Universal singularities of multilayer adsorption isotherms and determination of surface area of adsorbents

Journal Article · Mon Jul 15 04:00:00 EDT 1996 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1996.0383· OSTI ID:276720

Aranovich, G L; Donohue, M D ^[1]

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1. Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Chemical Engineering

The singularity in the adsorption isotherm for macroporous and nonporous adsorbents is considered as a universal function that can be characterized with two parameters: a coefficient of proportionality, K, and an exponent, d. It is shown that the value of K is proportional to the adsorbent surface area but does not depend on the nature of the adsorbent. This leads to a new method to determine the surface area of an adsorbent, S, that is independent of the form of the adsorption isotherm at low and moderate reduced pressures. Comparison with the BET areas for nitrogen shows that the new method gives the values of S which are very close to the BET results if K = 1.47 {times} 10{sup {minus}5} mol/m{sup 2} (for nitrogen). Analysis of adsorption data for macroporous adsorbents shows that the BET isotherm gives systematic deviations and that the experimental amount adsorbed is smaller than the value predicted by the BET equation (even in the range of the best agreement with experiment). These deviations lead to systematic error in the values of S of about 43%. Using K equal to K{sub f} = 1/{sigma}N{sub A} (=1.025 {times} 10{sup {minus}5} mol/m{sup 2} for nitrogen), the authors are able to eliminate systematic error in the surface area determination. Here {sigma} is the area occupied by one molecule and N{sub A} is the Avogadro number.

• DOE Contract Number: FG02-87ER13777
• OSTI ID: 276720
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 1 Vol. 181; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ADSORBENTS
ADSORPTION ISOTHERMS
MEASURING METHODS
POROUS MATERIALS
SURFACE AREA