Impact of the carbon pore size and topology on the equilibrium quantum sieving of hydrogen isotopes at zero coverage and finite pressures
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Carbonaceous slitshaped and squareshaped pores efficiently differentiate adsorbed hydrogenisotopes at 77 and 33 K. Extensive path integral Monte Carlo simulations revealed that thesquareshaped carbon pores enhanced the selectivity of deuterium over hydrogen in comparisonto equivalent slitshaped carbon pores at zero coverage as well as at finite pressures(i.e. quantum sieving of hydrogen isotopes is poretopologydependent). We show that thisenhancement of the D2/H2 equilibrium selectivity results from larger localization of hydrogenisotopes in squareshaped pores. The operating pressures for efficient quantum sieving ofhydrogen isotopes are strongly dependent on the topology as well as on the size of the carbonpores. However, for both considered carbon pore topologies the highest D2/H2 separation factoris observed at zerocoverage limit. Depending on carbon pore size and topology we predictedmonotonic decreasing and nonmonotonic shape of the D2/H2 equilibrium selectivity at finitepressures. For both kinds of carbonaceous pores of molecular sizes we predict highcompression of hydrogen isotopes at 77 and 33 K (for example, the pore density of compressedhydrogen isotopes at 77 K and 0.25 MPa in a squareshaped carbon pore of size 2.6 °A exceeds60 mmol cm3; for comparison, the liquid density of paraH2 at 30 K and 30 MPa is42 mmol cm3). Finally, by direct comparison of simulation results with experimental data it isexplained why ‘ordinary’ carbonaceous materials are not efficient quantum sieves.
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