Chemical modification of zeolite beta surface and its effect on gas permeation of mixed matrix membrane |
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Authors: | Doungporn Sirikittikul Asira Fuongfuchat Warintorn Booncharoen |
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Affiliation: | National Metal and Materials Technology Center (MTEC), Paholyothin Rd., Pathumthani 12120, Thailand |
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Abstract: | Chemical modification of zeolite beta (BEA) with a series of organosilane compounds [R(CH3)nSiX(3‐n), where X is a chloro or alkoxy group with n = 0 and 2, and R is an alkyl chain varying from CH3 to C18H37] was investigated. The results of FT‐IR and 29Si CP/MAS NMR indicated that the alkylsilyl species were covalently anchored onto the BEA surface. Grafting density of the alkylsilyl species was determined by CHN elemental analysis and thermogravimetric analysis (TGA). Evidently, it can be adjusted by varying the reaction time and organosilane concentration. The reaction kinetics was found to resemble the kinetics of the well‐known monolayer formation, i.e. SAMs. The kinetic plot illustrated two distinct regions, a rapid attachment followed by a gradual increase of grafting density. The degradation temperature at maximum rate (Tmax) of the surface‐grafted BEA was observed in the range of 440–460°C. The modified BEA showed surface hydrophobic characteristic by having a strong affinity to the non‐polar n‐heptane. Good particle distribution and strong interfacial adhesion were observed in the mixed matrix membranes of the BEA grafted with C3H7 to C18H37. The grafted chain length was found to have an effect on gas permeability. Carbon dioxide, oxygen, and ethylene permeabilities of the membranes containing the unmodified BEA were comparable to those of the CH3Si‐grafted BEA. Interestingly, the membranes containing the BEA grafted with C3H7 to C18H37 species showed enhancement of the carbon dioxide permeability. Affinity of the long alkyl chain to carbon dioxide probably caused the increase of carbon dioxide permeability. Copyright © 2008 John Wiley & Sons, Ltd. |
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Keywords: | zeolites chemical modification membranes gas permeation |
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