Process for producing butadiene from ethanol, comprising purification of a butadiene-loaded effluent by extractive distillation

Process for producing butadiene from an ethanol feedstock comprising at least 80% by weight of ethanol, said process comprising:

• a) a step for converting the ethanol into butadiene, comprising:
• a water-ethanol separation section fed with at least a fraction of said ethanol feedstock and with a fraction of the ethanol-water effluent obtained from step e) and producing an ethanol effluent and a purged water effluent;
• a reaction section fed with said ethanol effluent and operated at a pressure of between 0.1 and 1.0 MPa and at a temperature of between 200 and 500° C. in the presence of a catalyst and producing a reaction effluent;
• b) a distillation step fed with the reaction effluent obtained from step a) and producing a polluted reagent residue and a butadiene distillate, operated at a pressure of between 0.1 and 1 MPa;
• c) a step of washing with water comprising at least one gas-liquid washing section fed at the bottom with the butadiene distillate obtained from step b) and at the top with a stream of water, and producing at the top a hydrated butadiene extract and at the bottom a spent water raffinate;
• d) a butadiene purification step fed with the butadiene extract obtained from step c) and producing at least one light gas effluent and a purified butadiene effluent comprising at least:
• a section for separating the 1-butene by extractive distillation fed with said butadiene extract and with a stream comprising a solvent, separating at the top a light gas effluent and, at the bottom a butadiene residue;
• a section for separating out the solvent by distillation fed with said butadiene residue obtained from the 1-butene separation section and separating at the top a topped butadiene distillate and at the bottom a solvent residue;
• a final distillation section fed with the topped butadiene distillate obtained from the solvent separation section, separating at the top a purified butadiene effluent and at the bottom a butene residue;
• e) an effluent treatment step fed with the spent water raffinate obtained from step c) and with the polluted reagent residue obtained from step b) and producing at least one ethanol-acetaldehyde effluent, an ethanol-water effluent and one or more brown oil effluents.