An Evaluation of Method for Investigating Sorption and Diffusion in Porous Solids

Abstract

Transient response curves are obtained by perturbing the steady-state concentration of the input stream to a "gradient-free" sorption vessel. The response curves are interpreted by means of a mathematical model to give values of the slope of the sorption isotherm and the effective diffusivity. The method was evaluated using the system: zeolite NaX-propylene-nitrogen. The assumptions of the mathematical model are well supported except for the assumption of negligible truncation error in the values of the sorption parameter. The sorption isotherms and heats of sorption agree reasonably well with other results where comparisons can be made. The concentration dependence of the effective diffusivity is explained by the mathematical model and the nonlinearity of the sorption isotherm.

Use of stirred batch reactors for the assessment of adsorption constants in porous solid catalysts with simultaneous diffusion and reaction. Theoretical analysis

“…Thus, the conventional pulse techniques in gradientless reactors, leading to transient curves of concentrations at a given temperature (e.g. Ma and Roux, 1973;Furusawa et al, 1976;Kelly and Fuller, 1980;Oberoi et al, 1980;Frost, 1981;Schobert and Ma, 1981a,b;Miró et al, 1986), would be adequate for the estimation of adsorption and reaction parameters only when it is possible to change over a wide range of values. In cases where the design of the reactor or the system's capacity of adsorption imposes 1 or (K pE app /K) 1, alternative strategies and techniques need to be developed.…”

Adsorption characteristics of octadecylsilyl‐silica gel in gaseous systems

“…November 1993 Kawazoe et al, 1974;Kelly and Fuller, 1980;Ruthven, 1984;Ruthven and Doetsch, 1976;Ruthven and Kumar, 1979;Schneider and Smith, 1968a,b;Shah and Ruthven, 1977;Sladek et al, 1974). It is well established that in many cases surface diffusion has an important role for intraparticle mass transport, and that the surface and/or intraparticle diffusion coefficients show positive concentration dependence on the amount adsorbed (Chihara et al, 1978b;Gilliland et al, 1974;Higashi et al, 1963;Kawazoe et al, 1974;No11 et al, 1992;Okazaki et al, 1981;Ruthven and Loughlin, 1971).…”

Measurement of effective diffusivity from effluent concentration of a flow through diffusion cell

“…Overall effective diffusion coefficients, or their subsidiary components, have been found from the dynamic response of a packed bed to either pulse or step inputs, as typified by Hashimoto and Smith (1973) and Masamune and Smith (196S), or from numerous other methods typified by Burghardt and Smith (1979), Villermaux and Matras (1973), Kelly and Fuller (1980), Ma and Lee (1976), and Kondis and Dranoff (1971). While almost all of these methods were capable of isolating the individual internal rate constants that made up the overall effective diffusion coefficient from the external rate constants, they either were mathematically complicated, required special sample preparation, o r w e r e not conducive to high temperature-pressure operation.…”

“…andHashimoto and Smith (1973) have described the use of the response of a step input and an impulse input, respectively, to a packed bed for obtaining the various internal and external mass transfer coefficients. Burghardt and Smith (1979) have described pulse-response methods for two modifications of the single pellet Wicke-Kallenbach (1941) cell Kelly and Fuller (1980). have used response methods with six single-pellet diffusion cells, each having only one end open to a well-mixed, flow through vessel.…”