Adsorption equilibria binary mixtures

For liquid solid adsorption from binary mixtures consisting of molecules of equal sizes on a heterogeneous surface of a random distribution of adsorption sites the average equilibrium constant K12 referring to the whole surface has the following form [15] ... 

The present paper deals with the threedimensional diagram for description of the equilibrium adsorption of O2/N2 mixtures on clinoptilolite. This diagram shows the dependence of the amount adsorbed on the total pressure, as well as the equilibrium concentration of the gas mixtures. Adsorption from binary mixtures involves theoretical and experimental problems. Ruthven s and Loughlin s works (7,8) provide much detail and they succeed in describing fully enough the complicated systems, but all at the expense of considerable characteristic constants used and elaborate computation. The experimental... 

Wood, G O., "Review and Comparisons of D/R Models of Equilibrium Adsorption of Binary Mixtures of Organic Vapors on Activated Carbons," Carbon. 2002 40 231 239. 

When solid particles are immersed in liquid medium, solid-liquid interfacial interactions will cause the formation of an adsorption layer on their surface. The material content of the adsorption layer is the adsorption capacity of the solid adsorbent, which may be determined in binary hquid mixtures if the so-called adsorption excess isotherm is known. Due to adsorption, the initial composition of the hquid mixture, x , changes to the equilibrium concentration Xj, where n = n +rf2, the mass content of the interfacial phase (e.g., mmol/g). This change, Xj — Xj = Axj, can be determined by simple analytical methods. The relationship between the reduced adsorption excess amount calculated from the change in concentration, = n°(x — xj), and the material content of the interfacial layer is given by the Ostwald-de Izaguirre equation [1-5]. In the case of purely physical adsorption of binary mixtures, the material content of the adsorption layer ( = — n) for component 1 is... 

EXAMPLE 9.4 Kinetic-Theory-Based Description of Binary Adsorption. Assume that two gases A and B individually follow the Langmuir isotherm in their adsorption on a particular solid. Use the logic that results in Equation (46) to derive an expression for the fraction of surface sites covered by one of the species when a mixture of the two gases is allowed to come to adsorption equilibrium with that solid. 

Individuals of multicomponent mixtures compete for the limited space on the adsorbent. Equilibrium curves of binary mixtures, when plotted as x vs. y diagrams, resemble those of vapor-liquid mixtures, either for gases (Fig. 15.5) or liquids (Fig. 15.6). The shapes of adsorption curves of binary mixtures, Figure 15.7, are varied the total adsorptions of the components of the pairs of Figure 15.7 would be more nearly constant over the whole range of compositions in terms of liquid volume fractions rather than the mol fractions shown. 

A mathematical model has been developed to describe the kinetics of multicomponent adsorption. The model takes into account diffusional processes in both the solid and fluid phases, and nonlinear adsorption equilibrium. Comparison of model predictions with binary rate data indicates that the model predictions are in excellent for solutes with comparable diffusion rate characteristics. For solutes with markedly different diffusion rate constants, solute-solute interactions appear to affect the diffusional flows. In all cases, the total mixture concentration profiles predicted compares well with experimental data. 

The only approximate analytical solution for the RSA of a binary mixture of hard disks was proposed by Talbot and Schaaf [27], Their theory is exact in the limit of vanishing small disks radius rs — 0, but fails when the ratio y = r Jrs of the two kinds of disk radii is less than 3.3 its accuracy for intermediate values is not known. Later, Talbot et al. [28] observed that an approximate expression for the available area derived from the equilibrium Scaled Panicle Theory (SPT) [19] provided a reasonable approximation for the available area for a non-equilibrium RSA model, up to the vicinity of the jamming coverage. While this expression can be used to calculate accurately the initial kinetics of adsorption, it invariably predicts that the abundant particles will be adsorbed on the surface until 6=1, because the Scaled Particle Theory cannot predict jamming. 

The interface between the liquid and the vapour phase is assumed to be a liquid monolayer in which the molar fraction of B is YB (see also Figure 6.27). The use of the monolayer approximation in describing equilibrium adsorption in binary liquids is satisfactory only when the temperature is not close to the critical temperature of the liquid mixture i.e., the temperature below which the A-B solution consists of a mixture of two solutions (Defay et al. 1966, Eustathopoulos and Joud 1980). 

In a liquid binary solution, this accumulation is accompanied by the corresponding displacement of another component (solvent) from the surface region into the bulk solution. At equilibrium a certain amount of the solute will be accumulated on the surface in excess of its equilibrium concentration in the bulk solution, as shown in Figure 2-6. Excess adsorption E of a component in binary mixture is defined from a comparison of two static systems with the same liquid volume Vo and adsorbent surface area S. In the first system the adsorbent surface considered to be inert (does not exert any surface forces in the solution) and the total amount of analyte (component 2) will be no = VoCo. In the second system the adsorbent surface is active and component 2 is preferentially adsorbed thus its amount in the bulk solution is decreased. The analyte equilibrium concentration Ce can only be measured in the bulk solution, so the amount VoCe is thereby smaller than the original quantity no due to its accumulation on the surface, but it also includes the portion of the analyte in the close proximity of the surface (the portion U Ce, as shown in Figure 2-6 note that we did not define V yet and we do not need to define... 

A solution is t3q>lcally a system of more than one component. In actual cases, there are at least two substances that can adsorb. For a binary fluid mixture, including dilute solutions, adsorption of one type of molecule (say A) involves replacement of the other (B). Thus, adsorption from solution is essentially an exchange process. If one molecule of A replaces r molecules of B at the Interface, the adsorption equilibrium can be written as... 

Costa E., Sotelo J.L. Calleja G. and Marron C., Adsorption of binary and temaiy hydrocarbon gas mixtures on activated carbon experimental determination and theoretical prediction of the ternary equilibrium data, AlChE Journal 27(1) (1981) pp.5-12. 

The binary mixture adsorption is simulated by assuming an ideal AB-gas at fixed T, Pa and Pb- In equilibrium there are two ways to perform a change of the system state adsorbing (desorbing) one molecule onto (from) the surfece. 

IGC was also applied to generate adsorption data for organic vapor on polymeric materials. The vapor-adsorption phase equilibrium for various binary mixtures of organic compounds was further calculated on the basis of adsorption data for individual vapors. 

To calculate the adsorption equilibrium of a binary mixture for the given concentrations C and c2 the hypothetical concentrations c j and c, which fulfill Eqs. 2.55 and 2.56, have to be determined. 

Quinones et al. [17] measured by frontal analysis multisolute adsorption equilibrium data for the system benzyl alcohol, 2-phenylethanol and 2-methyl benzyl alcohol in a reversed-phase system. Data were acquired for the pure compoimds, for nine binary mixtures (1 3,1 1, and 3 1) and four ternary mixtures (1 1 3,1 3 1, 3 1 1, and 1 1 1). These data exhibited very good thermod5mamic consistency. The thermodynamic functions of adsorption were derived from the single-solute ad-... 

For experimental verification of these models, Foplewska et al. [33] used binary mixtures of methanol-water and acetonitrile-water as the mobile phases and measured the adsorption equilibrium isotherms of cyclopentanone on two similar adsorbents having different degrees of sruface heterogeneity, a Cis non-endcapped and a Cig endcapped silica. Ehie to its structure, cyclopentanone exhibits affinity for adsorption on the bonded alkyl chains and for the polar, im-covered silica sruface of the adsorbent. Overloaded elution bands of cyclopentanone in piue water were recorded (Figrue 15.3) and the isotherms were derived using an inverse method (see Chapter 3). Five independent parameters (the excess coefficients and the eqiulibrirun constants for partition-adsorption and for... 

The equilibrium amounts adsorbed of component i from a binary gas mixture (n ) are generally described as functions of gas phase mole fractions (y ) at a constant system temperature (T) and total gas pressure (P). An example is given in Fig. 4 for adsorption of binary N2-O2 mixtures on Na-mordenite at various temperatures where the total gas pressure was 1.0 atm. These binary isotherm shapes are typical for Type I adsorption systems on microporous adsorbents. 

The aim of the present paper is to present the adsorption equilibrium of binary Oj/l systems, as well as of pure sorbates on natural clinoptilolite and to try to predict the behaviour of each sorbate in mixtures under arbitrary pressures and concentration. 

The Chreedimensional diagram obtained could serve both theoretical and technological computations concerning oxygen enrichment of air on K-clinoptilolite. It is a basis for determining of adsorption isobars, fictitious and real isotherms, as well as thermodynamic data for adsorption from binary C /Nj mixtures. Freundlich and Henry constants (for the real adsorption isotherms) correlated with the equilibrium concentration are useful for computation of the amounts adsorbed at arbitrary partial pressures and equilibrium concentrations. 

We therefore believe that the Elovich equation may be used as a basis for a quantitative interpretation of rates of adsorption and desorption both from the single-gas phase, and from binary mixtures, and that it is a useful expression, like that for a Freundlich isotherm in equilibrium adsorption studies, as a means of describing the heterogeneous nature of many rate processes. We have not attempted to describe, in detail, the extensive experimental data that are available in the literature since this has been thoroughly and critically assessed up to 1960 by Low (5) who has written an excellent and comprehensive review in which he provides references to the original papers. 

The adsorption of three argon/nitrogen binary mixtures at 310 K and up to 0.6 bar are presented. A continuous, quasi-equilibrium flow technique of adsorptive introduction was used to allow high-resolution isotherms to be obtained. These are compared to differential enthalpies of adsorption determined using adsorption microcalorimetry. 

Adsorption of some organic solvent vapours onto HSZ were studied. Binary adsorption equilibriums except azeotropic mixture-HSZ systems could be correlated by Markham-Benton equation for the whole concentration range, and the break times could be estimated well by using the Extended-MTZ-Method. For azeotropic mixture-HSZ systems, the equilibriums and the break times could be correlated and estimated only for a part of the all concentration range. Then, two azeotropic points appeared in the adsorption equilibriums for IPA-TCE -Y-type system. For this binary systems adsorption equilibrium data could be expressed by proposed equation, similar to liquid-vapour azeotropic equilibrium equation. Breakthrough curve could be simulated using the Stop Go method in the whole range for azeotropic mixture systems as well as for zeotropic systems. 

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