The ethane is a simple hydrocarbon of formula CtwoH6 with a colorless and odorless nature gas that has a highly valuable and diversified use in the synthesis of ethylene. In addition, it is one of the terrestrial gases that has also been detected in other planets and stellar bodies around the Solar System. It was discovered by scientist Michael Faraday in 1834.
Among the large number of organic compounds formed by carbon and hydrogen atoms (known as hydrocarbons), there are those that are found in a gaseous state at ambient temperatures and pressures, which are widely used in numerous industries..
These usually come from the gaseous mixture called "natural gas", a product of high value for humanity, and make up alkanes of the methane, ethane, propane and butane type, among others; classified according to the number of carbon atoms in its chain.
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Ethane is a molecule with formula CtwoH6, typically seen as a union of two methyl groups (-CH3) to form the hydrocarbon of a single carbon-carbon bond. It is also the simplest organic compound after methane, and is represented as follows:
H3C-CH3
The carbon atoms in this molecule have sp-type hybridization3, so the molecular bonds present free rotation.
Likewise, there is an intrinsic phenomenon of ethane, which is based on the rotation of its molecular structure and the minimum energy required to produce a 360 degree bond rotation, which scientists have called the "ethane barrier".
For this reason, ethane can appear in different configurations according to its rotation, even though its most stable conformation exists where the hydrogens are opposite each other (as seen in the figure).
Ethane can be easily synthesized from Kolbe electrolysis, an organic reaction in which two steps occur: an electrochemical decarboxylation (removal of the carboxyl group and release of carbon dioxide) of two carboxylic acids, and the combination of the products intermediates to form a covalent bond.
Similarly, the electrolysis of acetic acid gives rise to the formation of ethane and carbon dioxide, and this reaction is used to synthesize the former..
The oxidation of acetic anhydride by the action of peroxides, a concept similar to that of Kolbe's electrolysis, also results in the formation of ethane..
In the same way, it can be efficiently separated from natural gas and methane by a liquefaction process, making use of cryogenic systems to capture this gas and separate it from mixtures with other gases..
The turbo expansion process is preferred for this role: the gas mixture is passed through a turbine, generating an expansion of the same, until its temperature falls below -100 ºC..
Already at this point, the components of the mixture can be differentiated, so the liquid ethane will be separated from the gaseous methane and the other species involved with the use of a distillation.
Ethane occurs in nature as an odorless and colorless gas at standard pressures and temperatures (1 atm and 25 ° C). It has a boiling point of -88.5 ºC, and a melting point of -182.8 ºC. Also, it is not affected by exposure to strong acids or bases..
Ethane molecules are symmetrical in configuration and have weak forces of attraction that hold them together, called dispersion forces..
When ethane is tried to dissolve in water, the attractive forces formed between gas and liquid are very weak, so it is very difficult for ethane to bind with water molecules..
For this reason, the solubility of ethane is considerably low, increasing slightly when the system pressure is raised..
Ethane can be solidified, resulting in the formation of unstable ethane crystals with a cubic crystalline structure..
With a decrease in temperature beyond -183.2 ºC, this structure becomes monoclinic, increasing the stability of its molecule.
This hydrocarbon, even though it is not widely used as fuel, can be used in combustion processes to generate carbon dioxide, water and heat, which is represented as follows:
2 CtwoH6 + 7Otwo → 4COtwo + 6HtwoO + 3120 kJ
There is also the possibility of burning this molecule without excess oxygen, which is known as "incomplete combustion", and which results in the formation of amorphous carbon and carbon monoxide in an unwanted reaction, depending on the amount of oxygen applied. :
2 CtwoH6 + 3Otwo → 4C + 6HtwoO + Heat
2 CtwoH6 + 4thtwo → 2C + 2CO + 6HtwoO + Heat
2 CtwoH6 + 5Otwo → 4CO + 6HtwoO + Heat
In this area, combustion occurs by a series of free radical reactions, which are numbered in the hundreds of different reactions. For example, in incomplete combustion reactions, compounds such as formaldehyde, acetaldehyde, methane, methanol and ethanol can be formed..
This will depend on the conditions under which the reaction occurs and the free radical reactions involved. Ethylene can also be formed at high temperatures (600-900 ° C), which is a highly desired product by industry..
Ethane is present in the atmosphere of planet Earth in traces, and it is suspected that humans have managed to double this concentration since they began to practice industrial activities.
Scientists think that much of the current presence of ethane in the atmosphere is due to the combustion of fossil fuels, although the global emission of ethane has decreased by almost half since shale gas production technologies were improved (a natural gas source).
This species is also produced naturally by the effect of sunlight on atmospheric methane, which recombines and forms an ethane molecule.
Ethane exists in a liquid state on the surface of Titan, one of Saturn's moons. This occurs in greater quantity in the Vid Flumina river, which flows for more than 400 kilometers towards one of its seas. This compound has also been evidenced on comets, and on the surface of Pluto.
The use of ethane is based mainly on the production of ethylene, the organic product most used in world production, through a process known as vapor-phase cracking..
This process consists of passing a feed of ethane diluted with steam to a furnace, rapidly heating it without oxygen..
The reaction occurs at an extremely high temperature (between 850 and 900 ° C), but the residence time (the time that the ethane spends in the furnace) must be short for the reaction to be effective. At higher temperatures, more ethylene is generated.
Ethane has also been studied as a main component in the formation of basic chemicals. Oxidative chlorination is one of the processes proposed to obtain vinyl chloride (a component of PVC), replacing other less economical and more complicated.
Finally, ethane is used as a refrigerant in common cryogenic systems, also showing the ability to freeze small samples in the laboratory for analysis..
It is a very good substitute for water, which takes longer to cool delicate samples, and can also cause harmful ice crystals to form..
-Ethane has the ability to ignite, mainly when it binds with air. At 3.0 to 12.5% volume percentages of ethane in air, an explosive mixture may be formed..
-It can limit the oxygen in the air in which it is found, and for this reason it presents a risk factor for suffocation for people and animals that are present and exposed.
-Ethane in frozen liquid form can severely burn skin if it comes into direct contact with it, and also act as a cryogenic medium for any object it touches, freezing it instantly.
-Liquid ethane vapors are heavier than air and are concentrated on the ground, this can present an ignition risk that can generate a combustion chain reaction.
-Ingesting ethane can cause nausea, vomiting, and internal bleeding. Inhalation, in addition to suffocation, causes headaches, confusion, and mood swings. Death from cardiac arrest is possible at high exposures.
-It represents a greenhouse gas that, together with methane and carbon dioxide, contributes to global warming and climate change generated by human pollution. Fortunately, it is less abundant and durable than methane, and absorbs less radiation than methane..
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