Calcium carbide

As a result of the interaction of carbon with metals at high temperatures, carbides are obtained. For example, calcium carbide: Ca + 2C → CaC2. Of all carbides, it has the greatest practical significance. Pure CaC2 is a well crystallizing solid, colorless crystals are formed by Ca2 + and C2- ions. Other names are calcium acetylenide or calcium carbonate. The molar mass is 64.1 g / mol. It is not volatile and is not soluble in any of the known solvents, but decomposes under the action of water. Its density is 2.22 g / cm³. The melting point is 2160 ° C, and the boiling point is 2300 ° C. By the degree of impact on the body refers to substances extremely dangerous (1st hazard class).

For the first time, calcium acetylenide was obtained in 1862 by the German chemist Friedrich Weller when heated with carbon from an alloy of zinc and calcium. He also described the reaction of carbonaceous calcium with H2O. Even with its traces (for example, with atmospheric moisture), calcium carbide reacts vigorously, with the release of a large amount of heat. But in the event of a lack of water, the resulting acetylene can self-ignite. Calcium carbide reacts violently with dilute inorganic acids and aqueous solutions of alkalis. At the same time, acetylene is also released. Being a strong reducing agent, CaC2 is able to restore all metal oxides to carbides or pure metals.

The production of calcium carbide is more convenient not from the calcium itself, but from its oxide. At a high temperature (2000 to 2300 ° C), it is restored. In this case, the metal and carbon are joined: CaO + 3C → CO ↑ + CaC2. The process takes place in an electric arc furnace, where a mixture of quicklime and coke or anthracite is heated. The technical product is colored, has a grayish color, since it contains impurities in the form of free carbon, oxide, as well as sulfide, calcium phosphide and other chemical compounds. The mass fraction of CaC2 in it is 80-85%.

In the interaction of carbides with water, either metal or acetylene is released. In the second variant, calcium carbide reacts with water. Acetylene, obtained as a result of the reaction, which has the industrial value: 2H2O + CaC2 → C2H2 + Ca (OH) 2, is technical and has an unpleasant odor, as it contains a number of impurities (NH3, H2S, PH3 and others). Although in its pure form it is a colorless gas with a characteristic slight odor, and it dissolves fairly well in water. It is of great importance for obtaining calcium cyanamide (it is a raw material in the production of cyanide compounds or used as a fertilizer) from carbide by its interaction with nitrogen according to the reaction equation: N2 + CaC2 → CaCN2 + C.

In the past, CaC2 was widely used in carbide lamps, where it served as a source of acetylene flame. Currently, the use of such a light source is limited mainly to speleology, it is also used in buoys and lighthouses. Other important uses of CaC2 are chemical technologies, where it is a raw material. For example, in the production of organic synthesis products, the main one is synthetic rubber. Also from carbonaceous calcium are obtained acetylene black, vinyl chloride, acetic acid, acrylonitrile, ethylene, acetone, artificial resins, styrene. In metallurgy it serves to deoxidize metals and desulfurize (reducing the oxygen and sulfur content, respectively). Calcium carbide is used to make plant growth regulator, powder carbide reagent (acetylene welding).

Receipt of each ton of CaC2 requires approximately 3 thousand kW / h of electricity. Therefore, it is justified in the presence of low prices for it. However, in general, the world production of carbonic calcium is growing. If in the 70 years of the preceding century, up to 5 million tons were produced annually, then in this century this number has grown approximately twice. Thus, in China, the production of acetylene based on calcium carbide is the main source of raw materials for the chemical industry, in particular for the production of PVC. Acetylene production from its raw materials is more economical than using imported oil. Therefore, its production in China is growing. In 2005, it reached 8.94 million tons, and there was a real opportunity to produce 17 million tons.

In contrast to China, in the US, Europe and Japan, the consumption of calcium carbon is usually reduced. The level of its production in the United States in the 90's was only 236 thousand tons per year. In our country, calcium carbide is produced according to the specifications set forth in GOST 1460-81. Its main consumers are Ukraine, Uzbekistan, Romania and Slovakia. Due to the high energy intensity of the product and the increase in electricity prices, the consumption of calcium acetylide in Russia and exporting countries has halved.