Technical carbon, its production

Carbon black (GOST 7885-86) is a type of industrial carbon products used mainly in the manufacture of rubber as a filler, enhancing its useful performance properties. Unlike coke and pitch, it consists of almost one carbon, in appearance it resembles soot.

Application area

About 70% of the carbon black produced is used for the manufacture of tires, 20% for the production of rubber products. Technical carbon is also used in paint and varnish production and printing inks, where it acts as a black pigment.

Another area of ​​application is the production of plastics and cable sheaths. Here the product is added as a filler and to impart special properties to the products. Carbon black is also used in small volumes in other industries.

Characteristic

Carbon black is a product of a process that includes 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 when unregulated internal combustion engines are running. 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 are currently not mixed in any way.

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

Reinforcing properties

Improving the physical properties of a material by introducing a filler is called reinforcement (reinforcement), and such fillers are called enhancers (carbon black, precipitated silica). Among all the amplifiers, carbon technical has truly unique characteristics. Even before vulcanization, it binds to rubber, and this mixture cannot be completely separated into carbon black and rubber with 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. It can be seen from the data that carbon filling significantly affects the tensile strength index of rubber. By the way, other dispersed powders used in rubber mixtures to give the desired color or reduce the cost of the mixture - chalk, kaolin, talc, iron oxide and others do not have reinforcing properties.

Structure

Pure natural carbons are diamonds and graphite. They have a crystalline structure, significantly different from one another. Using X-ray diffraction, a similarity was found between the structure of natural graphite and the carbon black artificial 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 called basal planes. The distance between the planes is strictly defined and amounts to 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 ordering, technical carbon is characterized by only two-dimensional ordering. It consists of well-developed graphite planes located approximately parallel to each other, but offset relative to adjacent layers - that is, the planes are arbitrarily oriented with respect to the normal.

Figuratively, the graphite structure 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 distance is greater 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 in the range of 1.76-1.9 g / cm ³ , depending on the brand (most often 1.8 g / cm ³ ).

Dyeing

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

• highly stained carbon black (NS);
• medium staining (MS);
• normal coloring (RC);
• low coloring (LC).

The third letter denotes the method of production - furnace (F) or channel (C). Designation example: HCF - Highly Stain Furnace Carbon Black (Hiqh Color Furnace).

The coloring ability of a product is related to its particle size. Depending on their size, technical carbon is divided into groups:

Classification

Carbon black for rubber according to the degree of reinforcing effect is divided into:

• Highly reinforcing (tread, solid). It is distinguished by increased strength and resistance to abrasion. The particle size is small (18-30 nm). Used in conveyor belts, tire treads.
• Semi-reinforcing (wireframe, soft). The particle size is average (40-60 nm). Apply in diverse rubber products, tire carcasses.
• Low reinforcing. The particle size is large (over 60 nm). In the tire industry is used to a limited extent. Provides the necessary strength while maintaining high elasticity in rubber products.

A complete classification of carbon black is given in ASTM D1765-03, adopted by all global manufacturers of the product and its consumers. In it, the classification, in particular, is carried out according to the range of the specific surface area of ​​the particles:

Carbon black production

There are three technologies for producing industrial carbon black, which use the cycle of incomplete combustion of hydrocarbons:

• stove;
• channel;
• lamp;
• plasma.

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

Numerous brands obtained through various technologies have a variety of characteristics.

Manufacturing technology

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

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

At a certain distance from the feed point, the thermo-oxidative reaction is terminated by water injection. The carbon black and reaction gases formed as a result of pyrolysis enter the air heater, in which they give part 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 the additional injection of water, the mixture of carbon black and gases is sent to a bag filter, where carbon black is separated from the gases and enters the filter hopper. The extracted carbon black from the filter hopper through the gas transport pipeline is supplied by a fan (turbo-blower) to the granulation compartment.

Carbon black producers

World production of carbon black exceeds 10 million tons. Such a great need for a product is explained, first of all, by its unique reinforcing properties. The 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:

• Omsktekhuglerod LLC - 40% of the Russian market. Factories in Omsk, Volgograd, Mogilev.
• OJSC Yaroslavl carbon black - 32%.
• OAO Nizhnekamsktekhuglerod - 17%.