Tuning the Pore Surface of an Ultramicroporous Framework for Enhanced Methane and Acetylene Purification Performance
Haipeng Li, Zhao-Di Dou, Ying Wang, Ying Xue, Yong Peng Li, Man‐Cheng Hu, Shu-Ni Li, Yu‐Cheng Jiang, Quan‐Guo Zhai
Abstract
Both methane (CH4) and acetylene (C2H2) are important energy source and raw chemicals in many industrial processes. The development of an energy-efficient and environmentally friendly separation and purification strategy for CH4 and C2H2 is necessary. Ultramicroporous metal–organic framework (MOF) materials have shown great success in the separation and purification of small-molecule gases. Herein, the synergy effect of tritopic polytetrazolate and ditopic terephthalate ligands successfully generates a series of isoreticular ultramicroporous cadmium tetrazolate–carboxylate MOF materials (SNNU-13–16) with excellent CH4 and C2H2 purification performance. Except for the uncoordinated tetrazolate N atoms serving as Lewis base sites, the pore size and pore surface of MOFs are systematically engineered by regulating dicarboxylic acid ligands varying from OH-BDC (SNNU-13) to Br-BDC (SNNU-14) to NH2-BDC (SNNU-15) to 1,4-NDC (SNNU-16). Benefiting from the ultramicroporous character (3.8–5.9 Å), rich Lewis base N sites, and tunable pore environments, all of these ultramicroporous MOFs exhibit a prominent separation capacity for carbon dioxide (CO2) or C2 hydrocarbons from CH4 and C2H2. Remarkably, SNNU-16 built by 1,4-NDC shows the highest ideal adsorbed solution theory CO2/CH4, ethylene (C2H4)/CH4, and C2H2/CH4 separation selectivity values, which are higher than those of most famous MOFs with or without open metal sites. Dynamic breakthrough experiments show that SNNU-16 can also efficiently separate the C2H2/CO2 mixtures with a gas flow rate of 4 mL min–1 under 1 bar and 298 K. The breakthrough time (18 min g–1) surpasses most best-gas-separation MOFs and nearly all other metal azolate–carboxylate MOF materials under the same conditions. The above prominently CH4 and C2H2 purification abilities of SNNU-13–16 materials were further confirmed by the Grand Canonical Monte Carlo (GCMC) simulations.