Page 79 - Chemical and process design handbook

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ACETYLENE

Acetylene (CH≡CH, ethyne or ethine, melting point –81.5°C, boiling point
–84°C) is an extremely reactive hydrocarbon that is moderately soluble in
water or alcohol and is markedly soluble in acetone (300 volumes of acety-
lene dissolve in 1 volume of acetone at 176 psi, 1216 kPa).
Acetylene burns when ignited in air with a luminous sooty flame,
requiring a specially devised burner for illumination purposes. An
explosive mixture is formed with air over a wide range (about 3 to 80%
acetylene), but safe handling is improved when the gas is dissolved in
acetone.
Acetylene is still manufactured by the action of calcium carbide, a prod-
uct of the electric furnace.

CaC + 2H O → HC≡CH + Ca(OH)
2 2 2
and there are two principal methods for generating acetylene from calcium
carbide.
The batch carbide-to-water, or wet, method takes place in a cylindrical
water shell surmounted by a housing with hopper and feed facilities. The
carbide is fed to the water at a measured rate until exhausted. The calcium
hydroxide is discharged in the form of a lime slurry containing about 90%
by weight water.
For large-scale industrial applications, dry generation, a continuous
process featuring automatic feed, is used, in which 1 kg of water is used,
per kilogram of carbide. The heat of the reaction is largely dissipated by
water vaporization, leaving the by-product lime in a dry state, and part of
this can be recycled to the carbide furnaces. Continuous agitation is nec-
essary to prevent overheating, since the temperature should be kept below
o
150 C and the pressure lower than 204 kPa.
The newest methods of manufacturing acetylene are through the pyrol-
ysis, or cracking, of natural gas or liquid hydrocarbon feeds. The processes
of most interest include partial oxidation, using oxygen, thermal cracking,
and an electric arc to supply both the high temper-attire and the energy.
Acetylene is produced from the pyrolysis of naphtha in a two-stage crack-

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