Mechanism of ethanol/water reverse separation through a functional graphene membrane: a molecular simulation investigation
Quan Liu1,2, Xian Wang1, Yanan Guo2(), Gongping Liu2(), Kai-Ge Zhou3
1. School of Chemical Engineering, Analytical and Testing Center, Anhui University of Science and Technology, Huainan 232001, China 2. State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 211816, China 3. Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China
Reverse-selective membranes have attracted considerable interest for bioethanol production. However, to date, the reverse-separation performance of ethanol/water is poor and the separation mechanism is unclear. Graphene-based membranes with tunable apertures and functional groups have shown substantial potential for use in molecular separation. Using molecular dynamics simulations, for the first time, we reveal two-way selectivity in ethanol/water separation through functional graphene membranes. Pristine graphene (PG) exhibits reverse-selective behavior with higher ethanol fluxes than water, resulting from the preferential adsorption for ethanol. Color flow mappings show that this ethanol-permselective process is initiated by the presence of ethanol-enriched and water-barren pores; this has not been reported in previous studies. In contrast, water molecules are preferred for hydroxylated graphene membranes because of the synergistic effects of molecular sieving and functional-group attraction. A simulation of the operando condition shows that the PG membrane with an aperture size of 3.8 Å achieves good separation performance, with an ethanol/water separation factor of 34 and a flux value of 69.3 kg∙m‒2∙h‒1∙bar‒1. This study provides new insights into the reverse-selective mechanism of porous graphene membranes and a new avenue for efficient biofuel production.
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