Selective Capture of Carbon Dioxide from Hydrocarbons Using a Metal-Organic Framework: Relevance to the Purification of Natural Gas and Acetylene

Efficient and sustainable methods for carbon dioxide (CO₂) capture are highly sought after. Mature technologies involve chemical reactions that absorb CO_2, but they have many drawbacks. Energy-efficient alternatives may be realized by porous physisorbents with void spaces that are complementary in size and electrostatic potential to molecular CO₂. Here, we present a robust, recyclable and inexpensive adsorbent termed MUF-16 (MUF = Massey University Framework). This metal-organic framework captures CO₂ with a high affinity in its one-dimensional channels. The position of the CO₂ molecules sequestered in the framework pores, as determined by X-ray crystallography, illustrate how complementary noncovalent interactions envelop the CO₂ while repelling other guest molecules. The low affinity of the MUF-16 pores for these competing gases underpins new benchmarks for the adsorption of CO₂ over methane, acetylene, ethylene, ethane, propylene and propane. IAST calculations show that for 50/50 mixtures at 293 K and 1 bar, the CO₂/CH₄ selectivity is 6690 and the CO₂/C₂H₂ selectivity is 510, for example. Breakthrough gas separations under dynamic conditions benefit from short time lags in the elution of the weakly-adsorbed component to deliver high-purity hydrocarbon products. Ultimately, MUF-16 may be applicable to the removal of CO₂ from sources such as natural gas and chemical feedstocks.