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Activated Carbon & Aerial Gases
What is Activated Carbon?
Activated carbon is a porous, amorphous, high surface area adsorbent composed largely of elemental carbon.
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Activated carbons can be produced in a variety of forms, including pellets, powders, granules and textiles and from a variety of raw materials. In fact, activated carbon can be produced from almost any carbonaceous substance. However, coal, coconut shell (CNS) and wood are the most common starting materials with established infrastructures for manufacture. The most common method for the manufacture of activated carbon involves the carbonisation (pyrolysis) of the raw material followed by activation with high temperature steam.
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The type of raw material used influences the porosity of the final product. For example, coconut shell-based activated carbon generates a product with a high proportion of micropores (pores with a width of < 2 nm) whilst wood generates a predominance of mesopores (pore diameters between 2 and
50 nm). All activated carbons contain macropores (>50 nm) which facilitate diffusion to the smaller pores.
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The distribution of pore sizes influences the properties of activated carbon. For example, coconut shell activated carbon, with its highly developed microporous content, is ideal for the adsorption of small molecules whereas wood-based carbon is better suited for the adsorption of larger molecules, such as those responsible for colour.
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These pores, which develop during the activation process, are responsible for the generation of a large internal surface area on the activated carbon and the carbon atoms that predominate the surface structure present short-range, attractive forces known as van der Waals forces. These attract molecules of the surrounding fluid resulting in their bulk adsorption onto the surface of the carbon. Some molecules have properties which enable stronger adsorption onto the activated carbon than others, depending to a great extent on the molecules’ size and polarizability.
How Does Simply Breathe make use of Activated Carbon?
Although commonly used to remove impurities from air or water (or other gases and liquids) activated carbon can be employed to store a variety of gases under pressure. The advantage here is that much more gas can be stored in a fixed volume than using just pressure alone.
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"much more gas can be stored in a fixed volume than using just pressure alone".
This phenomenon is used in the manufacturing assembly at Simply Breathe where aerial gases, such as oxygen, nitrogen, carbon dioxide or air itself, are compressed onto coconut shell-based activated carbon for deployment in aerosol type canisters. In this way, oxygen can be stored and delivered from a canister with three times more volume than a canister filled using only gas compression. A canister filled with activated carbon and pressurised to 10 barg pressure holds ten times more carbon dioxide than when using pressure alone.
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Coconut based activated carbon as seen when viewed through an electron microscope. Notice the complex system of pores.
