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.