Water isotherm models for 4A (NaA) zeolite

Abstract

The adsorption data of Gorbach et al. (Adsorption 10(1): 29-46, 2004) and Morris (J. Colloid Interface Sci. 28: 149-155, 1968) for the adsorption of water on 4A zeolite pellets is re-analyzed. Model isotherms are derived considering a two site hypothesis, one for the α cage and one for the β cage. Four simple model isotherms are fitted to the data. Both a dual site Toth or dual site Langmuir isotherm model fit the data adequately.The optimized standard enthalpy and entropy of adsorption parameters derived from the data are surprising for the β cage. The optimized standard enthalpy of the β cage is 1/3rd of that observed calorimetrically, and the standard entropy of adsorption is positive, a physical impossibility. Substituting the calorimetric enthalpy of adsorption corrected the standard differential entropy of sorption values resulting in the standard entropy of sorption values varying significantly with temperature. This variation is postulated to be due to either water of hydration formation, or clathrate formation, or the formation of clusters of water such as dimers, trimers, etc.Keywords Adsorption · Water · 4A (NaA) zeolite · Langmuir isotherm · Toth isotherm · Ruthven isotherm · Dual site isotherm · Standard enthalpy of adsorption · Standard entropy of adsorption Nomenclature f i fractional size of site i K ci dimensionless equilibrium constant ci, cβ for cage β and cα for cage α respectively

Evaluation of Adsorbents for Removal of Isopropanol from Humid Air#

“…The value of the isosteric adsorption heat for water is at low loadings smaller than the heat of condensation, thus indicating the hydrophobic nature of the surface of the adsorbents. The peak values are consistent with recent findings from litertature [23][24][25]. For isopropanol the opposite is true.…”

Gravimetric adsorption measurements of helium on natural clinoptilolite and synthetic molecular sieves at pressures up to 3500 kPa

“…when H1 was set to values less than 3 kJ/mol were significantly larger than the possible range of solid volumes that have been calculated from the cage structures of these zeolites and the other experimental measurements [13,26]. For the Escott zeolite the vs determined at H1 < 3 kJ/mol was smaller than the solid volume determined by helium pycnometry and this result is not consistent with the hypothesis that helium adsorption is none zero (adsorption cannot be negative).…”

Structured Ni@NaA zeolite supported on silicon carbide foam catalysts for catalytic carbon dioxide methanation

“…Five minutes after the start‐up based on the MS profiles associated with the m/z values of 2, 15, and 44, corresponding to H 2 , CH 4 , and CO 2 , respectively (m/z = 28 signals were also detected during the catalysis by MS, which could be assigned to species from CO 2 fragmentation and CO from the catalysis, and hence discussion on it was not made). It should be noted that the breakthrough time of water (m/z = 18) in the catalytic system is relatively longer than that of other gases, indicating the sorption enhanced CO 2 methanation due to the good water adsorption capability of NaA zeolite, 46 being in line with the findings reported previously 33‐36 . specifically, previous findings demonstrated that the regeneration of these structured catalysts was possible via a drying step using either reducing (e.g., H 2 ) or oxidizing gas (e.g., air) 36 .…”