Vacancy solution theory of adsorption using Flory‐Huggins activity coefficient equations

Abstract

New equations for the physical adsorption of gases on solids have been developed based on the vacancy solution model of adsorption in conjunction with the Flory-Huggins activity coefficient equations. The isotherm equation contains three regression parameters: a Henry's law constant, the limiting amount of adsorption, and a gas-solid interaction term. Pure-gas data over a range of temperature can be correlated using only five parameters. Gas-mixture equilibria can be predicted using only the parameters obtained from the pure-gas data. Pure-component, binary, and ternary adsorption equilibrium data on activated carbons, silica, and zeolites over a wide range of conditions have been used to evaluate the model. The results show that, except for a few systems, this model predicts gas-mixture equilibria better than any other model. SCOPEIn order to exploit the physical adsorption of gases in separation processes, quantitative characterization of the multicomponent adsorption equilibria are needed as functions of temperature and pressure. Experimental multicomponent adsorption data are difficult and tinie-consuming to obtain; therefore, a reliable method of predicting multicomponent equilibria at various temperatures and pressures from purecomponent adsorption data, and if necessary binary mixture data, would be preferred. Suwanayuen and Danner (1980a, b) proposed a vacancy solution model using the Wilson model for the activity coefficients. Although this approach has been successful for the prediction of isothermal multicomponent equilibria from single-gas isotherms alone, it fails to explicitly include the effect of temperature. Also, the equations in the Suwanayuen and Danner (S&D) model are complex, and it is often difficult to obtain physically significant parameters from the regression of limited isothermal data sets.The objective of this work was to develop a new gas adsorption model based on vacancy solution theory which corrects the deficiencies inherent in the S&D model and surpasses it in accuracy. Any new model should account for nonideal behavior in the adsorbed phase including the adsorbate-adsorbate interactions and should predict the temperature dependency of the equilibria as well as the pressure and compositional dependencies. The model should be flexible enough to allow the use of binary data to characterize the adsorbate-adsorbate interactions if such data are available and if such binary parameters are needed. Preferably the model should include a method of estimating these adsorbate-adsorbate parameters, thus eliminating the need for the binary data which are seldom available and difficult to obtain experimentally. The model presented in this paper meets these criteria. CONCLUSIONS AND SIGNIFICANCEA new model for pure-and multicomponent gas adsorption is developed based on the vacancy solution theory as presented by Suwanayuen and Danner (1980a, b). Activity coefficients based on a Flory-Huggins type expression have been introduced to account for the nonideality in the adsorbed phase. By regress...

Chromatographic study of alkanes in silicalite: Equilibrium properties

“…These are listed in Table 3. (The original nomenclature of Cochran et al, 1985, has been preserved.) Figure 6 clearly indicates that this model correlates the experimental data quite well.…”

“…Also illustrated in Figure 6 are correlations of the pure component data obtained with the Flory-Huggins vacancy solution model (FH-VSM) of Cochran et al (1985). Computer algo- rithm AD3 of the API Technical Data Book (Danner and Daubert, 1985) was used to conveniently regress the proper model parameters.…”

“…This type of data is not easy to obtain via traditional experimental techniques since both gas-and adsorbed-phase compositions must be determined. For this reason, a number of adsorption equilibrium models have been developed to predict multicomponent behavior from pure component data (Myers and Prausnitz, 1965; Ruthven et al, 1973; Cochran et al, 1985). This article deals with the measurement of pure and binary adsorption isotherms using different versions of the chromatographic technique.…”

Study of the adsorption and desorption of multiple adsorbates in a fixed bed

“…The Flory-Huggins form of the Vacancy Solution Model (FH-VSM) isotherm equation (Cochran et al, 1985a) for a pure adsorbate was found to fit the individual isotherm data well. The pure component isotherm equation is: A H ) in the above equations.…”

Sequestering Carbon Dioxide in Coalbeds

“…Among the theories widely used for adsorption are the Langmuir model, ideal adsorbed solution (IAS) theory , heterogeneous ideal adsorbed solution (HIAS) (Myers, 1987), vacancy solution model (VSM) Cochran et al, 1985), theory of volume filling micropores (TVFM) (Dubinin, 1966), twodimensional equations of state model (2-D EOS) , and the simplified local density (SLD) model . In general, all the models work well for low-pressure adsorptions.…”