General method of preparation of alkynes

Ethyne is made industrially from hydrocarbons obtained by cracking petroleum. The thermal cracking of butane with steam as a diluent. The first reaction is
3 C4H10  +  2 H2O   ==> 2 HCCH  +  2 C2H4 + 2 CH4 +  2 CO +  7 H2                                                           Ethyne                                                          
Subsequent reactions in this gas stream are
         C2H4     ==>     HCCH +    H2          


2 CH4 ==> HCCH + 3H2

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  

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.

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