Shaping of ZIF-8 and MIL-53(Al) adsorbents for CH4/N2 separation

Microporous materials, such as MOFs and ZIFs, have been proposed as adsorbents for many gas separation/purification applications. To be used in industry, their shaping is required. ZIF-8 (Basolite Z1200) and MIL-53(Al) (Basolite A100) were shaped employing the extrusion method. For that, two binders were used: alumina and carboxymethylcellulose (CMC). Loadings of 5, 10, and 15 %wt. of alumina were utilized to shape ZIF-8 and MIL-53(Al) into pellets. Additionally, pellets of ZIF-8 with 5 and 10 %wt. of CMC were also produced. The materials were characterized by SEM/EDS, N2 adsorption at 77 K, CO2 adsorption at 273 K, mercury intrusion porosimetry, and XRD to evaluate the effect of the shaping process on the materials. The shaping process does not result in significant alterations in the crystalline structure of the materials. Besides, as expected, in general, with the increase of the binder quantity the average pore diameter decreases along with the surface area of the materials. Furthermore, the mechanical strength of the material was analyzed through crush strength tests. In general, the increase of the binder amount in the pellets results in an improvement of the mechanical strength of the material. The adsorption equilibrium isotherms for CH4 and N2 were determined at 303 K up to 4 bar. Langmuir adsorption model was used to fit the experimental results. This study allows understanding the effect of shaping in the adsorption capacities of the materials. For both gases, the impact of shaping in the adsorption capacities is higher on the MIL-53(Al) materials than on ZIF-8 pellets. It also proves the extrusion method's potential to prepare structured materials to be used in CH4/N2 separation.