Technical Terms
Definitions of core terms used across this knowledge center. Terms are defined at the level needed for reading specifications, test reports and engineering calculations.
Adsorption
The adhesion of gas or liquid molecules onto a solid surface. Physical adsorption is driven by van der Waals forces and is reversible by heat or pressure swing. Chemisorption involves a chemical bond and is less easily reversed. Activated carbon relies mainly on physical adsorption; impregnated carbon adds chemisorption for specific species.
BET surface area
Total specific surface area (m²/g) measured by nitrogen adsorption using the BET method. It indicates how much internal surface an adsorbent exposes, but says nothing by itself about which molecules it can adsorb.
Iodine number
Milligrams of iodine adsorbed per gram of activated carbon (mg/g). A standard indicator of micropore development; most relevant to small-molecule adsorption.
Pore structure
The distribution of micropores (< 2 nm), mesopores (2–50 nm) and macropores (> 50 nm). Micropores adsorb small molecules; mesopores provide access and capacity for mid-sized molecules; macropores act as transport channels.
Breakthrough
The point at which the outlet concentration of an adsorber or reactor reaches an unacceptable level. Breakthrough defines the working capacity of a bed — capacity that cannot be used before breakthrough is wasted.
Working capacity
The amount of contaminant actually adsorbed before breakthrough, as a fraction of equilibrium capacity. Working capacity is what matters for bed economics, and it is always lower than equilibrium capacity.
Empty bed contact time (EBCT)
The time a gas would take to pass through an empty vessel of the same volume: EBCT = bed volume ÷ volumetric flow. Used for sizing carbon beds.
Space velocity (GHSV)
Volumetric flow rate of gas divided by catalyst volume (h⁻¹). A measure of how much gas a catalyst volume processes per hour; higher space velocity means shorter contact time.
Light-off temperature
The temperature at which a catalyst reaches a defined conversion (commonly T₅₀ or T₉₀ for 50% or 90%). Used to judge whether a catalyst fits an application's temperature window.
SCR (Selective Catalytic Reduction)
Reduction of NOx to N₂ and H₂O using a reducing agent (usually ammonia or urea) over a catalyst. The reaction is selective — it targets NOx rather than other gas components.
Catalyst deactivation
Loss of catalyst activity over time through poisoning (chemical), fouling (deposits), thermal sintering or mechanical damage.
Regeneration
Restoring spent material capacity or activity: thermal reactivation of carbon, steam regeneration of carbon beds, or catalyst regeneration processes. The feasible method depends on the material and the nature of the fouling.
Pressure drop
The pressure loss across a bed, reactor or catalyst. It determines fan or blower energy consumption and sets limits on bed depth and geometry.
LEL (Lower Explosive Limit)
The minimum concentration of a flammable gas in air that can ignite. Adsorption and oxidation systems keep VOC concentrations below a safety fraction of the LEL (commonly 25%).
CEMS (Continuous Emission Monitoring System)
Equipment for continuous measurement of stack emissions (dust, SO₂, NOx, and other parameters), used for compliance verification.
Isotherm
The equilibrium relationship between adsorbate concentration and adsorbed amount at constant temperature — the basis of adsorption capacity calculations.