Abstract
Applying a novel self-consistent Feynman - Kleinert-Sese variational approach (Sese, L. M. Mol. Phys. 1999, 97, 881-896) to quantum thermodynamics and the ideal adsorbed solution theory, we studied adsorption and equilibrium separation of Ne-20-He-4 mixtures in carbonaceous nanomaterials consisting of flat (graphite-like lamellar nanostructures) and curved (triply periodic minimal carbon surfaces) nanopores at 77 K. At the infinite mixture dilution, Schwarz P-carbon and Schoen G-carbon sample represents potentially efficient adsorbents for equilibrium separation of Ne-20-He-4 mixtures. The equilibrium selectivity of Ne-20 over He-4 (alpha(Ne-He)) computed for Schwarz P-carbon and Schoen G-carbon sample is very high and reaches 219 and 163 at low pore loadings, respectively. Graphite-like lamellar nanostructures with interlamellar spacing (Delta) less than 0.6 nm are also potential adsorbents for equilibrium separation of Ne-20-He-4 mixtures at cryogenic temperatures. Here, alpha(Ne-He) of 80 is predicted for Delta = 0.46 nm at low pore loadings. The quantum-corrected molar enthalpy of Ne-20 adsorption strongly depends on the curvature of carbon nanopores. For Schwarz P-carbon sample, it reaches 8.2 kJ mol(-1), whereas for graphite-like lamellar nanostructures the maximum enthalpy of Ne-20 physisorption of 5.6 kJ mol(-1) is predicted at low pore loadings. In great contrast, the quantum-corrected molar enthalpy of He-4 adsorption is only slightly affected by the curvature of carbon nanopores. The maximum heat released during the He-4 physisorption is 3.1 (Schwarz P-carbon) and 2.7 kJ mol(-1) (graphite-like lamellar nanostructure consisting of the smallest flat carbon nanopores). Interestingly, for all studied carbonaceous nanomaterials consisting of curved/flat nanopores, alpha(Ne-He) computed for the equimolar composition of Ne-20-He-4 gaseous phases is still very high at total mixture pressure up to 1 kPa. This circumstance is indicative of the possibility of carrying out the adsorption separation of Ne-20-He-4 mixtures at p(t) < 1 kPa and 77 K that do not require high-energy consumption. Presented potential models and simulation methods will further enhance the accuracy of modeling of confined inhomogeneous quantum fluids at finite temperatures.
