(160c) Mixed-Matrix Membranes Containing Engineered Nanoporous Materials for Biogas Purification

Biogas produced in anaerobic digestion process has been considered as a renewable energy source. For the recovery and the purification of biogas, various processes for CO₂ separation including amine-scrubbing and adsorption have been employed. Although membrane-based gas separation is an ideal platform for the biogas recovery/purification, the applications have been limited by the unsatisfactory performance of commercial polymeric membranes under the biogas separation conditions such as low CO₂ partial pressure. Thus, improving the performance of current polymeric membranes, which are inexpensive and mechanically stable, may facilitate the application of membrane technology in large-scale biogas upgrading processes. To this end, various porous materials that can selectively transport CO₂ can be incorporated into polymer matrices to design CO₂-selective mixed-matrix membranes.

Among various porous materials, metal-organic frameworks which comprise metal center and organic linkers to form three-dimensional porous structure have attracted vast research interests in the recent years as potential fillers for mixed-matrix membrane fabrication owing to their large pore volumes and tunable functionalities. In this work, a submicron-sized Zn(pyrz)₂(SiF)₆ metal-organic framework crystal possessing both an optimum pore size for selective CO₂ permeation and a strong affinity for CO₂ molecule was synthesized and incorporated into various polymer membranes to design mixed-matrix membranes for biogas upgrading. CO₂/CH₄ mixture gas permeation tests revealed that the separation properties of mixed-matrix membranes, especially selectivities, were significantly improved compared to those of pure polymeric membrane owing to the selective CO₂ uptake and transport in the metal-organic framework crystals.

Recently, our research group have developed hierarchical mesoporous Ca-A zeolites with amine-appended mesoporous domain for application in post-combustion CO₂ capture. Owing to the contributions of both the active sites in Ca-A zeolites and the amine groups in mesoporous surfaces, the material exhibited an excellent CO₂ uptake property even at low CO₂ partial pressure. Moving forward, amine-appended hierarchical Ca-A was employed as a filler for mixed-matrix membranes to improve CO₂ selectivity. Gas permeation testing revealed that the amine-appended hierarchical Ca-A is highly efficient in enhancing CO₂/CH₄ selectivity of polymeric membranes.

References

1. H. Gong, T. H. Nguyen, R. Wang, T. H. Bae, Separations of binary mixtures of CO₂/CH₄ and CO₂/N₂ with mixed matrix membranes containing Zn(pyrz)₂(SiF)₆ metal-organic framework, J. Membr. Sci. 2015, 495, 169-175

2. T. H. Nguyen, S. Kim, M. Yoon, T. H. Bae, Hierarchical LTA zeolites with amine-functionalized mesoporous domain for carbon dioxide capture, ChemSusChem, 2016, DOI:10.1002/cssc.201600004

3. T. H. Nguyen, H. Gong, S. S. Lee, T. H. Bae, Amine-appended hierarchical Ca-A zeolite for enhancing CO₂/CH₄ selectivity of mixed-matrix membranes, submitted