Adsorption-desorption process vapor phase applications

As we saw in Section 3.3, the concentration difference of one constituent of a gas or liquid solution at the surface of another phase is called adsorption. In other words, adsorption is the partitioning of a chemical species between a bulk phase and an interface. Desorption is the reverse of the adsorption process, showing that the molecules are leaving the interface towards the other phase. Adsorption is different from absorption where a species penetrates and is dissolved throughout the bulk phase of a liquid or a solid. For gas or liquid adsorption on solids, the solid material on which adsorption takes place is defined as the adsorbent the material in the adsorbed state (while bound to the solid surface) is called the adsorbate, and the gas, vapor or liquid molecule prior to being adsorbed is called the adsorptive. In this section, we will investigate only the principles and applications of gas adsorption on solids (see Section 9.4 for liquid adsorption on solids). 

Both adsorption from a supercritical fluid to an adsorbent and desorption from an adsorbent find applications in supercritical fluid processing.The extrapolation of classical sorption theory to supercritical conditions has merits. The supercritical conditions are believed to necessitate monolayer coverage and density dependent isotherms. Considerable success has been observed by flic authors in working with an equation of state based upon the Tofli isoterm. It is also important to note that the retrograde behavior observed for vapor-hquid phase equilibrium is experimentally observed and predicted for sorptive systems. 

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