Pore environment engineering in metal-organic frameworks for efficient ethane/ethylene separation

Selective adsorption of trace amounts of C2H6 from bulk C2H4 is a significantly important and extremely challenging task in industry, which requires an adsorbent with specific pore properties. Herein, we describe a strategy for adjusting the pore environment of metal-organic frameworks (MOFs) by introducing different amounts of methyl groups in the channel to enhance the guest-host interaction between C2H6 and the framework. To prove this concept, 2,3,5,6-tetramethylterephthalic acid (TMBDC) was deliberately added to a microporous MOF, Ni(BDC)(DABCO)(0.5), affording a series of mixed-ligand materials, Ni(BDC)(1-x)(TMBDC)(x)(DABCO)(0.5) (x = 0, 0.2, 0.45, 0.71, 1), having different pore environments. Significantly, these mixed-ligand materials demonstrated improved performance in terms of the adsorption capacity of C2H6 and C2H4 with an unprecedented C2H6 uptake of 2.21 mmol g(-1) for Ni(TMBDC)(DABCO)(0.5) at 0.0625 bar and 298 K. With the best theoretical C2H6/C2H(4) selectivity predicted by IAST, Ni(TMBDC)(DABCO)(0.5) exhibited effective separation of C2H6/C2H(4) (1/15, v/v) and great recyclability in five consecutive adsorption/desorption cycles throughout the breakthrough experiment.