Patent ID: 7556717

Claim:
A process for fractionating a starting mixture of at least two components by extractive distillation using a selective solvent in a dividing wall column, comprising carrying out the process in a dividing wall column having a dividing wall aligned in a longitudinal direction of the column and extending to an upper end of the column and dividing an interior of the column into a first region, a second region, and a lower combined column region, feeding the starting mixture into the first region, taking off a first top stream from the first region, and taking off a second top stream from the second region, with each of the streams having a preset composition, introducing the selective solvent in an upper part of the first region or in an upper part of the second region, and setting the flow of solvent into the first region or flow of solvent into the second region so that each of the preset compositions for the top streams are met, wherein at least one liquid stream or substream is taken off from the dividing wall column at at least one thermodynamically suitable theoretical plate, partly or completely vaporized by heat transfer from hot, degassed solvent stream, and returned to the dividing wall column.