New Developments in Flow-Through Apparatus for Measurement of Adsorption Mass-Transfer Rates by Frequency Response Method

Abstract

A new flow-through frequency response method based on a sinusoidal modulation of pressure is developed to measure gas adsorption equilibria and kinetics simultaneously. The transfer phenomena of pure N 2 and O 2 gases in carbon molecular sieve are investigated for different pressures and particle sizes by this method. Also, this apparatus has been extended to measure data for mixtures at different compositions at atmospheric pressure and room temperature. This is the first application of the flow FR system for a mixture. A negative cross-term diffusivity is reported. It shows that for co-diffusion, the fast diffusing molecule O 2 is decelerated by the slow diffusing molecule N 2 , and the slower moving molecule N 2 is sped up by the faster moving O 2 . The main-term diffusivities agree with the pure component diffusivities.

Kinetics of Water Adsorption in UiO-66 MOF

“…The FR method can characterize multiple mass-transfer resistances that may be present with a broad range of time constants. Over the past few decades, FR methods have been extensively studied both experimentally and theoretically. − Frequency response methods have also been used to measure the diffusion of water and other condensable vapors in adsorbent materials. ,,,, …”

“…Specifically, LeVan et al have done extensive theoretical and experimental development on frequency response methods. ,,,− Wang and LeVan developed a flow-through concentration-swing frequency response (CSFR) apparatus that perturbs the concentration of the system sinusoidally while maintaining a constant total flow rate . Use of a flow-through system minimizes heat effects thereby allowing the system to be treated isothermally.…”

Exploring Crystal Morphology of Nanoporous Hosts from Time‐Dependent Guest Profiles

“…It was common practice to apply Ficks 1st law to analyze the rate of molecular uptake or release following a change in the pressure of the surrounding atmosphere. [1,2] This approach, however led to much smaller effective diffusion coefficients, which could only be attributed to the existence of transport resistance on the external surface of the crystal (that is, surface barriers, there are numerous models concerning their origin [3][4][5][6][7] ). In addition there could be other barriers within the pore system of the zeolite bulk phase, acting in addition to the transport resistance.…”

Diffusion in nanopores: inspecting the grounds

“…Final equilibration therefore includes heat exchange with the surrounding which, especially for high intraparticle diffusivities, may become rate-determining for the overall kinetics. The development of strategies for keeping the influence of extra-particle effects on mass transfer as small as possible has served as a major driving force for the development and further accomplishment of experimental techniques for transient diffusion measurement, including the chromatographic methods (Haynes 1988), notably the zero-length column (ZLC) technique (Eic and Ruthven 1988;Brandani and Ruthven 1995;Ruthven and Brandani 2000), and the frequency response (FR) technique (Yasuda 1994;Rees and Song 2000;Wang and Levan 2005;Giesy et al 2012).…”