Patent ID: 7432411

Claim:
A continuous process for isolating butenes from a C 4 fraction which comprises butanes, butenes and optionally traces of other hydrocarbons by extractive distillation using a selective solvent; the process comprising: feeding the C 4 fraction in gaseous or liquid form into a scrubbing zone, feeding the selective solvent in liquid form into the scrubbing zone above the feed point of the C 4 fraction, separating the C 4 fraction into a first top stream comprising butane and a first bottom stream comprising the selective solvent laden with the butenes and optionally traces of other hydrocarbons, separating the first bottom stream into a second top stream comprising the butenes and said optional traces of other hydrocarbons and a second bottom stream comprising the selective solvent in a degassing zone, wherein energy is fed into the degassing zone via a bottom vaporizer, the temperature of the degassing zone is at a higher temperature and/or a lower pressure than the scrubbing zone, the heat of the second bottom stream from the degassing zone is utilized for increasing the temperature in the degassing zone, a first liquid or a substream of the first liquid is taken off from the degassing zone at a theoretical plate located one or more theoretical plates below the feed point for the first bottom stream from the scrubbing zone, heated and/or vaporized by indirect heat exchange with the second bottom stream from the degassing zone and returned to the degassing zone at or above the theoretical plate, wherein the theoretical plate from which the liquid or substream of liquid is taken off is selected to minimize the total energy requirement in the process.