FER membrane synthesized by a vapor-phase transport method: its structure and separation characteristics

The mechanism of formation of ferrierite (FER) membrane on an alumina support by a vapor-phase transport (VPT) method was studied using XRD, SEM, FE-SEM and EDX. The XRD measurement for a FER membrane after the removal of FER particles formed on the support showed that FER was formed in the pores of the alumina support, namely, a FER-alumina composite layer was formed. The FE-SEM image for the cross-sectional view of the FER-alumina composite layer showed that FER nanocrystals of about 50 nm diameter grew in the pores of the alumina support. Pervaporation tests for benzene/p-xylene mixtures were performed at 303 K. Even when the concentration of benzene in the feed solution was extremely small (0.5 mol%), the flux of benzene through the FER membrane was still greater than that of p-xylene. Therefore, a separation factor as high as 600 was obtained in the low feed concentration of benzene. Such a high selectivity for the benzene/p-xylene mixture suggested that the selectivity for the benzene/p-xylene mixture appears at the pore mouths of FER on the feed side of the FER-alumina composite layer.