Adsorption equilibrium of carbon dioxide and nitrogen on the MIL-53(Al) metal organic framework

The single-component adsorption equilibria of carbon dioxide (CO2) and nitrogen (N2) on a commercial sample of MIL-53(Al) metal organic framework were measured over a pressure range of 0-34 bar at 303 K, 323 K, and 353 K, using a magnetic suspension microbalance. The adsorption equilibria of both gases are characterized by type I isotherms that do not exhibit the guest-induced transition between MIL-53(Al)'s narrow-pore (np) and large-pore (lp) structures that has been observed on some MIL-53(Al) samples upon CO2 adsorption at the temperatures of this study. The observed CO2 loadings at high pressure are consistent with a np-stabilized MIL-53(Al) form that possesses no visible breathing behavior. The adsorption measurements show that CO2 is preferentially adsorbed over N2, indicating that MIL-53(Al) can be potentially employed in adsorption-based separation processes for environmental applications, such as carbon capture from flue gases emitted by fossil-fueled power stations. The Sips and Toth isotherm models were successfully fitted to the experimental adsorption data and the corresponding heats of adsorption determined from the isotherm models. The adsorption potential theory was also employed to correlate the CO2 and N2 adsorption data, as well as previously determined methane adsorption data on the same adsorbent. This approach successfully collapses the adsorption equilibrium data into a single temperature-independent characteristic curve.