GB577840A - Improvements in or relating to extractive distillation processes - Google Patents

Abstract

577,840. Extractive distillation of hydrocarbons. SHELL DEVELOPMENT CO. Sept. 6, 1943, No. 14594. Convention date, Aug. 14, 1942. Drawings to Specification. [Class 32] Two unsaturated hydrocarbons with close boiling points but different degrees of unsaturation are separated by subjecting a hydrocarbon mixture containing them to an extractive distillation with a solvent which does not form constant boiling mixtures with the components of the mixture; the distillation being conducted under superatmospheric pressure, e.g., between 4 and 8 atm., when the solvent is selective for the lower boiling of the two hydrocarbons to be separated, and under subatmospheric pressure, e.g., between 760 and 200 mm., when the solvent is selective for the higher boiling hydrocarbon. Butadiene (b.p.-4.5‹C.) and cis beta butylene (b.p.+3.73‹C,), present in narrow boiling fractions predominating in hydrocarbons of four carbon atoms, may be separated by distilling the fraction under superatmospheric pressure in the presence of a solvent selective for butadiene; but by distlling at a reduced pressure when a solvent is employed which is selective for cis beta butylene. In the first mode of operation butadiene is recovered upon regeneration of the solvent, in the second it is obtained as overhead during the extractive distillation. The separation of butadiene from alpha butylene is also referred to. A non-polar solvent is employed when the hydrocarbon to be extracted is more saturated than the other component, while a polar solvent, to which water may be added, is used in the separation of diolefines from mono-olefines. Lists of non-polar and polar solvents suitable for use in the process are included in the Specification.