A vinylene-linked covalent organic framework with optimized functional sites for efficient C2H2/C2H4 separation

Abstract

The high energy consumption, low selectivity, and high pollution of traditional separation techniques have spurred the development of more selective and efficient methods to purify C₂H₄. Owing to their tunable pore size and environment, covalent organic frameworks (COFs) can precisely regulate the affinity for different gas molecules, which naturally favors selective adsorption/removal of specific gas molecules from gas mixtures. Herein, a new nitrogen-rich vinylene-linked COF labeled as FZU-98 was constructed via aldol condensation between 4,4′,6,6′-tetramethyl-2,2′-bipyrimidine (TMBM) and 1,4-diformylbenzene (DFB). The obtained COF exhibits excellent thermal/chemical stability and a relatively high surface area. Interestingly, under ambient conditions, FZU-98 adsorbs much more C₂H₂ than C₂H₄, and its selectivity for C₂H₂/C₂H₄ can reach up to 4.9, exceeding that of its analogue COF-DFB and most of the reported COFs applied for C₂H₂/C₂H₄ separation while maintaining relatively high gas capacity. Column breakthrough experiments further validated its ability for separation of C₂H₄ from C₂H₂/C₂H₄ mixtures. Moreover, the distinct binding mechanism suggested by theoretical calculations effectively confirmed that the optimized nitrogen-rich sites facilitate selective C₂H₂/C₂H₄ separation.