Metal organic frameworks (MOFs) are known for its structural flexibility and excellent gas sorption selectivity which have been shown great potential for gas sensing, separation, and storage. Zeolitic imidazolate framework-95 (ZIF-95), a sub-category of MOF, exhibits selective adsorption of methane. Methane emission from municipal solid waste (MSW) landfills becomes an opportunity to use methane as an alternative fuel source. One of the major challenges in MSW controlling process is to purify methane from landfill gas (LFG) which is a mixture of CH4 (~55%), CO2 (~45%), and a small amount of N2, H2O, H2S (1%). In this study, we compared two types of hybrid porous materials, commercial Zeolite 4A and ZIF-95, toward selective methane adsorption. Both materials have structures with a pore aperture of 4 Å. However, Zeolite 4A has a rigid structure, whereas the pore size of ZIF-95 is expandable. Much of the work to this point has focused on the structural flexibility effect on selective gas adsorption. The crystal structures and chemical compositions of both materials were analysed by X-ray powder diffraction (XRD) and attenuated total reflectance infrared spectroscopy (ATR-IR). We studied the single gas isotherms of CO2, CH4, and N2 on commercial Zeolite 4A and ZIF-95 at 273 K and 298 K. The gas separation selectivity of CH4 /CO2 and CH4 /N2 were calculated based on the single gas isotherm results. By comparing to the adsorption of methane to that of CO2 and N2, this work reveals that little methane enters Zeolite 4A while a small amount of methane occupies the ZIF-95 pores with other gas molecules. Our results indicated that ZIF-95 is flexible, but the size-selection rule still holds true for an open framework aperture towards guest molecules with different sizes. We believe that our work will increase the understanding of gas interactions with flexible MOFs, and further benefit the studies of methane purification by porous solid materials.

Comparison of commercial zeolite 4a and zif-95 on separation of methane from carbon dioxide and nitrogen

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.