Modeling the Supercritical Adsorption of Hydrogen on A-and X-Type Zeolites with a Lattice Density Function

Abstract

Adsorption isotherms of hydrogen on the microporous zeolites A and X under supercritical conditions were modeled using lattice density function theory (LDFT) based on the three-dimensional Ono-Kondo equation. According to the sizes and shapes of the zeolite pores, the local arrangement of adsorption sites within the pores in the LDFT models were simulated by the clusters of simple cubic lattice, face-centered cubic lattice, and body-centered cubic lattice structures. Results indicate that the LDFT models appear to be effective in describing the multilayer or monolayer adsorption of hydrogen on zeolites A and X under supercritical conditions and the calculated adsorption isotherms agree well with the experimental isotherms measured previously. In particular, the hydrogen-zeolite interaction energy parameters used in LDFT models were verified by the Lennard-Jones (12-6) potential model for cylindrical pores based on a thermodynamics method. These results confirm the reliability of LDFT models in describing hydrogen adsorption on zeolite adsorbents. Using the obtained parameters, adsorption isotherms for hydrogen on zeolite X were predicted using the LDFT model over a wider range of temperatures and pressures.