Enrichment of spent SF6 gas by zeolite membranes for direct reuse in gas-insulated switchgear units

Zeolite membranes have attracted considerable attention in the separation industry owing to their high sepa-ration selectivity and permeance. However, their industrial applications have been hindered owing to a lack of case studies focusing on their commercialization. Herein, MFI and SAPO-34 zeolite membranes were employed to purify spent SF6 gas taken from a gas-insulated switchgear (GIS). This study demonstrated that separation by a single zeolite membrane produced ultrapure SF6 gas (>99.7 %) satisfying the reuse guidelines for GIS units. This level of purity is difficult to achieve using polymeric membranes due to the plasticization effect. The synthesized MFI membrane exhibited high N2 permeance with -2,000 gas permeation units (GPU) at 2 bar and low N2/SF6 selectivity (<50), whereas the SAPO-34 membranes exhibited the opposite trends, i.e., high N2/SF6 selectivity (>500) and relatively low permeance (<600 GPU at 2 bar). Interestingly, the MFI membrane system effectively enriched the SF6 gas, while lower feed pressures achieved by decreasing the feed flows were required for the SAPO-34 membranes to achieve the same purity. Changes in the feed pressure led to corresponding changes in the membrane separation performance, and the concentration polarization increased at high feed pressures. A MFI membrane area of -0.088 m2 was sufficient to purify the entire spent SF6 gas produced by GIS units at 145 kV in 6 h; this indicates an opportunity to realize compact SF6 enrichment systems. Thus, considering the high separation performance and the small size of the separation system, MFI membranes represent a promising option for the industrial purification of spent SF6 gas from GIS units.

Automated summary

Zeolite membranes have high separation selectivity and permeance, making them attractive for use in the separation industry. This study demonstrates the potential of MFI and SAPO-34 zeolite membranes for purifying spent SF6 gas from gas-insulated switchgear. The results show that the zeolite membranes can achieve ultrapure SF6 gas, which is difficult to achieve using polymeric membranes. The study also highlights the importance of feed pressure and membrane area in achieving desired separation performance.