Analysis of Adsorption Isotherms: Lattice Theory Predictions, Classification of Isotherms for Gas–Solid Equilibria, and Similarities in Gas and Liquid Adsorption Behavior
✍ Scribed by Grigoriy Aranovich; Marc Donohue
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 610 KB
- Volume
- 200
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
sorption isotherms, (1) which is illustrated in Fig. 1. Type Adsorption at fluid-solid interfaces is considered in the frame-I isotherms are characteristic of microporous adsorbents. work of a lattice with boundaries. Using ideas proposed by S. Types II and III describe adsorption on macroporous adsor-Ono and S. Kondo ( in ''Molecular Theory of Surface Tension in bents with strong and weak adsorbate-adsorbent interac-Liquids'' (S. Flu ¨gge, Ed.), Encyclopedia of Physics, Vol. 10, p. tions respectively. Types IV and V represent adsorption iso-134. Springer-Verlag, Berlin, 1960), a lattice model is derived, therms with hysteresis. In addition to the five types of isoboth rigorously and phenomenologically, and applied to macro-, therms identified by BDDT, the IUPAC classification meso-, and microporous adsorbents by imposing different boundincludes a sixth isotherm (Type VI) which has steps. All of ary conditions. It is shown that this lattice theory can predict the entire spectrum of behavior observed when gases, liquids, or these types of isotherms have been observed in numerous supercritical fluids adsorb on solid surfaces. In particular, it is able experiments (3) and have been analyzed theoretically (see, to predict steps in the isotherms, scaling behavior near saturation for example, (4, 5)).
conditions, supercritical behavior, and adsorption hysteresis. It is
However, the IUPAC classification has two deficiencies: shown that there is a profound analogy in the adsorption behavior it is incomplete and it gives the incorrect impression that of a one-component gas to that of a binary liquid mixture. This adsorption isotherms are always monotonic functions of analysis leads to a new classification of physisorption isotherms pressure. To illustrate these points, consider the following for fluid/solid equilibria. ᭧ 1998 Academic Press experimental isotherms.