GB877622A - Isopropanol purification process - Google Patents

Abstract

Aqueous isopropanol is recovered by a distillation process (see Group III) from crude aqueous isopropanol, such as is obtained by the sulphuric acid hydration of propylene, and is then dehydrated, at least in part, by contact with a suitable inorganic salt or an aqueous solution thereof. Specified salts are potassium carbonate, ammonium carbonate and ammonium nitrate, but the second Provisional Specification refers also to potassium fluoride. A 50% aqueous potassium carbonate solution is used in the example.ALSO:In recovering isopropanol from crude aqueous isopropanol, such as is obtained by the sulphuric acid hydration of propylene, the crude isopropanol is first distilled in the presence of water under such conditions that the concentration of isopropanol in the liquid at the base of the distillation column is not more than 3 moles per 100 moles of water. The crude isopropanol is preferably fed to an intermediate point in the distillation column and the water is preferably introduced at a higher point, preferably at a temperature of at least 90 DEG C. The column is preferably operated without external reflux. The dilute aqueous isopropanol from the base of the column is then distilled in a rectification column from which purified aqueous isopropanol, which may be of approximately azeotropic concentration, is withdrawn as an overhead product. This latter column is preferably operated with external reflux, a small amount of which may be removed to prevent the accumulation of volatile impurities in the column. A bleed of a fraction having a boiling point between that of the distillate and that of the liquid in the bottom of the column may also be withdrawn from an intermediate point on the column to remove impurities. The product from the top of the second column is then freed from water, at least in part, by contact with a suitable inorganic salt, or its aqueous solution, and this treatment may be followed by distillation to provide substantially dry isopropanol. Specified salts are potassium carbonate, ammonium carbonate and ammonium nitrate, but the second Provisional Specification refers also to potassium fluoride. In the example, the purified aqueous isopropanol from the top of the second column is treated in counterflow with a 50% aqueous potassium carbonate solution, and the partly dehydrated isopropanol is passed to a distillation column, from the base of which isopropanol containing only about 0.3% of water is withdrawn.