Activated Carbon a Natural Raw Material
The natural material activated carbon is refined by CARBONIT through a unique and internationally patented process. All raw materials processed by CARBONIT are residue-controlled and monitored by LGA. They comply with strict European standards for water filters. State-of-the-art technology ensures unparalleled performance. The CARBONIT water filters combine an exceptional filtration fineness of up to 0.45 µm with the high adsorption effect of activated carbon. Like spring water from the tap. No carrying heavy water crates.
Activated carbon is a material based on natural raw materials, which binds chemical compounds and molecules through its porous structure and thus extremely large internal surface area. Activated carbon is traditionally used in many processes of the chemical industry. Due to its high adsorptive property, it is mainly used for cleaning exhaust air, drinking and wastewater, as well as in food technology, pharmacy, and chemistry.
The starting materials for the production of activated carbon are carbon-containing raw materials such as wood, peat, lignite, hard coal, fruit stones, or coconut shells. But 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 carbon-containing materials are obtained similarly to charcoal production and then, as the name suggests, activated. This activation process increases the adsorptive property of the carbon and leads to an improvement in cleaning performance compared to conventional charcoal.
Activated carbon consists of an irregularly arranged crystal lattice of carbon atoms. These randomly displaced lattice planes lead to a very porous structure and thus a large internal surface area. It can range from 500 to 1500 square meters per gram in commercially available activated carbon.
For comparison: 4 to 5 grams of activated carbon contain the area of a complete football field. The internal surface of activated carbon is characterized by the pore system; simply put, pores of different sizes or diameters are distinguished. Thus, a distinction is made between macropores (the supply pores into the grain interior) and adsorption pores (i.e., the pores in which the actual attachment of molecules to the internal surface takes place).
The structure of the pore system influences the transport of the sorptive from the grain edge into the grain interior as well as the adsorption property of the respective substance on the surface.
Surface Properties of Activated Carbon
Besides the pore structure, the chemical property of the surface has another decisive influence on the adsorption capacity of activated carbon. Given the abundance of impurities that can occur in water or air, in practice, the cleaning performance of activated carbon is targeted at very specific groups of substances. A selection of problem substances, as they can occur in the example of drinking water purification, is named below:
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Odor and taste substances,
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Colors,
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Mineral oil hydrocarbons,
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Halogenated organic hydrocarbons,
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Organic hydrocarbons,
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Chlorine, chlorine dioxide, ozone, permanganate,
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Heavy metals,
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Ammonium, nitrate,
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Pharmaceutical active ingredients.
Since each of these compounds exhibits different adsorption behavior and binding capacity due to their chemical composition, the physical properties such as grain and pore size are combined with the chemical properties of the surface. This ultimately leads to optimal cleaning performance in the respective application case.
Adsorption
Adsorption refers to a process in which substances accumulate on a surface (Fig. B). Two types of adsorption are known. On the one hand, there is physical adsorption, which is mainly caused by van der Waals forces. The van der Waals force is a rather weak attractive force, but sufficient to hold molecules or atoms on a surface due to their charge (to adsorb). This force is reversible, i.e., if a stronger force occurs, e.g., Brownian molecular motion with increasing temperature, the adsorbed substance can be released again. It is different with chemical adsorption, also called chemisorption. Here, as with all chemical reactions, an activation energy must be overcome so that the contaminant (adsorptive) forms a chemical bond with the surface of the activated carbon (adsorbent). Chemisorption is stronger in its bonding than physical adsorption. Basically, desorption (release) of substances can also occur here if the bonding forces of other substance groups are stronger. 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. Often, the activated carbon contained in the filter can be regenerated by removing the adsorbed substances from the surface of the activated carbon. This desorption process (i.e., the reverse adsorption process) can be induced, for example, by reducing pressure or increasing temperature. After multiple desorptions or with adsorption of difficult-to-desorb substances, the loaded activated carbon must be fully reactivated. In this process, the loaded activated carbon undergoes a renewed – albeit shorter – activation process with the aim of restoring the internal surface to its original level. Another possibility to regenerate loaded activated carbon is extraction. Here, the adsorbed substances are removed from the surface of the carbon using an organic solvent. But microorganisms can also regenerate (macroporous) activated carbon by biologically breaking down organic, easily desorbable compounds. Regenerated activated carbons are especially used in industrial applications, for example in printing houses, food technology, drinking water treatment, and wastewater purification. Valuable substances can often be recovered through desorption, as demonstrated by the adsorptive recovery of toluene in printing houses, where the toluene recovered from exhaust air is returned to the printing process.
Manufacturing Process
Activated carbon can be made from almost any carbon-containing material. These starting materials can be present both in uncarbonized form and as coals and cokes. The basic principle of activation is to selectively break down part of the carbon under suitable conditions. The selective breakdown results in numerous pores, cracks, and fissures forming as volatile substances escape, where adsorption of substances can take place. Two methods are distinguished in the production of activated carbon: chemical activation and gas activation. In chemical activation, uncarbonized raw materials such as peat or sawdust are mixed with a dehydrating (water-removing) agent, e.g., zinc chloride or phosphoric acid, and then activated at temperatures of 400 - 600 °C. This mainly produces coarse-pored activated carbons, which can be used, for example, for decolorizing liquids due to their properties.
The second variant is gas activation. Generally, already carbonized natural products such as charcoal, peat coke, coconut shell coke, hard or lignite coal are used. These already have few small pores and thus a first, albeit still little developed, adsorption surface before activation. The activation process significantly increases the number of pores and thus the surface area. Activation is carried out at temperatures of 700 - 1000 °C using steam and carbon dioxide. The steam and carbon dioxide lead to partial oxidation, especially of the non-crystalline carbon. Tar-like products that clog the fine pores are driven out, and the carbon framework is largely exposed. Inside the raw material, the desired pores for a fine-pored activated carbon are now formed. Since activation requires a high temperature, rotary kilns, shaft, or chamber ovens have become established in industry. Here, activated carbons and their pore distribution can be tailored for various applications.
Activated carbon is marketed as powder or granular carbon or shaped carbon. In the production of shaped carbon, e.g., for water filters (activated carbon block filters), the carbonized semi-finished product is pulverized, activated, and then mixed with a binder and extruded or sintered as needed. The granulated carbon, a few millimeters in size, is available as broken particles or rod-shaped pellets. Granular carbon is used in adsorber containers through which the gas or liquid stream to be purified is passed. The broken, sharp-edged activated carbon is preferred for water purification. Due to its compact design, an activated carbon block filter replaces bulky loose fillings of powdered carbon. Also, the capacity to absorb unwanted substances is significantly increased, and the tendency to release once adsorbed substances (so-called chromatographic effect) is lower. In fine-pored block filters with high filtration fineness, besides chemical-physical adsorption, there is also good mechanical filtration against particles and microorganisms.
Drinking Water Treatment
Drinking water is mostly obtained from groundwater aquifers, but also in regions poor in groundwater, for example, from riverbank filtrate. A large proportion of the compounds and contaminants that humans release into nature are biologically broken down by soil bacteria during infiltration. Nevertheless, legal limit values are repeatedly exceeded, leading to the need to treat the obtained water before feeding it into the drinking water network. The filters used for this are called single-layer or multi-layer filters.
Single-layer filters consist entirely of only one filter material, whereas multi-layer filters are composed of a combination of different filter materials. Multi-layer filters usually consist of a layer (e.g., sand) for retaining coarse particles and a layer of activated carbon. Since suppliers are legally required to guarantee drinking water quality only up to the house connection, drinking water filters are increasingly used in private households as well.
These filters have the task of eliminating particles, bacteria, odor and taste substances, as well as heavy metals possibly introduced through the pipe network. It can also happen that pollutants are not completely retained in the waterworks. These can be pesticides, drug residues, or even hormonal substances that enter the groundwater diffusely and pass through the waterworks unhindered. Unsuitable or outdated house installations can release heavy metals into the drinking water. If the local different drinking water quality is insufficiently considered when selecting pipe materials, heavy metal ions can be dissolved. 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 at the drinking water outlet, 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 thus available even after filtration.
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