GB374901A - Improvements in or relating to the concentration of fatty acids - Google Patents

Abstract

Aqueous solutions of fatty acids, particularly lower fatty acids such as acetic acid, are concentrated by first treating them with heavy metals, i.e. metals other than alkali or alkaline earth metals, or oxides or other compounds of heavy metals to form the salts of the fatty acids, removing water from these salts, and thereafter subjecting them to reduction to obtain the free fatty acids. Copper is an example of a suitable heavy metal, and suitable heavy metal compounds include the oxides, hydroxides, and carbonates of copper, nickel, chromium, and cobalt. The solid heavy metal compound may be added either in the theoretical quantity or in excess to the aqueous acid, preferably in stages and with agitation, and if necessary, while heating the liquid. When excess of the heavy metal compound is employed, this may be removed from the solution by decantation or filtration before further treatment. When the heavy metal itself is employed, the salt may be formed by any known process, for example, copper powder may be reacted with aqueous acetic acid in the presence of oxygen or air. Water may be separated wholly or in part from the heavy metal salt solution, for example, by evaporation under ordinary or reduced pressure, and the salt thus obtained may be dehydrated in a current of dry air at 100-125 DEG C., or at a lower temperature in vacuo. Water may also be removed from the salt solution, either before or after concentration, by adding an organic liquid miscible with water but in which the salt is insoluble, to cause precipitation of the salt, which may then be washed with the organic liquid. The reduction of the salt may be effected with hydrogen or other reducing gas, for example, in a copper, silica, or staybrite tube heated to a temperature between 150 and 300 DEG C., at normal, increased, or reduced pressure, and with or without admixture of other gases, the free acid being condensed from the vapours leaving the reaction tube. The residue of reduced salt may be used again for concentrating further aqueous fatty acid, if desired, after oxidation or conversion into a suitable salt. The invention may be applied to the simultaneous purification and concentration of crude aqueous fatty acids, and is especially applicable to the concentration of dilute acetic acid such as that resulting from acetylation processes, for example, the acetylation of cellulose. An example is given.