Carbon membranes for efficient water-ethanol separation

TL;DR

This study uses molecular dynamics simulations to show that nanoporous carbon membranes can efficiently separate water from ethanol by exploiting ethanol's preferential adsorption, enabling pressure-driven dehydration suitable for bio-ethanol production.

Contribution

It introduces a novel separation mechanism based on self-semi-permeability in carbon membranes, supported by molecular dynamics, for efficient water-ethanol separation.

Findings

Carbon membranes exhibit self-semi-permeability to water in mixtures.

Ethanol adsorption prevents water entry into nanoconfined pores.

Separation process aligns with classic osmotic pressure models.

Abstract

We demonstrate, on the basis of molecular dynamics simulations, the possibility of an efficient water-ethanol separation using nanoporous carbon membranes, namely carbon nanotube membranes, nanoporous graphene sheets, and multilayer graphene membranes. While these carbon membranes are in general permeable to both pure liquids, they exhibit a counter-intuitive "self-semi-permeability" to water in the presence of water-ethanol mixtures. This originates in a preferred ethanol adsorption in nanoconfinement that prevents water molecules from entering the carbon nanopores. An osmotic pressure is accordingly expressed across the carbon membranes for the water-ethanol mixture, which agrees with the classic van't Hoff type expression. This suggests a robust and versatile membrane-based separation, built on a pressure-driven reverse-osmosis process across these carbon-based membranes. In particular, the recent development of large-scale 'graphene-oxide' like membranes then opens an avenue for a versatile and efficient ethanol dehydration using this separation process, with possible application for bio-ethanol fabrication.