Introduction 
     Sorption operations: certain components of a fluid phase, called 
     solutes,  are  selectively  transferred  to  insoluble,  rigid  particles 
     suspended in a vessel or packed in a column.
     Sorption includes selective transfer to the surface and/or into the 
     bulk of a solid or liquid.
            
              The substance that is transferred to the surafce is the 
            adsorbate.
            
              The material on which the adsorbate deposits is the 
            adsorbent.
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                Industrial Example
   Pressure-swing adsorption for the 
   dehydration of air
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                      SORBENTS
     (1) high selectivity to enable sharp separations
     (2) high capacity to minimize the amount of sorbent needed
     (3) favorable kinetic and transport properties for rapid sorption
     (4) chemical and thermal stability
      (5) hardness and mechanical strength 
     (6) a free-flowing tendency for ease of filling or emptying vessels
      (7) high resistance to fouling for long life
      (8) no tendency to promote undesirable chemical reactions
     (9) the capability of being regenerated
     (10) relatively low cost
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                      SORBENTS
    Most solids are able to adsorb species from gases and liquids. However, only a 
    few have a sufficient selectivity and capacity to make them serious candidates 
    for commercial adsorbents.
     Micro pore  <20 A
     Meso pore  20-500 A
     Macro pore >500 A (50 nm)
      The surface area-to-volume ratio
       The specific surface area, Sg is area per unit 
       mass of adsorbent is
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      Specific surface area of an adsorbent
    Sg is measured by adsorbing gaseous nitrogen.
     Typically, the BET apparatus operates at the normal boiling point of N2 (-195.8°C) by 
    measuring the equilibrium volume of pure N2 physically adsorbed on several grams of 
    the adsorbent at a number of different values of the total pressure in the vacuum
    range of 5 to at least 250 mmHg.
      Brunauer,  Emmett,  and  assumed  that  the  heat  of  adsorption  during  monolayer 
    formation                is constant and that the heat effect associated with subsequent 
    layers is equal to the heat of condensation. The BET equation is
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