What Activated Carbon is
Activated Carbon Production from Wood via Pyrolysis
The production of activated carbon (AC) from wood biomass through pyrolysis (high temperature incineration in a specially made kiln) involves a two-stage thermal process: carbonization followed by activation, typically conducted in rotary kilns at 500–900 °C under oxygen-limited conditions. Carbonization removes volatile matter, yielding a carbon-rich char, while steam or chemical activation etches and breaks open the char surface to develop micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm), achieving surface areas exceeding 1000 m²/g. A teaspoon of AC has a surface area of about a football field. Coal-derived AC dominates low-grade uses but generates hazardous by-products like polycyclic aromatic hydrocarbons; wood-based pyrolysis offers a sustainable alternative with lower ash and tenable porosity (maximised micropores) for nutrient/contaminant capture (adsorption).
Structural and Adsorption Properties
AC's hierarchical pore structure—resembling nested nanotubes—enables physisorption and chemisorption of pollutants via van der Waals forces and surface functional groups (e.g., -OH, -COOH). This versatility supports applications in water/air purification, where contaminants adhere to pore walls without absorption into the bulk.
Types of Activated Carbon
Activated carbon varies by morphology, precursor, and activation method, tailoring it to specific uses. [ from prior]
Powdered (PAC): Fine particles (<0.18 mm) for batch liquid dosing and rapid adsorption.
Granular (GAC): Irregular grains (0.2–5 mm) for fixed-bed filtration in water/air treatment, offering regenerability.
Pelletized/Extruded: Cylindrical forms (1–5 mm) minimize dust/pressure drop in gas filters.
Fibrous/Cloth or Honeycomb: Flexible monoliths for low-resistance HVAC or specialty shapes.
Absorption refers to the process by which one substance takes in or assimilates another substance, often through physical or chemical means into its bulk volume.
Mesoporous materials are nanoporous solids with pore diameters between 2 and 50 nm, as defined by IUPAC nomenclature, distinguishing them from microporous (<2 nm) and macroporous (>50 nm) materials.
Key Characteristics
These materials exhibit high surface areas o are, tunable for pore sizes, large pore volumes, and modifiable pore surfaces for functionalization. Such properties enable rapid adsorption/desorption kinetics.
Common Applications
Activated carbons, serve in catalysis, air purification, gas adsorption/separation, food supplements, fertilisers, water treatment, drug delivery, heavy metal removal, and sensors due to enhanced mass transport and active sites.