  • (for i and j from 1 to
    n)
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