Rapid diffusion of H2 and strong adsorption of D2 in Ni-4PyC realized the efficient separation of H2/D2 by gas chromatography

Abstract

In this work, Ni-4PyC was selected as the material for the separation of hydrogen isotopes H₂/D₂, and the mechanism of hydrogen isotope H₂/D₂ separation was investigated by molecular simulation. The results showed that the adsorption selectivity of Ni-4PyC for D₂/H₂ increased from 1.26 to 1.46 when the temperature was decreased from 77 K to 20 K, indicating that Ni-4PyC effected chemical affinity quantum sieving on D₂/H₂. Also, the diffusion rates of H₂/D₂ were different at different temperatures. At 20 K, the kinetic selectivity of D₂/H₂ reached 1.30, indicating that Ni-4PyC had a kinetic quantum sieving effect on D₂/H₂ at low temperatures. However, when the temperature was higher than 30 K, the diffusion rate of H₂ was faster than that of D₂, and when the temperature was 77 K, Ni-4PyC exhibited the kinetic sieving effect with a kinetic selectivity of 1.59 for H₂/D₂. Due to the chemical affinity quantum sieving and kinetic sieving effects of Ni-4PyC on H₂/D₂, the adsorption capacity of Ni-4PyC for D₂ was better than that for H₂ and the diffusion rate of H₂ was faster than that of D₂ at 77 K. Therefore, Ni-4PyC was expected to achieve the separation of H₂/D₂. In order to verify the accuracy of the theoretical calculation results, an Ni-4PyC@γ-Al₂O₃ composite material was synthesized by a liquid phase epitaxy method and was used to separate H₂/D₂ at 77 K in a 0.6 m × 2 mm chromatographic column. Under optimal separation conditions, the resolution R reached 1.84 with a separation time t = 7.47 min. In addition, Ni-4PyC@γ-Al₂O₃ showed excellent separation performances for different ratios of H₂/D₂ mixtures. The stationary phase was repeatable and reproducible.