ADSORPTION

ADSORPTIONBy Serdar ARICANKocaeli UniversityChemical Engineering DepartmentOutlineDefinitionTypes of AdsorptionAdsorption KineticsAdsorption IsothermsAdsorptionAdsoption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.This process creates a film of adsorbate on the surface of the adsorbend. The process is extremely important because for a heterogeneous catalyst to proceed, there must be adsorption of the reactants Types of AdsorptionThere are two types of adsorption;Physical Adsorption (Physorption);Relatively weak bondsMainly Van der Walls bondsChemical Adsorption (Chemisorption);Stronger bonds

Adsorption IsothermsAdsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if liquid) at constant temperature.some of these isotherms are:Freundlich IsothermLangmuir IsothermBET IsothermHenderson-Kisliuk

Freundlich IsothermLangmuir IsothermSemi-emphirical model derived from a propsed kinetic mechanism for gasesBased on four assumptions;All of the adsorption sites are equivalent and each site can only accommodate one molecule.The surface is energetically homogeneous and adsorbed molecules do not interact.There are no phase transitions.At the maximum adsorption, only a monolayer is formed. Adsorption only occurs on localized sites on the surface, not with other adsorbates.

Adsorption Kinetics