Separation of Isomeric Xylenes Using Cyclodextrin-Modified Ceramic Membranes

Cyclodextrin (CD)-modified ceramic membranes for the separation of xylene mixtures were investigated. CDs were directly immobilized to the surface of TiO 2 /Al 2 O 3 ceramic nanofiltration membranes, and a cross-linking agent was used to obtain further stabilization of the CD layer. Pervaporation tests showed that the order of permeation from ternary xylene mixtures was m -xylene > o -xylene > p -xylene. In p -xylene/ m -xylene binary mixtures, the separation was a strong function of the feed concentration ratio. The selectivity of p -xylene over m -xylene changed from 1.53 at 4 vol % to 0.72 at 32 vol % of p -xylene in the feed. To describe these observations, a mathematical model was derived based on Stefan−Maxwell theory assuming a surface-diffusion mechanism. Model parameters including sorption isotherms were obtained from experiments. The Stefan−Maxwell diffusion coefficients are obtained from molecular dynamics simulations. Finally, this model predicted the experimental observations well and revealed that the selectivity of this membrane is strongly influenced by differences in the diffusion rate of the xylene penetrants.