A cooperative adsorbent for the switch-like capture of carbon dioxide from crude natural gas

Natural gas constitutes a growing share of global primary energy due to its abundant supply and lower CO₂ emission intensity compared to coal. For many natural gas reserves, CO₂ contamination must be removed at the wellhead to meet pipeline specifications. Here, we demonstrate the potential of the diamine-appended metal-organic framework ee-2-Mg₂(dobpdc) (ee-2 = N,N-diethylethylenediamine; dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) as a next-generation CO₂ capture material for high-pressure natural gas purification. Owing to a cooperative adsorption mechanism involving formation of ammonium carbamate chains, ee-2-Mg₂(dobpdc) can be readily regenerated with a minimal change in temperature or pressure and maintains its CO₂ capacity in the presence of water. Moreover, breakthrough experiments reveal that water enhances the CO₂ capture performance of ee-2-Mg₂(dobpdc) by eliminating "slip" of CO₂ before full breakthrough. Spectroscopic characterization and multicomponent adsorption isobars suggest that the enhanced performance under humid conditions arises from preferential stabilization of the CO₂-inserted phase in the presence of water. The favorable performance of ee-2-Mg₂(dobpdc) is further demonstrated through comparison with a benchmark material for this separation, zeolite 13X, as well as extended pressure cycling. Overall, these results support continued development of ee-2-Mg₂(dobpdc) as a promising adsorbent for natural gas purification.