Patent ID: 7557257

Claim:
A process for fractionating a crude C 4 fraction comprising butanes, butenes, 1,3-butadiene and small amounts of other hydrocarbons including C 4 -acetylenes, 1,2-butadiene and C 5 -hydrocarbons by extractive distillation using a selective solvent, the process comprising feeding the crude C 4 fraction into a middle region of a first extractive distillation column and feeding the selective solvent into the column at a point above where the crude C 4 fraction is fed taking off a gaseous side stream from the first extractive distillation column at a point below the feed point for the crude C 4 fraction, wherein the gaseous side stream comprises the C 4 -acetylenes, 1,3-butadiene, 1,2-butadiene, C 5 -hydrocarbons and selective solvent; and wherein the concentration of the C 4 -acetylenes in the gaseous side stream is below a spontaneous decomposition limit; taking off an overhead stream comprising components of the crude C 4 fraction which are less soluble than the C 4 -acetylenes in the selective solvent from the top of the first extractive distillation column; feeding the gaseous side stream to a first side column in which the gaseous side stream is separated into an overhead stream and a bottom stream, wherein the overhead stream comprises the C 4 -acetylenes and is condensed in a condenser at the top of the first side column; a part of the condensed overhead stream is returned as runback to the first side column, and returning the bottom stream which comprises the selective solvent to the first extractive distillation column.