Carbon technical, its receipt

Technical carbon (GOST 7885-86) is a kind of industrial carbon products, used mainly in the production of rubber as a filler, enhancing its useful performance properties. Unlike coke and pitch, it consists of almost one carbon, similar in appearance to soot.

Application area

Approximately 70% of produced carbon black is used for tires, 20% for rubber products. Also, technical carbon finds application in paint and varnish industry and production of printing inks, where it performs the role of black pigment.

Another area of application is the production of plastics and cable sheaths. Here, the product is added as a filler and giving the products special properties. In small volumes, carbon black is also used in other industries.

Characteristic

Technical carbon is a product of a process that incorporates the latest engineering technologies and control methods. Due to its purity and a strictly defined set of physical and chemical properties, it has nothing to do with soot, formed as a contaminated by-product from the combustion of coal and fuel oil, or in the operation of unregulated internal combustion engines. According to the generally accepted international classification carbon black is designated Carbon Black (black carbon in English), soot in English - soot. That is, these concepts at present, in no way are mixed.

The effect of reinforcement due to the filling of rubbers with carbon black had no less significance for the development of the rubber industry than the discovery of the vulcanization of rubber by sulfur. In rubber compounds, carbon from a large number of ingredients used by weight ranks second after rubber. The influence of qualitative indicators of carbon black on the properties of rubber products is much greater than the quality of the main ingredient - rubber.

Strengthening properties

Improving the physical properties of the material by introducing filler is called reinforcement, and such fillers are called amplifiers (carbon black, precipitated silica). Among all the amplifiers, carbon has a unique technical characteristic. Even before vulcanization, it binds to rubber, and this mixture can not be completely separated into carbon black and rubber using solvents.

Strength of rubbers obtained on the basis of the most important elastomers:

The table shows the properties of vulcanizates obtained from various types of rubber without filling and filled with carbon black. From the data given, we can see how the carbon content significantly affects the tensile strength of rubbers. By the way, other dispersed powders used in rubber mixtures to impart the desired color or cheaper mixture - chalk, kaolin, talc, iron oxide and others do not possess reinforcing properties.

Structure

Pure natural carbons are diamonds and graphite. They have a crystalline structure, which differs significantly from one another. The method of X -ray diffraction establishes a similarity in the structure of natural graphite and the artificial carbon black material. The carbon atoms in graphite form large layers of condensed aromatic ring-shaped systems, with an interatomic distance of 0.142 nm. These graphite layers of condensed aromatic systems are commonly referred to as basal planes. The distance between the planes is strictly determined and is 0.335 nm. All layers are parallel to each other. The density of graphite is 2.26 g / cm ³ .

Unlike graphite, which has three-dimensional order, carbon technical is characterized only by two-dimensional order. It consists of well-developed graphite planes, located approximately parallel to each other, but displaced with respect to adjacent layers - that is, planes are arbitrarily oriented with respect to the normal.

Figuratively, the structure of graphite is compared with a neatly folded deck of cards, and the structure of carbon black with a deck of cards in which the cards are shifted. In it, the interplanar spacing is larger than that of graphite and is 0.350-0.365 nm. Therefore, the density of carbon black is lower than the density of graphite and is within the range of 1.76-1.9 g / cm ³ , depending on the brand (most often 1.8 g / cm ³ ).

Staining

Pigment (staining) grades of technical carbon are used in the manufacture of printing inks, coatings, plastics, fibers, paper and building materials. They are classified into:

• High-coloring carbon black (HC);
• Medium coloring (MS);
• Normal coloring (RC);
• Low coloring (LC).

The third letter denotes the method of obtaining - furnace (F) or channel (C). Example of designation: HCF is a high-color furnace charcoal (Hiqh Color Furnace).

The color of the product is related to the size of its particles. Depending on their size, the technical carbon is divided into groups:

Classification

Technical carbon for rubbers by the degree of reinforcing effect is divided into:

• Highly reinforcing (tread, hard). It is distinguished by increased strength and resistance to abrasion. The particle size is shallow (18-30 nm). Applied in conveyor belts, tire protectors.
• Half-reinforced (frame, soft). The particle size is medium (40-60 nm). They are used in various rubber products, tire carcasses.
• Low-strengthening. The particle size is large (over 60 nm). In the tire industry is used in a limited way. Provides the necessary strength while maintaining high elasticity in rubber products.

The complete classification of carbon black is given in ASTM D1765-03, adopted by all the world's manufacturers of the product and its consumers. In it, the classification, in particular, is conducted over the range of the specific surface area of the particles:

Carbon black production

There are three technologies for the production of industrial carbon black, which uses a cycle of incomplete combustion of hydrocarbons:

• Furnace;
• Channel;
• lamp;
• Plasma.

There is also a thermal method, in which decomposition of acetylene or natural gas takes place at high temperatures.

Numerous brands, obtained due to different technologies, have various characteristics.

Manufacturing technology

Theoretically, it is possible to obtain carbon black by all of the above methods, however, more than 96% of the produced product is produced by the furnace method from liquid raw materials. The method allows to obtain a variety of brands of carbon black with a certain set of properties. For example, at the Omsk plant of carbon black, this technology produces more than 20 brands of carbon black.

The general technology is as follows. The reactor, lined with highly refractory materials, is supplied with natural gas and air heated to 800 ° C. By burning natural gas, products of complete combustion with a temperature of 1820-1900 ° C are formed, containing a certain amount of free oxygen. In the high-temperature combustion products, a liquid hydrocarbon feedstock is injected, pre-carefully mixed and heated to 200-300 ° C. Pyrolysis of raw materials occurs at a strictly controlled temperature, which, depending on the brand of produced carbon black, has different values from 1400 to 1750 ° C.

At a certain distance from the feed point, the thermal oxidation reaction is stopped by injection of water. The resulting technical pyrolysis carbon and reaction gases are fed to the air heater in which they give up some of their heat to the air used in the process, while the temperature of the carbon-gas mixture decreases from 950-1000 ° C to 500-600 ° C.

After cooling to 260-280 ° C due to additional water injection, the mixture of technical carbon and gases is sent to the bag filter, where the technical carbon is separated from the gases and enters the filter hopper. Dedicated carbon black from the filter bunker is piped through a gas transmission pipeline by a fan (turbo-blower) to the granulation unit.

Manufacturers of carbon black

The world production of carbon black is more than 10 million tons. Such a great need for a product is due, first of all, to its unique reinforcing properties. Locomotives of the industry are:

• Aditya Birla Group (India) - about 15% of the market.
• Cabot Corporation (USA) - 14% of the market.
• Orion Engineered Carbons (Luxembourg) - 9%.

The largest Russian carbon producers:

• OOO Omsktehuglerod - 40% of the Russian market. Plants in Omsk, Volgograd, Mogilev.
• OJSC Yaroslavl Technical Carbon - 32%.
• OAO Nizhnekamsktehuglerod - 17%.