Adsorption Parameters of Activated Carbon
Capacity vs. Kinetics (Rate):
(a) Capacity parameters determine loading characteristics of activated carbon. Maximum adsorption capacity of activated carbon is only achieved at equilibrium.
(b) Kinetic parameters only determine the rate of adsorption and have negligible affect on adsorption capacity.
Surface Area: Adsorption capacity is proportional to surface area (determined by degree of activation).
Pore Size: Correct pore size distribution is necessary to facilitate the adsorption process by providing adsorption sites and the appropriate channels to transport the adsorbate.
Particle Size: Smaller particles provide quicker rates of adsorption. Note: Total surface area is determined by degree of activation and pore structure and not particle size.
Temperature: Lower temperatures increase adsorption capacity except in the case of viscous liquids.
Concentration of Adsorbate: Adsorption capacity is proportional to concentration of adsorbate.
pH: Adsorption capacity increases under pH conditions, which decrease the solubility of the adsorbate (normally lower pH).
Contact Time: Sufficient contact time is required to reach adsorption equilibrium and to maximize adsorption efficiency.
Activated Carbon Properties
CARBOCHEM produces a full line of activated carbon (pellets, granular, & powder) based on coal, wood and coconut shells with special emphasis on water treatment, food & beverage, chemical processing and pollution control. CARBOCHEM® carbon has been certified for ASNI/NSF Standard 61 and ISO 9002 and satisfies the requirements of the Food Chemical Codex.
Iodine Number
- most fundamental parameter used to characterize activated carbon performance
- measure of activity level (higher number indicates higher degree of activation)
- measure of micropore (0 – 20 Å) content
- equivalent to surface area of activated carbon in sq m/g between 900 – 1100
- standard measure for liquid phase applications
Methylene Blue
- measure of mesopore structure (20 – 500 Å)
Caramel dp (Molasses No.)
- measure of macropore structure (>500 Å)
- important for decolorizing performance
Surface Area
- measure of adsorption capacity (Note: pore size distribution/pore volume is also important to determine ultimate performance)
Apparent Density
- higher density provides greater volume activity and normally indicates better quality activated carbon
Particle Size
- smaller size provides quicker rate of adsorption which reduces the amount of contact time required
- smaller size results in greater pressure drop
Hardness/Abrasion Number
- Hardness/Abrasion is a measure of activated carbon`s resistance to attrition
- important indicator of activated carbon to maintain its physical integrity and withstand frictional forces imposed by backwashing etc.
Dechlorination half-value length
- test to measure the dechlorination efficiency of activated carbon
- depth of activated carbon to reduce influent chlorine level from 5 ppm to 2.5 ppm
- lower half-value length indicates superior performance
Ash Content
- reduces overall activity of activated carbon
- reduces efficiency of reactivation
- metals (Fe2O3) can leach out of activated carbon resulting in discoloration
- acid/water soluble ash content is more significant than total ash content
