Master curves for mass transfer in bidisperse adsorbents for pressure‐swing and volume‐swing frequency response methods

Abstract

A general model has been developed for pressure-swing and volume-swing frequency response methods with analytical solutions derived to analyze various mass transfer resistances in biporous adsorbents. The model can consider a combination of distributed mass transfer resistances acting independently or in series including macropore diffusion, micropore diffusion, and a surface barrier resistance at the entrance of micropores. Heat effects are included for nonisothermal systems. Temperature variations are shown to be less for pressure-swing compared with volume-swing systems. The general model is developed in such a way that information extracted from it is independent of whether a system is batch volume swing or flow-through pressure swing. Simulation results demonstrate that mass transfer mechanisms can be easily discriminated by the master curves. Isothermal models exhibit one-step curves, whereas nonisothermal effects are represented by two-step curves. Examples are given to demonstrate the use of the master curves to describe experimental data.

Measurement of Mass Transfer Rates in Adsorbents: New Combined-Technique Frequency Response Apparatus and Application to CO2 in 13X Zeolite

“…33 As they discuss, the amplitude ratio has been found to be useful by itself in identifying controlling mechanisms and evaluating rate parameters. For PSFR, the amplitude ratio is given by the following:…”

“…The work by Wang and LeVan 33 gives expressions for G n for various mass transfer mechanisms. An additional case, the case of nonisothermal macropore diffusion control, is of interest for bidispersed adsorbent systems with significant heats of adsorption and/or slow heat transfer rates.…”

Slow diffusion of methane in ultra-micropores of silicon carbide-derived carbon

“…Subsequently, some studies have resurrected the Schneider and Smith [26] approach, considering particle scale diffusion in the micropores with negligible transport resistance at the microscale, but with a nonlinear isotherm and finite mass exchange rate between macropores and micropores [36][37][38]. In other work, Loughlin et al [39], Qinglin et al [40,41] and Wang and LeVan [42] have considered a surface barrier resistance in series with a micropore diffusion resistance for the diffusion of gases in carbon molecular sieves, with negligible direct contribution of micropores to the macroscale flux.…”

Mass Transfer of Binary Mixtures of Oxygen and Argon in a Carbon Molecular Sieve

“…Expressions for G n,i can be derived for a variety of mass transfer mechanisms 39,40 including multicomponent models with cross coefficients. 33 Adsorbed-phase transfer functions are given here only for simple systems with no cross-coefficients.…”