Separations of F-gases from nitrogen through thin carbon membranes

• We fabricated thin carbon molecular sieve (CMS) membranes for N2/F-gas separation.
• Film thickness and pyrolysis conditions were optimized.
• Characteristics of F-gas diffusions through CMS membranes were thoroughly investigated.
• CMS membranes showed high N2 permeance while effectively rejecting F-gases.
• Resulted CMS membranes far outperformed polymeric membranes for N2/F-gas separation.

F-gases, such as NF3, CF4, and SF6, are strong greenhouse gases, and their emissions to the atmosphere should be prevented. We investigated F-gas separations by carbon molecular sieve (CMS) as a strong candidate for reduction of greenhouse gas. The viscosity of the precursor solution (Matrimid5218®) was controlled from 10 cP to 40 cP for fabricating defect-free thin polymer films on porous supports, and thermal pyrolysis protocols were subsequently optimized in order to produce high-performance membranes. CMS membranes pyrolyzed at 650 °C in high-purity He (99.9999%) exhibited the best performance for N2/NF3 separation (650 N2 GPU, N2/NF3 = 26.6). As compared with polymeric membranes, the CMS membranes performed far outperformed especially because of their high N2 permeance, which originated from the thickness of the thin film along with the rationally controlled micropores. Therefore, these high-flux CMS membranes are expected to provide high productivity when implemented in large-scale processes for F-gas separation and recovery.