Ethyne, C2H2, (i.e. Acetylene) is the first member of the ethyne homologous series of hydrocarbons and is the only member of the series of major industrial importance.
3 C4H10 + 2 H2O ==> 2 HCCH + 2 C2H4 + 2 CH4 + 2 CO + 7 H2 Ethyne Ethene Methane Carbon Hydrogen Monoxide
Subsequent reactions in this gas stream are
C2H4 ==> HCCH + H2 Ethene Ethyne Hydrogen
2 CH4 ==> HCCH + 3H2 Methane Ethyne Hydrogen
Ethyne is also made industrially by the combustion of natural gas, which is mainly methane using insufficient oxygen. The heat evolved in the incomplete combustion is used to heat a further supply of methane to about 1773 degK.
2 CH4 + O2 ==> 2 CO + 2 H2
1773 degK 2CH4 ==> HCCH + 3H2
The reaction time is very short (between 0.01 and 0.05 seconds). The optimum yield of ethyne is obtained by rapid cycling of the products.
Ethyne is also made industrially by the arc process in which a temperature of 1773 degK is achieved by an electric discharge. The feedstock is usually a mixture of C3 hydrocarbons and C4 hydrocarbons and the products are mainly ethyne, methane and hydrogen. Contact time is again very short.
The initial step in the purification of ethyne from these thermal processes to absorb it selectively into a suitable solvent, and then to separate the ethyne by fractional distillation. The solvent for the extraction is recycled.
Because calcium oxide and coke are obtained from limestone and coal, respectively, acetylene gas is obtained in a few steps from three abundant cheap raw materials (i.e. water, coal, and limestone).
Coal + Coke + Ca(OH) 2 ==> CaC2 Carbon Limestone Calcium Carbide
CaC2 + H2O ==> HCCH Calcium Carbide 2000 degC Ethyne
Enormous quantities of acetylene gas are consumed each year as a as fuel for the oxy-acetylene welding torch. The acetylene gas \ used for this purpose is distributed as a solution of acetylene in acetone under pressure contained in tanks.
Acetylene gas is also the starting material for the large scale synthesis of important organic compounds, including ethanoic acid (i.e. acetic acid) and a number of unsaturated compounds that are used to make plastics and synthetic rubber.
Many of the synthetic uses of acetylene have grown out of work done by W.Reppe in Germany before and during World War II. Because of the need to replace petroleum by the more abundant coal as the primary organic source, his work revolutionized the industrial chemistry of acetylene.