The C02 Pulse Technique for Determining the Condition of Adsorbent Charcoal Beds

Activated charcoal is widely used for the purification of air. Charcoal has a large surface area (ca. 1000 square meters per gram) and acts to purify air by adsorbing gaseous pollutants on its surface. When the capacity of the surface is exhausted, the charcoal is no longer effective and must be replaced.

The carbon dioxide (CO₂) pulse technique, developed at NRL, is a non-destructive method by which one can determine the remaining capacity, or the residual life of a charcoal bed before it has become exhausted. A dose of CO₂ is injected into the air stream ahead of the charcoal bed and is eluted through the bed. The shape of the emerging CO₂ elution peak is determined by the condition of the charcoal bed. For a new, unused charcoal bed the CO₂ elution peak is considerably dispersed (flattened and broadened) due to adsorption and desorption at the charcoal surface. For a partially spent bed the elution peak is dispersed to a degree proportional to the remaining capacity of the bed. For a fully spent bed the CO₂ elution peak is little affected by passage through the bed.

The carbon dioxide puise technique has been shown to be indicative of charcoal capacity for a wide range of non-polar materials (such as hydrocarbons, alcohols, etc.), which are taken up primarily by physical adsorption. The method is essentially insensitive to relative humidity in the range between 10 and 70%. An adaptation of the method has been used for detection of leaks in a charcoal bed, such as those caused by channeling, faulty packing, etc.