A Copper-Based Metal–Organic Framework for Selective Separation of C2 Hydrocarbons from Methane at Ambient Conditions: Experiment and Simulation
Sheikh M. S. Islam, Rashida Yasmeen, Gaurav Verma, Sammer M. Tekarli, Vladimir N. Nesterov, Shengqian Ma, Mohammad A. Omary
Abstract
C2 hydrocarbon separation from methane represents a technological challenge for natural gas upgrading. Herein, we report a new metal–organic framework, [Cu 2 L(DEF) 2 ]·2DEF ( UNT-14; H 4 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/CH 4 separation. Crystallographic data unravel an sql topology for UNT-14, whereby [Cu 2 (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 m 2 g –1 (vs 1868 m 2 g –1 from the crystallographic data). UNT-14a exhibits considerable C2 uptake capacity under ambient conditions vs CH 4 . 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 C 2 H n /CH 4 gas mixtures, attaining 31.1, 11.9, and 14.8 for equimolar mixtures of C 2 H 6 /CH 4, C 2 H 4 /CH 4, and C 2 H 2 /CH 4, respectively, manifesting efficient C2 hydrocarbon/CH 4 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.