ASTM METHOD AND ACTIVATED CARBON PROPERTIES

Carbon tetrachloride activity is a means of determining the degree of completion of the activation process, by measuring the ability of a carbon to adsorb an organic molecule (carbon tetrachloride).

Carbon tetrachloride activity is determined by flowing carbon tetrachloride-laden air through a dried sample of carbon of known weight, until there is no further increase in the weight of the sample. Activity is then expressed as the ratio (in percent) of the weight of carbon tetrachloride adsorbed to the weight of the original sample.



Moisture content affects the ability of adsorbents to perform against certain gases and vapors, and is reported as a percent by weight. For organic vapor adsorption on activated carbon, efficiency decreases as moisture content increases, since some adsorption sites within the pores are filled with water. For impregnated carbons, higher moistures generally result in an increase in efficiency, since the mechanisms of contaminant removal are chemical reactions that occur in the reagent solutions contained within the pores.



Apparent density is the dry density of a material, usually expressed in grams per milliliter or pounds per cubic foot. Density is essential for mass to volume conversions required for designing and filling equipment such as
filter trays, cartridges, and adsorber vessels. Actual density can be calculated using both apparent density and moisture content data.



The known particle size distribution, or "mesh", is important for achieving the proper contact of liquid or gas in a packed bed of adsorbent, and affects the rate of adsorption and pressure drop across the bed. Smaller particles are more efficient for adsorption, but also increase pressure drop, so the choice of particle size must optimize adsorption efficiency without exceeding acceptable pressure drop specifications.



Hardness is useful for measuring the resistance of an adsorbent to particle size degradation under service conditions. Coconut shell carbons are among the hardest carbons, with hardness numbers greater than 95%.