(33d) Frequency Response Methods for Mass Transfer Study On Porous Materials | AIChE

(33d) Frequency Response Methods for Mass Transfer Study On Porous Materials


Wang, Y. - Presenter, ExxonMobil Research and Engineering Co
Kortunov, P., ExxonMobil Research and Engineering
Paur, C., ExxonMobil Research and Engineering
Ravikovitch, P., ExxonMobil Research and Engineering

Frequency Response Methods for Mass Transfer Study on Porous Materials

Yu Wang, Pavel Kortunov, Charanjit Paur, Peter Ravikovitch

ExxonMobil Research and Engineering Company, Corporate Strategic Research

1545 Route 22 East, Annandale, NJ 08801

Knowledge of mass transfer mechanisms and rates is important for understanding transport phenomena inside porous adsorbents and catalysts as well as for the design of adsorption and catalytic processes.  By introducing harmonic perturbations at various frequencies of oscillation, frequency response (FR) permits the decoupling of individual mass transfer steps within a complex system. Thus, it is capable of discriminating among different rate-liming mechanisms. 

FR techniques developed for pure components include volume swing FR for a batch system and pressure swing FR for a flow system.  A general model is presented to unify these two approaches for analyzing various mass transfer resistances including macropore diffusion, micropore diffusion, and surface barrier represented by LDF model, either independently or in combination.  Heat effects can be included for non-isothermal cases.   Furthermore, the heterogeneous properties of adsorbent/catalyst such as pore size distribution or pore mouth size can be described by introduction of continuous distribution of mass transfer rates, such as LDF, micropore diffusion and macropore diffusion time constants.  With continuous development of the library of various mass transfer models, frequency response techniques can be applied to more complicated systems to determine accurate mass transfer mechanisms and rates.

Examples will be given for diffusion of light hydrocarbons on commercial microporous materials.  By incorporating volume-swing FR (covering very low pressure and fast frequency range), and pressure-swing FR (covering higher pressure and slow frequency range), we provide a thorough mass transfer study in a wide range of temperatures and pressures.