Sorption classification

Thus, in terms of a, the sorption isotherm for osmotically ideal solutions is of Type III in Brunauer s classification (29) and reduces to Henry s law for (Mi/M2)a< 1. 

The sorption isotherms can be grouped into five types, according to the classification of Brunauer, Emmet and Teller. l,2 3A However, we prefer a classification, based on the pore size of the adsorbent.5 The IUPAC classification6 of pores is given in table 2.1. 

Intracrystalline sorption is normally of Type 1 in Brunauer s classification ( V7) and isotherm contours therefore resemble those according to Langmuir s isotherm equation. This can describe actual isotherms well enough (18) to be of value in predicting, through Equations 5 or 6, some features of zeolite chemistry. 

As soon as interactions become important, also other types of sorption are observed. Fig. 18.8 gives a classification of sorption isotherms, proposed by Rogers (1965,1985). 

Equilibrium sorption of water (solubility) is described by the different isotherms of the Brunauer-Emmett-Teller classification. 

Adsorption-sorption, 355 Classification, 355-356 pH, 27, 160 Acid soils, 160 Phosphate, 342... 

The second set of data (Fig. 1, b) concerns a family of pillared clays Ali-xFe/)yVi ih systematically varied Al and Fe contents [16], The sorption data of the pillared clays samples exhibit at low pressure a high adsorption step and at higher relative pressure an H4-type (lUPAC classification) hysteresis loop that is transformed into an H2-type loop as the Fe content is being increased. Details of the preparation procedure and the results from the application of other characterization tests are provided in [16]. 

The texture properties of the ultrathin porous glass membranes prepared in our laboratory were initially characterized by the equilibrium based methods nitrogen gas adsorption and mercury porosimetry. The nitrogen sorption isotherms of two membranes are shown in Fig. 1. The fully reversible isotherm of the membrane in Fig. 1 (A) can be classified as a type I isotherm according to the lUPAC nomenclature which is characteristic for microporous materials. The membrane in Fig. 1 (B) shows a typical type IV isotherm shape with hysteresis of type FIl (lUPAC classification). This indicates the presence of fairly uniform mesopores. The texture characteristics of selected porous glass membranes are summarized in Tab. 1. The variable texture demanded the application of various characterization techniques and methods of evaluation. 

The models most frequently used to describe the concentration dependence of diffusion and permeability coefficients of gases and vapors, including hydrocarbons, are transport model of dual-mode sorption (which is usually used to describe diffusion and permeation in polymer glasses) as well as its various modifications molecular models analyzing the relation of diffusion coefficients to the movement of penetrant molecules and the effect of intermolecular forces on these processes and free volume models describing the relation of diffusion coefficients and fractional free volume of the system. Molecular models and free volume models are commonly used to describe diffusion in rubbery polymers. However, some versions of these models that fall into both classification groups have been used for both mbbery and glassy polymers. These are the models by Pace-Datyner and Duda-Vrentas [7,29,30]. 

A characteristic feature associated with pore condensation is the occurrence of sorption hysteresis, i.e pore evaporation occurs usually at a lower p/po compared to the condensation process. The details of this hysteresis loop depend on the thermodynamic state of the pore fluid and on the texture of adsorbents, i.e. the presence of a pore network. An empirical classification of common types of sorption hysteresis, which reflects a widely accepted correlation between the shape of the hysteresis loop and the geometry and texture of the mesoporous adsorbent was published by lUPAC [10]. However, detailed effects of these various factors on the hysteresis loop are not fully understood. In the literature mainly two models are discussed, which both contribute to the understanding of sorption hysteresis [8] (i) single pore model. hysteresis is considered as an intrinsic property of the phase transition in a single pore, reflecting the existence of metastable gas-states, (ii) neiM ork model hysteresis is explained as a consequence of the interconnectivity of a real porous network with a wide distribution of pore sizes. 

Sorption behavior of inorganic and carboxylic acids is reported in Table 4.2 (anions), but sorption behavior of amino acids and phenols is reported in Table 4.4 (organic compounds). This classification is arbitrary, e.g. some derivatives of phenol whose sorption is reported in Table 4.4 have higher acidic dissociation... 

Reports on H2S emissions from common mineral soils are not very consistent and in part contradictory. For example, Bloomfield (1969) and Siman and Jansson (1976) detected the evolution of H2S from water-logged soils amended with sulfate and incubated under nitrogen atmosphere, whereas Banwart and Bremner (1976), who studied 25 soils from Iowa, failed to detect H2S under any conditions, even the most favorable ones. The latter authors ascribe the lack of H2S emission to sorption by the soils, possibly accompanied by fixation as FeS. The field measurements of Jaeschke et al. (1978, 1980) indicate that normally aerobic soils absorb H2S rather than emit it. Farwell et al. (1979), who studied agriclutural, forest, and marsh soils, also found only the last type to emit measurable quantities of H2S. Delmas et al. (1980), by contrast, found H2S to evolve from various soils in France, whose classification was not given but that cannot have differed much from those studied by Jaeschke et al. (1978). 

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