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Transient measurements of adsorption and diffusion in H‐ZSM‐5 membranes
Author(s) -
Gardner Tracy Q.,
Flores Ana I.,
Noble Richard D.,
Falconer John L.
Publication year - 2002
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690480604
Subject(s) - zeolite , adsorption , diffusion , membrane , chemistry , permeation , calorimetry , gravimetric analysis , langmuir , analytical chemistry (journal) , differential scanning calorimetry , thermodynamics , chromatography , organic chemistry , catalysis , biochemistry , physics
A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H‐ZSM‐5 tubular membranes and modeled assuming Maxwell‐Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N 2 and CO 2 were nearly identical to those measured by calorimetry on H‐ZSM‐5 powders. The CH 4 isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na‐ZSM‐5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell‐Stefan diffusion coefficients D MS depended on concentration and were higher for higher feed partial pressures. Average D MS values for the two membranes were 7.5, 5 and 1.5×10 −10 m 2 /s for N 2 , CH 4 , and CO 2 , respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.