Determining surface areas from linear adsorption isotherms at supercritical conditions

被引:32
作者
Aranovich, G [1 ]
Donohue, M [1 ]
机构
[1] JOHNS HOPKINS UNIV, DEPT CHEM ENGN, BALTIMORE, MD 21218 USA
基金
美国国家科学基金会;
关键词
adsorption isotherm; monolayer coverage; specific surface area; macroporous and microporous adsorbents; supercritical conditions;
D O I
10.1006/jcis.1997.5099
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Here we demonstrate that there is a wide range of pressures at supercritical temperatures where there is essentially monolayer coverage (i.e., there is nearly a complete layer of molecules adsorbed adjacent to the surface, but very little excess density in the second and subsequent layers). In this regime, the dependence of the Gibbs adsorption on the density is linear, and coefficients of this linear function depend on the monolayer capacity and surface area. It is shown that measurements of the Gibbs adsorption in this regime can be used to determine surface area without knowledge of the area per molecule or a model for the adsorption isotherm. This new method has the potential to provide reliable values of specific surface area for macroporous, mesoporous, and microporous systems without the limitations of previous methods. Lattice-theory calculations suggest that the best conditions for surface area measurements are in the supercritical region with temperatures about twice the critical temperature and pressures well above the critical pressure. These conditions allow nearly complete monolayer coverage but there is not multilayer adsorption because the temperature is sufficiently above the critical temperature of the adsorbate. (C) 1997 Academic Press.
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页码:392 / 397
页数:6
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