Patent GB-390825-A (GB)
Title: Improvements in or relating to the concentration of aliphatic acids
Filed: 1931-10-10
Abstract: Aliphatic acids such as acetic or propionic acid are concentrated by treating with a heavy metal or compound thereof (other than the aliphatic acid salts of such metals) and then thermally decomposing the acetate or other aliphatic acid salt by heating them alone or in presence of salts of stronger acids.  The heavy metals mentioned are copper, aluminium, chromium, iron, cobalt, and nickel.  The acetate or like salt may be partially freed from water of crystallization before decomposition.  The heavy metal compound may be added to the dilute acid in stages; metallic copper may be used in presence of oxygen or air.  The heavy metal acetate may be separated from the solution by evaporation or crystallization or salting out (advantageously with an alkali acetate) or by precipitation with a water-miscible liquid.  The removal of part of the water of crystallization may be effected by heating to 50-125 DEG  C. in a current of air; or under reduced pressure, at a lower temperature. The aqueous mother liquor may be employed for the production of basic acetates, or may be evaporated and distilled with sulphuric acid. The decomposition of the heavy metal acetate may be effected by heating with a sulphate or chloride of the heavy metal; the heating may take place in a stream of air, carbon dioxide or other indifferent gas or inert vapour such as benzene, petroleum ether or the acid to be obtained, and ordinary, reduced or increased pressure may be employed.  When the water of crystallization is more than is desired in the final product, the water may be removed, in vapour form as an azeotropic mixture with an added substance such as benzene, which may be present during the decomposition or may be added subsequently before condensation; for instance the vapours may be passed up a tower in counter-flow with the added substance in liquid form.  When acetic acid is to be concentrated by means of cupric acetate, it is preferable to have free acetic acid present throughout so as to avoid the production of basic acetates, but when other heavy metal acetates are used this need not be done.  In an example, acetic acid from the cellulose acetate process is treated with cupric oxide at 90 DEG  C. and the solution is cooled to obtain pentahydrated cupric acetate, which is then heated in a current of air to 75 DEG  C. to remove 4 molecules of water and then to 300 DEG C. to liberate the acid.  Specification 381,963 is referred to.ALSO:Aliphatic acids such as acetic or propionic acid are concentrated by treating with a heavy metal or compound thereof (other than the aliphatic acid salts of such metals) and then thermally decomposing the acetate or other aliphatic acid salt by heating them alone or in presence of salts of stronger acids.  The heavy metals mentioned are copper, aluminium, chromium, iron, cobalt and nickel.  The acetate or like salt may be partially freed from water of crystallization before decomposition.  The heavy metal compound may be added to the dilute acid in stages; metallic copper may be used in presence of oxygen or air.  The heavy metal acetate may be separated from the solution by evaporation or crystallization or salting out (advantageously with an alkali acetate) or by precipitation with a water-miscible liquid.  The removal of part of the water of crystallization may be effected by heating to 50-125 DEG C. in a current of air; or, under reduced pressure, at a lower temperature.  The aqueous mother liquor may be employed for the production of basic acetates, or may be evaporated and distilled with sulphuric acid. In an example acetic acid from the cellulose acetate process is treated with cupric oxide at 90 DEG  C. and the solution is cooled to obtain pentahydrated cupric acetate, which is then heated in a current of air to 75 DEG  C. to remove 4 molecules of water and then to 300 DEG  C. to liberate the acid.  Specification 381,963, [Group IV], is referred to.