Improved CH4/N2 Separation Performance of Zirconium-Based Metal-Organic Framework By Introducing Various Functional Groups

Shale gas, low-grade natural gas, landfill gas, and industrial by-product gas contain considerable amounts of CH₄. However, in order to utilize CH₄ as fuel, various impurities such as CO₂, SOx, H₂O, and N₂ should be removed. Most impurities can be easily removed by existing techniques, but N₂ is very hard to be removed due to its very similar physical and chemical properties to CH₄. Cryogenic distillation has been used for the separation of CH₄/N₂ mixtures, but it is costly and energy intensive. Therefore, adsorptive CH₄/N₂ separation has been studied as a cost- and energy-effective alternative.

Metal-organic frameworks (MOFs) have been considered as potential adsorbents for various applications due to their large surface areas, high porosities, and well-defined pore sizes. In this study, we developed MOF-based adsorbents with excellent CH₄/N₂ separation performance through the introduction of various functional groups into a zirconium-based MOF with high hydrothermal stability. In addition, CH₄ adsorption mechanism was identified through grand canonical Monte Carlo (GCMC) and density functional theory (DFT) calculations. Moreover, for the best candidate material, CH₄/N₂ separation under dynamic mixture flow conditions and cyclic CH₄ adsorption-desorption for 15 cycles were performed to check its potential for pressure swing adsorption (PSA) process.

Acknowledgments

We would like to acknowledge the “Next Generation Carbon Upcycling Project” (Project No.2017M1A2A2043449) through the National Research Foundation (NRF) funded by the Ministry of Science and ICT, Republic of Korea.