Activated carbon a natural raw material
The natural substance activated carbon is refined by CARBONIT using a unique and internationally patented process. All raw materials processed by CARBONIT are residue-controlled and LGA monitored. They meet strict European standards for water filters. State-of-the-art technology ensures unparalleled performance. The CARBONIT water filters combine an exceptional filter fineness of up to 0.45 µm with the high adsorption effect of the activated carbon. Like spring water from the tap. No carrying heavy water boxes.
Activated carbon is a material based on natural raw materials, which binds chemical compounds and molecules due to its porous structure and the resulting extremely large inner surface. Activated carbon is traditionally used in many processes in the chemical industry. Due to its high adsorptive properties, it is mainly used to clean exhaust air, drinking water and waste water, as well as in food technology, pharmacy and chemistry.
The starting materials for the production of activated carbon are raw materials containing carbon such as wood, peat, lignite, hard coal, fruit kernels or coconut shells. However, other carbon-containing materials, such as plastic waste or petroleum products, can also be processed into activated carbon due to their high carbon content. These carbonaceous materials are obtained in a manner similar to charcoal manufacture and then, as the name suggests, activated. This activation process increases the adsorptive properties of the charcoal and leads to an improvement in the cleaning performance compared to conventional charcoal.
Activated carbon consists of an irregularly arranged crystal lattice of carbon atoms. These randomly shifted lattice planes lead to a very porous structure and thus a large inner surface. It can be in the range of 500 to 1500 square meters per gram for commercially available activated carbon.
For comparison: 4 to 5 grams of activated carbon cover the area of an entire soccer field. The inner surface of the activated carbon is characterized by the pore system. To put it simply, a distinction is made between pores of different sizes or diameters. A distinction is made between macropores (the supply pores into the interior of the grain) and adsorption pores (i.e. the pores in which the actual attachment of the molecules to the inner surface takes place).
The structure of the pore system influences the transport of the sorptive substances from the edge of the grain into the interior of the grain as well as the adsorption properties of the respective substance on the surface.
Surface properties of activated carbon
In addition to the pore structure, the chemical properties of the surface also have a decisive influence on the adsorption capacity of activated carbon. Given the abundance of impurities that can occur in water or in the air, in practice the cleaning performance of activated carbon is geared towards very specific groups of substances. A selection of problematic substances, as can occur in the example of drinking water purification, is listed below:
- smells and flavors,
- Colors,
- petroleum hydrocarbons,
- halogenated organic hydrocarbons,
- organic hydrocarbons,
- chlorine, chlorine dioxide, ozone, permanganate,
- heavy metals,
- ammonium, nitrate,
- pharmaceutical agents.
Since each of these compounds has a different adsorption behavior and binding capacity due to its chemical composition, the physical properties such as grain and pore size are combined with the chemical properties of the surface. Ultimately, this leads to optimal cleaning performance in the respective application.
adsorption
Adsorption is a process in which substances accumulate on a surface (Fig. B). Two types of adsorption are known. On the one hand, one speaks of physical adsorption, which is mainly caused by van der Waal's forces. The van der Waals force is a very weak force of attraction, but it is sufficient to hold (adsorb) molecules or atoms on a surface due to their charge. This force is reversible, ie if a stronger force occurs, eg Brownian motion when the temperature is increased, the adsorbed substance can be dissolved again. The situation is different with chemical adsorption, also known as chemisorption. As with all chemical reactions, an activation energy has to be overcome here, so that the interfering substance (adsorptive) forms a chemical bond with the surface of the activated carbon (adsorbent). Chemisorption is stronger in its binding than physical adsorption. In principle, however, it can also lead to a desorption (redissolution) of the substances here if the binding forces of other groups of substances are more pronounced. If the capacity (absorption capacity for pollutants) of an activated carbon filter is exhausted, this is referred to as a loaded filter. However, loaded filters do not necessarily have to be disposed of. The activated carbon contained in the filter can often be regenerated by removing the adsorbed substances from the surface of the activated carbon. This desorption process (ie the reverse adsorption process) can, for. B. be effected by a pressure reduction or temperature increase. However, after repeated desorption or when adsorbing substances that are difficult to desorb, the loaded activated carbon must be completely reactivated. The loaded activated carbon then goes through a new – albeit shorter – activation process with the aim of raising the inner surface back to the original level. Another way to regenerate loaded activated carbon is through extraction. The adsorbed substances are removed from the surface of the coal with the help of an organic solvent. However, microorganisms can also regenerate (macroporous) activated carbon by biologically degrading easily desorbable organic compounds. Regenerated activated carbon is used in particular in industrial applications, for example in printers, in food technology, drinking water treatment and wastewater treatment. Valuable substances can often be recovered through desorption, as is proven by the adsorptive recovery of toluene in printing works, in which the toluene recovered from the exhaust air is returned to the printing process.
production method
Activated charcoal can be made from almost any carbonaceous material. These feedstocks can be in uncharred form as well as in the form of coals and cokes. The basic principle of activation is to selectively break down part of the carbon under suitable conditions. The selective degradation means that the escape of volatile substances creates numerous pores, crevices and cracks in which the adsorption of substances can take place. There are two methods of producing activated carbon: chemical activation and gas activation. During chemical activation, uncharred raw materials such as peat or sawdust are treated with a dehydrating (water-removing) agent, e.g. zinc chloride or phosphoric acid. mixed and then activated at temperatures of 400 - 600 °C. This mainly produces coarse-pored activated carbon, which, due to its properties, can be used, for example, to decolorize liquids.
The second variant is gas activation. In general, already charred natural products such as charcoal, peat coke, coconut shell coke, hard coal or lignite are used. Even before activation, these have a few small pores and thus an initial, albeit not very pronounced, adsorption surface. The activation process increases the number of pores and thus the size of the surface considerably. Activation is carried out at temperatures of 700 - 1000 °C using steam and carbon dioxide. The water vapor and the carbon dioxide lead to a partial oxidation of the non-crystalline carbon in particular. In the process, tar-like products that clog the fine pores are expelled and the carbon framework is largely exposed. The desired pores for a fine-pored activated carbon are now formed inside the raw material. Since activation requires a high temperature, the use of rotary kilns, multi-deck or shaft furnaces has become established in industry. Activated carbon and its pore distribution can be tailored here for the various applications.
Activated carbon is sold as powder, granular or molded carbon. In the production of molded carbon, for example for water filters (activated carbon block filters), the charred semi-finished product is pulverized, activated and then mixed with a binder and extruded or sintered as required. The charcoal, which is a few millimeters in size, is available as broken particles or as rod-shaped pellets. Coal is used in adsorber vessels through which the gas or liquid stream to be cleaned is passed. The broken, sharp-edged activated carbon is preferably used for water purification. Thanks to its compact design, an activated carbon block filter replaces voluminous loose powdered carbon beds. The absorption capacity for the accumulation of undesirable substances is also significantly increased and the tendency to release substances once they have accumulated (the so-called chromatographic effect) is reduced. In addition to the chemical-physical adsorption, fine-pored block filters with a high filter fineness also have good mechanical filtration properties against particles and microorganisms.
drinking water treatment
Drinking water is usually obtained from aquifers, but also in regions with little groundwater, for example from the bank filtrate of rivers. A large proportion of the compounds and impurities that humans release into nature are biologically degraded when they seep away through soil bacteria. Nevertheless, the legal limit values are repeatedly exceeded, which means that the water obtained has to be treated before it is fed into the drinking water network. The filters used for this are called single-layer or multi-layer filters.
The single-layer filters consist entirely of just one filter material, whereas the multi-layer filters are made up of a combination of different filter materials. The multi-layer filters usually consist of a layer (e.g. sand) for retaining coarse particles and a layer of activated carbon. Since, according to the law, suppliers only guarantee the quality of drinking water up to the house connection, drinking water filters are also increasingly being used in the private sector.
These filters have the task of eliminating any particles, bacteria, odors and flavors as well as heavy metals that may have entered the pipe network. It can also happen that pollutants are not fully retained in the waterworks. This can be pesticides, drug residues or even hormonal substances that get into the groundwater through diffuse entry and pass through the waterworks unhindered. Unsuitable or outdated domestic installations can release heavy metals into the drinking water. Heavy metal ions can be dissolved if the different local drinking water properties are not sufficiently taken into account when selecting the pipe materials. These are ions of the elements copper, nickel, zinc and lead. In all these cases it is advisable to install an activated carbon filter directly in front of the tapping point of the drinking water, which can remove these heavy metals, drug residues and pesticides from the drinking water (Fig. F). The minerals, salts and trace elements essential for the human organism remain unaffected. Due to their small size and good mobility, they pass through the filter and are therefore also available after filtering.