Activated Carbon > Defining Activated Carbon Product Properties

Screen (Particle) Size Distribution
SSD is the range of screens over which activated carbon is sized. The screen size, or mesh size to be used is determined by a square root of two progression in screen opening, starting with the largest screen used. The Mean Particle Diameter (MPD) is calculated on the basis of screen size distribution. The weight percent of activated carbon passing through one screen sieve and remaining on the next smaller screen is first determined (material on the largest screen and passing through the smallest screen is ignored). The weight fraction is multiplied by the average screen opening for the larger screen and the screen on which the activated carbon was retained. The summation of these fractions is the MPD.

Iodine Number
The amount of Iodine adsorbed by activated carbon from a 0.02 NI2/KL aqueous solution. Iodine Number has been roughly correlated to the surface area in pores greater that 10 †diameter. However, it is best understood as an indicator of total pore volume.

Molasses Number
A measure of the relative decolorization of a boiling molasses solution by activated carbon. The Molasses Number has been interpreted as the surface area available in pores greater than 28 †diameter. Because molasses is a multi-component mixture, one must be careful in assigning too strict an interpretation to this parameter.

Apparent Density (AD)
A measure of the mass of carbon that occupies a particular volume. The test is performed by gradually filling a graduated cylinder to 100 cc and determining the mass of activated carbon contained. This value, corrected for less efficient settling in the field, is used for calculating the amount of activated carbon needed to fill a given adsorber volume.

Carbon Tetrachloride Number (CCL4) aka CTC Activity
Total pore volume indicator. This is measured by passing an airstream saturated with CCL4 at 00C through a carbon bed held at 25°C. The weight of the CCL4 adsorbed is determined at prescribed intervals until there is a negligible weight change in the sample.

Hardness Number
Measurement of the attrition resistance of activated carbon. It is the change in weight, expressed as a percentage, of a specific screen size fraction after 3 minutes of vigorous agitation with smooth steel balls.

Abrasion Number
Measurement of the mechanical strength of activated carbon. It is the change in weight, expressed as a percentage, of a specific screen size fraction after 3 minutes of vigorous agitation with smooth steel balls.

Ash Content
Inorganic material, primarily aluminum and silicon, contained in activated carbon. Ash is the residual from burning pulverized carbon in air for 3 hours at 1750°F (954°C).

Moisture Content
A measure of the water content of carbon. It is determined by boiling activated carbon in xylene using a Dean-Stark trap and condenser. The water is condensed and trapped in a volumetric arm in order to determine the water content. The moisture content of virgin activated carbon can also be estimated on the basis of the weight change that occures after oven drying at 150°C for 3 hours.

Safety Message

Wet activated carbon preferentially removes oxygen from air. In closed or partially closed containers and vessels, oxygen depletion may reach hazardous levels. If workers are to enter a vessel containing carbon, appropriate sampling and work procedures for potentially low oxygen spaces should be followed, including all applicable federal and state requirements.

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