GB588037A - Process for the separation of c diolefins from mixtures thereof with other hydrocarbons - Google Patents

Abstract

In the process of separating C5 diolefins from mixture thereof with hydrocarbons of similar boiling points, refractive indices, and degrees of unsaturation by fractionating to separate a distillate fraction concentrated in said diolefins, subjecting this to extractive distillation with a solvent which is continually recycled and which affects the relative volatilities of the hydrocarbons, separating a fraction concentrated in a desired C5 diolefin, and fractionating to purify the same, as described in the parent Specification, an azeotropic distillation is substituted for the first fractionation. The added solvent for the azeotropic distillation is, in general, of the same type as that used in the subsequent extractive distillation, e.g., liquid polar organic compounds containing oxygen, nitrogen, sulphur, selenium, or phosphorous, and having the ability to form azeotropes with the desired hydrocarbon. Saturated ketones, amines, alcohols, and their mixtures with water are specified. An amount of solvent sufficient only to give the azeotropes is normally employed in the first stage while a large excess is used in the extractive distillation step. A debutanized cracking distillate containing 4.1 per cent. isoprene is fractionated in the presence of entrainer liquid sufficient to form an isoprene azeotrope but insufficient to form an azeotrope with trimethylethylene. Using aqueous acetone, about 1 vol. to 10 of feedstock is necessary, a ternary azeotrope of isoprene, acetone and water being formed. With a reflux ratio of 5, and top and bottom temperatures of 140 and 275 DEG F., most of the isoprene and aqueous acetone are removed as overhead. The subsequent treatment is the same as that in the parent Specification.ALSO:In the process of separating C5 diolefins from mixtures thereof with hydrocarbons of similar boiling points, refractive indices, and degrees of unsaturation by fractionating to separate a distillate fraction concentrated in said diolefins, subjecting this to extractive distillation with a solvent which is continuously recycled and which affects the relative volatilities of the hydrocarbons, separating a fraction concentrated in a desired C5 diolefin, and fractionating to purify the same, as described in the parent Specification, an azeotropic distillation is substituted for the first fractionation. The added solvent for the azeotropic distillation is, in general, of the same type as that used in the subsequent extractive distillation, e.g. liquid polar organic compounds containing oxygen, nitrogen, sulphur, selenium or phosphorus, and having the ability to form azeotropes with the desired hydrocarbon. Saturated ketones, amines, alcohols, and their mixtures with water are specified. An amount of solvent sufficient only to give the azeotropes is normally employed in the first stage while a large excess is used in the extractive distillation step. A debutanized cracking distillate containing 4.1 per cent isoprene is fractionated in the presence of entrainer liquid sufficient to form an isoprene azeotrope but insufficient to form an azeotrope with trimethylethylene. Using aqueous acetone, about 1 vol to 10 of feedstock is necessary, a ternary azeotrope of isoprene, acetone and water being formed. With a reflux ratio of 5, and top and bottom temperatures of 140 and 275 DEG F. most of the isoprene and aqueous acetone are removed as overhead. The subsequent treatment is the same as that described in the parent Specification.