A Comparison of Atomistic Simulations and Experimental Measurements of Light Gas Permeation through Zeolite Membranes

Abstract

We present experimental and theoretical results for single-component permeance of CH 4 and CF 4 through a supported silicalite membrane at a range of temperatures and pressures. Our theoretical model uses a continuum description of molecular transport through zeolite crystals that is directly parametrized from atomically detailed simulations of molecular adsorption and transport. This approach does not require any assumptions regarding the loading dependence of the adsorbed species' transport or Maxwell-Stefan diffusivities. Our results are the first direct comparison between a fully atomistic description of intracrystalline transport and permeance measurements for a macroscopic zeolite membrane. These results help to isolate the contributions to the overall flux through polycrystalline zeolite membranes that arise from molecular transport through nonzeolitic pores. We also discuss avenues for future extensions and improvements of our atomistic approach to modeling practical zeolite membranes.

Transport Diffusivities of CH4, CF4, He, Ne, Ar, Xe, and SF6 in Silicalite from Atomistic Simulations

“…For higher pressures the adsorption isotherm for CH 4 in Figure 1 slightly underestimates the experimental values, while the CF 4 loading is overestimated relative to experiments. 21,36 The calculated isotherms for Ar slightly overestimate the experimental values at low pressures, while the isosteric heats of adsorption are slightly underestimated. 37 For SF 6 the loading is underestimated relative to experiments at low pressures while the isosteric heats of adsorption are overestimated.…”

“…To determine E ads , we computed the orientationally averaged D(0) for CF 4 , SF 6 , and CH 4 at 298, 373, and 473 K, then fitted these results to the usual Arrhenius form. This gives the apparent activation energy for self diffusion of an isolated adsorbate as 4.25 kJ/mol for CH 4 , 36 4.43 kJ/mol for CF 4 , and 7.44 kJ/mol for SF 6 . The ratio aa /E ads is therefore 3.5, 4.0, and 4.0 for CH 4 , CF 4 , and SF 6 , respectively.…”

Multiscale models of sweep gas and porous support effects on zeolite membranes

“…We have recently shown that atomically detailed calculations can be used to quantitatively predict the single‐component flux of light gases such as CH 4 and CF 4 through zeolite membranes 14. In our approach, atomistic simulations are used to determine the adsorption isotherms and loading‐dependent Fickian diffusion coefficient, D t ( c ).…”

Methane diffusion mechanism in catenated metal–organic frameworks

“…The infinite-dilution activation energies for methane diffusion in the two pairs of IRMOFs shown in Figure 2(b) and (c) were calculated by performing MD simulations at three temperatures: T ¼ 200, 300 and 400 K. The values obtained are 8.29 and 9.65 kJ/mol for IRMOF-11 and IRMOF-13, respectively, which are much larger than that in their corresponding non-catenated counterparts with the values of 4.89 and 4.90 kJ/mol for IRMOF-12 and IRMOF-14, respectively. The infinite-dilution activation energy of CH 4 in silicalite is found experimentally to be 5.7 kJ/mol [47] and the simulated result is 4.4 kJ/mol [48]. Therefore, the activation energy in the non-catenated IRMOFs is similar to that in silica zeolites, while it is greatly increased in its corresponding catenated IRMOFs, causing a much lower diffusivity in them.…”