Heat-pump assisted distillation versus double-effect distillation for bioethanol recovery followed by pressure swing adsorption for bioethanol dehydration

Bioethanol recovery (i.e., pre-concentration from 5 to 10 wt.% ethanol to near azeotrope composition) from the fermentation broth requires significantly more energy compared to bioethanol dehydration from near azeotrope composition to >99.5 wt.% ethanol. The present article proposes and evaluates two different alternatives, namely, double-effect distillation (DED) and heat-pump assisted distillation (HPAD) as opposed to simple distillation for bioethanol recovery followed by dehydration using pressure-swing adsorption (PSA). Preliminary design reveals that HPAD-PSA process outperforms DED-PSA process resulting in 19% savings in total annual cost. Multi-objective optimization is hence performed for HPAD-PSA process, and the obtained Pareto-optimal solutions for minimizing fixed capital investment and annual operating cost are presented and discussed. Compared to the simple distillation followed by PSA process, HPAD-PSA process reduces specific energy consumption (SEC) by 38% to 3.2 MJ-fuel/kg of bioethanol. Further, compared with other, recent bioethanol separation processes, HPAD-PSA process results in 35–64% lesser SEC.