Extractive distillation

A method of operating an extractive distillation column means at substantially maximum separation efficiencies so as to separate at least one component from a feedstock comprising an admixture of at least two organic components such that the relative volatilities of said components are sufficiently close as to substantially preclude effective separation by fractional distillation, wherein said extractive distillation column means comprises an upper extractive distillative zone and a contiguous lower stripping zone, which process comprises:

• feeding said feedstrock to said extractive distillative zone of said column means,
• contacting said feedstock with a lean highly selective solvent in amounts sufficient to provide predetermined ratios of solvent:feedstock effective to substantially change the relative volatilities of said components under extractive distillation conditions, so as to form an overhead vaporous stream of the more volatile of said components and a bottoms stream of the less volatile of said components plus said solvent,
• separating said bottoms stream into a stream of separated selective solvent and a stream of said less volatile components,
• recycling said separated selective solvent to said contacting step as said lean highly selective solvent,
• recycling at least a portion of said stream of less volatile components to the said stripping zone of said column means, to function as stripping vapor therein,
• condensing at least a portion of said vaporous overhead as a condensed stream,
• removing the remainder of said overhead as raffinate, and
• returning at least a portion of said condensed stream as reflux to said extractive distillative zone of said column means in amounts sufficient to provide effective substantially optimum predetermined ratios of reflux:raffinate,
• such that the said predetermined ratios of solvent:feedstock and reflux:raffinate are effective in combination to provide two immiscible liquid phases only in the upper portion of said extractive distillative zone of said column means, above the point of entry of said feedstock, and to operate said extractive distillation column means at said substantially maximum separation efficiencies, and wherein said two immiscible liquid phases represent a solvent-rich phase and a phase rich in the more volatile feedstock components.