Energy-efficient process for removing butenes from C4-hydrocarbon streams and subsequent n/iso separation

A process for separating butenes from a C4-hydrocarbon stream which contains at least butenes, n-butane, and isobutane, by extractive distillation with a solvent, the process comprising:

• a. at least partially evaporating a liquid C4-hydrocarbon stream in a feed evaporator, to obtain a gaseous C4-hydrocarbon stream, and supplying the solvent at a location spatially above the gaseous C4-hydrocarbon stream to an absorber in which the gaseous C4-hydrocarbon stream and the solvent are contacted with one another to transfer predominantly butenes from the gaseous C4-hydrocarbon stream to the solvent, to obtain a laden solvent, wherein the laden solvent is collected in a liquid collector of the absorber, passed through an absorber evaporator, and then passed into the bottom of the absorber below the liquid collector to outgas predominantly butanes from the laden solvent, and wherein the laden solvent is subsequently passed to a separate desorber as a bottoms stream and wherein a stream enriched in butanes relative to the C4-hydrocarbon stream is obtained at the top of the absorber;
• b. supplying the laden solvent to the desorber, the bottom of which is at an elevated temperature relative to the bottom of the absorber, and in which the butenes are separated from the solvent to obtain at the top of the desorber a stream enriched in butenes, wherein the solvent, at least partially freed of butenes, is collected in a liquid collector of the desorber, passed through a desorber evaporator, and then passed into the bottom of the desorber below the liquid collector to outgas any butenes remaining in the solvent, and wherein the solvent is subsequently recycled to the absorber as a stream;
• c. supplying the stream enriched in butanes to an n/iso splitter in which n-butane and isobutane are separated from one another to obtain a stream enriched in isobutane at the top of the n/iso splitter and a stream enriched in n-butane at the bottom of the n/iso splitter;
• wherein heat of the solvent withdrawn as a bottoms stream of the desorber is used for heat integration by employing the heat of the solvent in at least one respective heat exchanger for preheating the laden solvent passed to the desorber, for evaporation in the absorber evaporator, and for evaporation of the liquid C4-hydrocarbon stream, and
• wherein the stream enriched in butenes is withdrawn at the top of the desorber and subjected to a condensation, wherein heat of condensation is at least partially used for heating the n/iso splitter.