A Coupling Process of Distillation with Vapor Permeation and Adsorption for Production of Fuel Ethanol: A Comparative Analysis on Energy Consumption

Abstract

To efficiently produce fuel ethanol from fermentation broth, the distillation column was coupled with vapor permeation (VP) of a NaA zeolite membrane instead of using the adsorption technique to remove solvent water. The comparative analysis indicated that the energy efficiency was consistently higher for distillation-VP coupling, using a single-column distillation and three-column distillation, respectively. The best performance was obtained for the VP membrane coupling with a three-column distillation technique, where only 2.7 tons of steam per ton of fuel ethanol were consumed to produce fuel ethanol using a 3.0 wt % ethanol broth. This saved 0.25 tons of steam per ton of fuel ethanol in comparison with the results for the coupling with adsorption technique. The effect of ethanol content in broth on the energy efficiency was also investigated, which indicated that the ethanol content was a decisive factor to determine the energy consumption in the coupling techniques. The operation pressures were crucial to balance the energy consumption between columns coupled with the VP membrane. It was found that the operation pressure of the low-pressure column was the decisive factor to the whole energy efficiency, while the pressure of the high-pressure column was preferably adjusted according to practical production due to fewer disturbances in the system. This work benefits the process design for production of fuel ethanol from fermentation broth.