Adsorption of mixtures

Total mixture loading e i, molecules per unit cell 

The activity coefficient for component / in a bulk phase is defined by 

Defined in this way AF is the difference in molar free energy between the mixed adsorbed phase and the corresponding quantities for the pure components in a single-component adsorbed phase at the same temperature and spreading pressure (i.e., the standard state is taken as the pure adsorbed species at the same temperature and spreading pressure as the mixture). Since the free energy of the adsorbed phase is much more sensitive to w than is a bulk liquid or solid phase to P, the specification of constant spreading pressure in the definition of the standard state is important. 

The expression for the chemical potential follows by differentiation of Eq. (3.45) at constant temperature and spreading pressure  

Considering equilibrium with the vapor phase (assumed ideal) we have for the pure component 

For a single-component system the relationship between spreading pressure and adsorbed phase concentration may be obtained directly by integration of the Gibbs adsorption isotherm [Eq. (3.32)]  

---

The potential model has been applied to the adsorption of mixtures of gases. In the ideal adsorbed solution model, the adsorbed layer is treated as a simple solution, but with potential parameters assigned to each component (see Refs. 76-79). 

Adsorption of Mixtures. The Langmuit model can be easily extended to binary or multicomponent systems ... 

Isotherm Models for Adsorption of Mixtures. Of the following models, all but the ideal adsorbed solution theory (lAST) and the related heterogeneous ideal adsorbed solution theory (HIAST) have been shown to contain some thermodynamic inconsistencies. References to the limited available Hterature data on the adsorption of gas mixtures on activated carbons and 2eohtes have been compiled, along with a brief summary of approximate percentage differences between data and theory for the various theoretical models (16). In the following the subscripts i and j refer to different adsorbates. 

Adsorption of hard sphere fluid mixtures in disordered hard sphere matrices has not been studied profoundly and the accuracy of the ROZ-type theory in the description of the structure and thermodynamics of simple mixtures is difficult to discuss. Adsorption of mixtures consisting of argon with ethane and methane in a matrix mimicking silica xerogel has been simulated by Kaminsky and Monson [42,43] in the framework of the Lennard-Jones model. A comparison with experimentally measured properties has also been performed. However, we are not aware of similar studies for simpler hard sphere mixtures, but the work from our laboratory has focused on a two-dimensional partly quenched model of hard discs [44]. That makes it impossible to judge the accuracy of theoretical approaches even for simple binary mixtures in disordered microporous media. 

Carbon dioxide, 4 803-822. See also CO2 entries Ionic liquid/CC>2 mixtures Supercritical carbon dioxide in acid gas stream, 23 605 adsorption of mixtures with ethane on zeolite 5A, 7 603 from anaerobic digestion, 3 701 from ascorbic acid metabolism, 25 771 in beer, 3 582t... 

When retention times of mixture components decrease, there may be problems with either the mobile or stationary phase. It may be that the mobile phase composition was not restored after a gradient elution, or it may be that the stationary phase was altered due to irreversed adsorption of mixture components, or simply chemical decomposition. Use of guard columns may avoid stationary phase problems. 

The theories for the adsorption of mixtures of nonionic and ionic surfactants have been validated with tetraethylene glycol mono- -octyl ether (C8E4) and... 

By extending regular solution theory for binary mixtures of AEg in aqueous solution to the adsorption of mixture components on the surface (3,4), it is possible to calculate the mole fraction of AEg, Xg, on the mixed surface layer at tt=20, the molecular interaction parameter, 6, the activity coefficients of AEg on the mixed surface layer, fqg and f2s and mole concentration of surfactant solution, CTf=20 3t surface pressure tt=20 mn-m l (254p.l°C). The results from the following equations are shown in Table I and Table II. 

The same principles may be applied to the adsorption of mixtures of ethane and hydrogen. Let us assume that ethyl radicals and hydrogen atoms require a single site and ethylene molecules require two sites. The following relationships will hold ... 

Fig. 24a—e. Schematic illustration of monolayers formed by adsorption of mixtures of HStCHyhjOH and HS(CH2))9OH onto gold a pure monolayer of HS(CH2)19OH b-d monolayers containing different mixtures of the two components e pure monolayer of HS(CH2),, OH [175]... 

Several models were evaluated to obtain a satisfactory description of equilibria for the adsorption of mixtures from dilute solutions (9,10,11). The method of Radke and Prausnitz... 

The adsorptive separation is achieved by one of the three mechanisms steric, kinetic, or equilibrium effect. The steric effect derives from the molecular sieving property of zeolites. In this case only small and properly shaped molecules can diffuse into the adsorbent, whereas other molecules are totally excluded. Kinetic separation is achieved by virtue of the differences in diffusion rates of different molecules. A large majority of processes operate through the equilibrium adsorption of mixture and hence are called equilibrium separation processes. 

When a CO -I- H2 mixture was adsorbed on Pd(l 11) at 150 K (Fig. 29f), hydrogen was no longer confined to the surface, and CO was able to replace surface hydrogen, which moved to palladium subsurface/bulk sites. SFG (and FEED and TDS (273)) allowed detection of CO adsorbate structures identical to those observed after exposure to pure CO. Adsorption of mixtures of CO-I-H2 on palladium nanoparticles yielded CO-saturated surfaces, both at 100 and 150 K, attributed to the facile CO-induced displacement of adsorbed H into the particle volume. The SFG spectra were qualitatively the same as that in Fig. 31c. 

The adsorption of mixtures of surfactants has received comparatively little attention. The adsorption of mixtures of nonionic and anionic surfactants has been studied (10,25-27) and strong negative deviations from ideality were observed (10,27). Attempts to model the degree of non-ideality using regular solution theory failed (21). The adsorption of mixtures of anionic and cationic surfactants would be expected to exibit even larger deviations from ideality (28). 

Scamehorn et. al. ( ) also developed a reduced adsorption equation to describe the adsorption of mixtures of anionic surfactants, which are members of homologous series. The equations were semi-empirical and were based on ideal solution theory and the theory of corresponding states. To apply these equations, a critical concentration for each pure component in the mixture is chosen, so that when the equilibrium concentrations of the pure component adsorption isotherms are divided by their critical concentrations, the adsorption isotherms would coincide. The advantage of... 

Fig. 4. Adsorption of mixtures of C2H4 and C2H6 on NaX at 20 C for 10 mole % ethylene in gas phase. The individual isotherm for C2H4 is the difference between the total and the individual isotherm plotted for C2H6.

Gravimetric or manometric techniques have been used to establish adsorption data of gases on zeolites. Both techniques present problems, manometric equipment has an accumulation of the error and data obtained by the gravimetric method are influenced by effects associated with flow patterns, bypassing, and buoyancy. In the mixture s adsorption behaviour, isomers mixtures have the highest degree of difficulty to study. Isomers can not be differentiated in standard commercial adsorption equipment. This problem has been solved in this study by coupling a manometric apparatus with an NIR spectrometer, which allows us to measure the gas phase composition (in time, if necessaiy). In this paper we report this new approach to study the adsorption of mixtures of butane and iso-butane. 

Grand Canonical Monte Carlo Simulations of Adsorption of Mixtures of Xylene Molecules in Faujasite Zeolites. 

Figure 5 Individual and total isotherms at 20 °C for isobaric adsorption of mixtures of ethylene (1) and ethane (2) in NaX (zeolite structure FAU), where n is the amount adsorbed and y is the mole fraction of ethylene in the gas. Dashed lines calculated from Equations (13 - ]5. (17) and (18) using the constants for pure gases in Table 1. Solid lines indicate experimental data ...

Heuman, D.M., Bajaj, R.S., and Lin, Q. (1996) Adsorption of mixtures of bile salt taurine conjugates to lecithin-cholesterol membranes implications for bile salt toxicity and cytoprotection. Journal of Lipid Research, 37 (3), 562-573. 

Do, D.D. and Do, H.D. (2002). Adsorption of mixtures containing sub-critical fluids on micro-mesoporous carbon media. AIChE J, 48, 2213-29. 

Capacitive current has also been successfully measured by the Kalousck commutator technique (Cosovic and Branica, 1973). This technique has some advantages for t he study of adsorption of mixtures of adsorbable solutes, because... 

Interactions between adsorbed species complicate the problem by making the energy of adsorption a function of surface coverage. Attractive forces in the adsorbed layer increase surface concentrations and cause formation of a more condensed layer, while repulsion results in decrease of surface concentration and a formation of a more loose adsorption layer. In the adsorption of mixture of two organic substances, one should take into consideration all possible interactions between the molecule of the same type and between different molecules. 

The displacing effect observed in mixtures is not identical at all pressures. Lorenz and Wiedbrauck,16 in studying adsorption of mixtures of ethylene and carbon dioxide, found the adsorption of ethylene to be greater than that of carbon dioxide at low pressures, whereas at higher pressures this is reversed.17 Richardson and Wood-house18 observed that at 2870 millimeters pressure, carbon dioxide and nitrous oxide are adsorbed in almost equal volumes whereas at 72 millimeters pressure, two-thirds of the adsorbed gas is nitrous oxide. 

Most of the data in the literature referring to the adsorption of mixtures has been obtained by first adsorbing component 1 and subse-... 

---