Efficient Helium Separation with Two-Dimensional Metal–Organic Framework Fe/Ni-PTC: A Theoretical Study

Abstract

Helium (He) is one of the indispensable and rare strategic materials for national defense and high-tech industries. However, daunting challenges have to be overcome for the supply shortage of He resources. Benefitted from the wide pore size distribution, sufficient intrinsic porosity, and high specific surface area, metal–organic framework (MOF) materials are prospective candidates for He purification in the membrane-based separation technology. In this work, through first-principles calculations and molecular dynamics (MD) simulations, we studied the permeability and filtration performance of He by the newly synthesized two-dimensional Fe-PTC MOF and its analogue Ni-PTC MOF. We found that both Fe-PTC and Ni-PTC have superior high performance for He separation. The selectivity of He over N2 was calculated to be ~1017 for Fe-PTC and ~1015 for Ni-PTC, respectively, both higher than most of the previously proposed 2D porous membranes. Meanwhile, high He permeance (10−4~10−3 mol s−1 m−2 Pa−1) can be obtained for the Fe/Ni-PTC MOF for temperatures ranging from 200 to 500 K. Therefore, the present study offers a highly prospective membrane for He separation, which has great potential in industrial application.

Simulation Studies on Improved Separation of Helium and Helium Isotopes by Strain Modulated r-N-GY Monolayer Nanostructure

“… a All data for selectivities S were calculated based on DFT energy barriers, and permeances Q were estimated by the MD simulations. b This study. c ref . d ref . e ref . f ref . g ref . h ref . …”

“…As demonstrated in previous studies, 20,21,28,29,74 the tradeoff between permeance and selectivity is the limiting factor that restricts the efficiency of separation membranes. Therefore, we inspected the selectivity of the strained r-N-GY membrane (along the AC direction) through MD simulations, as shown in Scheme 1c.…”

“…Calculation of the Selectivity and Permeance Based on DFT Energy Barriers. The He-selectivity with respect to other gases (S He/gas ) can be evaluated by the Arrhenius equation 21,29,52…”

“…The He-selectivity with respect to other gases ( S He/gas ) can be evaluated by the Arrhenius equation ,, S H e / g a s = r normalH normale r normalg normala normals = A normalH normale e − E H e / R T A normalg normala normals e − E g a s / R T where r is the diffusion rate, A is the diffusion prefactor of gas molecules, and E is the diffusion energy barrier. Consistent with former researches, we assign that the diffusion prefactor A = 10 11 s –1 of all gases is identical …”

“…For example, experimentally synthesized g-C 3 N 4 membrane, possessing uniformly distributed sub-nanopores around 4.76 Å, has demonstrated extremely high selectivity for He extraction from natural gas (10 7 to 10 65 ) at room temperature . Similar natural porous membranes such as C 2 N, CTF-0, g-C 2 O, IGP, and Fe/Ni-PTC MOF, have also been theoretically investigated and shown superior He separation properties, which have greatly stimulated experimental explorations. − In addition, the separation of 3 He is of utmost importance as it plays a critical role in various advanced technologies, including cryogenics, isotope labeling, and power generation. , Therefore, 2D porous membranes, such as g-C 3 N 4 , 2DPPH, and graphdiyne, − have also been investigated for separation of He isotopes, some of which even possess industrial acceptable permeance, showing great potential in practical applications.…”