Investigation of Mixture Diffusion in Nanoporous Adsorbents via the Pressure-Swing Frequency Response Method. 2. Oxygen and Nitrogen in a Carbon Molecular Sieve

and, Yu Wang; LeVan, M. Douglas

doi:10.1021/ie0489352

Cited by 19 publications

(18 citation statements)

References 34 publications

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“…Similar trends were observed for the N 2 -O 2 mixture on 4A at 273 K [92]. Later, Wang and LeVan [94] applied the flow-through PSFR system to investigate the N 2 -O 2 mixture in CMS system at several concentrations and found the cross-term diffusivities can be essential to describe mass transfer rates for mixture separation of kinetic origin. Their correlation results showed that the main-term diffusivities are weak functions of the concentration, while the diffusive cross-terms are strong functions of the composition.…”

Section: Multi-component Mixtures In Microporous Materialssupporting

confidence: 62%

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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Section: Multi-component Mixtures In Microporous Materialssupporting

confidence: 62%

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

Wang

2021

Adsorption

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“…In general, the kinetics or mass transfer rate of adsorption and desorption of a pure gas in a microporous adsorbent can be controlled by a single mechanism, like micropore diffusion, macropore diffusion, or macropore advection, or any combination of these mechanisms . In recent decades, frequency response (FR) methods − have proven to be one of the best macroscopic techniques for investigating the kinetic behavior of gas adsorbate–adsorbent systems due to their ability to discriminate among different rate limiting mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…Besides VFR, another type of widely used frequency response is a flow-through technique that involves perturbation of variables like inlet flow rate, inlet stream concentration, − or pressure. − In recent years, LeVan and co-workers used a combined frequency response technique using volumetric and flow-through experiments to study pure gas mass transfer rates in adsorbents or combined pressure-swing and concentration-swing frequency response experiments to study mass transfer rates for both single and mixed gases in various adsorbents. , Most recently, Wang et al used a pressure swing frequency response to study the mass transfer mechanism of ethane in ZIF-8 material and verified the results against VFR.…”

Section: Introductionmentioning

confidence: 99%

110th Anniversary: New Volumetric Frequency Response System for Determining Mass Transfer Mechanisms in Microporous Adsorbents

Hossain

Holland

Ebner

et al. 2019

Ind. Eng. Chem. Res.

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A new volumetric frequency response (VFR) system was developed for studying the mass transfer characteristics of gases in microporous adsorbents. For this VFR system, the differential pressure response from a small perturbation in volume was measured in a closed system after equilibrium was established for a gas adsorbate–adsorbent pair at constant temperature and pressure. It operates over a wide range of frequencies from 10–5 to 10 Hz, from atmospheric pressure down to vacuum pressures of 100 Torr, and at temperatures from 5 to 80 °C. The sample chamber holds up to 100 g of adsorbent. These operating ranges make this new VFR system capable of measuring mass transfer characteristics of adsorbate–adsorbent systems at conditions relevant to many commercial separation processes using a relatively large volume of adsorbent in a unique packed bed arrangement. The apparatus and procedure were described in detail, including the use of runs with different gases and different porous and nonporous solid beads and pellets to fully characterize the system in terms of its dynamic behavior especially at high frequencies and in terms of various volumes required in the analyses. It was shown how to analyze these baseline runs to correct for gas compression heating and pressure drop effects in the high frequency region of the pressure change amplitude response curves and to determine intensity (or amplitude ratio) and phase shift (or lag) response curves from which fundamental thermodynamic and kinetic information for an adsorbate–adsorbent pair could be extracted. To demonstrate the utility of this new VFR system, experiments were carried out with CO2 in 13X zeolite beads at 25 °C and 100, 200, and 760 Torr using 32 frequencies at each pressure. Slopes of this isotherm estimated from the intensity response curves at low frequency showed very good agreement with those measured independently. The mass transfer time constant estimated from the maximum in the phase lag response curve also agreed well with that reported in the literature. Unique features of the intensity and phase lag response curves were revealed.

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“…47 The model developed for the concentration swing apparatus is similar to the model used to describe the dynamics of their pressure swing frequency response apparatus. [48][49][50] It should be noted that most of the FR works discussed above assume that small perturbations to the system allow for portions of the kinetic model to be linearized. However, several studies have investigated nonlinear kinetic modeling of FR data.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of Condensable Vapors in Single Adsorbent Particles Measured via Concentration-Swing Frequency Response

2008

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A concentration-swing frequency response method is extended to examine mass transfer mechanisms and the concentration dependence of mass transfer rates for adsorption of condensable vapors in single adsorbent particles. The adsorption kinetics of water and hexane in BPL activated carbon and the adsorption of water in silica gel are determined at several different concentrations. The mechanism that best describes the adsorption of water in BPL activated carbon is nanopore diffusion. The diffusivity of water in BPL activated carbon has a clear minimum at approximately P/Po = 0.5, and the concentration dependence of the diffusion data are not described well by the Darken relationship. Both nanopore diffusion and the Glueckauf linear driving force models can be used to describe the diffusion of hexane in BPL activated carbon for the pressure range studied, and the dependence of the diffusivity on concentration can be described approximately using the Darken relationship. However, the diffusion of water in silica gel cannot be described by the nanopore diffusion model and is best characterized by the Glueckauf linear driving force model. The results illustrate the ability of concentration-swing frequency response to accurately determine adsorption rate mechanisms and quantify the complex adsorption kinetics of condensable vapors using small quantities of adsorbent.

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Investigation of Mixture Diffusion in Nanoporous Adsorbents via the Pressure-Swing Frequency Response Method. 2. Oxygen and Nitrogen in a Carbon Molecular Sieve

Cited by 19 publications

References 34 publications

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

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

110th Anniversary: New Volumetric Frequency Response System for Determining Mass Transfer Mechanisms in Microporous Adsorbents

Diffusion of Condensable Vapors in Single Adsorbent Particles Measured via Concentration-Swing Frequency Response

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