Optimized mass transfer of PHI-type zeolite for nitrogen/methane sieve separation

The separation of nitrogen and methane via molecular sieving is often accompanied by mass transfer limitations. Here, we report a NaK-PHI zeolite that not only achieves the precise sieving of nitrogen and methane, but also significantly enhances the diffusion rate of nitrogen. By adjusting the framework composition of the zeolite, the metal cation in the NaK-PHI channel allows smaller nitrogen molecules to enter the channel but blocks methane entry, achieving precise N2/CH4 sieving. A growth inhibitor (GI) was introduced to reduce the crystal size of the NaK-PHI@GI zeolite, and the adsorption kinetics were optimized, resulting in a diffusion rate enhancement of approximately three times; NaK-PHI@GI also exhibited an enhanced nitrogen adsorption capacity (10.5 cm3 g−1) as well as a higher nitrogen/methane uptake ratio (20.9). After multiple cycle-breakthrough tests and regeneration processes involving evacuation and depressurization, NaK-PHI@GI maintained a stable separation capacity, confirming its good recyclability.