Efficient continuous SF6/N2 separation using low-cost and robust metal-organic frameworks composites

Physisorption presents a promising alternative to cryogenic distillation for capturing the most potent greenhouse gas, SF6, but existing adsorbents face challenges in meeting diverse chemical and engineering concerns. Herein, with insights into in-pore chemistry and industrial process design, we report a systematic investigation that constructed two low-cost composites pellets (Al(fum)@2%HPC and Al(fum)@5%Kaolin) coupled with an innovative two-stage Vacuum Temperature Swing Adsorption (VTSA) process for the ultra-efficient recovery of low-concentration SF6 from N2. Record-high selectivities (> 2×104) and SF6 dynamic capacities (~ 2.7 mmol/g) were achieved, while exceptional SF6 productivities (~ 58.7 L/kg), yields (~ 96.8%), and recyclability (~ 1000 cycles) were demonstrated in fixed-bed adsorption-desorption experiments under mild regeneration conditions. 2D solid-state NMR/in-situ FTIR, DFT-D binding/diffusion simulation analyses revealed the multi-site binding mode and the ultra-fast diffusion of SF6 within the channels. The proposed VTSA processes successfully met the dual stringent requirements of both environmental protection and electricity equipment operation: the SF6 recovery of 99.91% accompanied with a SF6 purity/working capacity of 99.91%/2.1 mmol/g, which significantly outperformed the industrial employed adsorbent zeolite 13X and showed only 18.7% the energy consumption of the cryogenic distillation. SF6/N2 separation is crucial for sustainable development. Here, the authors prepared low-cost and robust MOF composite pellets and established a vacuum temperature swing adsorption process with both high recovery and high purity of SF6.