Fabrication of high-quality SSZ-13 zeolite membranes for efficient SF6 recovery

Sulfur hexafluoride (SF6) is a greenhouse gas with a global warming potential of 23900 times higher than CO2. It is essential to develop effective methods to separate and recover SF6 from spent gas to prevent its strong release into the atmosphere. Herein high-quality SSZ-13 zeolite membranes were synthesized on four-channel hollow fiber substrates for N2/SF6 separation. The ball-milled seeds are more reliable to synthesize thinner membranes with enhanced intergrowth. The thickness decreased from 14 μm for the pristine seeds to 5.2 μm for the ball-milled ones. The membrane quality was initially evaluated by CO2/CH4 separation at 0.2 MPa, where the CO2 permeance was 4.1 × 10−7 mol m−2 s−1 Pa−1 (∼1200 GPU) and the separation factor was 134. The average N2/SF6 separation factor was 325 and the N2 permeance was 5.4 × 10−8 mol m−2 s−1 Pa−1 (∼160 GPU), which was slightly influenced by feed pressure up to 1.6 MPa. SF6 concentration in the permeate was around 800 ppm for the feed stream containing 70 % N2 and 30 % SF6, which is a typical insulating gas in electrical utilities. The humid feed improved the size exclusion effect of the SSZ-13 zeolite membrane, making it an ideal material for practical N2/SF6 separation.