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 accurately regulate the affinity for different gas molecules, which will naturally favor certain gas molecule adsorption/removal from the mixed gases. 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 comparative high surface areas. Interestingly, under ambient conditions, FZU-98 adsorbs much more C2H2 than C2H4, and its selectivity for C2H2/C2H4 can reach up to 4.92, exceeding its analogue COF-DFB and most of the reported COFs applied for C2H2/C2H4 separation while maintained comparative high gas capacity. Column breakthrough experiments further validated its ability for separation C2H4 from C2H2/C2H4 mixtures. Moreover, the distinct binding mechanism suggested by theoretical calculations effectively confirmed the optimized nitrogen-rich sites facilitate selective C2H2/C2H4 separation.