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Adsorption of CO2, CH4, and N2 on 8-, 10-, and 12-Membered Ring Hydrophobic Microporous High-Silica Zeolites: DDR, Silicalite-1, and Beta

Yang, Jiangfeng, Li, Junmin, Wang, Wei, Li, Libo, Li, Jinping
Industrial & Engineering Chemistry Research 2013 v.52 no.50 pp. 17856-17864
X-ray diffraction, adsorption, aluminum, carbon dioxide, engineering, equations, heat, hydrophobicity, metal ions, methane, models, nitrogen, porous media, scanning electron microscopy, silicon, sorbents, sorption isotherms, thermogravimetry, water vapor, zeolites
Three hydrophobic microporous high-silica zeolites, DDR (with an 8-membered ring), silicalite-1 (a 10-membered ring), and beta (a 12-membered ring) were synthesized. The Si/Al ratios were 230, 1350, and 35, respectively. The samples were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, water vapor adsorption, and volumetric nitrogen adsorption. They were tested for their CO₂, CH₄, and N₂ adsorption properties at pressures of up to 10 bar at 288–313 K after activation, and the results were correlated with the Langmuir model. The heat of adsorption was calculated using the Clausius–Clapeyron equation based on the adsorption isotherms. These data were used to estimate the separation selectivities for CO₂/CH₄ and CH₄/N₂ binary mixtures at 298 K, using the ideal adsorbed solution theory (IAST) model. Experimental results showed that DDR and beta have good selectivities for CO₂/CH₄, because they have narrow pores (DDR) or more balance metal ions (relatively low Si/Al ratios beta) effect separately. The synthesized silicalite-1 has the lowest SCO₂/CH₄ but has the most suitable orifices for methane adsorption and the highest SCH₄/N₂. In addition, the breakthrough data for CH₄/N₂ mixtures further indicates that silicalite-1 is more suitable for the CH₄ enrichment than the commercially used sorbents zeolite-5A and 13X. From the reproducibility of CH₄ and N₂ adsorption isotherms on silicalite-1, we can infer that which has the potential to be a commercial sorbent by the stable adsorption properties.