Sorption affinity constant

FIGURE 9.4 Dependence of constants (a, b, and c present Henry constant, sorption affinity constant, and Langmuir sorption capacity respectively) of the model of dual-mode sorption of hydrocarbons by glassy polyphenylene oxides on boiling temperatures of hydrocarbons Z), is pDMePO, poly-2,6-dimethyl-l,4-phenylene oxide o is pDPhPO, poly-2,6-diphenyl-l,4-phenylene oxide is pDMePO/pDPhPO copolymer (97.5/2.5% mol) v is pDMePO/pDPhPO copolymer (75/25% mol). (From analysis of results presented in Lapkin, A.A., Roschupkina, O.P., and Ilinitch, O.M., J. Membr. Sci., 141, 223, 1998.)... 

Henry constant, m STP)xm xkPa sorption affinity constant, kPa pressure, kPa membrane thickness, m... 

The sorption data of Cd2+ and Pb2+ by B. subtilis and E. coli were well described by a one-site complexation model (r2 > 0.9) with Cd2+ showing somewhat lower sorption affinities than Pb2+ (Kulczycki et al. 2002). A two-site sorption model yielded an improved fit but only for the E. coli data. The stability constants for the high- and low-affinity sorption sites differed by several orders of magnitude. The total metal sorption capacity of E. coli increased, and moved closer to the value of B. subtilis when the presence of low-affinity sorption sites was allowed. Ngwenya et al. (2003) used potentiometric titrations to assess the different types of sites present... 

Interaction on the solid phase involves the hypervariable region of the antibody and sorption efficiency is related to the affinity constant. When this latter is very high and requires elution conditions that can have a deleterious effect on the integrity of the antibody, it may be necessary to chemically modify the structure of the antigen to decrease the affinity constant. 

If the sorption curves pictured in Fig. 9 are caused by heterogeneity, what distribution of site properties would give rise to such curves Sposito [64] reported that a Freundlich curve could be derived if the log of the affinity constants of a series of Langmuir equations had a distribution which was similar to a normal distribution. 

The solubility in glassy polymers is usually described by the so-called dual-mode model, which implies that there is a need for a more detailed definition of the sorption, c, in the flux Equation 7.1. The following Equations 7.20 and 7.21 illustrate this and can be referred to Figure 7.6. The term Cg accounts for Henry s law, while Cu is the Langmuir term with b being the hole affinity constant (bar ) and is the saturation constant (cm [STP]/cm ) ... 

A criterion often used to characterize the sorptivity of a poUutant on a sorbent is the Freundlich constant (A p), which can be normalized to the carbon mass (Me) of the target molecule (Me (PFOA and PFOS) 96 g carbon mol ). Based on the sorption affinity of different fi-actions of natural organic matter on activated carbon, Kc values of below 20 (mg C/g) (mg C/l) indicate a poor adsorbabihty, whereas compounds with Kc > 50 (mg C/g) (mg CA) can be considered as strongly adsorbable (derived from [19]). 

In Eq. (9), [solute] is the molar solute concentration in the solution, 6 is the surface coverage (adsorbed amount of solute divided by total amount of surface sites), / is the fraction of surface sites of class j, Tif soiute is the affinity constant for the local sorption isotherm describing the interaction between the solute and the surface site y the index t stands for the overall (total) adsorption. 

C -.Langmuir sorption capacity cm STP/cm polym. kp Henry s law solubility coefficient cm STP/ (cm polym. cmHg). b affinity constant of Langmuir site cmHg... 

The working capacity of a sorbent depends on fluid concentrations and temperatures. Graphical depiction of sorption equilibrium for single component adsorption or Binary ion exchange (monovariance) is usually in the form of isotherms [nt = nt(c,) or n,(p,) at constant T] or isosteres [p, = p,(T) at constant n,]. Representative forms are shown in Fig. 16-1. An important dimensionless group dependent on adsorption equilibrium is the partition ratio [see Eq. (16-125)], which is a measure of the relative affinities of the sorbed and fluid phases for solute. 

Depending on the electron affinity of the catalyst, one of these two routes predominates. The dependence of the hydroperoxide decomposition rate on [ROOH] is in agreement with the conception of preliminary equilibrium sorption of hydroperoxide on the catalyst surface (Me2PhCOOH, AgO, 16m2 L 343 K) [263]). The equilibrium constant was estimated to be K 1 mol L and effective rate constant of described ROOH decomposition is /cis = 70s I[263]. 

The quantitative formulation of the site sorption mode, on the other hand, has the virtue of simplicity, but is undoubtedly rather highly idealised. Ideally, Eq. (9) refers to a collection of distinct, permanent and independent sites each accomodating one penetrant molecule Sq measures the concentration of these sites in the membrane and K2 their affinity for the penetrant assuming them to be isoenergetic 35,36). On this basis, the temperature dependence of K2 should yield a constant enthalpy for this sorption mode AH2 35,36). Consistency with the physical picture presented above requires moreover that AH2 be more exothermic than AH, U). 

The solubility coefficients of gases in glassy polymers are not constant, but decrease with increasing concentration of the gas in the polymers (2). Calculations of the isosteric enthalpy of sorption in several gas-polymer systems confirm that the gas-polymer affinity is reduced with increasing sorbed gas concentrations (24, 25, 26). The change in the isosteric enthalpy of sorption is a result of the changes in the polymer matrix induced by the presence of the sorbed gas. 

As a conclusion, we can say that the interlayer cations have an important role in the valine sorption mechanism. The total quantity of the adsorbed valine increases in the following order calcium-montmorillonite < copper-montmorillonite < zinc-montmorillonite. This order can be explained by the cumulative effect of the affinity of cations to the layer charges (Table 2.2) and the stability constants of metal ion-valine complexes in the solution (Table 2.11). 

The sorption isotherm is the most widely used expression to quantify a substance s affinity for water. It is, as the term implies, a relationship at a constant temperature. 

Uptake increases with pH, low affinity" sorption isotherms at constant pH. 

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