Adsorption processes are as obscure as they are ubiquitous. They are rarely introduced in the undergraduate chemical engineering curriculum; and thus, they remain very ambiguous to the practicing engineer. Yet, as a phenomenon or as a unit operation, adsorption processes show up just about everywhere. They are readily found in the chemical plant drying air, cleaning water, purifying hydrogen, producing oxygen or nitrogen from air, and separating linear from branched hydrocarbons, to name just a few applications. Adsorption processes are also found in the private sector as in-home water purification, medical oxygen and odor removal systems. They are even used in automotive applications for odor removal, and aerospace applications for inerting fuel systems, producing oxygen for pilots, and removing water vapor, carbon dioxide and trace contaminates from spacecraft cabins. The list of applications for adsorption processes goes on and on, with new ones appearing continually.

All of these applications have one thing in common. They are all based on the decades, if not centuries, old notion that the surface of a solid material may have a different affinity for different substances, species, molecules or atoms when contacted with a fluid phase, thereby effecting separation of certain species from each other in the fluid phase. It is this simple affinity difference concept imparted by the solid phase that has allowed the adsorption process to evolve into one of the most important separation processes that exist today for purifying or separating components from either the gas or liquid phase.

Although adsorption processes have been around seemingly forever, it has been only recently, maybe within the past 40 or 50 years, that widespread commercial applications have flourished. What is truly remarkable about the prosperity of these commercial adsorption processes is that most, if not all of them, have relied on just a few different types of adsorbent materials. Just four classes of adsorbent materials have lead the way for huge commercial successes, including activated carbons, activated aluminas, silica gels and aluminosilicates. This presentation will provide a brief history of adsorbent and adsorption process technology and also discuss some of the recent developments in the area.