Method for selectively separating impurities present in a hydro-alcoholic cut by recycling through a liquid-liquid extraction column

A process for the treatment by liquid-liquid extraction and distillation of a liquid feedstock comprising at least ethanol, water and acetaldehyde and at least one hydrocarbon-based impurity with a boiling point of between 20° C. and 100° C. at atmospheric pressure, or generating, with at least one of the compounds of the liquid feedstock and/or with the organic extraction solvent and/or with the aqueous back-washing solvent, an azeotrope whose boiling point is between 20 and 100° C. at atmospheric pressure, and a partition coefficient of between 0.1 and 5 at any point in the back-washing (BW) column of the extraction section, comprising:

• a) a liquid-liquid extraction step comprising an extraction section comprising a washing (W) column and a back-washing (BW) column, said extraction section being fed with said liquid feedstock at an intermediate point located between the top of the washing (W) column and the bottom of the back-washing (BW) column,
• said washing (W) column being fed at the top with the stream originating from the bottom of the back-washing (BW) column and at the bottom with a stream of an organic extraction solvent,
• said back-washing (BW) column being fed at the top with a stream of an aqueous back-washing solvent and at the bottom with the stream originating from the top of the washing (W) column,
• said extraction section comprising at least one injection (F2) of the cut withdrawn in step b), said injection (F2) being located in the top half of the back-washing (BW) column,
• said extraction section producing, at the bottom of the washing (W) column, a raffinate comprising at least water, ethanol, acetaldehyde and a portion of said hydrocarbon-based impurity and, at the top of the back-washing (BW) column, an extraction effluent comprising at least a portion of said hydrocarbon-based impurity;
• b) a distillation step comprising:
• at least one acetaldehyde separation step comprising an acetaldehyde separation section, composed of at least one distillation column (D1) fed with the raffinate originating from step a) in an intermediate zone of the column (D1) and producing at the top an acetaldehyde-rich effluent and at the bottom a water/ethanol effluent;
• and
• at least one ethanol separation step comprising an ethanol separation section, composed of at least one distillation column (D2) fed with the water/ethanol effluent originating from the bottom of the column (D1) in an intermediate zone of the column (D2), and producing at the top an ethanol-rich effluent and at the bottom a water-rich effluent,
• at least one side withdrawal on the column (D1) or the column (D2) of a cut comprising at least one of the compounds ethanol or acetaldehyde, at a mass fraction of at least 10% of the total mass of the withdrawn cut, and said hydrocarbon-based impurity, at a mass fraction of between 0.5% and 50% of the total mass of the withdrawn cut, the side withdrawal being located in an intermediate zone of the column (D1) or (D2).