Self-adjusted MOF pore environment through realigning adsorption orientation of guests for boosting separation of gaseous C1-C3 alkanes

Effective methane separation of gaseous C2-C3 alkanes from natural gas is crucial yet challenging industrial process. Herein, we report the impressive MOF ( 1a ) with rigid topology and ultramicroporous characters that can realize effective methane purification. Adsorption isotherms on 1a show the differential adsorption capacity, with values of 22.7 cm 3  g −1 for CH 4 , 69.1 cm 3  g −1 for C 2 H 6 and 83.6 cm 3  g −1 for C 3 H 8 at 298 K and 1 bar. IAST analysis reveals the calculated C 3 H 8 /CH 4 selectivity of 1a is 1228/1776 with the molar ratio of 50/50 and 10/90 at zero coverage, respectively. The higher selectivity is also demonstrated by C 2 H 6 /CH 4 mixtures. Breakthrough tests reveal the effective purification of CH 4 /C 2 H 6 /C 3 H 8 (85/10/5, v/v/v) mixtures, achieving >99.95 % CH 4 purity at a productivity of 88.7 L kg −1 . Further, scalable 1a with customized grain-size (3.4 g) also reveal the breakthrough performance under higher gas flux (30 sccm or 1.50 × 10 −3  kg h −1 ), indicative of great potential for industrial methane upgrading. Experimental and theoretical calculations show that the pore polarity of 1a can be effectively modulated upon the adsorption of C 3 H 8 molecules with abundant methyl groups without post-modification of MOF structure or introducing heterogeneous species (such as metals or ligands). This guests-induced self-regulatory strategy and decent adsorption orientation further enhances the gas diffusion and continuous adsorption of subsequent C 3 H 8 molecules. Such a strategy affords a novel perspective in adjusting pore polarity and enables methane upgrading from natural gas mixtures.