An efficient heat-pump extractive distillation process for recovering lower alcohols from bioethanol fusel oil

Abstract

Fusel oil is a common mixture of several alcohols produced as a by-product of alcoholic fermentation. After removing the main ingredient (amyl alcohol), it also contains lower alcohols such as ethanol (EtOH), n-propanol (NPA) and isobutanol (IBA), each of which forms an azeotrope with water and has a similar boiling point. In order to efficient recover high purity products from the EtOH/NPA/IBA/water mixture, this article investigates different extractive distillation processes with heat pump in terms of economic, environment and thermodynamic properties. Firstly, 1,4-butanediol is screened as the best dehydration solvent based on the thermodynamic and molecular quantization analysis; Next, a conventional extractive distillation sequence (CED) is proposed and optimized using total annual costs (TAC) and CO₂ emissions as dual objectives. Finally, introducing heat integration, vapor recompressed heat pump and bottom flash heat pump into the CED process, three energy-saving processes (i.e., HICED, DVRHPs-HICED and BFVRHPs-HICED) are designed. The results show that compared with the CED process, the DVRHPs-HICED process reduces TAC by 17.5 %, exergy loss by 42.2 %, and gas emissions (CO₂, SO₂, NO_x) by 49.2 % while the BFVRHPs-HICED process reduce TAC by 17.8 %, exergy loss by 40.8 %, and gas emissions (CO₂, SO₂, NO_x) by 48.5 %.