Theoretical study on the adsorptive separation of ethane/ethylene in DUT-8 metal-organic frameworks

Abstract

Separation of C2H6/C2H4 mixture is still a challenging issue due to their similar physicochemical properties. Among several methods, an adsorbent-based gas separation has been considered as an alternative to replace inefficient separation process. Rigid metal-organic framework DUT-8(M) (M = Cu and Ni), which consists of paddle-wheel metal node and 2,6-naphthalene dicarboxylic acid (NDCA) linkers, is good candidate as C2H6-selective adsorbent. In this study, to understand the gas adsorption characteristic of the rigid DUT-8(M), we applied grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations. GCMC simulations provided well-fitted curves of C2H6/C2H4 adsorption isotherms with experimental results up to 1 bar at 273 K. The adsorption occurred predominantly near the corners of the square-shaped pore of DUT-8(M), where the gases could interact with two adjacent NDCAs. Furthermore, binding energy of C2H6 obtained from DFT calculation was about 4 kJ/mol higher than that of C2H4 because of the C–H‧‧‧π interaction near the linkers. Through this study, it was proven that rigid DUT-8 is the effective adsorbent for C2H6/C2H4 separation.