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

摘要

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 similar to 99.5 wt% ethanol is energy-intensive because of dilute feed (similar to 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. (c) 2018 Society of Chemical Industry