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Polanyi potential theory micropores adsorption

Peculiarities of Adsorption in Microporous Carbons (the Polanyi Potential Theory Dubinin and Related)... [Pg.123]

A major development in understanding the adsorption of gases and vapors on microporous carbons was provided by the potential theory of adsorption by Polanyi. This theory assumes that, on the adsorbent surface, the gas molecules are compressed by attractive forces acting between the surface and the molecules, and these forces decrease with the increasing distance from the surface. The force of attraction at any given point near the surface is measured by the adsorption potential (A), which can be defined as the work done to transfer a molecule from the gas phase to a given point above the surface. [Pg.124]

In the Dubiiiin-Radushkevitch (DR) equation [115], an adsorption model derived from a concept of Dubinin [20] based on Polanyi potential theory, the fluid volume V adsorbed in micropores at pressure P is represented empirically as... [Pg.237]

The potential theory of adsorption was introduced by Polanyi in 1914. Dubinin [48,49] and Stoeckli et al. [50] improved the theory and termed it the theory of volume filling of micropores (TVFM). This theory has been widely used in correlating the effect of temperature on the adsorption isotherms of pure gases. The modern formulationof TVFM is the Dubinin-Astakhov (DA) equation, which is expressed as... [Pg.413]

Based on the Polanyi potential theory, different approaches to describe the adsorption behavior of a purely microporous material (isotherm type I, Figure 21.25) have been undertaken by Dubinin and Stockli in collaboration with different other scientists. The simplest relationship that can be considered the base for all other variants is the Dubinin-Radushkevich equation [58] ... [Pg.475]

The potential theory of adsorption first introduced in 1914 by Polanyi" " and later modified by Dubinin for adsorption on microporous adsorbents is still regarded as fundamentally sound and accepted as correct and better than all the other theories. This longevity of the theory is due to its essentially thermodynamic character and lack of insistence on a detailed physical picture. [Pg.112]

Adsorption theory of the volume filing of micropores (TVFM theory) has been proposed by Dubinin and Radushkievich [136], but this approach has originated from the potential theory of adsorption introduced by Eucken [112] and Polanyi [113,114]. [Pg.16]

An alternative to the localized theory of adsorption is the so-called potential theory, which has been developed as a slab adsorption theory on a surface and its analog for adsorption in microporous media, the theory of volume filling in micropores (TVFM). The potential theory of adsorption, first formulated by Polanyi [91], is widely used for the description of adsorption of gases on a solid. The TVFM is applied to adsorption in activated carbons, silica gels, and other types of microporous medium. [Pg.408]

Microporous materials exhibit type 1 isotherms since the size of the pores restricts adsorption into a few layers. The Held strength within the pores is so great that it is difficult to determine whether the adsorbate packs as a liquid or in a more condensed form. Polanyi [51] assumed that above the critical temperature the adsorbate can adsorb only as a vapor whose density increases as it approaches the surface around the critical temperature the vapor near the surface starts to liquefy, and substantially below the critical temperature the adsorbate completely liquefies. Under this final condition, the adsorbed volume of liquid (v) can be determined from the adsorption isotherm. Polanyi potential theory states that the adsorption potential for adsorbate in the liquid state is given by the isothermal work required (e) to compress the vapor from its equilibrium pressure (P) to its saturated vapor pressure... [Pg.58]

This equation is based on the Polanyi potential theory for the determination of micropore volume [53,54]. In this theory it is postulated that the force of attraction at any point in the adsorbed film is given by the adsorption potential (e), defined as the work done by... [Pg.58]

The Dubinin-Radushkevich (DR) equation was originally devised as an empirical expression of the Polanyi adsorption potential theory, and due to its simplicity it has been widely used to correlate adsorption data in many microporous sohds despite its failure in giving the correct Henry constant at extremely low pressures. This equation is based on the premise that adsorption in micropores follows a mechanism of pore filhng rather than the molecular layering and capillary condensation as proposed for mesoporous sofids. It has the form ... [Pg.247]

The POLANYI-DUBININ adsorption potential theory is used to characterize the micropore network of zeolites (ref. 10). An isotherm at a given temperature T (expressed in volume adsorbed per activated zeolite mass unit, W, as a function of the relative pressure p/Pq) is treated in the DUBININ-RADUSHKEVICH model (ref. 11) (denoted D-R) in the linear form log W = f[(Tlog Po/p) ] ... [Pg.567]

Dubinin and coworkers, during the course of their extensive studies on activated carbons, have developed the so-called theory of volume filling of micropores. Based on numerous experimental data, Dubinin and collaborators have added a second postulate to the Polanyi theory, which complements it. For an identical degree of filling of the volume of adsorption space, the ratio of adsorption potentials for any two vapors is constant ... [Pg.125]

The Dubinin adsorption isotherm equation is a good tool for the measurement of the micropore volume. This isotherm can be deduced with the help of Dubinin s theory of volume filling, and Polanyi s adsorption potential [11,26], The Dubinin adsorption isotherm equation has the following form [11]... [Pg.292]

The Dubinin-Radushkevieh (DR) equation is usually applied to describe the physical adsorption of organic vapors on microporous adsorbents. It is based on the micropore volume-filling theory and the Polanyi concept of adsorption potential. The DR equation can be expressed as... [Pg.286]

Now let us overview the theoretical adsorption models for characterization of the pore structures according to the pore size range. For physical adsorption of the gas molecules on such microporous sohds as activated carbons and zeolites, Dubinin and Radushkevich developed an empirical equation, which describes the volume filling process in the micropoies. Their theory incorporates earlier work by Polanyi in regard to the adsorption potential ad defined as... [Pg.151]

In Chapter 2, we discussed the fundamentals of adsorption equilibria for pure component, and in Chapter 3 we presented various empirical equations, practical for the calculation of adsorption kinetics and adsorber design, the BET theory and its varieties for the description of multilayer adsorption used as the yardstick for the surface area determination, and the capillary condensation for the pore size distribution determination. Here, we present another important adsorption mechanism applicable for microporous solids only, called micropore filling. In this class of solids, micropore walls are in proximity to each other, providing an enhanced adsorption potential within the micropores. This strong potential is due to the dispersive forces. Theories based on this force include that of Polanyi and particularly that of Dubinin, who coined the term micropore filling. This Dubinin theory forms the basis for many equations which are currently used for the description of equilibria in microporous solids. [Pg.149]


See other pages where Polanyi potential theory micropores adsorption is mentioned: [Pg.3]    [Pg.285]    [Pg.235]    [Pg.265]    [Pg.7]   
See also in sourсe #XX -- [ Pg.123 , Pg.124 ]




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