Acetylene

Acetylene or ethyne is the simplest alkyne. It is a highly flammable gas, slightly lighter than air and colorless. It produces one of the highest adiabatic flame temperatures (3250 °C).

It was discovered by Edmund Davy in England in 1836.

History

In 1836, Edmund Davy—a cousin of the famous chemist Humphry Davy—discovered a gas that he recognized as "a new carbide of hydrogen." It was an accidental discovery while trying to isolate the metal potassium. By heating potassium carbonate with carbon to very high temperatures, a residue of what is now known as potassium carbide, (K
4C), which reacts with water to release the new gas. (A similar reaction between calcium carbide and water was later widely used for the manufacture of acetylene.)

In the article he read at the British Association in Bristol, Davy anticipated the value of acetylene as a lighting gas: "From the brilliance with which the new gas burns in contact with the atmosphere it is, in the opinion of the author, admirably adapted for artificial light, if it can be achieved cheaply".

However, it was forgotten until Marcellin Berthelot rediscovered it in 1860 and gave it the name "acetylene".

Summary

In petrochemical the acetylene is obtained quenching (quick cooling) of a natural gas flame or volatile oil fractions with high boiling point oils. The gas is used directly in plant as a product of departure in alternative synthesis. An alternative synthesis process, more suitable for the laboratory, is the water reaction with calcium carbide (CaC2){displaystyle (CaC_{2}}}}; calcium and acetylene hydroxide is formed, the gas formed in this reaction often has a characteristic garlic odor due to phosphane traces that form the present calcium fosfure as impurity:

CaC2+2H2O→ → Ca(OH)2+C2H2{displaystyle CaC_{2}+2H_{2}Orightarrow Ca(OH)_{2}+C_{2}H_{2}}}}

Combustion

• Complete

2C2H2+5O2→ → 4CO2+2H2O{displaystyle 2C_{2}H_{2}+5O_{2}rightarrow 4CO_{2}+2H_{2}O}

• Incomplete

2C2H2+3O2→ → 4CO+2H2O{displaystyle 2C_{2}H_{2}+3O_{2}rightarrow 4CO+2H_{2}O}

• Reduced

2C2H2+O2→ → 4C+2H2O{displaystyle 2C_{2}H_{2}+O_{2}rightarrow 4C+2H_{2}O}

Features

The decomposition of acetylene is an exothermic reaction. It has a calorific value of 24,000 kcal/kg. Likewise, its synthesis usually requires high temperatures in some of its stages or the contribution of chemical energy in some other way.

Acetylene is an explosive gas if its content in air is between 2 and 82%. It also explodes if it is compressed alone, without dissolving in another substance, so to store it is dissolved in acetone, a liquid solvent that stabilizes it.

Uses

First uses (20th century)

At the beginning of the XX century, acetylene had multiple applications due to the fixity and clarity of its light, its power heat, its ease of obtaining and its low cost. The generating devices had also been perfected, being almost all of them of the system in which the water falls on the carbide, the fall of that being graduated in such a way by various sets of valves, levers and counterweights that the overproduction of water was almost avoided. gas that so damaged the previous devices.

Acetylene was used in generators, in mining lamps or in the oxyacetylene torch used in autogenous welding, producing temperatures of up to 3000 °C, lighting projectors for the navy and for cinematographs. Cars also had headlights at the beginning of the century with self-generating acetylene devices. They came to build various rescue devices such as belts, vests, buoys, etc., inside which and in an ad hoc deposit they carried a dose of calcium carbide arranged in such a way that when putting on the carbide in contact with water would produce acetylene gas, leaving the device properly swollen.

Currently

Acetylene is used as a source of light and heat. In daily life, acetylene is known as a gas used in welding equipment due to the high temperatures (up to 3000 °C) reached by mixtures of acetylene and oxygen when burned.

Acetylene is also an important starting product in the chemical industry. Until the Second World War, a good part of the synthesis processes were based on acetylene. Today it is losing more and more importance due to the high energy costs of its generation.

Solvents such as trichlorethylene, tetrachloroethane, base products such as vinyl ethers and vinyl esters, and some carbocycles (synthesis according to Walter Reppe) are obtained from acetylene. It is also used especially in the manufacture of chloroethylene (vinyl chloride) for plastics, ethanal (acetaldehyde) and neoprene synthetic rubber.