Predicting Gas Transport in Formed Zeolite Adsorbents from NMR Studies

• Published in: Journal of the American Chemical Society Vol. 124; no. 19; pp. 5264 - 5265
• Main Authors: Rittig, Frank, Coe, Charles G., Zielinski, John M.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.05.2002
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; Surface physical chemistry; Zeolites: preparations and properties; Methane; Nitrogen 15; Nitrogen molecules; Aluminosilicates; NMR spectrometry; Inorganic adsorbent; Experimental study; Molecular sieve; Transport process; Carbon monoxide; Diffusion coefficient; Carbon 13; Physicochemical properties
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja020194d

The self-diffusion of nitrogen, methane, and carbon monoxide within a 5A zeolitic adsorbent has been examined with use of pulsed field gradient (PFG) NMR. In all cases, the diffusion process is well-described by a refined version of the long-range diffusion model (LRDM), adapted here for use with pelletized adsorbents, which uses exclusively adsorbent porosity and isotherm data as inputs. Correlation of the experimental data with this model yields tortuosity factors that are characteristic of the adsorbate and reflect the longer diffusive path a molecule must take due to the winding nature of the pore structure. It is demonstrated that the diffusion model can be used to accurately predict the diffusion coefficients for a ternary gas mixture within a 5A zeolite. To fully characterize the diffusive process, the surface excess on the PFG NMR samples has been obtained by a novel gas-phase NMR technique that is well-suited for measuring pure and multicomponent isotherms.