Method for preventing three-phase separation of butenes from C4 hydrocarbon streams

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

• a. at least partially evaporating a liquid C4-hydrocarbon stream in a feed evaporator, to supply a gaseous CA-hydrocarbon stream, and supplying the solvent to a liquid distributor above a gaseous C4-hydrocarbon stream inlet to an absorber which comprises more than two random-packing beds and 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, wherein the thus-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 a liquid collector to outgas predominantly butanes from the thus-laden solvent, wherein a butanes-depleted laden solvent is subsequently passed to a desorber as a bottoms stream and wherein a stream enriched in butanes relative to the liquid C4-hydrocarbon stream is obtained at the top of the absorber and at least partially condensed and a portion of a condensate is returned to the top of the absorber as reflux;
• and
• b. supplying the butanes-depleted laden solvent, to the desorber, which is at an elevated temperature relative to the absorber and in which butenes are separated from the butanes-depleted laden solvent, to obtain at the top of the desorber a stream enriched in butenes and to obtain at the bottom of the desorber a solvent at least partially freed of 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 at least partially freed of butenes, and where the solvent at least partially freed of butenes is subsequently recycled to the absorber as a bottoms stream,
• wherein heat of the solvent at least partially freed of butenes withdrawn as a bottoms stream of the desorber is used for heat integration by employing the heat of the solvent at least partially freed of butenes withdrawn as a bottoms stream in at least one respective heat exchanger for preheating the butanes-depleted laden solvent passed to the desorber, for evaporation in an absorber evaporator, and for evaporation of the liquid C4-hydrocarbon stream in said feed evaporator, and
• wherein (i) at least a portion of a liquid phase is withdrawn at the liquid distributor above a first or second random-packing bed and separated into a heavy liquid phase and a light liquid phase in a decanter, of which the heavy liquid phase is returned to the absorber, and/or (ii) the reflux in the absorber is withdrawn from the absorber via a runoff cup, mixed with the solvent in a static mixer and then, with the solvent, supplied to the liquid distributor above the first random-packing bed.