Polarization enhanced CH4/N2 separation in bromine functionalized ZIF-62 based mixed-matrix membranes

Owing to the similarities in polarity, kinetic size, and boiling point, CH4 and N2 separation remains difficult and energy-consuming. However, the difference in polarizability offers an opportunity for boosting the separation by differentiating their interactions with the metal-organic framework (MOF). Herein, bromine (Br) functional group is rationally introduced into ZIF-62 to strengthen CH4/N2 separation through the polarization effect. The anisotropic charge distribution on Br atom can induce electron cloud deformation of gas molecules, especially CH4 molecules with higher polarizability, thus generating differentiated interactions. As a result, ZIF-62-Br exhibits a 69.7% increase in CH4 adsorption capacity and obviously improved selectivity compared with the ZIF-62, and embedding ZIF-62-Br in the polyethyleneimine (PEI) matrix endows the obtained mixed-matrix membranes (MMMs) with good CH4/N2 separation performance (CH4 permeance of 3157 GPU and CH4/N2 ideal selectivity of 7.6 for single gas permeations, and CH4 permeance of 2235 GPU and CH4/N2 selectivity of 4.2 for mixed gas tests). The good separation performance and stability suggest that MMMs fabricated with ZIF-62-Br in this work can be a promising candidate for facilitating the exploration of CH4/N2 membrane separation.