Diffusion and adsorption in arrested-flow chromatography

✍ Scribed by Moonsoo Oh; J. M. Smith; B. J. McCoy

• Publisher: American Institute of Chemical Engineers
• Year: 1989
• Tongue: English
• Weight: 359 KB
• Volume: 35
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690350723

✦ Synopsis

Arrested-flow chromatography has proven successful for measuring gas-phase diffusion coefficients in open tubes (McCoy and Moffat, 1986), and intraparticle diffusion coefficients in columns packed with large-pore particles (Park et al., 1987). The approach was verified experimentally by measurements with nonadsorbing species. For small-pore particles with nonadsorbing gases, the intraparticle transport was too small to yield accurate intraparticle diffusivities. The present work shows that this limitation to large-pore particles can be overcome by using an adsorbing gas.

Suppose adsorption rates are very large with respect to diffusion rate, for example, as in physical adsorption. Then the expression for the spatial variance of a chromatographic peak that has broadened during a period of arrested flow (Park et al., 1987) is:

The spatial variance is equal to the observed temporal variance, divided by the square of the peak velocity. For adsorbing gases, the total capacity of the column now includes the adsorption equilibrium coefficient, K , i.e.,