The most common process used to recover water soluble alcohols from aqueous-alcohol mixtures is distillation. Many of the water soluble alcohols form azeotropic mixtures with water and cannot be completely dehydrated by simple binary distillation techniques. Even where substantial dehydration of alcohol-water mixtures can be achieved by distillation, distillation has a disadvantage of requiring high energy input in order to achieve the separation. Also, a distillation process requires substantial startup and shutdown times to bring the system to equilibrium conditions so that the desired separation of components is achieved. The loss of 1-2% or more of the alcohol being recovered by distillation is common.
It is known that dehydration of certain water soluble alcohols can be achieved by the addition of a base or an electrolyte to an aqueous-alcohol mixture to cause separation of the mixture into two immiscible layers, the upper layer of which is alcohol-rich. U.S. Pat. No. 1,452,206 issued to Mann on Apr. 17, 1923, discloses the dehydration of higher alcohols, that is, of alcohols containing three or more carbon atoms, especially isopropyl alcohol (IPA), by the addition of caustic alkali such as sodium hydroxide or potassium hydroxide to cause the formation of two immiscible layers, the upper layer being alcohol-rich. Similar dehydration processes are disclosed in U.S. Pat. No. 2,461,048 issued to Frejacques on Feb. 8, 1949, for normal propyl alcohol and isopropyl by the addition of ammonium carbonate; and by U.S. Pat. No. 2,534,259 issued to Gee & Bossche on Dec. 19, 1950, for ethanol by the addition of aluminum sulfate. However, such processes have not often been used in industrial applications due to the cost of the chemicals required, or the impurities introduced into the recovered alcohol.

The base is selected from the group consisting of ammonium or an alkali or alkaline metal hydroxide, ammonium or an alkali or alkaline metal carbonate, or mixtures thereof. With regard to the dehydration of IPA-water mixtures, the preferred base is sodium hydroxide, potassium hydroxide, sodium carbonate or mixtures thereof; especially preferred is sodium hydroxide.
The quantity of base incorporated in the aqueous-alcohol mixture to achieve dehydration according to the present invention is a concentration of preferably greater than about 0.5% in the aqueous-alcohol mixture. A more preferred range of base concentration in the mixture if from about 1% to about 12%; especially preferred is from about 2% to about 8%.

A distilled water-IPA solution comprising 82.7% IPA was divided into measured volume samples. To the samples various amounts of 50% aqueous solution of sodium hydroxide were added such that the weight of sodium hydroxide incorporated into the mixture was between 0.01 gram NaOH and 0.14 gram NaOH per gram of the starting IPA-water solution. In each case, the addition of sodium hydroxide caused a separation of the mixture into two immiscible layers. The top layer of each sample was analyzed for its IPA content. The results are presented in Table 3 below and are shown as Curve C in the FIGURE.