GB393690A - Improvements in the manufacture and production of acetaldehyde from acetylene - Google Patents

Abstract

Acetaldehyde is produced by absorbing acetylene in an aqueous solution containing a neutral salt of a solid, heavy base metal having an acid reaction, the absorption being effected above atmospheric pressure at such concentration that the boiling point of the solution is at least 4 DEG C. below that of a saturated solution while still showing an acid reaction to methyl orange. Suitable salts are the halides of zinc, chromium, iron, and cadmium, but promoters may be added such as mercury compounds (including organic compounds such as mercury diphenyl), water-soluble salts of uranium, gold, and the metals of the platinum group. The process may also be effected by using the concentrated solutions described in the parent Specification while employing enough water vapour admixed with the acetylene to reduce the concentration of the solution to the limits defined above. The acetylene need not be as pure as is required in the process of the parent Specification. When cadmium chloride is used, as its solubility is relatively low, a chloride of iron, zinc or chromium may be added. If the acetylene is produced by thermal treatment of hydrocarbons such as by arc treatment or the cracking of mineral oils, other unsaturated hydrocarbons such as diacetylene and butadiene and also carbon black are removed before the absorption, which may be effected at 20 atmospheres pressure, but if the carbon black only is removed, a smaller pressure such as up to 3 atmospheres is preferred. Or the unpurified gas may be used, when the absorption liquid is periodically purified by absorbents such as fuller's earth, bleaching earth, or active carbon. This treatment of the solution may also be effected when partially purified gas is used. The absorption may be effected in a cylindrical vessel containing Raschig rings or the like. The temperature may be 80-250 DEG C., and the gas may be preheated. Examples describe the treatment of a gas containing acetylene with zinc chloride solutions. In one example a fifth of the solution is continuously circulated to a filter of bleaching-earth, and in another the gas is passed through a filter of ceramic material and is introduced into the solution in very finely-divided form.