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Adsorption of gases on carbon molecular sieves used for air separation. Spherical adsorptives as probes for kinetic selectivity

Lookup NU author(s): Calum Reid, Emeritus Professor Mark Thomas

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Abstract

The adsorption of oxygen, nitrogen, and a series of noble gases (neon, argon, and krypton) on a carbon molecular sieve were studied over a range of temperatures above the critical temperature of the adsorptives as a function of pressure in order to understand further the mechanism of air separation. The noble gases were used as probes for the selective porosity in the carbon molecular sieve. The uptakes of all gases studied were virtually linear at low equilibrium pressures in agreement with Henry's law, but deviation occurred at higher pressures. The isosteric enthalpies of adsorption were calculated from the variation in the Henry's law constant with temperature. The adsorption kinetics were studied with different amounts of preadsorbed gas for pressure increments in the range 1-100 kPa. The adsorption kinetics obey a linear driving force mass transfer model for oxygen, nitrogen, argon, and krypton for the experimental conditions studied. The adsorption kinetics for neon deviate from this model, and the data fit a kinetic model which combines diffusion and barrier resistance characteristics. The ratios of the rate constants (k(O2)/k(N2)) for each pressure increment in the pressure range 0-9 kPa over the temperature range 303-313 K were typically 25, and this clearly demonstrates the molecular sieving characteristics. The activation energies for the adsorption process were in the order krypton > argon > nitrogen > oxygen ∼ neon. The results are discussed in terms of the mechanism of gas separation using carbon molecular sieves.


Publication metadata

Author(s): Reid CR, O'koye IP, Thomas KM

Publication type: Article

Publication status: Published

Journal: Langmuir

Year: 1998

Volume: 14

Issue: 9

Pages: 2415-2425

Print publication date: 09/04/1998

ISSN (print): 0743-7463

ISSN (electronic): 1520-5827

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/la9709296

DOI: 10.1021/la9709296


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