Amine-functionalized MIL-53(Al) for CO2/N2 separation: Effect of textural properties

Abstract

A high-quality amine-functionalized metal organic framework, amino-MIL-53(Al), was synthesized by a solvothermal method in DMF and evaluated as an adsorbent for CO2/N2 separation both at ambient and high-pressure conditions. The textural properties of the amino-MIL-53(Al) gradually improved as the synthesis time was extended, and the optimized sample showed excellent crystallinity accompanied by a high surface area (937m2g−1) and large pore volume (0.53cm3g−1), both of which being significant improvements over the literature values reported by Kapteijn et al. (675m2g−1 and 0.22cm3g−1). The amino-MIL-53(Al) framework exhibited the typical breathing behavior of both CO2 and N2 during high-pressure gas adsorption measurements. This characteristic was affected not only by the adsorption temperatures but also by the textural properties of the adsorbents. The amino-MIL-53(Al) framework achieved both high CO2 sorption capacities (82 and 302mgg−1 at 0.1 and 3.0MPa, respectively) and high selectivity against N2 (>30 at 2.0MPa) at 298K due to the open-metal sites and free-standing amino groups. The heat of adsorption for CO2 near zero coverage by amino-MIL 53(Al) was ca. 60kJmol−1 compared to ca. 50kJmol−1 by MIL-53 (Al), providing evidence of the contribution of the amino groups towards CO2 adsorption. Repeated pressure swing adsorption–desorption cycles six times between 0.5 and 2.0MPa both at 298 and 323K showed no deterioration in the CO2 adsorption capacity. Reversible adsorbent regeneration was also maintained for a total duration of 240min.