Calorimetric Heats of Adsorption and Adsorption Isotherms. 2. O₂, N₂, Ar, CO₂, CH₄, C₂H₆, and SF₆ on NaX, H-ZSM-5, and Na-ZSM-5 Zeolites

Abstract

Isosteric heats of adsorption and adsorption isotherms have been measured simultaneously in a calorimeter for a series of gases of increasing size and magnitude of quadrupole moment (Ar, O2, N2, CH4, C2H6, SF6, CO2) on adsorbents of varying pore structure and ion type (NaX, H-ZSM-5, Na-ZSM-5). Adsorption isotherms have been checked for reversibility by desorption experiments. The average experimental error in loading is ±0.6%; the average uncertainty in the isosteric heat of adsorption is ±0.5 kJ/mol. Heats of adsorption of nonpolar molecules (CH4, C2H6, SF6) increase in the order NaX, silicalite, H-ZSM-5, Na-ZSM-5 at low coverage. Heats of adsorption of nonpolar molecules are almost identical on silicalite, H-ZSM-5, and Na-ZSM-5 at high coverage. Heats of adsorption of the quadrupolar molecule CO2 increase in the order silicalite, H-ZSM-5, Na-ZSM-5, NaX. The electric field adjacent to Na+ sites is 6.2 V/nm, on the basis of the difference between the heat of adsorption of CO2 in Na-ZSM-5 and the heat of adsorption of CO2 in silicalite.

Elucidating alkane adsorption in sodium-exchanged zeolites from molecular simulations to empirical equations

“…Fig. 1 shows the excellent agreement of our computed isotherms for ethane with available experimental data [40]. The number of sodium cations and the temperature used for each isotherm were chosen to facilitate comparison with these experimental data.…”

Predicting Large CO2 Adsorption in Aluminosilicate Zeolites for Postcombustion Carbon Dioxide Capture

“…Overall for NaX, there was good agreement between our moving-cations simulation data and other reported adsorption isotherm data under same conditions. 10,19 The fixed-cations method generally underpredicted the CO 2 loading for most pressure values; however, there was good enough agreement that the method can be considered to provide a conservative estimate of the CO 2 uptake for our screening purposes. For CaA and CaX, there was reasonable agreement between the fixed-cations method and the experimental data of Bae et al, 9 although the simulation parameters for Ca 2+ were not optimized.…”

Application of the Integral Equation Approach to the Study of Enthalpic Effects Accompanying Mixed-Gas Adsorption on Heterogeneous Solid Surfaces

“…New equations for isosteric heats of component mixtures were examined using the experimental data obtained by Dunne et al (1996aDunne et al ( ,b, 1997, i.e. C 2 H 6 , CH 4 adsorbed on silicalite and CO 2 , C 2 H 6 adsorbed on NaX zeolite.…”

“…Dunne et al (1996aDunne et al ( ,b, 1997) also compared the experimental results with theoretical calculations based on the IAS approach. Only the experimental results for the adsorption of C 2 H 6 and C 3 H 8 on zeolites were presented by Hampson and Rees (1993).…”

“…As a result, very simple equations describing the isosteric heats of mixture components were obtained. The advantage of the model presented is the possibility of predicting the phase diagrams and enthalpic effects accompanying mixed-gas adsorption from a theoretical viewpoint based on purecomponent adsorption data.New equations for isosteric heats of component mixtures were examined using the experimental data obtained by Dunne et al (1996aDunne et al ( ,b, 1997, i.e. C 2 H 6 , CH 4 adsorbed on silicalite and CO 2 , C 2 H 6 adsorbed on NaX zeolite.…”