Pervaporation behavior of PVA membrane containing β-cyclodextrin for separating xylene isomeric mixtures

To evaluate molecular recognition function of β-cyclodextrin to xylene isomers, β-CD polymer of branching chain extension (β-CD-EGDE) was synthesized by crosslinking β-CD with ethylene glycol diglycidyl ether (EGDE). The pervaporation blend membranes of β-CD-EGDE/PVA were prepared by casting an aqueous solution of PVA and β-CD polymer mixture, and the membranes were used for separation of p-/m- and p-/o-xylene mixtures. It was observed that the pristine PVA membrane almost had no selectivity for xylene isomer mixtures. The PVA membrane incorporating β-CD polymer had molecular recognition function, which selectively facilitated the transport of the xylene isomers. To ascertain pervaporation behavior, the sorption and desorption processes of the membrane in xylenes were investigated. The sorption result showed that the complex formation constant between β-CDs and xylenes played a key role in swelling behavior. There was a significant difference between diffusion coefficients D and D⁰, calculated from the sorption and desorption measurements, respectively, indicating that the diffusivity selectivity in desorption stage may have remarkable effect on the total selectivity during pervaporation process.