Patent GB-663751-A (GB)
Title: Improvements in or relating to the separation and purification of diolefins by distillation
IPC: C07C7/08
Filed: 1948-06-08
Abstract: Diolefines containing 5 atoms in the molecule are separated from hydrocarbon mixtures by submitting the mixture to fractional distillation to obtain a distillate-fraction containing C5-diolefines free of hydrocarbons which boil substantially higher than the boiling point of isoprene, and then subjecting the distillate-fraction to extractive distillation using a sulpholane as solvent.  A fraction containing a C5 diolefin in high concentration is withdrawn, either as a side-stream or as bottoms, from the extractive distillation zone.  A debutanized distillate obtained by cracking gas oil in the liquid phase, and containing isoprene (4 mole per cent), pentene, piperylene and other C5 to C9 hydrocarbons, was fractionated; and a distillate containing isoprene (20 mole per cent), pentene (50 mole per cent) and other C5 hydrocarbons, was taken-off overhead.  This distillate was introduced into the mid-portion of a fractionating column supplied at the upper portion with dimethyl sulpholane (which may contain 3 per cent of water), and maintained under a gauge-pressure of 25 lbs. per square inch.  A vaporous side-stream was taken-off at the plate where the temperature is 160 DEG  F.; this contained isoprene in high concentration-the impurities being solvent, piperylene, cyclopentadiene and polymers which may, if necessary be removed by rectification. Relatively pure solvent is withdrawn from the base of the column; this is cooled and recycled to the upper portion.  Specification 625,505 is referred to.ALSO:Diolefines containing 5 atoms in the molecule are separated from hydrocarbon mixtures by submitting the mixture to fractional distillation to obtain a distillate-fraction containing C5-diolefines free of hydrocarbons which boil substantially higher than the boiling point of isoprene, and then subjecting the distillate-fraction to extractive distillation using a sulpholane as solvent, the volume of solvent being at least equal to the volume of hydrocarbon.  A fraction containing a C5 diolefin in high concentration is withdrawn, either as a side-stream or as bottoms, from the extractive distillation zone.  A debutanized distillate obtained by cracking gas oil in the liquid phase, and containing isoprene (4 mole per cent), pentene, piperylene and other C5 to C9 hydrocarbons, was fractionated in a 50-plate column at a gauge-pressure of 25 lbs. per square inch using a reflux ratio of 5, and maintaining a head-temperature of 141 DEG F.  The overhead distillate-product contained isoprene (20 mole per cent), pentene (50 mole per cent) and other C5 hydrocarbons, and was introduced into the mid-portion of a fractionating column supplied at the upper portion with 2-4 volumes of dimethyl sulpholane (which may contain 3 per cent water) per volume of hydrocarbon feed. Top and bottom temperatures of 140 DEG F. respectively are maintained in the column under a gauge-pressure of 25 lbs. per square inch.  A vaporous side-stream is taken-off at the plate where the temperature is 160 DEG F.; this contained isoprene in high concentration-the impurities being solvent, piperylene, cyclopentadiene and polymers which may, if necessary, be removed by rectification. Relatively pure solvent is withdrawn from the base of the column; this is cooled and recycled to the upper portion.  Specification 625,505 is referred to.