PNNL

Abstract

Graphene oxide (GO) is a promising membrane system for applications of chemical separation due to 2-D nanofluidics and an ability to control interplanar spacing for selectivity. We investigated the potential of the GO membrane system for alcohol-water separations using highly aligned GO grains produced by slip casting process. Liquid transport was studied through pressure driven permeance and osmosis experiments. The permeance of water, MeOH and IPA through 5 µm thick membranes was found to be 0.4, 0.12 and 0.8 LMH/Bar respectively. Interestingly, the permeance of alcohol-water mixture was found to be dramatically lower (consistently at 0.01 LMH/Bar level) than any of its individual components. Upon removal of the solvent mixture, the pure solvent flux across membrane was recovered to near original permeance. Similar flux decrease phenomenon was also observed in osmosis tests when alcohol-water mixture was in present on the feed side of membrane. The osmotic flux can be recovered when using single component solvents. Rejection of salt and selectivity of water over alcohol through GO membranes was demonstrated by the osmosis experiments. The interlayer space of a dried GO membrane was found to be 8.52 Å which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. A decrease in d-space, about 2 Å, was consistently observed when adding alcohol to water wetted GO membrane as well as an optical color change. A newly proposed mechanism of a partial reduction of GO through a catalytic reaction with the alcohol-water mixture is consistent with experimental observations.