Investigation on the pore structure-performance relationship of porous carbon adsorbents for SF6/N2 separation via fine pore modulation

The capture and recovery of SF6 as electron specialty gas from SF6/N2 by adsorptive separation have obvious advantages such as the mitigation of greenhouse effect and resource utilization of waste gas. The comprehensive understanding of pore structure-performance relationship of porous materials is beneficial for guiding the design of highly-efficient adsorbents for separating SF6/N2, but is presently limited. In this work, a series of citric acid (CA) and KOH with different molar ratios are designed to synthesize carbon adsorbents denoted as CAK via a one-step carbonization-activation method and probed for the adsorptive separation of SF6/N2. Characterization results reveal that the micropores in carbon adsorbents are finely tuned from 0.73 to 0.88 nm at an angstrom level through increasing the KOH/CA molar ratios in precursors, and the significant mesopores are formed in CAK4. Static adsorption results indicate that the SF6 adsorptive capacity at low pressure of 10 kPa increases and then decreases with the increasing contents of KOH, and the highest value is obtained in CAK2, while the diffusion rates illustrated from the adsorption kinetics continuously increase. By correlating the pore structures with adsorption capacity of adsorbents, the critical role of micropores with size ≤ 0.9 nm in determining the SF6 capacity at 10 kPa and mesopores in enhancing the mass transfer is quantitatively confirmed. The dynamic breakthrough results of CAKx carbon adsorbents for SF6/N2 separation are well explained with these understandings, which are important for guiding the design of porous adsorbents with high-performance for SF6 capture and recovery.