Application of the model of Part I is made to several systems with various graphitized carbon blacks over wide ranges of temperatures and submonolayer coverage. Agreement with all data for equilibrium and transport is probably within experimental error. Equilibrium adsorption and the flux of adsorbable gases through porous media with homogeneous surfaces have been of experimental interest for many years. A number of theoretical models have addressed this system as the initial case for more complex situations. However, most of these thmries do not attempt to represent all possible cases with a single model based on statistical mechanics and utilizing intermolecular potential parameters. Instead, only one property or type of system is considered. C. S. LEE and J. P. O'CONNELLPart I (Lee and OConnell, 1985) has developed a fully generalized theory that includes the essential molecular phenomena and formulates expressions for all the measurable properties of pure and mixed systems at submonolayer coverages. The present paper describes application of the model to gases physically adsorbed on graphitized carbon blacks with surfaces that are essentially homogeneous. Difficulties and inconsistencies of data analysis are discussed and a strategy for fitting the several molecular parameters to the data is indicated. CONCLUSIONS AND SIGNIFICANCEEquilibrium and transport data for several pure nonpolar and polar gases have been examined and compared with correlations from the model of Part I. The agreement is probably within experimental error in all cases; the best results occur when the values are compared directly with measurements rather than with manipulated information. As expected, surface diffusion results are quite sensitive to the parameters of the structured adsorption potential but equilibrium isotherm data are not. Localized adsorption is always present to some degree, even on graphitized carbon black surfaces.At low temperatures, the structure of the adsorption potential C. S. Ltx is on leave from Department of Chemical Engineering. Korea University, Seoul is the dominant factor for surface diffusion. At higher temperatures, normal vibration and its anharmonicity have an important effect. However, since the model formulation is based on known physical phenomena, it provides a parameterization for these effects that uses temperature-independent quantities having values that are consistent with other information. Application to mixed gas adsorption is also successful. Further, the case of binary flux of adsorbable and nonadsorbable substances with interactions between the bulk and adsorbed phase is well predicted.Finally, an initial attempt at estimating the important parameter for surface diffusion indicates that for these surfaces, rough predictions of surface flux might be made using only equilibrium information.
SCOPEThe adsorption and surface mobility of substances on solids is relevant in such diverse processes as catalysis, some proposed separations, and olfactory reception by insects. As is well known, there is an attractive potential for fluid molecules toward the surface.This potential varies along the surface because the arrangement of adsorbent atoms causes the adsorbate molecules to suffer varying momentum changes as they move. In fact, if the local variation is large enough, admolecules may become localized, the amount being a function of temperature and surface coverage. In addition, the admolecules vibrate normal to the surface; this is a momentum exchange mechanism with the surface as well as an equilibrium energy effect, which was ignored in an earlier treatment (Lee and OConnell, 1972). Further, the admolecules interact with each other, the quantitative effects depending upon whether they are mobile or not and upon their location in the structured potential. Finally, there may be important interaction between the gaseous and adsorbed molecules which affect the total flux.There are several important physical cases to be considered. The bulk gas phase may be pure or mixed, with the amount ad-sorbed ranging from negligible to a significant fraction of a monolayer. The solid can be packed in a porous bed, with the flux being due to different pressures at the inlet and outlet for a pure component, or to different partial pressures of the components in a mixture while the total pressure is constant throughout the system. A special case of the latter is tracer flow of one isotope present at very low concentrations in another isotope. Each of the above cases results in slightly different macroscopic relations, although the molecular phenomena are the same.A number of treatments of adsorption and surface diffusion exist. However, these theories often treat only equilibrium or transport, rather than both. Surface equilibrium and transport should be amenable to a unified potential model and statistical mechanical treatment such as second virial coefficients and ideal gas transport properties are. Part I of the present study gives the development of the expressions for all of the physical situations of adsorption and flux of gases through a porous beds of homogeneous adsorbents with submonolayer coverage. In Part I1 the expressions are applied to several cases of pure and mixed gases with graphitized carbon black. CONCLUSIONS AND SIGNIFICANCEEkpressions have been developed from statistical mechanics to model the equilibrium isotherms and all of the transport properties for an important class of adsorption systems. Specifically, these include pure and mixed gases, which can be localized or mobile when adsorbed at submonolayer coverage on homogeneous surfaces in porous beds where the gas phase is in the Knudsen C S Lee IS on leave from the Department of Chemical Engneenng, Korea Unnerslt), Seoul Regime. The important physical effects rigorously or approximately included are gas-adsorbate interactions, including enhanced...
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