Pervaporation Separation Of Xylene Isomers By Hybrid Membranes Of PAAS Filled With Silicalite-1 Zeolite

Pervaporation is a promising separation technique and attracts great attention. The hybrid pervaporation membranes containing zeolite have both advantages of inorganic and polymeric membranes, and can be used for separating xylene isomers according to the differences of kinetic diameter of p-xylene, o-xylene and m-xylene. In this paper, the hybrid PAAS membrane loaded with Silicalite-1 zeolite was prepared, but the zeolite easily aggregated in the hybrid membranes and the compatibility between PAAS and Silicalite-1 was poor. In order to improve the performance of pervaporation (PV) membranes, the Silicalite-1 zeolite was organized by surface modification, and the PAAS/modified Silicalite-1 hybrid membranes were prepared, and their pervaporation performances of xylene isomers mixtures were investigated.Firstly, Silicalite-1 zeolite was prepared by the hydrothermal synthesis method, and then was modified by 3-aminopropyl-triethoxysilane(APTES). Characterization results of Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) confirmed that chemical modification on zeolite surface had taken place and the zeolite structure wasn't destroied. And the result of zeolite particle size analysis revealed that the dispersion of the zeolite in water was significantly improved by surface modification, it was because priming amine groups were introduced and the -NH3+ was formed on the surface of zeolite particles which prevented aggregating in the water.Then we prepared the PAAS/Silicalite-1 hybrid membrane by solution casting method. The morphologies of the PAAS/modified Silicalite-1 hybrid membranes showed the zeolite in the hybrid membrane had good dispersibility. And also these membranes'contact and adhesion at the PAAS-zeolite interface were improved because of the ion interaction between -NH3+ groups on the surface of modified zeolite and the -COOH groups on PAAS. The swelling results showed the order of swlling degree was:S(m-xylene)<S(o-xylene)<S(p-xylene). Based on the sorption equilibrium experiment, the diffusion coefficients of permeates in the membrane were obtained, and the order of the diffusion coefficients was:D(o-xylene)<D(m-xylene)< D(p-xylene).The effects of the original versus modified zeolite loading on the pervaporation performance were compared. With original zeolite as the loading, the permeation flux of the binary xylene mixtures showed little change while the selectivity of the hybrid membrane exhibited some enhancement. After the zeolite surface modification, the compatabilitity of the membrane became good and the selectivity of the hybrid membrane was clearly improved and the permeation flux of the membrane slightly decreased, and the maximum separation factors of the p-/o-xylyne (αp/o) and p-/m-xylene(αP/m) mixtures were determined to be 2.62 and 2.68, respectively.