Mechanism of ethanol/water reverse separation through a functional graphene membrane: a molecular simulation investigation

Abstract

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.

Graphical abstract

Keywords

reverse separation / graphene membrane / ethanol/water separation / molecular simulation

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Acknowledgments

This work was financially supported by the University Natural Science Research Project of Anhui Province (Grant No. KJ2020A0286), the Anhui Provincial Natural Science Foundation (Grant No. 2108085QB50), and the Natural Science Foundation of Jiangsu Province (Grant No. BK20220002). The numerical calculations in this paper have been done on the supercomputing system in the Supercomputing Center of University of Science and Technology of China.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://dx.doi.org/10.1007/s11705-022-2246-z and is accessible for authorized users.

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