On the nanogate-opening pressures of copper-doped zeolitic imidazolate framework ZIF-8 for the adsorption of propane, propylene, isobutane, and n-butane
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In this study, a zeolitic imidazolate framework-8 (ZIF-8) and its copper-doped variants (Cu-doped ZIF-8) were synthesized using a rapid microwave technique. The products were characterized by XRD, NanoSEM, FTIR, Raman spectra, TGA, XPS, and EDX. The gas adsorption properties of samples were performed using C3 and C4 hydrocarbons including propane, propylene, isobutane, and n-butane gases at 25 °C. Both equilibrium adsorption and kinetics were studied. It was found that ZIF-8 and Cu-doped ZIF-8 samples open their nanogates (i.e., six-membered rings) at some threshold pressures when adsorbing different gases, which it is denotes later as the gate-opening pressure (p0). The p0 value for each ZIF toward each gas was evaluated by fitting equilibrium adsorption data against a modified version of the Langmuir adsorption isotherm model. It was observed that the value of p0 differs significantly for each gas utilized, and with different extents for ZIF samples. The overall mass transfer coefficient values of adsorption process were estimated. Therefore, it is possible that the distinct values of p0 afford a unique chance to separate and purify these gases at mass production, and the best-studied adsorbent to for this purpose was Cu30%/ZIF-8.
This publication was made possible by the NPRP Awards (NPRP 08-014-2-003 and NPRP-8-001-2-001) from the Qatar National Research Fund (a member of The Qatar Foundation). H.K.-J. acknowledges support from the National Science Foundation (CMMI-1561897). The statements made herein are solely the responsibility of the authors. Technical support from the Department of Chemical Engineering, the Central Laboratory Unit (CLU) and the Gas Processing Centre (GPC) at Qatar University is also acknowledged.
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Conflict of interest
The authors declare that they have no conflict of interest.
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