Contributions to frequency response models for mass transfer in adsorbents

Giesy, Timothy J.; LeVan, M. Douglas

doi:10.1016/j.ces.2014.05.056

Cited by 3 publications

(4 citation statements)

References 23 publications

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“…The theory has been further developed and established for the analytic expressions for adsorbed‐phase functions including contributions from micropore and macropore diffusion, surface barrier resistance, and nonisothermal effects . In addition to this, core‐shell models have been developed for “shell and core” interpretation of the carbon molecular sieve surface barrier with different levels of complexity.…”

Section: Introductionmentioning

confidence: 99%

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

2016

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A new pressure‐swing frequency response (PSFR) method has been developed to study mass transfer in adsorption systems as a function of temperature and pressure, from −70 to 180°C, and up to 7 bar. New in‐phase and out‐of‐phase functions have been derived for the PSFR in a general way to allow information extracted from it independent of whether the system is operated in a batch volume swing or a flow‐through pressure swing mode. A new mathematical model that considers distribution of diffusion rates has been introduced to account for diffusive transport in heterogeneous samples. Numerical simulation results have shown that a single rate diffusion model works well when heterogeneity can be described by a normal distribution, but not for asymmetrically bimodal distributions. As a test reference system, the transport of ethane in ZIF‐8 was investigated at different pressures and temperatures using the new PSFR method. The mass transfer was found to be dominated by micropore diffusion. Diffusivity was found to be weakly dependent on pressure or loading, but quite strongly dependent on temperature. The results agree very well with our independent batch volume frequency response technique experiments. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1077–1090, 2017

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Section: Introductionmentioning

confidence: 99%

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

2016

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“…As mentioned in the introduction section, general adsorbed-phase mathematical models have been derived to represent multiple dynamic processes, including diffusion, surface barrier, and heat effects, as well as a more complex combination of these mass transfer resistances. A summary of these general functions can be found in detail elsewhere [39,40,68,69,75]. The real and imaginary parts of the adsorbed-phase transfer function G n in the PSFR and CSFR can be expressed in terms of the dimensionless characteristic functions (δ c and δ s ), which is widely adopted in the traditional analysis of VSFR to have Therefore, FR data from different techniques can be analyzed with similar mathematical models developed over decades, and some commonly used models are summarized in the following sections.…”

Section: Adsorbed-phase Transfer Functionsmentioning

confidence: 99%

Identification of mass transfer resistances in microporous materials using frequency response methods

Wang

2021

Adsorption

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The frequency response (FR) method, a pseudo-steady state relaxation technique employing perturbation frequency, plays an essential role in discriminating between multi-kinetic mechanisms in microporous materials for separation and catalytic processes. Experimental and theoretical principles are reviewed for three frequency response methods, including one commonly used batch system with volume perturbation and two recently developed flow-through systems with pressure or concentration oscillation. Even though these methods have different overall transfer functions, they can be linked closely through the adsorbed-phase functions, which account for individual or coupling of mass transfer resistances and heat effects. Mass transfer resistances include micropore diffusion, macropore diffusion, surface barriers, and external film resistance. By judicious application of FR methods, it is not only possible to identify dominating mass transfer resistances but also to extract reliable mass transfer coefficients based on corresponding mathematical models. Representative examples to display the ability of the FR methods in studies of zeolites, carbon molecular sieves, and other microporous materials are discussed. Mixture studies and future developments, including nonlinear frequency response and chemical reactions, have also been briefly described.

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“…A summary of these general functions can be found in detail elsewhere. 54,55 Here, representative models considered in this paper are given in the following.…”

Section: G S G S Tanmentioning

confidence: 99%

“…General adsorbed-phase transfer functions have been derived to represent multiple dynamic processes, including diffusion, surface barrier, and heat effects. A summary of these general functions can be found in detail elsewhere. , Here, representative models considered in this paper are given in the following.…”

Section: Theorymentioning

confidence: 99%

Evidence of Combined Heat-Transfer and Surface Barrier Resistances for Propane in Commercial ZIF-8 Crystals Probed by Pressure-Swing Frequency Response

Wang

2021

Ind. Eng. Chem. Res.

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Shedding light on the controlling transport step in nanoporous materials, the pressure swing frequency response has been developed to investigate the mass-transfer mechanisms and rates for propane in commercial ZIF-8 crystals with submicron sizes, at multiple pressures and temperatures.The system shows a bimodal response that cannot be described by a single diffusion or surface barrier model. The concept of introducing inert metal beads is adequate to elucidate the cause for the bimodal behavior from additional heat or mass-transfer steps. The resulting change of the response curves demonstrates the heat transfer is the dominating step, leading to the bimodal behavior with a mass-transfer step faster than the heat-transfer step. Furthermore, mathematical treatment has been developed to eliminate nonadsorption dynamics at high frequencies, permitting the upper frequency to extend at least 1 order of magnitude to 1 Hz for the current system. As a result, it allows the determination of the mass-transfer mechanism for systems with relatively fast kinetics. Propane in the submicron ZIF-8 crystals is found to be controlled by the combined heat-transfer and surface barrier resistances, in contrast to most accounts of micropore diffusion in the literature. The surface barrier exhibits a concentration dependence stronger than the Darken prediction, having the activation energy of 29 kJ/mol, which is close to values of the isosteric heat. This example suggests extreme caution should be taken with respect to the isothermal diffusion mechanism assumed to be in play during the evaluation of kinetic data. The contribution of the heat and surface barriers can be significant for the adsorption systems with appreciable isosteric heat and small crystals. Accordingly, their interference could hinder the separation performance as opposed to the expectation from diffusion alone.

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Contributions to frequency response models for mass transfer in adsorbents

Cited by 3 publications

References 23 publications

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

Identification of mass transfer resistances in microporous materials using frequency response methods

Evidence of Combined Heat-Transfer and Surface Barrier Resistances for Propane in Commercial ZIF-8 Crystals Probed by Pressure-Swing Frequency Response

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