Process for the treatment of mixtures of hydrocarbons to effect segregation of desired hydrocarbons

摘要

A C3 or higher diolefin is separated from complex hydrocarbon mixtures of wide boiling range containing undesired hydrocarbons of closely similar boiling point to said diolefin by reflux distillation of said fraction in a column under such conditions that the phase in the upper portion of the column comprises a narrow boiling fraction containing the diolefin while that in the lower portion comprises the higher boiling resi-due, an excess of a selective solvent being introduced into the said upper portion whereby an extractive distillation of said narrow boiling fraction yields an azeotrope of said diolefin with excess of solvent which is withdrawn as a side stream, the azeotrope then being distilled from excess solvent. Suitable solvents are polar organic liquids containing oxygen, nitrogen, sulphur, selenium or phosphorus, for example, acetone, furfural, pyridine, and amines, and mixtures thereof with water. Particulars of various C5 hydrocarbon-acetone-water ternary azeotropes are given. The hydrocarbon feed is introduced into the combined fractional and extractive distillational tower for example a bubble plate tower of 70 plates of which 40 are in the upper, extraction zone, upon one of the upper plates, and the solvent is introduced a few plates above. Heat is supplied by a boiler and reflux. Acetone containing 10 per cent. of water is suitable for C5 diolefin recovery from a debutanized cracked stack. The overhead consists of ternary azeotropes with acetone and water of C5 paraffin and mono-olefins; and lighter hydrocarbons. A vapour side stream removed near the middle of the tower is treated in a fractionating tower of say 30 plates, in the upper portion of which a piperylene-acetone-water azeotrope is separated from excess solvent.ALSO:A C3 or higher diolefin is separated from complex hydrocarbon mixtures of wide boiling range containing undesired hydrocarbons of closely similar boiling point, degree of unsaturation and refractive index to said diolefin, by reflux distillation of said fraction in a column under such conditions that the phase in the upper portion of the column comprises a narrow boiling fraction containing the diolefin while that in the lower portion comprises the higher boiling residue, an excess of a selective solvent being introduced into the said upper portion whereby an extractive distillation of said narrow boiling fraction yields an azeotrope of said diolefin with excess of solvent which is withdrawn as a side stream, the azeotrope then being distilled from excess solvent. A debutanized refinery cracked stack containing up to 5 per cent of C5 diolefins may be treated to recover piperylenes. Suitable solvents are polar organic liquids containing oxygen, nitrogen, sulphur, selenium or phosphorus, for example acetone, furfural, pyridine and amines, and mixtures thereof with water. By controlling the fractionating conditions and choosing the solvent according to its known vapour depressant properties for the hydrocarbons present and the boiling points of the azeotropes formed, an azeotrope of a desired diolefin may be withdrawn as a side stream. Particulars of various C5 hydrocarbon-acetone-water ternary azeotropes are given. The hydrocarbon feed is introduced into the combined fractional and extractive distillation tower, for example a bubble plate tower of 70 plates of which 40 are in the upper, extraction zone, upon one of the upper plates, and the solvent which boils within the same range is introduced up to about twice the volume a few plates above. Acetone containing 10 per cent of water is suitable for C3-diolefin recovery from a debutanized cracked stock. Heat is supplied by a reboiler and reflux. The overhead consists of ternary azeotropes with acetone and water of C5 paraffins and mono-olefins and lighter hydrocarbons. A vapour side stream removed near the middle of the tower is treated in a further fractionating tower of say 30 plates, in the upper portion of which a piperylene-acetone-water azeotrope is separated from excess solvent. The solvent is recovered and returned.