(594c) Enhanced SF6 adsorption Kinetics By Hierarchically Structured Nanoporous Materials

Research on greenhouse gas capture have been extensively conducted in view of the rising concerns of global warming phenomena. Nonetheless, sulfur hexafluoride (SF₆), which is commonly incorporated in metal-working industries and electronic sectors possess much higher global warming potential (GWP) and atmospheric lifetime than carbon dioxide (CO₂), a common greenhouse gas. Thus, recovery of SF₆ is necessary to prevent strong release of this gas to the atmosphere. Conventionally, liquefaction process which had been utilized industrially to remove SF₆ are considerably energy intensive due to low SF₆ content in the feed (typically 10%, with N₂ as the balance). Therefore, adsorptive-based separation which uses zeolites and metal-organic frameworks displays its promising behavior in overcoming the limitation. However, detailed studies and analyses are required so as to assure its practicability in industrial process.

In this study, HKUST-1 which possess coordinatively unsaturated open metal sites was conducted for its potential application in SF₆/N₂ separation. It was observed that the creation of hierarchically-structured HKUST-1 nanocrystal demonstrates improved SF₆ adsorption, SF₆/N₂ selectivity as well as faster SF₆ adsorption kinetics as compared to conventional HKUST-1. The creation of mesoporosity as well as high accessible surface area allows strong facilitation and transport of SF₆ to the active sites, leading to such enhancement. The analysis of idealized vacuum swing adsorption further validates its capability of hierarchically-structured HKUST-1 in this process.

Besides, using similar strategy, a series of hierarchically-structed zeolite MFI was also studied for its potential utility in SF₆/N₂ separation. In this study, enhanced SF₆/N₂ selectivity at slight elevated temperature (40 ^oC) was observed as compared to bulk MFI. Most importantly, a clear enhancement in SF₆ adsorption kinetics was seen, owing to the presence of mesoporosity that allows strong facilitation of SF₆ to the available active sites. Further evaluation through the SF₆/N₂ breakthrough analysis have verified that a sharper breakthrough curves can be seen on hierarchically-structured MFI, indicating that the diffusion of SF₆ in such structure can be facilitated easily under dynamic condition.

References:

1. C. Y. Chuah, K. Goh, T. H. Bae, Hierarchically Structured HKUST-1 nanocrystals for enhanced SF₆ capture and recovery, J. Phys. Chem. C, 121 (12), 6748-6755

2. C. Y. Chuah, S. Yu, K. Na, T. H. Bae, Enhanced SF₆ recovery by hierarchically structured MFI zeolite, J. Ind. Eng. Chem., in press