Separation of methane-nitrogen mixtures using synthesis vertically aligned carbon nanotube membranes

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• 作者：Neda Gilani^a ; Jafar Towfighi Daryan^a ; ^{towfighi@modares.ac.ir} ; Alimorad Rashidi^b ; Mohammad Reza Omidkhah^a
• 关键词：Carbon nanotubes ; Anodic aluminum oxide ; Gas separation ; CH4/N2 mixture
• 刊名：Applied Surface Science
• 出版年：2012
• 期刊代码：6_01694332
• 类别：ms
• 出版时间：1 March, 2012
• 卷：258
• 期：10
• 页码：4819-4825
• 文件大小：579 K

摘要

In this paper, capabilities of carbon nanotube (CNT) membranes fabricated in cylindrical pores of anodic aluminum oxide (AAO) substrate to separate the binary mixtures of CH₄/N₂ are studied experimentally. For this purpose, the permeability and selectivity of three CNT/AAO membranes with different growth time as 6 h, 12 h and 18 h are investigated. CNTs are grown vertically through holes of AAO with average pore diameter of 45 nm by chemical vapor deposition (CVD) of acetylene gas. CNT/AAO membranes with the same CNTs鈥?outer diameters and different inner diameters are synthesized. The AAO are characterized by SEM analysis. In addition, SEM, TEM, BET N₂ adsorption analysis and Raman spectroscopy are employed to characterize aligned CNTs. Study on permeability and selectivity of membranes for three binary mixtures of CH₄/N₂ showed that when the CNT inner diameters are 34 nm and 24 nm, viscous flow is the governing mechanism and insignificant selectivities of 1.2-1.24 are achieved. However, the membrane with CNT inner diameter and wall thickness of 8 nm and 16 nm respectively is considerably selective for CH₄ over N₂. It was also found that CH₄ mole fraction in the feed and upstream feed pressure have major effect on permeability and selectivity. The membrane with 18 h synthesis time showed the selectivity is in the range of 1.8-3.85. The enhancement factor for N₂ single gas diffusivity was also found to be about three times larger than that predicted by Knudsen diffusion model.