Modelling carbon membranes for gas and isotope separation

Abstract

Molecular modelling has become a useful and widely applied tool to investigate separation and diffusion behavior of gas molecules through nano-porous low dimensional carbon materials, including quasi-1D carbon nanotubes and 2D graphene-like carbon allotropes. These simulations provide detailed, molecular level information about the carbon framework structure as well as dynamics and mechanistic insights, i.e. size sieving, quantum sieving, and chemical affinity sieving. In this perspective, we revisit recent advances in this field and summarize separation mechanisms for multicomponent systems from kinetic and equilibrium molecular simulations, elucidating also anomalous diffusion effects induced by the confining pore structure and outlining perspectives for future directions in this field.

Graphdiyne Pores: “Ad Hoc” Openings for Helium Separation Applications

“…In the case of the graphdiyne pore, the average effective polarizability of the C atom has been used. In particular, a value equal to 1.1Å 3 , consistent with that reported by Gavezzotti 42 describing the average behavior of C atom in various aliphatic and unsaturated molecules, has been adopted to estimate the dispersion energy contribution and the ε parameter associated to each rare gas (methane)-C interacting pair (see also Ref. 43 ).…”

“…We have found exceptionally favorable He/CH 4 and Ne/CH 4 selectivities in a wide range of temperatures which largely exceed the performance of the best membranes used for helium chemical separation. Thermally weighted helium tunneling calculations have been also performed to show selective transmissions of 3 He versus 4 He. For temperatures below 100K the 3 He/ 4 He selectivity becomes appreciably larger than 1, reaching an acceptable value of 6 at about 20K.…”

“…It can be seen that, for kinetic energies lower than the classical barrier (see last column of Table 1), the 3 He transmission probability is significantly higher than that of 4 He, while the opposite occurs for higher kinetic energies. For this reason, it makes sense to keep the gas temperature as low as possible in order to exploit the low energy side of the transmission curve.…”

“…Thermally weighted transmission probabilities as well as the corresponding 3 He/ 4 He selectivity as a function of temperature are reported in Fig. 4 (lower panel).…”

“…1,2 In particular, graphene-based materials 3 exhibit vantage points with respect to conventional 3D materials, by virtue of their thermal and chemical stability as well as a low molecular weight and efficient transport capability.…”