Rates of flow through microporous solids

Gilliland, E. R.; Baddour, R. F.; Russell, J. L.

doi:10.1002/aic.690040117

Cited by 153 publications

(67 citation statements)

References 19 publications

(4 reference statements)

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“…In the surface pressure driving force model, the gradient of the surface pressure is assumed to be the driving force of surface diffusion. 44 Similar to Eq. (27), the following equation is derived.…”

Section: Fick's Law 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.

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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...

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Section: Fick's Law 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.

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“…A sample set of constants is taken from Chen and Yang [26] where the values have been extracted from the experimental measurements of Gilliand et al [27]. As an example, the system propylene (C3H6) in (Vycor-) glass is taken, which was found to exhibit monolayer adsorption, which corresponds to our model.…”

Section: Physical Constants Used For the General Modelmentioning

confidence: 99%

An alternative procedure for modeling of Knudsen flow and surface diffusion

Argönül¹,

Keil²

2008

Per. Pol. Chem. Eng.

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An alternative procedure for the calculation of impingement rate distribution and simultaneously the transmission probability in pores under Knudsen diffusion conditions is introduced. It is based on a combination of the finite difference method and a projection approach. Pore entrance and exit effects, and the influence of the pore length on diffusive fluxes are investigated. Later on, it is applied for a simultaneous Knudsen and surface flow system. In the model, the equation system is built without the independent flow and adsorption-desorption equilibrium assumptions. For the conditions investigated, the results indicate that if the surface flow rate is substantial, the independent flow and adsorption equilibrium assumptions become improper estimates for the behaviour of the system. The surface and gas flow rates, the impingement rate distribution and the surface coverage behave much more complex than the characteristics found with such assumptions. KeywordsKnudsen flow · surface diffusion · equilibrium assumption · cylindrical pore · projection approach Acknowledgement One of the authors would like to thank to Mr. Erkan Aksoy and Mr. Denis Chaykin for their comments concerning mathematical calculations.

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“…1. Essentially, the experimental technique consists of flowing a pure gas through a sample of activated alumina (3), which is immersed in a constant-temperature bath (4). The physical properties of the sample are presented in Table 1.…”

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Surface flow phenomenon of adsorbed gases on activa ted alumina.

Tamon

Kyotani

Wada

et al. 1981

J. Chem. Eng. Japan

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Surface flow of hydrocarbons, such as ethylene, propylene and isobutane, through activated alumina at 10°C and 30°C is measured over a mean pressure level range of a few kPa to about 100 kPa using a permeation apparatus. The surface flow coefficient is also determined as a function of amount adsorbed and temperature. The dependence of the surface flow coefficient on the above quantities can be well correlated using the random hopping model previously proposed by the authors. In addition, data from the literature for three other systems are correlated by this model. Intr oductionIt is of considerable interest from the viewpoint of fundamental research or practical applications such as adsorption, catalytic reaction, gaseous separation and drying to evaluate the mass transfer rate through adsorptive porous materials. Whenadsorbable gases flow or diffuse through porous media, the flux is increased appreciably in the presence of the adsorbed phase. This additional flow, that is, the surface flow, is important in order to estimate the mass transfer rate.

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Rates of flow through microporous solids

Cited by 153 publications

References 19 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

An alternative procedure for modeling of Knudsen flow and surface diffusion

Surface flow phenomenon of adsorbed gases on activa ted alumina.

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