Interpretation of surface flow phenomenon of adsorbed gases by hopping model

Okazaki, Morio; Tamon, Hajime; Toei, Ryozo

doi:10.1002/aic.690270213

Cited by 106 publications

(72 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Yang et al 39 and Okazaki et al 40 proposed modified equations including many physical parameters, such as Qst, the latent heat of vaporization, and the activation energy of the liquid viscosity of the adsorbate. In this study, Eq.…”

Section: Hopping Modelmentioning

confidence: 99%

See 1 more Smart Citation

Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Enantiomeric Separation on a Polymeric Imprinted Stationary Phase

Miyabe

Guiochon

2000

ANAL. SCI.

View full text Add to dashboard Cite

Molecular imprinting is a most attractive method of preparation of dedicated stationary phases for chromatography. Its use for enantioseparations is attracting considerable interest. 1,2 Imprinted materials can provide a very high selectivity for the objective compound, i.e., the imprinted molecule. [1][2][3][4][5] Although analytical applications are rapidly developing, the situation on the preparative front is less rosy. 1 Columns packed with imprinted stationary phases exhibit a poor efficiency and elution peaks are often unsymmetrical, especially for the more retained enantiomer. Sellergren et al. 1,2 suggested that the nonlinear behavior of the adsorption isotherm was the main cause of the broad and unsymmetrical bands observed for L-phenylalanine anilide (PA) on an L-PA imprinted chiral stationary phase. Although the possibility of a slow mass transfer kinetics was also pointed out, no detailed study supported this assumption. Yet, information on the mass transfer characteristics of imprinted stationary phases is necessary to clarify strategies for the improvement of these materials.Most kinetic studies in chromatography assume that four mass transfer processes are involved in a column, (1) axial dispersion, (2) fluid-to-particle mass transfer, (3) intraparticle diffusion, and (4) adsorption/desorption. 6 The contributions of these four processes to peak spreading are evaluated separately. Axial dispersion and the fluid-to-particle mass transfer resistance are inherent to flow processes through packed beds. They are well understood, relatively easy to control, and their contributions are often small. By contrast, intraparticle diffusion and adsorption/desorption give often larger contributions to the mass transfer resistance in the column. Their properties are intrinsic to each packing material and they are still often poorly understood. In order to evaluate the actual performance of packing materials, the characteristics of the mass transfer kinetics inside stationary phase particles must be clarified.Sajonz et al. 7 measured the adsorption equilibrium isotherm and the mass transfer kinetics of L-and D-PA on a polymeric stationary phase imprinted with L-PA, using a staircase frontal analysis method. The isotherm was well represented by either the Bi-Langmuir or the Freundlich models, but not by the simple Langmuir isotherm. The equilibrium data suggested that the distribution of the adsorption energy on the surface of the imprinted stationary phase is heterogeneous and showed that this phase has a high selectivity for the imprinted L-enantiomer. The lumped mass transfer rate coefficient (km,L) was calculated from each single breakthrough curve by applying the transport model of chromatography. 6 The values of km,L increased with increasing concentration of the enantiomers. The extent of the positive concentration dependence of km,L was larger for L-PA than for D-PA. It is expected that a more detailed analysis of the overall mass transfer rate parameter, km,L, could provide new, useful information and all...

show abstract

Section: Hopping Modelmentioning

confidence: 99%

“…[38][39][40] Higashi et al 38 proposed the following simple function to explain the concentration dependence of Ds.…”

Section: Hopping Modelmentioning

confidence: 99%

Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Enantiomeric Separation on a Polymeric Imprinted Stationary Phase

Miyabe

Guiochon

2000

ANAL. SCI.

View full text Add to dashboard Cite

show abstract

“…The hopping model (Weaver and Metzner, 1966) would be unsatisfactory if the mobile fraction of admolecules is significant, as in most of the cases here. In addition, its dependence on surface coverage must be found empirically (Okazaki et al, 1981). Finally, these methods are incomplete because they ignore the interaction between bulk and surface flows (Thakur et al, 1980).…”

Section: Calculatmdmentioning

confidence: 98%

A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part II: Applications

Lee

O’Connell

1986

AIChE Journal

View full text Add to dashboard Cite

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.

show abstract

“…The object of this paper is tc demonstrate and explain the occurrence of a dual breakthrough phenomenon for single-component adsorption, which had been observed by Cagliostro et al (1985), in terms of a moving-boundary model for the rapid transport of an adsorbed vapor. The occurrence of this dual breakthrough phenomenon is shown to permit the separation of surface and volume diffusivities, which has not previously been possible (Riekert, 1985).The surface flux of lighter gases has been characterized by surface hopping models and spreading pressure models (Okazaki et al, 1981), but the dynamics of adsorption of condensable vapors have been little characterized to date. Flood et al (1952) found that surface transport of strongly adsorbed organic vapors was highest for the lowest partial pressures of the adsorbate, corresponding to the steepest region of their adsorption isotherm, and attributed this to a greater thermodynamic driving force for surface spreading.…”

mentioning

confidence: 98%

Anomalous mass transfer for vapor adsorption on activated carbon

Klotz¹,

Rousseau

1988

AIChE Journal

View full text Add to dashboard Cite

The phenomenon of surface transport has become widely recognized as a significant contributor to dynamic intraparticle mass transfer during adsorption. The object of this paper is tc demonstrate and explain the occurrence of a dual breakthrough phenomenon for single-component adsorption, which had been observed by Cagliostro et al. (1985), in terms of a moving-boundary model for the rapid transport of an adsorbed vapor. The occurrence of this dual breakthrough phenomenon is shown to permit the separation of surface and volume diffusivities, which has not previously been possible (Riekert, 1985).The surface flux of lighter gases has been characterized by surface hopping models and spreading pressure models (Okazaki et al., 1981), but the dynamics of adsorption of condensable vapors have been little characterized to date. Flood et al. (1952) found that surface transport of strongly adsorbed organic vapors was highest for the lowest partial pressures of the adsorbate, corresponding to the steepest region of their adsorption isotherm, and attributed this to a greater thermodynamic driving force for surface spreading. Flood termed the adsorbed vapor surface transport "anomalous." In more recent work, Thackur and Brown (1983) have indicated that a transition between the two types of surface fluid transport occurs with an increase in momentum transfer from the gas to the adsorbed fluid, and between fluid layers. The initial adsorption of mobile chemisorbed films has been suggested (Illinger and Rivin, 1970), so the assumption of physisorption is not necessary. This paper considers two models for adsorption. The first, the moving-boundary model (MBM), considers transport of an organic vapor on activated carbon using an expression for the rate of surface spreading derived by Gilliland and Russell Correspondence concerning this paper should be addressed to W. L. Klotzwhere n, is the adsorbed layer flow rate (kmol/s), P is the vapor pressure of the spreading film (kPa), I, is a spatial coordinate (m) along the solid surface that incorporates the tortuosity factor k (dimensionless), A, is the cross-sectional area of the porous material (m'), S, is the specific surface over which adsorbed molecules are mobile (m2/kg), x is the surface concentration of the film at 1, (kmol/kg adsorbent), p, is the apparent density of the solid (kg/m3), R is the appropriate ideal gas constant, T is the absolute temperature (K), and C, is Gilliland's coefficient of flow resistance. In dimensionless terms, this equation takes the form:where up is the surface concentration and qs is the dimensionless spreading flux, alg is a constant, and yP+ is the equilibrium concentration in a pore for a given surface concentration up, as determined by the isotherm, and ( , is the spatial coordinate for the normal direction of spreading. The definitions of these and other dimensionless terms are given in Table 1 . The second model, the pore-volume diffusion model (PVDM) is more conventional with a pore diffusion transport term for gas adsorption in macropor...

show abstract

Interpretation of surface flow phenomenon of adsorbed gases by hopping model

Cited by 106 publications

References 12 publications

Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Enantiomeric Separation on a Polymeric Imprinted Stationary Phase

Kinetic Study of the Concentration Dependence of the Mass Transfer Rate Coefficient in Enantiomeric Separation on a Polymeric Imprinted Stationary Phase

A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part II: Applications

Anomalous mass transfer for vapor adsorption on activated carbon

Contact Info

Product

Resources

About