Soot (from ahd. Ruos , dark-, dirty-colored ) is a black, powdery solid that, depending on the quality and use, consists of 80% to 99.5% carbon . Soot is colloquially used to refer to industrial products as well as undesirable, harmful by-products of combustion processes .
Industrial soot ( English Carbon Black , CAS No .: 1333-86-4) is carbon black specifically produced as an industrial base material. Due to its purpose, carbon black is a modification of carbon with a high surface-to-volume ratio and is mainly used as a filler and as a black pigment .
The production of carbon black as a black pigment for inks → carbon black and inks goes back to the early high cultures of mankind. At the time of the ancient advanced civilizations of the Chinese and Egyptians , the need for small and tiny soot particles increased steadily in order to be able to produce large quantities of inks and inks from them. The soot required for this was obtained through the targeted combustion of resins , vegetable oils or asphalt in special ovens or shallow tubs. The Roman builder Marcus Vitruvius Pollio (1st century BC) writes in his standard work on antiquity, De Architectura, about the art of making black pigment: “ Pine resin is now put into the furnace , and when it is burned, soot is collected becomes. ”A particularly elegant black, the“ leg black ”, was created from the charring of ivory . The production of "leg black" is said to have been invented by the Greek painter and scholar Apelles (around 325 BC).
In the Middle Ages, the soot extraction was the business of soot burners , who in their forest huts - mostly together with tar smelters and pitch boilers - burned highly fuming, resinous wood and the residue ( pitch cake ) from the production of pitch . The one with the smoke escaping soot was reflected in the Rußkammer of withdrawal , where he could be scraped off. Soot of the finest quality was the lamp soot (also lamp black), which was made from oils, fats, tears , pitch and tar oil (in China , the wick was soaked with juice from real stone seeds ) in the "soot lamp" with the help of a thick cotton wick (in China the wick was soaked with juice from real stone seeds ) also camphor oil and tung oil ) was burned with reduced air supply. Soot was used to make leather paint, paints, printer's ink, inks and car grease . Instructions for making soot can be found in Codex latinus Monacensis 4 , a manuscript created around 1470 in the Tegernsee Monastery . In order to produce particularly fine soot for special applications, tree resins in particular were burned with a limited supply of air → bad luck . Up until the 16th century, this was the only known process for producing carbon black with extremely small particle sizes that are comparable to carbon black . This process is still used under the name of the flame black process . From the 19th century onwards, soot was increasingly extracted from natural gas and coal tar .
The term “carbon black” spread in the 1870s when products made from natural gas were sold under this name. In 1882 Godfrey Lowell Cabot founded the first production facility for carbon black , which was operated with the channel black process to "Channel Black". The carbon black was mainly used as a component of printing ink. Since natural gas was only available in insignificant quantities in Germany, alternatives using local raw materials were sought intensively . Coal tar accumulates in gasworks in significant quantities during the condensation of gas. In 1889 Otto Thalwitzer developed the furnace process based on tar oil from coal tar . Although "closed reactors" had been developed and the furnace processes produced significantly higher yields, the oil furnace process did not gain acceptance until 1943 due to the shortage of primary energy sources .
The mass production of carbon black began in the first half of the 20th century as a result of the expanding tire industry. As a reinforcing filler, carbon blacks optimize the physical properties of tires and promote their longevity . The first larger plants were built as Channel Black plants on the oil fields in the USA in order to utilize part of the natural gas escaping from the oil production . The yields were low (5%), which played no role because of the excess of natural gas. From 1920 the thermal soot process was developed in the USA , first for the production of hydrogen for airships, and the gas furnace process , these have a higher yield and produce fewer emissions . The oil furnace process was patented in 1922, but it was not used until later.
In Germany, in 1934 Degussa - gas black : "Gas-Black" based on tar oils developed. Under the National Socialists , carbon black was an important raw material for the war effort, and it was produced using the gas black process in the newly founded joint ventures between Degussa and tire manufacturers . In 1936, " Deutsche Gasrußwerke GmbH & Co. KG " was founded in Dortmund. The rapidly increasing demand of the "tire industry" ensured the further development of the oil furnace carbon black process in the USA from 1937 , which achieves a yield of 10% to 70% depending on the product properties . It was first used commercially in 1943.
Technically, the development of the "furnace blacks" proceeded in four waves: A first generation of products differed mainly in the size of the primary particles and thus the specific surface (N110, N220, ... N990), in a second generation the aggregation behavior, i.e. the " Degree of intergrowth ”of the primary particles , the“ structure ”, varies. In the 1970s and 1980s, for example, the application properties of the rubber were directly influenced by the dwell time . In the 1990s, other fillers finally came onto the market, such as the silica - silane system in the green tire patented by Michelin , which reduced rolling resistance and thus fuel consumption . So were nanostructured industrial carbon as the fourth innovation generation developed by Reifenrußen.
International carbon black manufacturers
The largest manufacturers of carbon black include:
- Birla Carbon (a company of the Indian conglomerate Aditya Birla )
- Cabot Corporation (specialty chemicals company and one of the largest carbon black manufacturers)
- Orion Engineered Carbons (the former global carbon black business of Evonik Industries , independent since 2011 and listed on the New York Stock Exchange since 2014 )
- Phillips Carbon Black (largest national carbon black producer in India)
Two fundamental properties of carbon black determine the two main areas of application: the reinforcement effect in rubber (natural and synthetic rubber) and the color of carbon black as the most common black pigment. In special applications, thermal and electrical conductivity and resistance to UV radiation are used. Carbon black consists of the smallest , mostly spherical particles (“primary particles” or nodules). These are usually 10 to 300 nanometers in size , i.e. less than a thousandth of the diameter of a hair . These “primary particles” have grown together to form chain-like , sometimes lump-like aggregates . Many of these aggregates accumulate and thus form the agglomerates . With these dimensions, it is less the chemical composition alone that determines the properties , but rather the size and shape of the particles . The optical, electrical and magnetic properties as well as the hardness , toughness and melting point of nanomaterials differ significantly from those of the respective macroscopic solids. This explains the special properties of carbon black. The specific surface area of carbon black is about BET 10 to 1500 m 2 / g. Carbon black can be produced specifically with special property profiles, influencing variables for this are: the type of manufacturing process, changes in "process parameters" such as pressure, temperature, reaction time, injection, raw material . The size of the "primary particles" and their aggregation can be specifically selected. The bulk density of carbon black powder is about 80 kg / m 3 .
The following list gives an overview of the properties of carbon black grades.
|Soot type||Type of carbon black||Grain diameter nm||BET surface area m 2 / g||PH value||composition||Yield%|
|Channel Black||0-30||110-120||3-5.5||C 95.6; H 0.6; S 0.2; O 3.5||3-6|
|Carbon black||Gas Black||8-30||90-500||3-5.5||C 96; H 1 ; S 0.2 ; O 2.5||10-60|
|Furnace soot||Furnace Black||10-110||PEMFCS )24–600 to 1500 (||2.1-9||C 97.9; H 0.4; S 0.6; O 0.7||10-70|
|Lampblack||Lamp Black||60-110||16-24||6-9||C 98; H 0.2; S 0.8 ; O 0.8||50|
|Soot||Thermal Black||100-500||10-50||7-9||C 99.3; H 0.4; S 0.01; O 0.2||35-40|
|Acetylene black||Acetylene Black||30-50||20-80||4.8-7||C 99.7; H 0.1; S 0.02; O 0.2||35-40|
Carbon black is an important technical product that is produced in large quantities by incomplete combustion or pyrolysis of hydrocarbons . In 2006, 8.1 million tons were produced worldwide , in 2011 10.8 million tons were produced.
- Combustion soot : which is caused by incomplete combustion
- Soot , which is produced by thermal decomposition (pyrolysis)
Carbon black is differentiated according to its production or its application.
- Soot: from natural gas, methane and acetylene
- Acetylene black process: soot obtained through incomplete combustion of acetylene, acetylene blacks are high-purity carbon blacks .
- Thermal black process: Thermal black is created in a discontinuous or cyclical process in special furnaces in which natural gas or methane is the most frequently used raw material. However, mineral oils can also be used as the starting material. The natural gas is injected into the furnace's inner atmosphere, where it is broken down into soot and hydrogen. One speaks here of a thermal crack. Thermal blacks have the largest primary particle sizes (larger than in the flame black process) and belong to the types of carbon black with the lowest surface area and structure. Since they are made from natural gas, they are very pure types of soot.
- Channel black process: Natural gas is burned in many small, glowing flames against water-cooled iron channels (channels). Because of the low yield (3% - 6%), this process is no longer used.
- Lamp black process: it is the industrial variant for the production of "lamp black", oil , tar , pitch , woods rich in resin are burned, this results in coarse, dense soot
- Gas black process: it was developed by Degussa in the 1930s in competition with manufacturers from the USA with the support of the National Socialist government . In this process, a hydrogen-containing gas is passed over heated oil rich in aromatic compounds (mostly coal tar oils ) and the carrier gas, saturated with oil vapors , is burned off by means of a burner in front of a water-cooled roller . The resulting soot is partly deposited directly on the roller and partly fed to the end product via a suspended matter filter . In contrast to the furnace black process, the carbon black process works in a system that is open to the outside air. The process can only be regulated by means of the raw material feed via the lifting gas and offers little opportunity for intervention. Nevertheless, the method is very adaptable in terms of particle size . The structure of this carbon black is due to its manufacture: loose and easily dispersible . The carbon black process is only of minor importance (approx. 5%). It is used almost exclusively in the pigment sector (carbon black), hardly as a tread black .
- Furnace black process: the furnace black process is the most widely used process with around 95% worldwide. Carbon black is produced by incomplete combustion of the heavy fractions , mostly residues from FCC or steam crackers or from the distillation of coal tar . In this method, in an becomes combustor ( English furnace ), a hot gas from 1200 to 1800 ° C by natural gas - or oil combustion generated. A soot raw material, mostly aromatic-rich carbon and petroleum-based soot oils, is injected into this hot gas . The soot is formed by incomplete combustion and thermal cleavage (pyrolysis) of the carbon black raw material, whereby the competing reactions of nucleation and growth in the reaction zone are controlled by "process parameters" such as oil load and residence time in such a way that the carbon black is created with the desired property profile . After a certain dwell time , the process gas mixture is suddenly cooled by water injection ( quenching ), and the soot is separated off in bag filters. The systems are operated continuously in shifts .
Suitable aftertreatments are carried out on the carbon black for many applications. For example, carbon blacks for high-color lacquers are produced from base black through subsequent oxidation . Better wetting with binders and resins is achieved through oxidic groups .
More than 90% of the amount of carbon black is used as a filler in the rubber industry, of which about 70% is for car tires and about 20% for technical rubber items such as conveyor belts , V-belts , hoses and damping elements . The vehicle industry is by far the largest consumer of carbon black: In 2011 it consumed more than 7.8 million tons for tires. There are almost 40 different types of carbon black for car tires, each of which gives the rubber specific properties. The classification of “standard blacks” according to the US ASTM standard is customary internationally . In the area of CIS -Staaten the deviating is GOST - Standard common. Carbon black with a large surface area and corresponding reinforcing activity (N1xx to N3xx according to the following table) are processed in the tread of tires to give them the necessary hardness and abrasion resistance . This group of industrial blacks is therefore also called tread blacks , hard blacks or active blacks . The group of semi-active carbon blacks (N5xx to N7xx) is used for the sidewalls ( carcass ) of the tire in order to set the necessary suspension and damping . They make the rubber more elastic . They are called Carcass Blacks , Soft Blacks or semi-active carbon blacks . Typically, the production facilities are designed so that either one or the other group is optimally produced. In addition to the other raw materials and, in particular, the tire technology itself, the property profiles of the carbon blacks used in the tire determine its three parameters : rolling resistance , wet slip resistance and abrasion .
|Super abrasion furnace||SAF||N 110||very abrasion-resistant type|
|Intermediate SAF||ISAF||N 220||Carbon black for tire treads|
|ISAF - Low Modulus||ISAF-LM||N 234||ISAF variant with better processing properties|
|Super conductive furnace||SCF||N 294||electrically conductive type|
|High abrasion furnace||HAF||N 330|
|HAF - Low Structure||HAF-LS||N 326||type used for adhesive mixtures and consumption maximization|
|HAF - High Structure||HAF-HS||N 347||similar to N 220|
|Fine furnace||FF||N 440||US type (not in use in Europe)|
|Extra Conductive Furnace||XCF||N 472||no longer in use type|
|FEF - Low Structure||FEF-LS||N 539|
|Fast Extrusion Furnace||FEF||N 550||Use z. B. in profiles|
|FEF - High Structure||FEF-HS||N 568|
|High Modulus Furnace||HMF||N 601||US type (not in use in Europe)|
|General Purpose Furnace||GPF||N 660||Carcass black|
|SRF - low modulus, non staining||SRF-LM-NS||N 762||Type for non-discoloring technical articles|
|Semi Reinforcing Furnace||SRF||N 770|
|Multi processing furnace||MPF||N 785||rarely used type|
|Fine thermal||FT||N 880||US type (rarely used in Europe)|
|Medium thermal||MT||N 990||most inactive type|
If the soot has small "primary particles" and has widely ramified aggregates, it has electrical conductivity for different applications. These types and product qualities are listed as conductivity black. It is used in the electrical industry and as a raw material for engineering ceramics, as well as for electrode material . A special application is the production of electrically conductive printing inks , which are particularly suitable as security features for documents. Another application is the printing of conductor tracks with black conductive inks .
Acetylene black is used as an additive in the manufacture of cathodes for zinc-carbon batteries . The addition of acetylene black increases the electrical conductivity of the electrochemically active manganese dioxide ( manganese dioxide ) and allows better absorption of the electrolyte solution in the cathode.
Carbon black is used as a black pigment ( C.I. Pigment Black 7 and 6 Lamp Black ) for printing inks , inks , lacquers and for coloring plastics (especially as UV protection). It is also used as a black pigment in special products such as mascara , grave soil , decorative paper and fibers .
Color carbon blacks are nano- sized carbon blacks which, due to their fineness, increasingly lose their brown base tone . They are used in the production of black printing inks in a wide variety of printing processes . Since the printed layers are very thin and partially transparent , the carbon blacks need a special quality. For a sufficient depth of color (black tone) of inexpensive carbon black qualities, especially in newspaper printing inks, blue pigments are often used to suppress a red / brown cast . Carbon blacks for high-color lacquers are produced by subsequent oxidation of the base black . The oxidic groups result in better incorporation into the binders and resins. Carbon black is used as a coloring pigment in most tattoo inks , not just black.
Ecology and toxicology
Carbon black is used so widely that it occurs everywhere, but it is always embedded in the basic substance of the application system. It gets into the environment through abrasion from tires or from the printing inks of recycled newspapers . Fundamental damage effects are conceivable due to the chemistry of the manufacturing process and due to its properties as fine dust or nanomaterial. During production, PAH-containing (polycyclic aromatic hydrocarbons) and thus highly carcinogenic starting material is converted into an inorganic pigment. Traces of residues of the starting material could remain on the carbon black produced; this may be the case depending on the manufacturing process conditions. On the other hand, the hazard potential is limited by the fact that these residues are firmly adsorbed by the high surface activity ( van der Waals forces ) of the carbon black . The current toxicological assessment of carbon black can be found at the International Agency for Research on Cancer (IARC). Thereafter applies: "Carbon black is possibly carcinogenic to humans ( Group 2B )". Short-term exposure to high concentrations of “carbon black dust” can possibly trigger impairment of the upper respiratory tract through mechanical irritation . Carbon black is seen as "potentially carcinogenic to humans". Although there are sufficiently conclusive studies with animals , there are no corresponding studies with humans. The main statements on carcinogenicity in animal studies come from studies on rats , two of them on chronic inhalation and two on direct infusion into the trachea . These studies showed a significantly increased incidence of lung cancer in the rats examined. Another inhalation study, this time on mice , showed no increase in lung cancer. Epidemiological data are available on three different cohorts of production workers. Two studies, one from Great Britain and one from Germany ( Kalscheuren production plant near Cologne), each with more than 1000 workers in each group examined, showed increased mortality from lung cancer. Another study on over 5000 carbon black workers from the USA did not show this increased mortality.
Carbon black was included by the EU in 2016 in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation in the Community's ongoing action plan ( CoRAP ). The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The causes of the uptake of carbon black were concerns about consumer use , cumulative exposure , exposure of sensitive population groups , exposure of workers , high (aggregated) tonnage and widespread use, as well as the suspected risk of carcinogenic properties and the possible risk of reproductive toxicity . The re-evaluation is to be carried out by France from 2021 .
However, soot often occurs as an undesirable product in combustion processes. Oily products are formed if the combustion is incomplete. Such soot (English soot) has the potential in animal studies cancer trigger. However, the risk of cancer is caused by the polycyclic aromatic hydrocarbons (PAHs) that are formed when the combustion is incomplete .
In heating systems , soot is deposited as a product of incomplete combustion when it cools down and, together with condensed tar , can lead to fireplace fires . To prevent this (because the fire can ignite dry roof trusses) the chimney sweep ( chimney sweep ) sweeps the inside walls of the chimney with a sharp brush at regular intervals.
The emission measurement of soot from combustion plants can be done using the Bacharach method . It is used to determine the soot number semi-quantitatively . A comparable method for determining the soot number is based on the change in the reflectivity of an impacted measuring filter.
In the targeted measurement of the immission of soot, carbon deposited on a filter is heated and the optical transmission of the filter is measured. In another method, the elemental carbon deposited on a filter is separated from the organic carbon by liquid extraction and thermal desorption, and is then burned so that the carbon dioxide formed can be determined coulometrically . As a rule, there is no separate measurement of soot within the scope of immission surveys.
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