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Development and optimization of a novel process of double‐effect distillation with vapor recompression for bioethanol recovery and vapor permeation for bioethanol dehydration

Singh, Ashish, Rangaiah, Gade P
Journal of chemical technology and biotechnology 2019 v.94 no.4 pp. 1041-1056
adsorption, bioethanol, biomass, carbon dioxide, distillation, economic investment, energy efficiency, ethanol, fermentation, operating costs, permeability, specific energy, transportation, vapors
BACKGROUND: Bioethanol, an important biofuel, obtained from biomass fermentation is dilute and unsuitable for direct use as fuel for transportation. Its recovery and dehydration to ∼99.5 wt% ethanol is energy‐intensive because of dilute feed (∼10 wt% ethanol) and occurrence of ethanol–water azeotrope. From an energy efficiency perspective, hybrid separation processes consisting of a membrane‐based module coupled with distillation are a promising alternative to conventional separation by distillation alone. RESULTS: The present article proposes the novel process of double‐effect distillation with vapor recompression (DED) for bioethanol recovery followed by vapor permeation (VP) for bioethanol dehydration (to 99.8 wt% ethanol) from a ternary feed of ethanol (10 wt%), water (89.9 wt%) and CO₂ (0.1 wt%) and compares it with the process of simple distillation followed by vapor permeation (D‐VP). Multi‐objective optimization is performed for both processes, and the obtained Pareto‐optimal solutions for minimizing fixed capital investment and annual operating cost are presented and discussed. Compared with the optimal D‐VP process, the optimal DED‐VP process is found to be better, with 17 and 11% savings in energy consumption and total annual cost (TAC) respectively. CONCLUSION: Specific energy consumption (SEC) of the DED‐VP process is 5% lower than that of the hybrid process of distillation for recovery followed by pressure swing adsorption for dehydration (D‐PSA) used industrially. Continued developments in membranes that can provide high permeance, selectivity and/or operating life can further reduce TAC and SEC of the DED‐VP process. © 2018 Society of Chemical Industry