Integration of multi-affinity sites into confined channels allows a bismuth-based metal-organic framework to sequestrate multi-component impurities from methane

One-step adsorptive purification of methane (CH4) from the multi-component mixtures containing CO2, acetylene (C2H2) and ethane (C2H6) is of great significance but challenging as distinct mechanisms are involved in the uptake of various gas molecules. Herein, a bismuth-based metal-organic framework (SU-100) bearing multiaffinity sites is applied for simultaneously sequestrating these impurities from CH4. The intrinsic unsaturated Bi (III) sites endow SU-100 with specific recognition of CO2 and C2H2 via complexation with the open metal sites, while the dense distribution of carboxylate and biphenyl moieties in the nano-channels provides strong affinity for C2H6 as well as additional affinity sites for C2H2. Profiting from the exposed functional sites and suitable pore size, SU-100 exhibits decent ideal adsorbed solution theory (IAST) selectivity (CO2/CH4, C2H2/CH4 and C2H6/ CH4) under ambient conditions. Moreover, the adsorption capacity remains unchanged for 10 consecutive cycles. The practical CH4 purification performance is fully demonstrated by dynamic breakthroughs of various binary, ternary (CO2/C2H2/CH4), and quaternary (CO2/C2H2/C2H6/CH4) mixtures, in which more than 2.44 mol kg-1 of pure CH4 can be produced from typical quaternary mixtures. Based on theoretical calculation and in-situ infrared analysis, synergistic effect of multiple interactions (pi complexation, hydrogen bonding and CH- pi interactions) accounts for simultaneous adsorption of multiple gases from CH4. These results underpin highly selective capture of a range of gas mixtures that are relevant to one-step purification of natural gas.

Automated summary

One-step adsorptive purification of methane from multi-component mixtures is significant but challenging. A bismuth-based metal-organic framework (SU-100) with multiaffinity is utilized to simultaneously remove CO2, C2H2, and C2H6 from CH4. The framework exhibits good selectivity under ambient conditions and maintains stable adsorption capacity. The results demonstrate the potential for highly selective capture of gas mixtures in the purification of natural gas.