Methane Adsorption on Zeolitic Imidazolate Framework -8 (ZIF-8)

Zeolitic Imidazolate frameworks (ZIFs) are porous Metal Organic Framework materials that have zeolite-like structures. ZIF -8 has shown structural transition when adsorbing gas molecules, this leads to increment in loading. This has been previously observed with N₂, CO, O₂ and Xe adsorption. Adsorption studies of energy related gasses are great significant to the petroleum and automotive industries. Among those gasses methane is a good alternative to petroleum based fuels. We present the results of an experimental study of methane sorption in ZIF-8. We measured isotherms at five different temperatures between ~ 85 K and 107 K. We have observed three sub-steps in each of the isotherms. The intermediate sub-step had not been observed experimentally in previous studies of this system. We measured a sharp increase in the equilibration times at loadings corresponding to the intermediate sub-step in the isotherms. We have explored the isosteric heat of adsorption, and its dependence on sorbent loading, for this system.