GAED, or Gravimetric Adsorption Energy Distribution full characterization, has solved a wide variety of sorbent problems (mostly activated carbons, but also zeolites, organoclays, carbonaceous and non-carbonaceous adsorbents and absorbents) over the last decade. Dr. Mick Greenbank, the inventor and developer of this most powerful instrumental test method, has presented a new model for AC at molecular scale represented in this illustration.

Manufacturers and users of activated carbon (AC) and other sorbent materials need to be aware of this powerful test method coined GAED. This method enables users to select the best AC for specific aqueous-phase and vapor-phase AC applications. GAED provides sorbent adsorption and desorption characteristic curves. These cumulative characteristic curves provide the Polanyi adsorption potential and pore volume function. The differential pore volumes and adsorbate binding energies are obtained from the raw cumulative characteristic adsorption-desorption curve data. This enables full sorbent characterizations: Isotherms for a wide variety of organics, which is the most important GAED outcome, pore size distributions or adsorption space distributions, BET surface areas, calculated trace capacity numbers and other data. A typical GAED report is 20 pages.

Adsorption isotherms provide practical information to determine if your problem is solvable with AC. Isotherms provide the amount adsorbed on 100 grams of sorbent sample at equilibrium. Isotherms are expressed in X- and Y-coordinates. The X-axis is the equilibrium concentration in water or air and Y-axis is the equilibrium loading capacity in adsorbate mass to sorbent mass. The isotherm is critical for calculating the amount of AC required for the user’s job and how long the AC will last before it needs changed out. In summary, isotherms are the critical needed information because they provide feasibility for plant designs and help to select the best AC for your applications. 

Henry Nowicki is president for Professional Analytical and Consulting Services Inc. (PACS) and Activated Carbon Services. Offices are in Pittsburgh, Pa. and Orlando, Fla. He is chairman for the International Activated Carbon Conference (IACC) and Activated Carbon School. For more information, visit www.pacslabs.com or email Henry@pacslabs.com.