Ethylene or ethene is a colorless combustible gas with a faint muscat and sweet smell. Its chemical formula is C2H4. Ethene is the simplest alkene (unsaturated hydrocarbons having one double bond between adjacent carbon atoms). Molar mass is 28.05 g / mol. Melting point - -169.2 ° , boiling point - -103.7 ° . Flash point - -136 ° , autoignition - +542.8 ° . In 1680, I. Bercher (a German doctor and chemist) from wine alcohol when exposed to it with vitriol oil (as sulfuric acid was called at that time ) , ethylene was first obtained from ethyl alcohol. The structural formula of ethylene in 1860 was established by the Russian chemist A. M. Butlerov as a result of the reaction of methylene iodide with copper. This gas is slightly lighter than air, it is poorly soluble in water, in organic solvents - well.
The production of ethylene and the study of its properties, the beginning of which dates back to the middle of the 19th century, today led to the fact that ethylene is the most popular organic compound. Its world production in 2006 reached more than 109 million tons. Today, ethylene production continues to evolve. By 2010, it was produced by at least 117 companies in 55 countries. Ethylene is used as a raw material in the production of high and low pressure polyethylene, sevilen and other polymeric materials obtained in the process of copolymerization with various comonomers. It is also used to produce ethylbenzene and styrene, ethylene oxide, vinyl chloride, vinyl acetate, acetic acid, ethyl alcohol and ethylene glycol.
What caused the growth of production capacities aimed at producing ethylene? Mainly expanding the market for polymer materials. Various types of polyethylenes consume more than half of the world's ethylene production. This polymer material is the most used plastic in the world. Films of various purposes are made from it. Linear alpha-olefins obtained by oligomerization (formation of short polymer chains) are used as precursors, detergents, plasticizers, synthetic lubricants, additives, and also as comonomers in the production of polyethylene. Another important area of ethylene use is its oxidation in order to produce ethylene oxide, which is the main raw material in the production of surfactants and detergents. Ethylene oxide undergoes hydration, resulting in ethylene glycol. It is widely used as automobile antifreeze.
Today, ethylene is produced mainly as a result of pyrolysis of straight-run gasoline or a wide fraction of light hydrocarbons. Installations of various capacities are built in Russia and the former republics of the USSR, built both according to domestic (Giprokauchuk, VNIPINeft, Bashgiproneftekhim) and foreign technologies (Linde AG). Existing production can be divided into three groups: small capacity (30 and 60 thousand tons of ethylene per year), medium (100 and 200 thousand tons per year) and high (300 and 450 thousand tons of ethylene per year). Now in the world, plants with much greater capacity are in operation: from 400 to 500 and even up to 800 thousand tons of ethylene per year. Such an increase in production allows us to reduce specific material, energy and capital costs.
Ethylene is produced at chemical plants, including a pyrolysis unit, a gas separation unit, and a chemical water treatment unit. Raw materials - gasoline or other light fraction of oil production or refining mixed with water vapor (to reduce the process of coke formation in the pipes of furnaces). The raw material enters the pyrolysis furnace, where at a temperature of 750 to 900 ° C, pyrogas is formed, consisting of hydrogen and hydrocarbons, the molecules of which contain from one (methane) to twenty carbon atoms. The heat of the pyrogas is utilized in special apparatuses where high pressure steam is generated from chemically purified water, and the cooled pyrogas is fed to the pyrolysis (heavy) resin and pyrocondensate separation unit. After that, the pyrogas containing mainly hydrocarbons from C1 to C4 is fed to a turbocharger (the turbines are driven by high pressure steam), from where it is fed under pressure to the distillation columns of the gas separation unit. Here, the main products, such as ethylene and propylene, are separated (its yield, compared with ethylene, is always 2 times less), as well as by-products: hydrogen, methane, ethane, propane, butylene-butadiene fraction, light pyrolysis resin or components automotive gasolines.
It is also possible to obtain ethylene by catalytic pyrolysis. On an industrial scale, this method has not been implemented, although its tests in our country at one time were carried out not only in laboratory facilities, but also in industrial conditions. Its advantage is the possibility of lowering the pyrolysis temperature due to the use of catalysts. As a result of increasing the selectivity (selectivity) of the process, the yield of ethylene and propylene increases compared to thermal pyrolysis, and the formation of by-products as well as coke is reduced. Currently, researchers in different countries are working towards finding an effective catalyst and instrumentation of the process.