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Abstract: A thin and compact mesoporous MCM-48 membrane had been successfully synthesized on vacuum-coated α-Al2O3 support with pore size of 1μm. The pretreated supports and the membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation test. The pretreated supports were gas permeable for N2 and the as-synthesis membrane was gas tight, indicating that the defects left in the vacuum step disappeared in the multi-hydrothermal synthesis process. The XRD pattern of the membrane was represented to the typical cubic space group. And the SEM images showed that the membrane was continuous and 4-μm thick. Additionally, the separation factor of the calcined membrane for H2/N2 was up to 3.33 and the Knudsen contribution to the total flux for N2 permeation was 97.8%. All the results indicated that the good surface conditions of the large-pore supports improved by the vacuum coating method were favorable for the formation of a compact MCM-48 membrane on it. [Copyright &y& Elsevier]

Abstract: Five kinds of micro-porous SiO2–ZrO2 (ZrO2; 50mol%) membranes of slightly different pore sizes less than 1nm were prepared by the sol–gel techniques to study the pervaporation characteristics of some aqueous solutions of organic chemicals. Since no direct evaluation techniques to determine the membrane pore-sizes less than 1nm have yet been established, the pore sizes of the membranes fabricated were estimated by observing the permeances of gases of various molecular diameters at 200°C. Some pervaporation measurements of aqueous solutions of organic chemicals such as iso-propanol, ethanol and acetone have been done with the membranes fabricated in order to study the effects of the membrane pore size and the molecular interaction with the pore wall on the pervaporation performance. The pervaporation results for IPA/water mixture at 10wt.% of water and at 75°C showed a long time dependency of IPA and water fluxes. The IPA flux decreased drastically, while that of water decreased slightly, giving a large separation factor, larger than 15,000, after several hours of pervaporation with water fluxes of 120–300mol/m2 h, for example. The observed concentration dependency of the IPA flux showed a maximum at around 48mol% of IPA and then decreased with increasing IPA concentration in the feed. A similar behavior of the ethanol flux was observed for ethanol/water mixtures, but not for acetone/water mixtures. The acetone flux increased monotonously with the increase of acetone concentration in the feed. The pervaporation results obtained for the membranes of different pore sizes suggest that the separation performance depends largely on the pore size and also on the interaction between the molecules and the pore wall. [Copyright &y& Elsevier]