The second article in our series about air purification technologies concerns tair purifiers with activated carbon filter. Discover the truth about them.
Activated carbon filters are used to stop contaminants at a molecular level. They make it possible to purify the air from chemicals, odors and gas but they do not filter particles.
Activated carbon is mainly composed of carbonaceous matter with porous structure. It can be produced from wood, nutshells, coconut husk, etc. Once activated (physically or chemically), the surface of the carbon can reach from 400 to 2 000 m².g-1. Then, the carbon can trap gas and water molecules. Its efficiency depends on humidity.
The pore size depends on activation method and the number of pores in the base material used. Wood can provide pores larger than 50 nm. The gas-adsorption requires 1-2 nm pores.
Activated carbon filters use a process called adsorption. Gas, chemicals and odors are trapped inside the pore structure of the carbon substrate. The air - purified from contaminants - comes out the filter.
There should be no confusion between absorption and adsorption. Absorption involves the diffusion of molecules of a substance into the bulk of liquid or solid to form a solution. Adsorption is a surface phenomenon.
There are 2 predominant types of carbon filters : granular loose-fill and bonded filters.
Granular loose-fill filters consist of grains which can measure up to 3 mm long. They have a longer life span and are lighter than the bonded ones. In this form, the carbon can be found in combination with other substances. Some manufacturers use zeolite. Its pore structure is supposed to be better suited for the removal of formaldehyde and ammonia. However, there is no reliable scientific evidence to demonstrate these claims. In fact, zeolite is an inexpensive filler.
Bonded carbon filters consists of grains which measure from 10 to 50 µm. They are considered to be more manageable than granular loose-fill filters. IBR laboratories reseachers think that manufacturers use bonded carbon filters since they are cheaper. Concerning isoproponal filtration, bonded carbon filters are 26,8% less efficient that granular loose-fill filters.
The activated carbon efficiency can be limited by many factors :