Adsorption of Water and Ethanol in MFI-Type Zeolites

详细信息    查看全文

• 作者：Ke Zhang ; Ryan P. Lively ; James D. Noel ; Michelle E. Dose ; Benjamin A. McCool ; Ronald R. Chance ; William J. Koros
• 刊名：Langmuir
• 出版年：2012
• 出版时间：June 12, 2012
• 年：2012
• 卷：28
• 期：23
• 页码：8664-8673
• 全文大小：436K
• 年卷期：v.28,no.23(June 12, 2012)
• ISSN：1520-5827

文摘

Water and ethanol vapor adsorption phenomena are investigated systematically on a series of MFI-type zeolites: silicalite-1 samples synthesized via both alkaline (OH^{鈥?/sup>) and fluoride (F鈥?/sup>) routes, and ZSM-5 samples with different Si/Al ratios as well as different charge-balancing cations. Full isotherms (0.05鈥?.95 activity) over the range 25鈥?5 掳C are presented, and the lowest total water uptake ever reported in the literature is shown for silicalite-1 made via a fluoride-mediated route wherein internal silanol defects are significantly reduced. At a water activity level of 0.95 (35 掳C), the total water uptake by silicalite-1 (F鈥?/sup>) was found to be 0.263 mmol/g, which was only 12.6%, 9.8%, and 3.3% of the capacity for silicalite-1 (OH鈥?/sup>), H-ZSM-5 (Si/Al:140), and H-ZSM-5 (Si/Al:15), respectively, under the same conditions. While water adsorption shows distinct isotherms for different MFI-type zeolites due to the difference in the concentration, distribution, and types of hydrophilic sites, the ethanol adsorption isotherms present relatively comparable results because of the overall organophilic nature of the zeolite framework. Due to the dramatic differences in the sorption behavior with the different sorbate鈥搒orbent pairs, different models are applied to correlate and analyze the sorption isotherms. An adsorption potential theory was used to fit the water adsorption isotherms on all MFI-type zeolite adsorbents studied. The Langmuir model and Sircar鈥檚 model are applied to describe ethanol adsorption on silicalite-1 and ZSM-5 samples, respectively. An ideal ethanol/water adsorption selectivity (伪) was estimated for the fluoride-mediated silicalite-1. At 35 掳C, 伪 was estimated to be 36 for a 5 mol % ethanol solution in water increasing to 53 at an ethanol concentration of 1 mol %. The adsorption data demonstrate that silicalite-1 made via the fluoride-mediated route is a promising candidate for ethanol extraction from dilute ethanol鈥搘ater solutions.}