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Activated Carbon as Protection: what is important?

A brief history of activated carbon

Even in prehistoric times, Neanderthals used charred residues from burnt wood. Charcoal was used to color cave paintings and to embalm the deceased. Meat rubbed with it had a much longer shelf life and unpleasant odors were adsorbed. This was an important method of hiding fresh meat from insects and predators. In ancient Greece, Hippocrates (460–370 BC) documented the use of charcoal to treat food poisoning. Even today, activated charcoal is used to treat diarrhea and poisoning, as it removes toxins from the gastrointestinal tract.

In the 15th century, it was known that carbonizing wooden barrels kept drinking water fresher for longer. Christopher Columbus already made use of this knowledge. Charcoal was first used industrially in 1794 by the English sugar industry to decolorize raw sugar syrup. The first attempts to increase the decolorizing power of charcoal involved pre-treating it with steam. The "Chimecal Activation of Wood" patent by the Lithuanian chemist Rafael Ostrejko in 1900 marked the beginning of modern activated carbon production.

What is Activated Carbon?

Activated carbon is an industrially manufactured product made from carbonaceous materials with a high internal adsorptive surface. It consists mainly of carbon (> 90%) and has a highly porous structure. The pores are connected to each other like a sponge. They are open-pored.

Manufacturing Process

Carbonaceous raw materials such as hard coal, lignite, wood, olive stones and peat are used as starting materials for the production of activated carbon. This material is then carbonized without the addition of oxygen. Almost everything that is not carbon is burned. This creates a complex pore system with very small pores. This raw activated carbon is then activated by removing volatile components (hydrogen, oxygen, nitrogen, sulfur, etc.).

Use for Protection in Laboratories

Due to its large internal surface area or porosity, it is perfectly suited to adsorbing volatile and organic compounds and can therefore efficiently bind a considerable amount of solvent vapors from the air. Solvents are frequently used in analytical laboratories and are highly toxic. Uncontrolled solvent vapors in the air are a health hazard and also promote fires and explosions. The use of activated carbon filters minimizes these potential hazards and thus ensures laboratory safety. An indispensable protection to ensure the health of laboratory staff and prevent accidents.

Key Figures

Not all activated carbon is equally suitable for reliable protection against solvent vapors. The following figures provide an indication of the performance of the type of activated carbon used:

The abrasion number or ball-pan hardness measures the resistance of the activated carbon to wear and is measured in percent by weight. Mechanical influences (e.g. during transport) cause the activated carbon particles to rub against each other. This leads to abrasion in the form of tiny particles (powder). Increased abrasion leads to blockages and clumping, which impairs filter performance. A higher value for the ball-pan hardness means higher resistance and therefore more consistent filter performance.

The internal surface area refers to the totality of the surfaces in porous or granular solids, including those between the grains and the pore edges. The higher the internal surface area, the more area is available to bind solvent vapors. Average activated carbon in powder form has an internal surface area of ​​500-600 m2/g. The market leader SCAT has increased the inner surface of its activated carbon from 1,100 to 1,500 m2/g, making it the undisputed leader among industrial activated carbons.

Adsorption describes the ability of the activated carbon to absorb pollutants. A higher percentage means better absorption capacity. In CTC adsorption according to ASTM D3467, the SCAT activated carbon (now in the 3rd generation) reaches the maximum value of 90% (previously: 70%).

The grain size describes the size of the individual particles in the activated carbon, which is important depending on the application. The right particle size ensures optimal flow and adsorption of the solvent vapors within the activated carbon. Particles that are too small impede the flow and lead to blockages, while particles that are too large form gaps through which solvent vapors can escape unfiltered. For an optimal balance between low flow resistance and high filter performance, SCAT activated carbon particles with a size of 1.4 to 3 mm are produced.

Ash content and water content are also relevant figures. The ash content is an indicator of the purity of the activated carbon. It describes the proportion of foreign substances or elements that are present in residual quantities after the activated carbon has been produced. A lower ash and water content means more effective carbon and a higher filter performance of the activated carbon.

Tip: To be on the safe side, always ask your manufacturer for the data sheet of your activated carbon.

Table 1: Performance indicators of SCAT activated carbon.

Special case: Collect HPLC buffer safely

To adjust the pH value of an eluent, alkaline (basic) or acidic additives or buffers are added. After the eluent has passed through the HPLC system, it is collected in a collecting container. This is equipped with an activated carbon filter to adsorb escaping vapors.

The disadvantage: Classic activated carbon for solvents is unsuitable for acids or alkalis. To bind alkaline and acidic gases, SCAT exhaust air filters therefore have two additional activated carbon layers: The first layer converts alkaline vapors through chemsorption and binds them as "reacted" components. The second layer also consists of highly activated carbon, which binds acidic, gaseous components.

With its 3 layers, the latest generation of SCAT exhaust air filters currently covers the broadest range of substances in the field of HPLC safety. The main advantage for the user is that a single filter type is used for all applications - even if the method or solvent composition changes.

In terms of service life, SCAT still offers 3 sizes (3, 6 and 12 months). This distinction has proven to be useful for users: smaller sizes offer more flexibility when HPLC devices are used at different rates. If you want to optimize your annual requirements, e.g. when the HPLC is in continuous operation, the larger filters offer cost savings of up to 35%.

The laboratory operator can therefore not only meet the highest safety standards in terms of occupational safety and environmental protection, but also benefits from predictability and cost-effectiveness – making work in the laboratory “doubly” safe.