Separation of xylene isomers controlled by adsorption configuration on fluorinated lamellar membrane

Abstract

Separation of the xylene isomers has always been of great challenge and interest to the industry. Here, separation factors of 51 and 9 for p-/o-xylene and p-/m-xylene with a p-xylene permeance of 1.2 × 10⁻⁷ and 2.2 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹, respectively, are achieved on the simple tandem fluorinated MXene lamellar membranes with 11%F and 1%F content through insight into the inversion behavior of the adsorption configuration enabled by the difference in dipole moments of xylenes under the combined interaction of xylene–CH₃ ^… F attraction and xylene–π–bond ^… F repulsion. The favorable configuration of p-xylene maintains the flat adsorption, while that of m- and o-xylene undergoes a transition from upright to tilted and flat adsorption. DFT calculations confirm the weak flat adsorption of p-xylene on MXene-11%F repelled by the π–bond ^… F repulsion and the strong upright adsorption of m- and o-xylene via the regulation of the repulsion, which contributes to a high throughput of p-xylene. As the F content decreases to 1 %, the low π–bond ^… F repulsion results in strong flat configuration of p-xylene and weak flat configuration of m- and o-xylene. This work provides ideas for separating isomers by controlling the adsorption configuration through understanding their interaction forces in the membrane channel.