New distillation sequences for bioethanol production by extractive distillation

In a bioethanol production plant the separation unit performs the recovery of the ethanol from the raw fermentation beer to produce high purity ethanol. Although different separation techniques are available, distillation or distillation combined with other unit operations, remains the main technology considered for the ethanol purification. The formation of a homogeneous minimum-boiling azeotrope limits the purity allowable employing a simple distillation unit. The classical configuration for the separation of an ethanol-water mixture by extractive distillation employs three columns: the pre-concentrator, the extractive column and a stripping section. Starting from this configuration, new separation sequences are obtained applying the thermal coupling principle. Then, the column sections were rearranged taking into account the limits imposed by the recycle streams. The new arrangements were simulated considering a typical broth composition and ethylene glycol as a solvent. The new sequences report capital and energy cost reductions compared to the classical separation sequence proposed in the literature.