Re: [new_distillers] Re: Activated carbon
- Thank you Harry. You answered everything I wanted to know in words
suitable for a poor Archaeology major, not a chemist :)) What amazing
stuff it is!!! Thanks again..... blanikdog.
----- Original Message -----
Subject: [new_distillers] Re: Activated carbon
Date: Mon, 03 Oct 2005 04:37:36 -0000
--- In email@example.com, "sonum norbu" <blanik@o...>
> A question for the chemists out there. How is activated
carbon "activated"? What does "activated" mean? Could one use
charcoal from a fire burning Box (australian hardwood) and crushing
the hell out of it? blanikdog
Charcoal is carbon. Activated charcoal is charcoal that has been
treated with oxygen to open up millions of tiny pores between the
According to Encylopedia Britannica...
The use of special manufacturing techniques results in highly porous
charcoals that have surface areas of 300-2,000 square metres per
gram. These so-called active, or activated, charcoals are widely
used to adsorb odorous or coloured substances from gases or liquids.
The word adsorb is important here. When a material adsorbs
something, it attaches to it by chemical attraction. The huge
surface area of activated charcoal gives it countless bonding sites.
When certain chemicals pass next to the carbon surface, they attach
to the surface and are trapped. Activated charcoal is good at
trapping other carbon-based impurities ("organic" chemicals), as
well as things like chlorine.
Many other chemicals are not attracted to carbon at all -- sodium,
nitrates, etc. -- so they pass right through. This means that an
activated charcoal filter will remove certain impurities while
ignoring others. It also means that, once all of the bonding sites
are filled, an activated charcoal filter stops working. At that
point you must replace the filter.
Activated Carbon: How and Why It Works
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.
: Organic Compounds: Acids, Alcohols, Aldehydes
: Chlorinated Hydrocarbons: Esters, Ethers, Ketones, Mercaptans,
: Inorganic Compounds: Halogen Acids, Halogens, Sulphuric Acid,
Sulphur Dioxide, Phosgene
: Odors: Human, Animals, Food, Waste Processes, Cooking
James W. Kasmark Jr.; B.S. Mechanical Engineering; President D-
MARK; "Activated Carbon" Why is it used?, ©2000, D-Mark Inc.
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- --- In firstname.lastname@example.org, "sonum norbu" <blanik@o...>
> Thank you Harry. You answered everything I wanted to know in wordsYou can download a free 28 page pdf from Gert Strand about activated
> suitable for a poor Archaeology major, not a chemist :)) What amazing
> stuff it is!!! Thanks again..... blanikdog.
carbon and details of how it's made and used. Apart from the glaring
mistake of ADsorption vs ABsorption, the booklet is an interesting