Patent GB-407065-A (GB)
Title: Improvements in or relating to the manufacture of aliphatic anhydrides
IPC: C07C51/56
Filed: 1932-08-26
Abstract: In the production of aliphatic anhydrides by the thermal decomposition of the corresponding acids such as acetic acid, the acid vapour is preheated by passing through a liquid bath comprising one or more of the following substances, viz. a salt of a halogen acid, a metal oxide, a salt of a weak oxy-acid such as a molybdate, arsenate, borate or vanadate, or an organic compound stable at the temperature employed, which is below that at which the anhydride is formed.  Suitable substances are cadmium, cuprous, lead, and thallium chlorides or mixtures such as potassium and cuprous chlorides, silver and cuprous chlorides, and sodium and lithium chlorides; and high boiling petroleum hydrocarbons and aromatic hydrocarbons such as diphenyl, p-p-dixylenyl, diphenyl diphenylene methane, a a  g g tetraphenyl propane, 2 - methyl - 9 - 10 diphenyl anthracene, triphenyl benzyl methane and 9--10 diphenyl anthracene.  The molten bath may also contain elements such as lead, tellurium or metal alloys as described in the parent Specification.  The preheated vapour may be treated for the production of anhydride by passing through a molten bath at 400--900 DEG  C., and this bath may comprise the salts mentioned for the preheating or mixtures of lead and potassium chlorides, sodium and strontium chlorides, sodium and thallium chlorides, sodium and potassium arsenates, sodium and lithium borates, molybdic oxide and sodium molybdate, sodium molybdate and sodium pyromolybdate, lead oxide and chloride, lead oxide and metasilicate, mixed silicates, and mixtures of silicates and other naturally-occurring salts of weak acids and halogen acids; when the reaction temperature is above 700 DEG  C. it is preferred to use salt mixtures having a high melting-point such as sodium and strontium chlorides, sodium and lead fluorides, potassium chloride and fluoride, sodium molybdate and pyromolybdate, or sodium and lithium borates.  The decomposition bath may also contain catalysts, for instance the following mixtures may be used:--potassium borate or chloride and metaphosphate, or naturally occurring mixtures comprising phosphates such as pyromorphite.  The anhydride may be separated from the reaction mixture as described in Specifications 256,663, 289,972, 298,667, 303,772, and 310,863, [all in Class 2 (iii)]; or the water may be removed chemically as described in Specification 387,365, in which case the removal may be effected by treating the reaction vapours with hydrocarbons or carbon monoxide or by adding such gases to the acid vapour, in which latter case there is preferably incorporated in the decomposition bath a catalyst for promoting the reaction with the water.  In examples: (1) acetic acid of 95 per cent strength is vaporized and led through a bath of sodium and lithium chlorides at 350 DEG  C. and then through a bath of sodium and potassium chlorides at 750 DEG  C.; (2) propionic acid vapour is led through a petroleum fraction of boiling-point 350 DEG C. or higher, heated to 300 DEG  C., and the vapours leaving the bath are passed up a condensing column at 280 DEG  C. to condense vapour of the hydrocarbon, the further treatment being as described above.