Generalization of thermodynamic Langmuir isotherm for mixed‐gas adsorption equilibria

Abstract

This work presents a comprehensive thermodynamic model for both pure component isotherms and mixed‐gas adsorption equilibria. A generalization of thermodynamic Langmuir isotherm, the proposed model assumes competitive adsorption of multiple adsorbates on adsorbent surface for mixed‐gas adsorption equilibria, and it applies an area‐based adsorption nonrandom two‐liquid activity coefficient model in the activity coefficient calculations for the adsorbate phase. The resulting generalized Langmuir isotherm properly captures both surface loading dependence and adsorbate phase composition dependence for mixed‐gas adsorption equilibria. The model is validated with accurate representations of gas adsorption equilibrium data for varieties of unary, binary, and ternary gas systems. The model results are further compared with those calculated from extended Langmuir isotherm and Ideal Adsorbed Solution Theory.

Interactions during the Adsorption of Heterocycles on Zeolites, Silica Gels, and Activated Carbons

“…Since there are vast differences in the properties of adsorbents and adsorptives as well as distinct differences in the adsorption mechanisms, no model exists that can describe all adsorption isotherms. Thermodynamic isotherm models − portray a promising method to fit the data, especially when the fitting parameter are physically meaningful. By fitting the isotherms, the heats of adsorption and thus the interaction potentials can be calculated.…”

Thermodynamic modeling of adsorption at the liquid-solid interface

“…In this work, the generalized Langmuir isotherm model (gL) [26] (see § 2.3) was used to calculate the equilibrium amount adsorbed as a function of pressure for each pure component constituting the binary mixture, using the available experimental data for pure vapor adsorption [6,18]. The spreading pressure of each pure component was subsequently computed as a function of vapor phase pressure using the Gibbs adsorption isotherm equation [29] given below.…”

“…The second method for the calculation of surface excess of binary liquid adsorption is the generalized Langmuir isotherm model (gL) [26] . This model is an extension and generalization of the thermodynamic Langmuir isotherm model (tL) for pure component isotherms [33,36,37].…”

“…The activity coefficients used in equations 12 and 13 are computed by a modified aNRTL model, which takes into account the adsorbent heterogeneity and the size of the molecules [26].…”

“…For the latter, we have implemented the adsorption Non-Random Two-Liquid (aNRTL) model for evaluating the adsorbed phase activity coefficients [25]. We have also performed the surface excess computations using the recently developed generalized Langmuir isotherm model (gL) [26]. The framework of the gL isotherm model does not require the calculation of the spreading pressure of the adsorption system, making the implementation computationally inexpensive.…”