Patent GB-586474-A (GB)
Title: Improvements in or relating to the separation of hydrocarbons from mixtures thereof
IPC: C10G53/06
Filed: 1943-11-01
Abstract: A complex hydrocarbon mixture is treated to separate therefrom at least two aliphatic paraffins, olefins or polyolefins of from 3-8 carbon atoms, and having similar boiling points, refractive indices, and degrees of unsaturation, by fractionating to obtain a narrow boiling distillate containing the desired hydrocarbons, subjecting this to an extractive distillation with at least twice as much solvent as is required to form azeotropic mixtures to obtain the desired hydrocarbons as a concentrated distillate which is then subjected to azeotropic distillation in the presence of an amount of solvent not greatly in excess of that necessary to form azeotropes, the resulting azeotropes then being fractionated to yield the pure desired hydrocarbons.  Stable organic liquids of high dielectric constant such as polar organic compounds containing oxygen, nitrogen or sulphur are suitable for extractive distillation.  For separation of C5 hydrocarbons, acetone, furfural, pyridine and other amines, and their mixtures with water are suitable.  Similar liquids are suitable for azeotropic distillation but should be capable of forming minimum boiling azeotropes with the desired hydrocarbons.  Saturated ketones, amines, alcohols and their aqueous mixtures are specified. Aqueous acetone may be used for both distillations or acetone, aqueous acetone or pyridine for the extractive distillation, and a monohydric alcohol or an aliphatic or aromatic amine for the azeotropic.  A debutanized refinery cracked stock containing 5-10 per cent. of the C5 diolefins isoprene and trans-piperylene is fractionated to obtain a fraction which may contain 15-30 per cent. of the said diolefins. Pressure is generally 25 p.s.i. gauge and, with a reflux ration of 3, temperatures at top and bottom are about 140 and 275 DEG F. respectively.  The said fraction is extractively distilled using about twice the volume of aqueous acetone or up to 7 times the volume of furfural.  The overhead containing the paraffins and mono-olefins, together with part of the distillation residue, which consists of solvent and is recycled to the still, is water-washed to recover the solvent.  An intermediate fraction comprising isoprene and trans-piperyline is taken off to a further still also having reflux and reboiler vapour lines, where an overhead consisting of isoprene, acetone, and water azeotrope with some azeotropes of cyclopentadiene and cyclopentene is taken off.  A side stream consisting of trans-piperylene, acetone, and water is also recovered.  The overhead is washed with water to give an isoprene concentrate which is fractionated to yield pure isoprene.  The side stream is similarly treated to recover pure piperylene.  Acetone is recovered from the various solutions for recycling.ALSO:A complex hydrocarbon mixture is treated to separate therefrom at least two aliphatic paraffins, olefins or polyolefins of from 3-8 carbon atoms, and having similar boiling points, refractive indices and degrees of unsaturation, by fractionating to obtain a narrow boiling distillate containing the desired hydrocarbons, subjecting this to an extractive distillation with at least twice as much solvent as is required to form azeotropic mixtures to obtain the desired hydrocarbons as a concentrated distillate which is then subjected to azeotropic distillation in the presence of an amount of solvent not greatly in excess of that necessary to form azeotropes, the resulting azeotropes then being fractionated to yield the pure desired hydrocarbons.  Stable organic liquids of high dielectric constant such as polar organic compounds containing oxygen, nitrogen or sulphur are suitable for extractive distillation.  For separation of C5 hydrocarbons, acetone, furfural, pyridine and other amines, and their mixtures with water are suitable.  Similar liquids are suitable for azeotropic distillation, but should be capable of forming minimum boiling azeotropes with the desired hydrocarbons.  Saturated ketones, amines, alcohols and their aqueous mixtures are specified.  Aqueous acetone may be used for both distillations or acetone, aqueous acetone or pyridine for the extractive distillation, and a monohydric alcohol or an aliphatic or aromatic amine for the azeotropic.  A debutanized refinery cracked stock containing 5-10 per cent of the C5 diolefins isoprene and trans-piperylene is fractionated to obtain a fraction which may contain 15-30 per cent of the said diolefins.  Pressure is generally 25 p.s.i. gauge and, with a reflux ratio of 3, temperatures at top and bottom are about 140 DEG  and 275 DEG  F. respectively.  The said fraction is extractively distilled using about twice the volume of aqueous acetone or up to 7 times the volume of furfural.  The overhead containing the paraffins and mono-olefins, together with part of the distillation residue, which consists of solvent and is recycled to the still, is water-washed to recover the solvent.  An intermediate fraction comprising isoprene and trans-piperylene is taken off to a further still also having reflux and reboiler vapour lines, where an overhead consisting of isoprene, acetone and water azeotrope with some azeotropes of cyclopentadiene and cyclopentane is taken off. A side stream consisting of transpiperylene, acetone and water is also recovered.  The overhead is washed with water to give an isoprene concentrate which is fractionated to yield pure isoprene. The side stream is similarly treated to recover pure piperylene. Acetone is recovered from the various solutions for recycling.