Improvements in or relating to the purification of alcohols by extractive distillation

摘要

Crude aliphatic alcohols obtained from olefins, particularly C2 to C6 alcohols obtained by the hydration of olefins using sulphuric acid, are purified from both highand low-boiling impurities by extractive distillation using an aqueous solution of a glycol, a glycol ether or a glycol ether-ester containing 20 to 80 volume per cent of the glycol component, as solvent. The crude alcohol is introduced at an intermediate position of the fractionating column; and the solvent is introduced at or near the top of the column in sufficient quantity to maintain 70 to 99.9 volume per cent of solvent in the internal reflux. The impurities are withdrawn from the top of the column-normally 8 to 15 per cent of the organic material in the crude alcohol feed is ejected in the heads. A 5 to 30 volume per cent solution of the purified alcohol in the aqueous solvent is withdrawn from the base of the column, and the purified alcohol is recovered from this extract by ordinary fractionation. In the case of the higher alcohols such as the pentanols, the watersolubility may be enhanced by addition of isopropanol or tertiary butanol. A list of suitable solvents is given in the Specification. Crude secondary butanol containing about 70 volume per cent of secondary butanol, the remainder being water, and impurities such as butyl ether, was fed through line 1 on to the 40th plate of 50plate fractionating column, and an aqueous solution containing 40 volume per cent of ethylene glycol was introduced into the top of the column through line 3. The heads taken off through line 5, comprised 13.7 per cent of the organic material in the feed. After condensation, the heads were rejected from the system through 7-none was returned to the column as reflux. The extract withdrawn frim the column through line 4 contained 21.75 volume per cent of secondary butanol; this extract was fractionated in 30-plate column 13, and the pure secondary butanol/water azeotrope was withdrawn through line 15. Aqueous ethylene glycol was recovered from the base of column 13 and recycled through line 18, together with make-up water added through line 17, to the top of column 2.