Energy-efficient process for separating butenes from c4-hydrocarbon streams

Process for separation of butenes from a C4-hydrocarbon stream which contains at least butenes and butanes by extractive distillation with a solvent, wherein the process comprises the steps of:

• a. supplying the gaseous C4-hydrocarbon stream and the liquid solvent to an absorber which comprises at least three random-packing beds arranged one below the other and in which the C4-hydrocarbon stream and the solvent are contacted with one another to transfer predominantly butenes from the C4-hydrocarbon stream into the solvent to form a laden solvent, wherein the thus-laden solvent is collected in a liquid collector of the absorber and 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 desorber as bottoms stream;
• b. supplying the laden solvent to the desorber, the bottom of which is at an elevated temperature and preferably a lower pressure 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 a solvent, at least partially freed of butenes, is collected in a liquid collector of the desorber and passed through a desorber evaporator and then passed into the bottom of the desorber below the liquid collector to outgas any butenes still remaining in the solvent and wherein the solvent is subsequently recycled to the absorber as bottoms stream;
• characterized in that at least one of the random-packing beds of the absorber contains different random packings, wherein the random packings in the upper region of the random-packing bed have a specific surface area y and the random packings in the lower region of the random-packing bed have a specific surface area x,
• wherein the specific surface area x is greater than the specific surface area y.