Measurement of transverse and axial apparent dispersion coefficients in packed beds

Tallarek, Ulrich; Albert, Klaus; Bayer, Ernst; Guiochon, Georges

doi:10.1002/aic.690421106

Cited by 96 publications

(61 citation statements)

References 57 publications

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“…22 À6 cm 2 /s and the residence time is 545 s. The average radial diffusion distance is now equal to 0.068 cm, a value still smaller than the column radius (30%). Clearly, transcolumn effects are essentially governed by the radial flow pattern at high reduced linear velocities.…”

Section: Determination Of the Eddy Dispersion Termmentioning

confidence: 97%

New insights on mass transfer kinetics in chromatography

Gritti

Guiochon

2011

AIChE Journal

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Wiley Online Library (wileyonlinelibrary.com).The mass transfer kinetics of thiourea, phenol, ethylbenzene, propylbenzene, butylbenzene, and amylbenzene were studied on a Gemini-C 18 (5 lm, 110 Å , 375 m 2 /g) column (150 mm Â 4.6 mm) eluted with methanol/water solutions (100, 90, and 20% v/v). Each of the successive steps of the mass transfer of these solutes (axial diffusion, eddy dispersion, film mass transfer resistance, and transparticle mass transfer resistance) was unambiguously measured, using a combination of the peak parking method, the total pore blocking method, and moment analysis, in a wide range of reduced linear velocities. The results obtained offer new insights on the mass transfer kinetics in chromatographic columns. They show first that the eddy dispersion A-term is strongly correlated with the particle porosity. The complex, anastomosed transcolumn flow pattern causes extra band broadening. This transcolumn effect was found to be markedly smaller with porous particles than with nonporous particles of the same size. Second, the film mass transfer coefficient of retained compounds is smaller for porous than for nonporous particles, a result consistent with concentration gradients being steeper at the wall of solid particles than across the entrance surface of pores. The external mass transfer coefficient decreases with increasing fraction of the surface area of the particles that is open to pores, e.g., with increasing particle porosity.

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Section: Determination Of the Eddy Dispersion Termmentioning

confidence: 97%

New insights on mass transfer kinetics in chromatography

Gritti

Guiochon

2011

AIChE Journal

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“…According to precise NMR experiments, the constant c r is close to 0.30 for packed beds. 41 Nonporous particles or blocked mesopores: Flow-controlled mechanism When access to the mesopores is blocked by n-nonane, and the column is eluted with pure water, neither thiourea nor sodium nitrate can diffuse through the particles and X ¼ 0. They diffuse only across the intersticial space.…”

Section: Transcolumn Eddy Dispersionmentioning

confidence: 99%

Impact of retention on trans‐column velocity biases in packed columns

Gritti

Guiochon

2009

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).The heights equivalent to a theoretical plate of a weakly and strongly retained compounds were measured on two packed columns having different average mesopore sizes. The measurements were carried out in two different cases, with access to the mesopores by the sample molecules blocked (filled with n-nonane) or not. The experimental results demonstrate that the eddy dispersion terms of both columns are significantly smaller for porous than for nonporous particles. Two simultaneous phenomena explain this observation. First, packed columns are radially heterogeneous which causes significant trans-column velocity biases warping the bands. Second, radial dispersion contributes to mass transfer across the column, relaxing the radial concentration gradients that are caused by these velocity biases. The impact of these biases is minimized when the pores of the particles are not blocked; it decreases with increasing residence time and radial dispersion coefficient of the solutes. V

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“…Knox et al, 1976;Tallarek et al, 1995Tallarek et al, , 1996 . This is true for Ž columns packed with dry Eon, 1978;Horne et al, 1966;Knox .…”

Section: Introductionmentioning

confidence: 98%

“…Ž Tallarek et al, 1995Ž Tallarek et al, , 1996 , for analytical Baur et al, 1988;Baur and Wightman, 1989;Bayer et al, 1989Bayer et al, , 1995Eon, 1978;Farkas et al, 1994Farkas et al, , 1996Farkas et al, , 1997Farkas and Guiochon, 1997;Guiochon et al, 1997;Horne et al, 1966;Knox et al, 1976; . Tallarek et al, 1995Tallarek et al, , 1996 and for preparative columns ŽFarkas et al, 1997;Farkas and Guiochon, 1997;Guiochon et . al., 1997 .…”

Section: Introductionmentioning

confidence: 99%

Mechanics of column beds: I. Acquisition of the relevant parameters

2003

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The efficiency of chromatographic columns is ad®ersely affected by large-scale radial ®ariations of the packing density or ®oid ratio of the material used to prepare the bed. This heterogeneity is due to wall friction effects that take place during the preparation of the column and to seepage effects operating during the packing process and the subsequent operation of the column. The dependence of the bed's ®oid fraction on the stress applied during its consolidation was determined, as well as its permeability at ®arious stages of the consolidation process and the coefficient of friction between typical packing materials and the stainless steel wall of chromatographic columns. These results are required to de®elop and use numerical models of the ®olumetric response to axial compression of the bed and models of the coupled mechanical-seepage rheology of particulate materials.

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Measurement of transverse and axial apparent dispersion coefficients in packed beds

Cited by 96 publications

References 57 publications

New insights on mass transfer kinetics in chromatography

New insights on mass transfer kinetics in chromatography

Impact of retention on trans‐column velocity biases in packed columns

Mechanics of column beds: I. Acquisition of the relevant parameters

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