A Copper-Based Metal-Organic Framework for Selective Separation of C2 Hydrocarbons from Methane at Ambient Conditions: Experiment and Simulation.

C2 hydrocarbon separation from methane represents a technological challenge for natural gas upgrading. Herein, we report a new metal-organic framework, [Cu2 L(DEF)2 ]·2DEF ( UNT-14 ; H4 L = 4,4',4″,4‴-((1 E ,1' E ,1″ E ,1‴ E )-benzene-1,2,4,5-tetrayltetrakis(ethene-2,1-diyl))tetrabenzoic acid; DEF = N , N -diethylformamide; UNT = University of North Texas). The linker design will potentially increase the surface area and adsorption energy owing to π(hydrocarbon)-π(linker)/M interactions, hence increasing C2 hydrocarbon/CH4 separation. Crystallographic data unravel an sql topology for UNT-14 , whereby [Cu2 (COO)4 ]···[L]4- paddle-wheel units afford two-dimensional porous sheets. Activated UNT-14a exhibits moderate porosity with an experimental Brunauer-Emmett-Teller (BET) surface area of 480 m2 g-1 (vs 1868 m2 g-1 from the crystallographic data). UNT-14a exhibits considerable C2 uptake capacity under ambient conditions vs CH4 . GCMC simulations reveal higher isosteric heats of adsorption ( Q st ) and Henry's coefficients ( K H ) for UNT-14a vs related literature MOFs. Ideal adsorbed solution theory yields favorable adsorption selectivity of UNT-14a for equimolar C2 H n /CH4 gas mixtures, attaining 31.1, 11.9, and 14.8 for equimolar mixtures of C2 H6 /CH4 , C2 H4 /CH4 , and C2 H2 /CH4 , respectively, manifesting efficient C2 hydrocarbon/CH4 separation. The highest C2 uptake and Q st being for ethane are also desirable technologically; it is attributed to the greatest number of "agostic" or other dispersion C-H bond interactions (6) vs 4/2/4 for ethylene/acetylene/methane.