Energy Efficient Bioethanol Purification by Heat Pump Assisted Extractive Distillation

The purification of bioethanol fuel requires an energy demanding separation process to concentrate the diluted streams obtained in the fermentation stage and to overcome the azeotropic behaviour of ethanol-water mixture. The classic separation sequence consists of three distillation columns that carry out several energy demanding tasks: pre-concentration of ethanol, extractive distillation and solvent recovery. 

To solve this problem, we propose a novel heat pump assisted extractive distillation process taking place in a dividing-wall column (DWC). In this configuration, the ethanol top vapour stream of the extractive DWC is recompressed from atmospheric pressure to over 3.1. bar (thus to a higher temperature) and used to drive the side reboiler of the DWC, which is responsible for the water vaporization. The results show that the specific energy requirements drop from 2.07 kWh/kg (classic sequence) to only 1.24 kWh/kg ethanol (VRC assisted extractive DWC), thus energy savings of over 40 % and 24 % reduced total annual costs are possible, as compared to the conventional process.