Adsorption binary

There is a number of very pleasing and instructive relationships between adsorption from a binary solution at the solid-solution interface and that at the solution-vapor and the solid-vapor interfaces. The subject is sufficiently specialized, however, that the reader is referred to the general references and, in particular, to Ref. 153. Finally, some studies on the effect of high pressure (up to several thousand atmospheres) on binary adsorption isotherms have been reported [154]. Quite appreciable effects were found, indicating that significant partial molal volume changes may occur on adsorption. 

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. 

Kinetic-theory-based description of binary adsorption 425... 

The differences in critical molecular sizes of the different components involved in the multicomponent adsorption of large molecules give additional complexities in the problem of the pore network accessibility. Here we will briefly describe the influence of percolation phenomena and accessibility on binary adsorption. Further details of this are presented elsewhere [9,10]. 

Here, we consider the binary adsorption of two components, component 1 has a critical molecular size, dci, and component 2, dc2- The critical molecular size of component 1 is smaller than component 2. Figure 1 depiets the adsorption behaviour of the binary mfarture in the pores. 

Figure 1. Schematic diagram of binary adsorption process in micropore network.

The effect of the pore network connectivity on the prediction of binary adsorption equilibria is studied. The Ideal Adsorbed solution theory (lAST) is used in conjunction with modified DR single component isotherm, and it is found that incorporation of the connectivity... 

There are several experimental techniques to characterize binary adsorption. The conventional techniques like volumetric or volumetric-gravimetric are full information techniques that yield both the total amount adsorbed and sur ce composition and hence the selectivity. In these techniques the error in selectivity goes to infinity... 

There are several reports in the literature that measure binary adsorption equilibria using gas chromatography [4,S,6]. In GC techniques the adsorbent is equilibrated with a continuous flow of carrier gas (gas 1). Then a pulse of gas 2 is injected at the column inlet. A peak of the gas 2 is eluted at the exit of the column after some time. Net retention time (or volume) is calculated from the first moment of the peak after correcting for void volume (by measuring the retention time of a non-adsorbing species). If the carrier gas is inert (i.e. helium) the net retention time is related to the pure component Henry s constant. Typical binary measurements reported so r use a mixture of the two gases as carrier and introduce a small perturbation in composition. The net retention volume is related to the thermodynamic properties by [4]... 

Harlicl PJ.E. and Tezel, F.H., A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data , Adsorption, 6 (2000), pp.293-309... 

Fig. 1 shows the uptake of pure hexane and decane frx)m their mixture with iso-octane on ZSM-S. The amounts adsorbed in the zeolite remain constant after 20 hours, indicating that the experiments were performed under equilibrium conditions. In order to verify that iso-octane can be used as inert solvent, a comparative experiment was performed in which the binary adsorption isotherm of hexane and decane was determined using isooctane and l,3,S-trimethyl benzene as respective solvents. The same adsorption isotherms are obtained with both solvent (Fig. 1 b), demonstrating that iso-octane does not interfere with the adsorption of the linear alkanes, and that the relative adsorption of the short and long n-alkanes is not influenced by the nature of the solvent, given that the solvent is not able to enter the pore system. 

Fig lb Binary adsorption isotherm of C6 and CIO. Open symbols mesitylene solvent closed symbols iso-octane solvent 60... 

In Fig 3a, the binary adsorption isotherms of a C8/C12 mixture is shown. C12 is adsorbed in a very selective way from the mixture, as can be seen in the selectivity diagram (Fig 3b), in which x and y represent the molar fractions in the liquid and adsorbed phases respectively. This selectivity for the longer chain can be explained by its higher interaction with the zeolite. 

This study firstly aims at understanding adsorption properties of two HSZ towards three VOC (methyl ethyl ketone, toluene, and 1,4-dioxane), through single and binary adsorption equilibrium experiments. Secondly, the Ideal Adsorbed Solution Theory (IAST) established by Myers and Prausnitz [10], is applied to predict adsorption behaviour of binary systems on quasi homogeneous adsorbents, regarding the pure component isotherms fitting models [S]. Finally, extension of adsorbed phase to real behaviour is investigated [4]. 

Role of Pore Size Distribution in the Binary Adsorption Kinetics of Gases in Activated Carbon... 

Fig. 6. Binary adsorption dynamics of ethane and propane onto Norit activated carbon of...

Role of pore size distribution in the binary adsorption kinetics of gases in activated carbon... 

The application of Equations (13)-(20) is illustrated for binary mixtures of ethylene (1) and ethane (2) adsorbed on NaX zeolite (faujasite). The constants for the singlegas adsorption equations of state are given in Tables 1 and 2. The selectivity of NaX for ethylene relative to ethane is a function of temperature, pressure, and the composition of the gas. The selectivity at constant temperature (20 °C) is shown in Figure 3. The selectivity at the limit of zero pressure is the ratio of Henry s constants (Xi/X2=33.7). At constant mole fraction of ethylene in the gas, the selectivity decreases rapidly with increasing pressure. At constant pressure, the selectivity decreases with increasing mole fraction of ethylene in the gas. The selectivity at constant pressure and gas composition decreases with temperature, as shown in Figure 4. Decrease of the selectivity with temperature, pressure, and the mole fraction of the preferentially adsorbed species is typical behavior for binary adsorption. 

V. Validation of the accuracy of the perturbation peak method for determination of single and binary adsorption isotherm parameters in LC. 

Liapis, A. I., Rippin, D. W. T. The simulation of binary adsorption in continuous counter-current operation and a comparison with other operation modes, AIChE/., 1979, 25(3), 455-460. 

Therefore the development of concentration bands in the column downstream of the displacer front is governed by the binary adsorption equilibrium of A and B, not just their single component isotherm as predicted by Glueckauf using Langmuir isotherm. 

Experimental results [7,8] obtained in the case of the breakthrough curves of binary mixtiues imder constant pattern condition have been compared with the anal5ttical solution. Figure 16.1 compares the experimental breakthrough curves obtained in the case of the vapor phase adsorption of benzene and toluene carried by nitrogen through a bed of activated carbon [8] with the analytical solution calculated from the binary adsorption data and imder the assumption of constant pattern behavior [1,3]. The agreement achieved is excellent. 

Figure 8. Water-ethanol binary adsorption isotherm on Alcoa H-152 alumina at 30°C.

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. 

P-2S - The use of binary adsorption studies to investigate the effect of hydrothermal treatment on zeolites Rho and Mordenite... 

Figure 9 shows the binary adsorption data of n-hexane and 2-methylpentane at 433 K as a function of the gas-phase ratio of the hydrocarbons. Obviously, the n-hexane loading monotonically decreases upon an increase of the partial pressure and loading of the 2-methylpentane. The total hydrocarbon loading only sUghtly decreases at high 2-methylpentane fraction in the gas phase. The preference for adsorption of n-hexane over the monobranched isomer is in line with the above-mentioned entropic considerations. 

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