Activated Carbon: How and Why It Works

Developing the FumeTrap™ meant selecting the right filter material was crucial to producing an effective product. Removing the gas and vapors generated during the soldering process involved removing particles .01 microns (.000000393 inches) and smaller. After much research and testing, it was evident that activated carbon filters were the best choice as an effective material for this application.

Adsorption vs. Absorption
    Removing gases and vapors involves capturing particles .01 microns and smaller. A micron is 1/25,400 of an inch. Particulate filters, like HEPA filters are effective into the .3 micron range. They can not and do not remove material that is as small as a gas. Activated carbon uses the process of ADSORPTION to remove gases and vapors from the air stream. The question often asked is what is the difference between ADSORPTION and ABSORPTION.

      ADSORPTION is the physical attraction and adherence of gas or liquid (vapor) molecules to the surface of a solid. Gas and vapor molecules are adsorbed by the solid activated carbon.

      ABSORPTION is the dissolving and even mixing of a substance in a liquid. Think of sugar being mixed into coffee. In an industrial application the gas is absorbed by a "scrubbing" liquid.

Why is activated carbon a good adsorbent?
   Activated carbon is a unique material. No other material natural or man made has all these properties and abilities:

  1. It has the ability to adsorb some of almost any vapor.
  2. It has a large capacity for organic molecules, especially solvents.
  3. It adsorbs and retains a wide variety of chemicals at the same time.
  4. It works well under a wide range of temperatures and humidity levels.
  5. It is inert and safe to handle and use.
  6. It is readily available and affordable.

What is activated carbon?
   It is a material that has been treated, or activated, to increase the internal surface area to the range of 950 to 1150 square meters per gram. The internal surface area is what holds the adsorbed gases and vapors. It is where the "work" of the filter is done. The term activated charcoal is often used interchangeably with activated carbon. They refer to the same material.

How does it work?
   The Non-technical Explanation: It starts with the gas molecule coming in contact with the surface of an activated carbon particle. The gas molecule comes to rest in a large surface pore on the particle. Unbalanced forces on and within the carbon particle cause the gas molecule to move down into the smaller pores of the carbon particle where it will stop and be held in place. At some point the gas molecule will condense and become a liquid particle, trapped inside the carbon.

   The Technical Explanation: The adsorbate (gas) diffuses through the surface film of macropore structure (activated carbon). Van der Walls' forces cause the gas to migrate into the micropore structure, condensing during this movement. It stops when either the forces become balanced or it is physically blocked.

What types of gases and vapors are adsorbed?
   Activated carbon is the universal adsorbent and will adsorb "some of almost any vapor". Below is a partial list of gases that are removed by activated carbon filter systems.

Source:
James W. Kasmark Jr.; B.S. Mechanical Engineering; President D-MARK; "Activated Carbon" Why is it used?, ©2000, D-Mark Inc.