In summary, we have demonstrated that a commercially available tetramethylpyrazine monomer can be used to create a new orthorhombic olefin-linked COF via the melt polymerization method. Notably, kilogram-level COF was firstly fabricated using an autoclave by one-pot reaction at a cost of <75$/kg, which surpassed the most reported COFs and promoted the industrial application of olefin-linked COFs. This COF possessed the smallest eclipsed pore (~0.7 nm) among all orthorhombic 2D COFs, which afforded unique selective adsorption of C 2 H 2 and C 2 H 6 over C 2 H 4 . Thereby, NKCOF-62 can be applied to purify C 2 H 4 not only from C 2 H 2 /C 2 H 4 and C 2 H 6 /C 2 H 4 binary mixture, but also from challenging C 2 H 2 /C 2 H 4 /C 2 H 6 ternary mixture. Furthermore, this case is the first time that a single COF is used to directly produce polymer grade C 2 H 4 in one step from the ternary C2 Hydrocarbon gas mixture. Its separation performance is comparable to the top-performing MOFs, but with far lower cost. This work not only provides a new robust COF-based adsorbent for one-step C 2 H 4 purification but also extensively facilitates the research of emerging cheap and efficient COF adsorbents for important industrial separations.