Enhancing CH4/N2 separation performance within aluminum-based Metal-Organic Frameworks: Influence of the pore structure and linker polarity

Efficient CH 4 /N 2 separation is necessitated for obtaining purified methane from natural gas. Aluminum-based metal–organic frameworks (Al-MOFs) have potential for industrial separation applications due to their structure-tunable, low-cost, and scalable features. Intrigued by the impressive selectivity of a recently reported Al-MOF (Al-CDC) toward CH 4 over N 2 , we herein further study the potential of Al-MOFs as adsorbent for CH 4 /N 2 separation, mainly considering the effects of pore geometry and linker polarity. Utilization of two bent ligands and two linear ligands with different polarity afforded two one-dimensional square-shaped Al-MOFs i.e., CAU-10-H, MIL-160, and two rhombic-shaped counterparts i.e., Al-Fumarate (Al-Fum), MIL-53(Al)), respectively. Afterward, pure CH 4 and N 2 adsorption experiments were conducted at 273–313 K for assessing the CH 4 /N 2 separation performance. The results indicated that all the Al-MOFs exhibited superior affinity toward CH 4 over N 2 , and the CH 4 uptake followed the sequence of Al-Fum > CAU-10-H > MIL-53(Al) > MIL-160. Exhilaratingly, Al-Fum exhibited unprecedented CH 4 /N 2 selectivity (17.2) and high CH 4 uptake at 273 K and 1.0 bar. The mechanism underlying the disparity of Al-MOFs affinity toward CH 4 was deciphered via theoretical simulation, suggesting that the synergetic effects of accessibility of strong affinity sites (μ 2 -OH) on AlO 6 chains and polar pore surface induced by varying linkers highly promoted the CH 4 uptake. Furthermore, the results of cyclic adsorption–desorption experiments and binary breakthrough tests validated the feasibility of Al-Fum for practical application.