Patent GB-585211-A (GB)
Title: An improved process for the separation of diolefins from mixtures thereof with other hydrocarbons
IPC: C07C7/00
Filed: 1943-08-17
Abstract: C5 Diolefins are separated from a hydrocarbon mixture containing them by fractionally distilling said mixture to separate a fraction concentrated in said diolefins, subjecting this fraction to extractive distillation in presence of a solvent which is continuously recycled direct to the distillation zone and which has a substantial effect upon the relative volatility of the hydrocarbons, separating a distillate fraction concentrated in a desired C5 diolefin, and fractionally distilling the resultant material to purify the individual C5 diolefin. Suitable solvents are organic liquids of high dielectric constant or polar organic compounds containing oxygen, nitrogen or sulphur, e.g., acetone, furfural, pyridine, amines, and their mixtures with water.  A debutanized refinery by-product distillate from the cracking of gas oil, naphtha or the like containing about 4 per cent. isoprene is fractionated to give a C5 fraction containing 15-20 per cent. isoprene while rejecting as much as possible of the piperylene, cyclopentadiene, and pentenes.  Top and bottom temperatures of 141 and 270 DEG F. respectively, and a reflux ratio of 5 are satisfactory.  In the extractive distillation of this fraction, aqueous acetone may be used in an amount of twice the volume of the hydrocarbons flowing down the tower.  With furfural, the ratio may be as high as 7 : 1.  A side stream product consisting of isoprene with some piperylene, cyclopentadiene, and solvent such as acetone is withdrawn, concentrated in a fractionating tower, treated with water to remove acetone and fractionated to yield pure isoprene. Temperatures in the extractive distillation tower are 140 DEG F. at the top rising to 155 DEG  at the point of solvent entry, 160 at point of side stream withdrawal, and 208 DEG F. at the base.  In the concentrating tower, the top temperature is 145 DEG F.  Reflux ratios are 5.5 and 20 at the top of the extractive distillation and concentration towers respectively.  Part of the solvent from the bottom of the extractive distillation tower is withdrawn to maintain a low concentration of impurities, combined with the overhead distillate, and extracted with water to recover the solvent.  Specifications 324,350, [Class 32], and 559,297 are referred to.ALSO:C5 Diolefins are separated from a hydrocarbon mixture containing them by fractionally distilling said mixture to separate a fraction concentrated in said diolefins, subjecting this fraction to extractive distillation in presence of a solvent which is continuously recycled direct to the distillation zone and which has a substantial effect upon the relative volatility of the hydrocarbons, separating a distillate fraction concentrated in a desired C5 diolefin, and fractionally distilling the resultant material to purify the individual C5 diolefin. Suitable solvents are organic liquids of high dielectric constant or polar organic compounds containing oxygen, nitrogen or sulphur, e.g. acetone, furfural, pyridine, amines and their mixtures with water.  A debutanized refinery by-product distillate from the cracking of gas oil, naphtha or the like containing about 4 per cent isoprene is fractionated to give a C5 fraction containing 15-20 per cent isoprene while rejecting as much as possible of the piperylene, cyclopentadiene, and pentenes.  Top and bottom temperatures of 141 DEG  and 270 DEG  F. respectively, and a reflux ratio of 5 are satisfactory.  In the extractive distillation of this fraction, aqueous acetone may be used in an amount of twice the volume of the hydrocarbons flowing down the tower.  With furfural, the ratio may be as high as 7 : 1.  A side stream product consisting of isoprene with some piperylene, cyclopentadiene, and solvent such as acetone is withdrawn, concentrated in a fractionating tower, treated with water to remove acetone and fractionated to yield pure isoprene. Temperatures in the extractive distillation tower are 140 DEG  F. at the top, rising to 155 DEG  at the point of solvent entry, 160 DEG at point of side stream withdrawal, and 208 DEG  F. at the base.  In the concentrating tower, the top temperature is 145 DEG  F.  Reflux ratios are 5.5 and 20 at the top of the extractive distillation and concentration towers respectively.  Part of the solvent from the bottom of the extractive distillation tower is withdrawn to maintain a low concentration of impurities, combined with the overhead distillate, and extracted with water to recover the solvent. Specifications 324,350, [Class 2 (iii)], and 559,297 are referred to.