Activated Carbons As An Indispensable Aid - Their Types And Features

Technical Background

Activated carbon is an extensively used adsorbent in various industries. For each different application of activated carbon, different pore structures, types of granules, and carbon surfaces are required. A parametric study is conducted to recognize a specific carbon for a particular application, with varying activating agents, precursor materials and process conditions. Generally, analysis of carbon is performed by running adsorption isotherms, evaluating the BET surface area, and measuring pore volume amongst other procedures.

Activated carbon is defined as a carbonaceous material with a wide internal surface area and highly structured porous surface resulting from the processing of raw materials under high temperature reactions. It is formulated with 87% to 97% carbon. Activated carbon’s porous structure allows it to adsorb materials from liquid and gaseous forms.

• Its pore volume typically ranges between 0.20 to 0.60 cm3/g, and has been found to be as wide as 1 cm3/g.
• Its surface area typically ranges between 800 to 1500 m2/g. Alongside, it has also been concluded to be in excess of 3,000 m2/g.
• The surface area consists of mostly micropores with pore diameters smaller than 2 nm.
• All these parameters make activated carbon a popular adsorbent for multiple applications.

Factors affecting adsorption of Activated Carbon

Better adsorption of activated carbon depends on several factors as mentioned below :

Pore structure

Activated carbons with open pore structures and good desorption characteristics are utilized in the retrieval of solvents with mid-to-high boiling points, whereas activated carbon types with higher micropore concentrations are used for highly volatile substances.

Surface Area

The primary goal when carbon is activated is to increase the surface area to allow better adsorption of organic molecules. In general, the more the surface area is, the greater the ability to adsorb organic contaminants, such as tastes, odours and toxins etc from water supplies.

Bulk Density

The bulk density of powdered activated carbon, relates to the physical weight per volume of powder and is generally evaluated in milligrams/c.c. It plays a vital role while comparing the speed of adsorption of carbons with similar specifications.

Physical Size

The speed of adsorption is inversely proportional to the particle size.

Raw Materials

Raw materials have a major regulating effect on the adsorptive ability of activated carbon products in use. The source of the raw material is important when comparing activated carbons, as the source directly influences the suitability of the carbon to its proposed application as well as plays a vital role in evaluation of better sustainability of different material types.

Activation Process

Activation is a function of time taken in the activation furnace: the longer the time is taken, the greater the activation will be. Activation process is accomplished by two alternative methods as steam or chemical. The degree of activation, is evaluated by the carbons specific surface area and adsorption ability.

Types

Granular Activated Carbon

Granular Activated Carbon (GAC) is produced from organic materials with high carbon contents such as wood, lignite and coal. It typically has a diameter ranging between 1.2 to 1.6 mm and an apparent density ranging between 400.46 kg/m3 and 496.57 kg/m3, depending on the material used and manufacturing process. Iodine and molasses numbers are normally utilized to characterize GAC. GAC is used for the adsorption of volatile organic compounds (VOC), odor and organic compounds for municipal, industrial and remedial vapor and water treatment.

Powder Activated Carbon

Powder Activated Carbon (PAC) or pulverised activated carbon is a black, powdered, extremely porous material that can adsorb impurities and contaminants from air and water. It has a complex, porous internal structure, with internal surface areas averaging about 900 m2 /g and a bulk density of 250–600 kg/m3. They are small activated carbon particles, with a size that is predominantly less than 0.075mm, produced by milling or pulverising activated carbon. PAC is used in refinery, petrochemical, pharmaceutical, chemical, textile/dye and other industrial wastewaters treatment.

Pelletised Activated Carbon

Pelletized activated carbon offers lower pressure drop than granular activated carbon in fixed-bed purification of gases and vapors. Its applications feature gasoline vapor recovery for automotive applications, air purification, odor control, solvent recovery, catalysis and removal of corrosive gases.

Silver Impregnated Activated Carbon

Silver impregnated carbons are used for preventing bacteria growth on activated carbons used in household potable water filters. Iodine impregnated carbons are used to remove hydrogen sulfide from biogas. Further applications of Silver Impregnated Activated Carbon includes pitcher and dispenser home water filters (POU),

point-of-entry (POE) in Whole-home water filtration and Pharmaceutical stream purification.