(608a) Determining CO2/H2s and CO2/CH4 Binary Adsorption Selectivities in Metal-Organic Frameworks for Biogas Purification
AIChE Annual Meeting
Thursday, November 17, 2022 - 8:00am to 8:25am
Biogas is a promising alternative to natural gas as the global energy sources shift from fossil fuels to renewables. Biogas contains mainly CH4 (35-70%), CO2 (15-60%), and N2 (15-50%), with trace impurities such as NH3, H2O, and H2S. To reduce Greenhouse Gas release from biogas and prevent pipeline corrosion and catalyst poisoning in the transport and downstream process of biogas, removal of H2S and CO2 is critical. Besides the traditional acid gas removal methods involving aqueous amine scrubbing, less energy-intensive adsorption methods using microporous materials such as zeolites, metal-organic frameworks (MOFs), and porous organic cages (POCs) are being developed. In particular, MOFs have received much attention as they exhibit high CO2 uptake and have tunable selectivity. Much research has focused on measuring single-component adsorption isotherms and predicting the mixture selectivity using the Ideal Adsorbed Solution Theory (IAST). As the functional groups and unsaturated metal sites often interact with quadrupolar CO2 molecules more strongly than CH4 or N2, IAST predictions may not capture the nonideal adsorption behavior.1 Mixture containing H2S and CO2 poses more challenges in binary adsorption selectivity prediction due to the competitive sorption of H2S and CO2 to active sorption sites.2 Thus, understanding the mixture adsorption performance is valuable in adsorption process design and adsorbent selection. This work aims to measure the binary adsorption uptakes of CO2/H2S and CO2/CH4 in MIL-125-NH2(Ti), amine-appended Mg2(dobpdc), MIL-101(Cr), and MOF-74(Mg, Ni). A zero-length column methodis used, where a small amount of MOF is first saturated with the gas mixture of interest. Then the mixture gas is desorbed using an inert gas under equilibrium conditions.3 A mass spectrometer is used to measure the concentration of the desorption effluent gas. The experimental mixture gas results are compared to the IAST predictions, and the pre and post-adsorption MOFs are characterized by SEM, N2 physisorption, PXRD, and XPS to understand the competitive adsorption behavior and H2S stability in these MOFs.
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- Joshi, J. N.; Zhu, G.; Lee, J. J.; Carter, E. A.; Jones, C. W.; Lively, R. P.; Walton, K. S., Probing Metal-Organic Framework Design for Adsorptive Natural Gas Purification. Langmuir 2018, 34 (29), 8443-8450.
- Brandani, F.; Ruthven, D., Measurement of adsorption equilibria by the zero length column (ZLC) technique part 2: Binary systems. Industrial & Engineering Chemistry Research 2003, 42 (7), 1462-1469.