467239 Incorporation of 1-Butyl-3-Methylimidazolium Hexafluorophosphate into ZIF-8: Elucidation of Interactions and Their Consequences on Gas Separation Performance

Thursday, November 17, 2016: 9:58 AM
Union Square 17 & 18 (Hilton San Francisco Union Square)
Fatma Pelin Kinik1, Seda Keskin1 and Alper Uzun2, (1)Chemical and Biological Engineering, Koç University, Istanbul, Turkey, (2)Chemical and Biological Engineering, Koc University, Istanbul, Turkey

 Incorporation of 1-butyl-3-methylimidazolium hexafluorophosphate into ZIF-8: Elucidation of Interactions and Their Consequences on Gas Separation Performance

Fatma Pelin Kinik, Seda Keskin,* and Alper Uzun*

Chemical and Biological Engineering Department, Koç University, Istanbul 34450, Turkey

Metal organic frameworks (MOFs) have been popular recently in adsorption-based gas separation applications due to their configurable pores, large surface areas, robust framework structures and high chemical and thermal stabilities.[1] Lately, ionic liquids (ILs) have been used to enhance the gas separation performances of MOFs. ILs are liquid salts at room temperature which consist of organic cations and inorganic or organic anions.[2] Because of their favorable physical and chemical properties such as non-flammability, negligible volatility, high thermal stability and remarkable gas solubility (especially towards CO2), ILs have been used in gas adsorption and separation processes.[3] In this work, an IL was used to improve gas adsorption and separation properties of a MOF. The influence of IL confinement into MOF structure was examined for CO2/CH4, CO2/N2 and CH4/N2 gas separations. ZIF-8 (2-methylimidazole zinc salt) was selected as the MOF as it is a thermally and chemically stable zeolite-type material with large pore size of 11.6 Å and small pore size of 3.4 Å.[4] Because of having high surface area, significant porosity, water resistance and commercial availability, ZIF-8 has been commonly used in gas separation applications.[5] As IL, 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], was selected because of its hydrophobic nature, low cost, and notable affinity for CO2.[6]

Crystalline structures, thermal stabilities and interionic interactions were investigated by combining various characterization techniques. XRD and SEM results showed that the crystalline structure of the MOF is preserved upon the incorporation of IL. Moreover, XRF and BET measurements indicated that impregnation of the IL was successfully achieved at an IL loading of 24 wt.%. TGA and FTIR results proved that there is an interaction between IL and MOF. Adsorption measurements of CO2, CH4, and N2 gases in ZIF-8 and [BMIM][PF6]/ZIF-8 were performed using the volumetric method at room temperature up to 35 bar and ideal selectivities were calculated for CO2/CH4, CO2/N2, and CH4/N2 separations. It was shown that the CO2 selectivities of IL/MOF samples at low pressures significantly increased compared to the pristine ZIF-8, while CH4/N2 selectivity of IL/MOF samples remained lower than the one of pristine ZIF-8. There is a considerable improvement in the CO2/N2 selectivity of IL-incorporated MOF, which is almost three times of pristine ZIF-8 up to 0.3 bar and two times of pristine ZIF-8 up to 1 bar. Also IL-incorporated MOF has approximately two times more CO2/CH4 selectivity than pristine ZIF-8 up to 1 bar. As a conclusion, IL-modified ZIF-8 is a promising material for gas separation applications, especially for CO2 capturing processes such as natural gas sweetening and removing COfrom power plant flue gas. Tunable physicochemical properties of ILs and MOFs offer great potential for optimizing these structures for better gas separation performance.

Acknowledgement

This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under 1001-Scientific and Technological Research Projects Funding Program (project number: 114R093) and by Koç University Seed Fund Program. Financial support provided by the KUTEM (Koç University TUPRAS Energy Center) is gratefully acknowledged. S.K. acknowledges TUBA-GEBIP and A.U. acknowledges the support by the Science Academy of Turkey under the BAGEP Award Program. Authors thank Koç University Surface Science and Technology Center (KUYTAM) for providing help with the sample characterization.

*Corresponding authors: skeskin@ku.edu.tr and auzun@ku.edu.tr

References:

[1] Li, J.-R.; Kuppler, R. J.; Zhou, H.-C., Selective Gas Adsorption and Separation in Metal-Organic Frameworks. Chemical Society Reviews 2009, 38, 1477-1504.

[2] Marsh, K.; Boxall, J.; Lichtenthaler, R., Room Temperature Ionic Liquids and Their Mixtures—a Review. Fluid Phase Equilibria 2004, 219, 93-98.

[3] Hasib-ur-Rahman, M.; Siaj, M.; Larachi, F., Ionic Liquids for CO2 Capture—Development and Progress. Chemical Engineering and Processing: Process Intensification 2010, 49, 313-322.

[4] M. Zhu; Venna, S. R.; Jasinski, J. B.; Carreon, M. A., Room-Temperature Synthesis of ZIF-8: The Coexistence of Zno Nanoneedles. Chemistry of Materials 2011, 23, 3590-3592.

[5] Venna, S. R.; Carreon, M. A., Highly Permeable Zeolite Imidazolate Framework-8 Membranes for CO2/CH4 Separation. Journal of the American Chemical Society 2009, 132, 76-78.

[6] Chen, Y.; Hu, Z.; Gupta, K. M.; Jiang, J., Ionic Liquid/Metal–Organic Framework Composite for CO2 Capture: A Computational Investigation. The Journal of Physical Chemistry C 2011, 115, 21736-21742.


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