Process for the separation of butenes and butanes by extractive distillation

A process for the separation of butanes and butenes from a charge containing the same, comprising:

• introducing said charge into an extractive distillation column under pressure;
• contacting said charge in said extractive distillation column with a first polar solvent S1, in which the butanes have a higher volatility than the butenes;
• withdrawing an overhead from the top of said extractive distillation column, said overhead consisting essentially of butanes;
• withdrawing residue from the bottom of said extractive distillation column, said residue comprised mainly of solvent S1 and butenes;
• providing a second solvent S2 having a volatility between that of the first solvent S1 and that of the butenes, which does not form an azeotrope with the butenes and which is miscible with said first solvent S1;
• passing said residue and said second solvent S2 into a desorption column under pressure;
• withdrawing from said desorption column an overhead consisting essentially of butenes;
• withdrawing a residue from said desorption column, said residue consisting essentially of a mixture of solvents S1 and S2;
• feeding said mixture into a purification column;
• withdrawing from said purification column an overhead consisting essentially of said solvent S2;
• condensing the latter overhead to form a distillate consisting essentially of said solvent S2;
• recycling the resultant distillate to the desorption column;
• withdrawing from the bottom of the purification column a bottom residue consisting essentially of purified solvent S1;
• and
• recycling said purified solvent to the extractive distillation column.