TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred System: The system further comprises feed vaporization system for vaporizing the hydrocarbon mixture upstream of the extractive distillation column; flow conduit for feeding the bottoms fraction to the stripper at a location above the stripping section and below the wash section. The stripper overheads system comprises a two-stage condensation system comprising: a first condenser for partially condensing the overheads fraction to condense and recover the water as the condensed water fraction and to recover a vapor fraction comprising the butenes; a second condenser for condensing the vapor fraction comprising the butenes to form the product butene fraction. The system further comprises flow conduit for withdrawing a liquid side draw from the stripper; a first heat exchanger for at least partially vaporizing the liquid side draw by indirect heat exchange with the lean solvent mixture recovered as a bottoms fraction from the stripper; a flow conduit for returning the at least partially vaporized side draw to the stripper; flow conduit for recovering a partially cooled lean solvent mixture from the first heat exchanger; second heat exchangers for contacting at least one of (a) the enriched solvent fraction as a bottoms fraction from the extractive distillation column and (b) liquid side draw from the extractive distillation column via indirect heat exchange with the partially cooled lean solvent mixture. At least one of the first heat exchanger and the second heat exchanger is a once-thru vaporization type exchanger; and third heat exchanger for contacting a partially cooled lean solvent mixture recovered from at least one of the first heat exchanger and the second heat exchanger via indirect heat exchange with the hydrocarbon mixture to at least partially vaporize the hydrocarbon mixture.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The hydrocarbon mixture is a vapor fraction recovered from a butadiene recovery process. The process (P1) further involves vaporizing the hydrocarbon mixture in a feed vaporization system prior to the contacting. The bottoms fraction is fed to the stripper above the stripping section and below the wash section. The condensed water fraction used as the second reflux is a single liquid phase. The condensing the overheads fraction involves condensing the overheads fraction in a two-stage condensation process involving partially condensing the overheads fraction to condense and recover the water as the condensed water fraction and to recover a vapor fraction comprising the butenes; condensing the vapor fraction comprising the butenes to form the product butene fraction. The stripper overheads fraction comprises less than 10 (preferably less than or equal to 5) ppm solvent, by weight. The product butene fraction comprises less than 1 ppm solvent, by weight. The process (P1) further involves withdrawing a liquid side draw from the stripper; at least partially vaporizing the liquid side draw by indirect heat exchange in a first heat exchanger with the lean solvent mixture recovered as a bottoms fraction from the stripper; returning the partially vaporized side draw to the stripper; recovering a partially cooled lean solvent mixture from the first heat exchanger; contacting at least one of (a) the enriched solvent fraction as a bottoms fraction from the extractive distillation column and (b) liquid side draws from the extractive distillation column via indirect heat exchange in a second heat exchanger with the partially cooled lean solvent mixture. At least one of the first heat exchanger and the second heat exchanger is a once-thru vaporization type exchanger. The process (P1) further involves contacting a partially cooled lean solvent mixture recovered from at least one of the first heat exchanger and the second heat exchanger via indirect heat exchange with the hydrocarbon mixture to at least partially vaporize the hydrocarbon mixture prior to the contacting.