GB963451A - Separation of hydrocarbon mixtures by distillation - Google Patents

Abstract

<PICT:0963451/C4-C5/1> Benzene is separated from a mixture containing benzene, n-heptane, methylcyclohexane and possibly other relatively high-boiling hydrocarbons by submitting the mixture to fractional distillation so as to obtain the benzene and n-heptane as an overhead vapour leaving the methylcyclohexane and other heavy impurities as a liquid residue, and subsequently separating the benzene and n-heptane by using an azeotropic or pseudo-azeotropic agent to enhance the volatility of the n-heptane. A feedstock containing 42% benzene, 1.0% n-heptane, 0.3% methylcyclohexane and other hydro-carbons passes through line 1 into section I of a fractionating column; and a fraction containing very little benzene is discharged through line 3. Vapours comprising benzene and nearly all the n-heptane enter section II which also contains acetone and water; and vapours containing n-heptane and the auxiliary agents are withdrawn overhead, and passed to condenser VI. Some of the condensate is returned via line 5 to section II as reflux, and the remainder is passed to water-extraction column IV for removal of the acetone from the n-heptane. The reflux liquid descending section II is collected on a decanting-tray 2a; and some of the hydro-carbon liquid weirs over this tray into section I. The aqueous layer on tray 2a and the remainder of the hydrocarbon layer flow into stripping section III, which is also supplied via line 9 with an aqueous solution of entraining agent from column IV. The vapours from the head of section III are passed via line 11 into section II. A mixture of benzene and water is withdrawn from the base of section III, and is passed to decanter V.