GB762974A - Dehydrating alcohols by extractive distillation - Google Patents

Abstract

Aqueous alcohols are dehydrated by extractive distillation employing as extractant a hydrocarbon having boiling-point at least 40 DEG C. above that of the alcohol, whereby the water passes over in the distillate leaving a still-residue comprising a substantially anhydrous mixture of the alcohol and hydrocarbon; this mixture is then subjected to further distillation in order to separate the alcohol. Ethyl, n-propyl and isopropyl alcohols may be dehydrated by the process. Suitable hydrocarbons are cumene, ethylbenzene and diethylbenzene. The extractive distillation is preferably carried out continuously in a fractionating column equivalent to at least 20 theoretical plates; and is operated to obtain a bottoms mixture containing 5 to 25 per cent alcohol. In an example aqueous isopropyl alcohol (containing 12 per cent water) was fed to a 32-plate fractionating column at the 15th plate above the reboiler. Commercial cumene (containing about 5 per cent of low boiling impurities) was preheated to the stillhead temperature, and then fed to the top plate. The distillate separated into two phases; and the upper phase (which comprised cumene, isopropyl alcohol and a little water) was returned to the column at the feed point. The bottoms from the column comprised 10 per cent isopropyl alcohol in cumene, and this mixture was fractionated to separate the alcohol from the cumene. Substantially dry alcohol and cumene were obtained; but it was found that the impurities present in the cumene employed has been extracted into the isopropyl alcohol.