Energy of sorption

Nevertheless, surfactant sorption isotherms on natural surfaces (sediments and biota) are generally non-linear, even at very low concentrations. Their behaviour may be explained by a Freundlich isotherm, which is adequate for anionic [3,8,14,20,30], cationic [7] and non-ionic surfactants [2,4,15,17] sorbed onto solids with heterogeneous surfaces. Recently, the virial-electrostatic isotherm has been proposed to explain anionic surfactant sorption this is of special interest since it can be interpreted on a mechanistic basis [20]. The virial equation is similar to a linear isotherm with an exponential factor, i.e. with a correction for the deviation caused by the heterogeneity of the surface or the energy of sorption. 

Although Eq. (4.32) can be derived as a general rate law expression under the assumption of an exponential decrease in number of available sorption sites with r and/or a linear increase in activation energy of sorption with T, the Elovich Equation is perhaps best regarded as an empirical one for the characterization of rate data (Sposito, 1984). 

Figure 5. Variation of integral molar energy of sorption with coverage for (x) methane and ( ) Kr on 5A zeolite (EU data of Rolniak for CHt (--------) theo-...

The bulk of evidence which we have discussed so far indicates that the mechanism of catalysis at solid surfaces takes place via the reaction of catalyst atoms (or ions) with the adsorbate to form a monolayer of chemically active intermediates. Since the initial act of chemisorption is a chemical reaction, it is not surprising to find that it may be accompanied by an activation energy of sorption. In general, however, the act of chemisorption is very rapid and occurs at a reasonable proportion of the estimated collisions of the gas molecule with the geometrical surface. Even when we might expect the rates of sorption to decrease as the surface monolayer nears completion, it is often found that the rate is only slightly diminished. This has been interpreted as due to the formation of a loosely held second sorbate layer, fonned on top of the monolayer, which is capable of migrating fairly rapidly to uncovered sorption sites. 

The proposed form of data presentation became highly popular and opportune in gas chromatography. Up to the present, some thousand references to the Kovat s work [1] have been known. The RI values are proportional to the free energies of sorption this is their thermodynamic interpretation. Further development of the RI concept was aimed at its application to nonisothermal conditions of gas chromatographic (GC) analysis. For linear temperature programming regimes (which are characterized by two variables initial temperature, Tq, and rate of its increase, r, deg X min ), the linear relationship (3) does not hold. In some partial cases, other linear dependence seems more precise for the retention time approximation ... 

The total partial molar Gibb s free energy of sorption (aG°t = aG°s) is directly related to Kp by... 

The polymeric sorbents are available from several vendors (Hamilton, 3M, and 1ST). In all cases, these sorbents are the styrene-divinylbenzene structure but vary in surface area. Generally speaking the greater the surface area, the greater the capacity of the sorbent for trace organic compounds. Furthermore, the aromatic rings of the matrix network permit electron-donor interactions between the sorbent and ti bonds of the solute, which may further increase analyte-sorbent interactions, which increases the energy of sorption. Thus, the... 

The variable sorptive tendencies of different classes of organic molecules can best be understood by evaluating all of the energy and entropy terms that contribute to the total free energy of sorption from aqueous solution. The important energy terms are ... 

An eqnation has been derived relating the effective diffusivity of porous foodstuffs to various physical properties such as molecular weight, bulk density, vapor space permeability, water activity as a function of material moisture content, water vapor pressure, thermal conductivity, heat of sorption, and tanperature [80]. A predictive model has been proposed to obtain effective diffusivities in cellular foods. The method requires data for composition, binary molecular diffusivities, densities, membrane and cell wall permeabilities, molecular weights, and water viscosity and molar volume [81]. The effect of moisture upon the effective diffusivity is taken into account via the binding energy of sorption in an equation suggested in Ref. [77]. 

From enthalpy AH, entropy AS and Kelvin temperature T, the free energy of sorption process AG has been obtained by adopting Gibbs s thermodynamics expression (Equation (27.19)). ... 

This paper deals with the principles, advantages and limitations of measurement of sorption equilibria under isosteric conditions. It further assesses the sorption-isosteric method (SIM) as an effective tool for providing complete sets of sorption-thermodynamic functions, viz., enthalpy, standard entropy and standard Gibbs free energy of sorption, for nanoporous solids, i.e., micro- and mesoporous ones, as functions of sorption-phase concentration, n, over its entire range, and to approach such data for mixtures. The usefulness of SIM is exemplified by sorption systems that comprise atmospheric gases on zeolites and carbon dioxide, CO2, on carbonaceous sorbents, as well as several of their mixtures. 

The sorption and transport of four aliphatic hydrocarbons (n-hexane, n-heptane, n-octane and n-nonane) into NR crosslinked using conventional, efficient, dicumyl peroxide(DCP) and mixed sulphur/peroxide vulcanisation systems were investigated at temp, of 28 to 60C. The NR vulcanised by DCP exhibited the lowest penetrant uptake of the systems studied. It was observed that the kinetics of liquid sorption in every case deviated from the regular Fickian trend, characteristic of sorption of liquids by rubbers. The diffusion coefficient, activation energy of sorption, enthalpy, entropy and rubber-solvent interaction parameter were evaluated for the four systems from the swelling data. 30 refs. 

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